RealClimate

Fresh hockey sticks from the Southern Hemisphere

eric — Tue, 22 May 2012 12:28:45 +0000

In the Northern Hemisphere, the late 20th / early 21st century has been the hottest time period in the last 400 years at very high confidence, and likely in the last 1000 – 2000 years (or more). It has been unclear whether this is also true in the Southern Hemisphere. Three studies out this week shed considerable new light on this question. This post provides just brief summaries; we’ll have more to say about these studies in the coming weeks.

First, a study by Gergis et al., in the Journal of Climate uses a proxy network from the Australasian region to reconstruct temperature over the last millennium, and finds what can only be described as an Australian hockey stick. They use an ensemble of 3000 different reconstructions, using different methods and different subsets of the proxy network. Worth noting is that while some tree rings are used (which can’t be avoided, as there simply aren’t any other data for some time periods), the reconstruction relies equally on coral records, which are not subject to the same potential (though often-overstated) issues at low frequencies. The conclusion reached is that summer temperatures in the post-1950 period were warmer than anything else in the last 1000 years at high confidence, and in the last ~400 years at very high confidence.

Gergis et al. Figure 4, showing Australian mean temperatures over the last millennium, with 95% confidence levels.

Second, Orsi et al., writing in Geophysical Research Letters, use borehole temperature measurements from the WAIS Divide site in central West Antarctica, a region where the magnitude of recent temperature trends has been subject of considerable controversy. The results show that the mean warming of the last 50 years has been 0.23°C/decade. This result is in essentially perfect agreement with that of Steig et al. (2009) and reasonable agreement with Monaghan (whose reconstruction for nearby Byrd Station was used in Schneider et al., 2012). The result is totally incompatible (at >~~95%~~>80% confidence) with that of O'Donnell et al. (2010).

Probability histograms of temperature trends for central West Antarctica (Byrd Station [80°S, 120°W; Monaghan] and WAIS Divide [79.5°S, 112°W; Orsi, Steig, O'Donnell]), using published means and uncertainties. Note that the histograms are normalized to have equal areas; hence the greater height where the published uncertainties are smaller.

This result shouldn’t really surprise anyone: we have previously noted the incompatibility of O’Donnell et al. with independent data. What is surprising, however, is that Orsi et al. find that warming in central West Antarctica has actually accelerated in the last 20 years, to about 0.8°C/decade. This is considerably greater than reported in most previous work (though it does agree well with the reconstruction for Byrd, which is based entirely on weather station data). Although twenty years is a short time period, the 1987-2007 trend is statistically significant (at p<.1), putting West Antarctica definitively among the fastest-warming areas of the Southern Hemisphere -- more rapid than the Antarctic Peninsula over the same time period.

We and others have shown (e.g. Ding et al., 2011), that the rapid warming of West Antarctica is intimately tied to the remarkable changes that have also occurred in the tropics in the last two decades. Note that the Orsi et al. paper actually focuses very little on the recent temperature rise; it is mostly about the "Little-ice-age-like" signal of temperature in West Antarctica. Also, these results cannot address the question of whether the recent warming is exceptional over the long term -- borehole temperatures are highly smoothed by diffusion, and the farther back in time, the greater the diffusion. We'll discuss both these aspects of the Orsi et al. study at greater length in a future post.

Last but not least, a new paper by Zagorodnov et al. in The Cryosphere, uses temperature measurements from two new boreholes on the Antarctic Peninsula to show that the decade of the 1990s (the paper state “1995+/-5 years”) was the warmest of at least the last 70 years. This is not at all a surprising result from the Peninsula — it was already well known the Peninsula has been warming rapidly, but these new results add considerable confidence to the assumption that that warming is not just a recent event. Note that the “last 70 years” conclusion reflects the relatively shallow depth of the boreholes, and the fact that diffusive damping of the temperature signal means that one cannot say anything about high frequency variability prior to that. The inference cannot be made that it was warmer than present, >70 years ago. In the one and only century-long meteorological record from the region — on the Island of Orcadas, just north of the Antarctica Peninsula — warming has been pretty much monotonic since the 1950s, and the period from 1903 to 1950 was cooler than anything after about 1970 (see e.g. Zazulie et al., 2010). Whether recent warming on the Peninsula is exceptional over a longer time frame will have to await new data from ice cores.

References

J. Gergis, R. Neukom, S.J. Phipps, A.J.E. Gallant, and D.J. Karoly, "Evidence of unusual late 20th century warming from an Australasian temperature reconstruction spanning the last millennium", Journal of Climate, 2012, pp. 120518103842003-. DOI.
A.J. Orsi, B.D. Cornuelle, and J.P. Severinghaus, "Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide", Geophysical Research Letters, vol. 39, 2012. DOI.
E.J. Steig, D.P. Schneider, S.D. Rutherford, M.E. Mann, J.C. Comiso, and D.T. Shindell, "Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year", Nature, vol. 457, 2009, pp. 459-462. DOI.
D.P. Schneider, C. Deser, and Y. Okumura, "An assessment and interpretation of the observed warming of West Antarctica in the austral spring", Climate Dynamics, vol. 38, 2012, pp. 323-347. DOI.
R. O’Donnell, N. Lewis, S. McIntyre, and J. Condon, "Improved Methods for PCA-Based Reconstructions: Case Study Using the Steig et al. (2009) Antarctic Temperature Reconstruction", Journal of Climate, vol. 24, 2011, pp. 2099-2115. DOI.
Q. Ding, E.J. Steig, D.S. Battisti, and M. Küttel, "Winter warming in West Antarctica caused by central tropical Pacific warming", Nature Geoscience, vol. 4, 2011, pp. 398-403. DOI.
V. Zagorodnov, O. Nagornov, T.A. Scambos, A. Muto, E. Mosley-Thompson, E.C. Pettit, and S. Tyuflin, "Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula", The Cryosphere Discussions, vol. 5, 2011, pp. 3053-3084. DOI.
N. Zazulie, M. Rusticucci, and S. Solomon, "Changes in Climate at High Southern Latitudes: A Unique Daily Record at Orcadas Spanning 1903–2008", Journal of Climate, vol. 23, 2010, pp. 189-196. DOI.

OHC Model/Obs Comparison Errata

gavin — Tue, 22 May 2012 12:21:55 +0000

This is just a brief note to point out that a few graphs that I have put together showing Ocean Heat Content changes in recent decades had an incorrect scaling for the GISS model data. My error was in assuming that the model output (which were in units W yr/m2) were scaled for the ocean area only, when in fact they were scaled for the entire global surface area (see fig. 2 in Hansen et al, 2005). Therefore, in converting to units of 10²² Joules for the absolute ocean heat content change, I had used a factor of 1.1 (0.7 x 5.1 x 365 x 3600 x 24 x 10^-8), instead of the correct value of 1.61 (5.1 x 365 x 3600 x 24 x 10^-8). This problem came to light while we were redoing this analysis for the CMIP5 models and from conversations with dana1981 at skepticalscience.com.

These graphs appeared in Dec 2009, May 2010, Jan 2011 and Feb 2012. In each case, I have replaced the graph with a corrected version while leaving a link to the incorrect version. Links to the figures will return the corrected image (and this is noted on the image itself). Where possible I used the data that were current at the time of the original post. Fortunately this only affects the figures used in these blog postings and not in any publications. Apologies for any confusion.

This figure shows the comparison using the most up-to-date observational products (NODC, PMEL):

The basic picture is unchanged – model simulations were able to capture the historical variance in OHC (as best we know it now – there remains significant structural uncertainty in those estimates). There are clear dips related volcanic eruptions (Agung, El Chichon, Pinatubo), and an sharp increase in the 1990s. Note that in GISS-EH (same AGCM but with a different ocean model) OHC increases at a slightly slower rate than seen with GISS-ER above. Looking at the last decade, it is clear that the observed rate of change of upper ocean heat content is a little slower than previously (and below linear extrapolations of the pre-2003 model output), and it remains unclear to what extent that is related to a reduction in net radiative forcing growth (due to the solar cycle, or perhaps larger than expected aerosol forcing growth), or internal variability, model errors, or data processing – arguments have been made for all four, singly and together.

Analyses of the CMIP5 models will provide some insight here since the historical simulations have been extended to 2012 (including the last solar minimum), and have updated aerosol emissions. Watch this space.

References

J. Hansen, "Earth's Energy Imbalance: Confirmation and Implications", Science, vol. 308, 2005, pp. 1431-1435. DOI.

Another fingerprint

rasmus — Sun, 20 May 2012 08:49:09 +0000

When my kids were younger, they asked me why the ocean was blue. I would answer that the ocean mirrors the blue sky. However, I would not think much more about it, even though it is well-known that the oceans represent the most important source for atmospheric moisture. They also play an important role for many types of internal variations, such as the El Nino Southern Oscillation. Now a new study by Durack et al. (2012) has been published in Science that presents the relationship between the oceans and the atmosphere.

When it rains over the ocean, the salty ocean water gets diluted by fresh water from the clouds, whereas in regions with high evaporation and little rainfall, the evaporation takes away the water and leaves the salt behind in the ocean. If there is a systematic increase in rainfall over some regions and enhanced evaporation in others, then this ought to leave a fingerprint in form of reduced and increased salinity in the respective regions. This is exactly what Durack et al. (2012) have found.

This finding is consistent with earlier model-based suggestions that dry regions will become drier and wet regions will become wetter in response to warming (Giorgi et al., 2011). The Durack et al. (2012) study was based on surface salinity measurements from the ARGO floats combined with sparser historical data over a period of 50 years (Durack et al., 2010). They studied the changes in the spatial structure in terms of linear regression against time over the 50-year period. The change in salinity was consistent with the notion of a strengthening of the hydrological cycle by ~8%/°C.

They also compared their results with global climate model simulations (which involve coupled atmosphere-ocean models) as well as ocean model simulations (forced by atmospheric data). Ocean models use the laws of physics to describe how the ocean currents flow, the water masses mix, and how these processes affect temperature and salinity. The most important inputs to the ocean models are wind forcing, evaporation and rainfall.

The model results give a similar picture as the observations, albeit with an under-estimation of the hydrological cycle speed-up. By looking at projections for the future, the Durack et al. (2012) analysis points to a “substantial (16 to 24%) intensification of the global water cycle [that] will occur in a future 2°C to 3°C warmer world”.

The mean surface salinity of the world oceans. Source: http://serc.carleton.edu/eslabs/corals/4c.html

There is a sinister twist to these inferences. A warmer world is predicted to result in both increased rainfall intensity (mean precipitation estimated for the wet days only) as well as increased length of dry spells (Giorgi et al., 2011). Moreover, in a recent paper, I have together with two colleagues shown that the more extreme rainfall amounts closely follow the rainfall intensity (Benestad et al. (2012). From these results, it seems that we can expect more extremes in both floods and droughts.

Finally, the analysis by Durack et al. (2012) provides another fingerprint of a global warming. However, this finding aspect is not entirely new: the last IPCC report already concluded there is an enhancement of the hydrological cycle, based on observed ocean salinity changes. The method and the conclusion are therefore not new, but the new Argo data confirm earlier findings and strengthen previous observations: the global warming and changes to the hydrological cycle are closely entangeled.

References

P.J. Durack, S.E. Wijffels, and R.J. Matear, "Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000", Science, vol. 336, 2012, pp. 455-458. DOI.
F. Giorgi, E. Im, E. Coppola, N.S. Diffenbaugh, X.J. Gao, L. Mariotti, and Y. Shi, "Higher Hydroclimatic Intensity with Global Warming", Journal of Climate, vol. 24, 2011, pp. 5309-5324. DOI.
P.J. Durack, and S.E. Wijffels, "Fifty-Year Trends in Global Ocean Salinities and Their Relationship to Broad-Scale Warming", Journal of Climate, vol. 23, 2010, pp. 4342-4362. DOI.
R.E. Benestad, D. Nychka, and L.O. Mearns, "Spatially and temporally consistent prediction of heavy precipitation from mean values", Nature Climate Change, 2012. DOI.

Plugging the leaks

group — Thu, 17 May 2012 11:54:50 +0000

Guest commentary by Beate Liepert, NWRA

Clouds and water vapor accounts for only a tiny fraction of all water on Earth, but in spite of it, this moisture in the atmosphere is crucially important to replenishing drinking water reservoirs, crop yields, distribution of vegetation zones, and so on. This is the case because in the atmosphere, clouds and water vapor, transports a vast amount of water from oceans to land, where it falls out as precipitation. Scientists generally agree that rising temperatures in the coming decades will affect this cycling of water. And most climate models successfully simulate a global intensification of rainfall. However, physical models often disagree with observations and amongst themselves on the amount of the intensification, and global distribution of moisture that defines dry and wet regions.

In a paper published in Environmental Research Letters, my co-author and I investigated these model discrepancies (Liepert and Previdi, 2012) (see also here). We developed a “quality control test” for climate models that is solely based on physical principles. We retroactively sum up all possible source, sink and storage terms of atmospheric moisture in models and postulate that a perfectly balanced physical model is a model without artificial leaks or floods in the system (note that small terms like methane oxidation fluxes into the atmosphere, or changes in total cloud water were not included). This approach of “self-consistency” is in contrast to previous studies where scientists performed model “reality checks” of comparisons with uncertainty prone precipitation observations. Eighteen state-of-the-art climate models as described in the United Nations 4th Assessment Report (IPCC-AR4) of the Intergovernmental Panel on Climate Change were included.

We found that most models predict an increase in moisture coming towards land in the course of the 21st century due to larger warming of land versus ocean surfaces with moderately increasing greenhouse gas concentrations. Some models, however predict radically opposite results, But these few models have large biases, which strongly affects the multi-model mean. The multi-model mean is often used in climate science and climate impact studies as “best predictor” since it smooths over model inconsistencies. These biases appear to be associated with ‘leaks’ in the model whereby water does not appear to be conserved. Some model leaks are even bigger than the anticipated global precipitation changes in the 21st century. The multi-model average is therefore biased by these few and has an average “leak” of the size of the discharge of the Mississippi river!

With our self-consistency test we were able to identify the outliers and narrow the prediction uncertainty. Only using the consistent models, we expect that in this century, the atmosphere will increasingly transport moisture towards land by the size of the river Nile, and with a model uncertainty of up to 13 percent of increase.

It is difficult for models to keep track of the small amount of water contained in the atmosphere (a thousandth of a percent of the total water on Earth). On the other hand, it is crucially important to plug leaks in physical climate models because water in the atmosphere plays an important role in the energy balance of the Earth. A bit fewer clouds, due to the leaks, can let extra solar energy reach the earth surface and heat up the planet – lost water vapor would have the opposite effect. This spurious energy flux in leaky models constitutes a “ghost” forcing of climate. We calculate that the ghost forcing in the IPCC models ranges from -1 to +6 watts per square meter, a forcing comparable to the size of non-carbon dioxide greenhouse gases – though since it is roughly constant in time it doesn’t impact the transient runs directly.

These results show that independent quality controls on climate model simulations are crucial for assessing the quality of future climate change predictions. Not all models are equally good and should be utilized in climate impact studies.

Climate impact models are used, along with crop yield, and hydrology models for instance, to inform far reaching decision-making. Climate research institutions are under pressure to build more accurate, more complex models that incorporate not only the physical climate, but also ecosystem processes and perhaps eventually, economic impacts. Testing and quality control should of course accompany these model developments, and it is to the credit of the modeling groups that they archive enough information in the public archives of CMIP3 and now CMIP5 that we can do these tests independently, assess the remaining problems and hopefully improve the predictions.

References

B.G. Liepert, and M. Previdi, "Inter-model variability and biases of the global water cycle in CMIP3 coupled climate models", Environmental Research Letters, vol. 7, 2012, pp. 014006-. DOI.

Greenland Glaciers — not so fast!

eric — Tue, 15 May 2012 15:41:41 +0000

There have been several recent papers on ice sheets and sea level that have gotten a bit of press of the journalistic whiplash variety (“The ice is melting faster than we thought!” “No, its not!”). As usual the papers themselves are much better than the press about them, and the results less confusing. They add rich detail to our understanding of the ice sheets; they do not change estimates of the magnitude of future sea level rise.

One of these recent papers, by Hellmer et al., discusses possible mechanisms by which loss of ice from the great ice sheets may occur in the future. Hellmer et al.’s results suggest that retreat of the Ronne-Filchner ice shelf in the Weddell Sea (Antarctica) — an area that until recently has not received all that much attention from glaciologists — might correspond to an additional rise in global sea level of about 40 cm. That’s a lot, and it’s in addition to, the “worst case scenarios” often referred to — notably, that of Pfeffer et al., (2008), who did not consider the Ronne-Filchner. However, it’s also entirely model based (as such projections must be) and doesn’t really provide any information on likelihood — just on mechanisms.

Among the most important recent papers, in our view, is the one by Moon et al. in Science earlier this May (2012). The paper, with co-authors Ian Joughin (who won the Agassiz Medal at EGU this year), Ben Smith, and Ian Howat, provides a wonderful new set of data on Greenland’s glaciers. This is the first paper to provide data on *all* the outlet glaciers that drain the Greenland ice sheet into the sea.

The bottom line is that Greenland’s glaciers are still speeding up. But the results put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest, an idea that some had raised after a doubling over a few years was reported in 2004 for Jakobshavn Isbræ (Greenland’s largest outlet glacier). Let it not be said that journals such as Science and Nature are only willing to publish papers that find that thing are “worse than we thought”! But neither does this new work contradict any of the previous estimates of future sea level rise, such as that of Vermeer and Rahmstorf. The reality is that the record is very short (just 10 years) and shows a complex time-dependent glacier response, from which one cannot deduce how the ice sheet will react in the long run to a major climatic warming, say over the next 50 or 100 years.

These new data provide an important baseline and they will remain important for many years to come. We asked Moon and Joughin to write a summary of their paper for us, which is reproduced below.

Guest Post by By Twila Moon and Ian Joughin, University of Washington

The sheer scale of the Greenland and Antarctic ice sheets pose significant difficulties for collecting data on the ground. Fortunately, satellites have brought in a new era of ice sheet research, allowing us to begin answering basic questions – how fast does the ice move? how quickly is it changing? where and how much melting and thinning is occurring? – on a comprehensive spatial scale. Our recent paper, “21st-century evolution of Greenland outlet glacier velocities”, published May 4th in Science, presented observations of velocity on all Greenland outlet glaciers – more than 200 glaciers – wider than 1.5km [Moon et al., 2012]. There are two primary conclusions in our study:
1) Glaciers in the northwest and southeast regions of the Greenland ice sheet, where ~80% of discharge occurs, sped up by ~30% from 2000 to 2010 (34% for the southeast, 28% for the northwest).
2) On a local scale, there is notable variability in glacier speeds, with even neighboring glaciers exhibiting different annual velocity patterns.

There are a few points on our research that may be easy to misinterpret, so we’re taking this opportunity to provide some additional details and explanation.

Melt and Velocity

The Greenland ice sheet changes mass through two primary methods: 1) loss or gain of ice through melt or precipitation (surface mass balance) and 2) loss of ice through calving of icebergs (discharge) (Figure 1) [van den Broeke et al., 2009]. It is not uncommon for people to confuse discharge and melting. Our measurements from Greenland, which are often referred to in the context of “melt”, are actually observations of velocity, and thus relate to discharge, not in situ melting.

Figure 1. Components of surface mass balance and discharge. Most components can change in both negative (e.g., thinning) and positive directions (e.g., thickening).

When glaciologists refer to “increased melt” they are usually referring to melt that occurs on the ice sheet’s top surface (i.e., surface mass balance). Surface melt largely is confined to the lower-elevation edge of the ice sheet, where air temperature and solar radiation can melt up to several meters of ice each year during summer. Melt extent depends on air temperatures which tend to be greatest at more southerly latitudes. Meltwater pools in lakes and crevasses, often finding a path to drain through and under the ice sheet to the ocean. Glaciologists and oceanographers have found evidence for notable melt where the ice contacts ocean water [Straneo et al., 2010]. So, when you hear about ice sheet “melt”, think surface lakes and streams and melting at the ends of the glaciers where they meet the ocean.

So, why focus on velocity instead of melt? Velocity is more closely related to the discharge of ice to the ocean in the process of which icebergs break off, which float away to melt somewhere else potentially far removed from the ice sheet. You can picture outlet glaciers as large conveyor belts of ice, moving ice from the interior of the ice sheet out to the ocean. Our velocity measurements help indicate how quickly these conveyor belts are moving ice toward the ocean. Given climate change projections of continued warming for the Greenland ice sheet [IPCC, 2007], it’s important to understand at what speeds Greenland glaciers flow and how they change. On the whole, the measurements thus far indicate overall speedup. It turns out that on any individual glacier, however, the flow may undergo large changes on an annual basis, including both speeding up and slowing down. With these detailed measurements of glacier velocity, we can continue to work toward a better understanding of what primary factors control glacier velocity. Answers to this latter question will ultimately help us predict the ice sheet’s future behavior in a changing climate.

Sea Level Rise

Translating velocity change into changes in sea level rise is not a straightforward task. Sea level change reflects the total mass of ice lost (or gained) from the ice sheet. Determining this quantity requires measurements of velocity, thickness, width, advance/retreat (i.e., terminus position), and density – or, in some cases, an entirely different approach, such as measuring gravity changes.

Our study does not include many of the measurements that are a part of determining total mass balance, and thus total sea level rise. In another paper that we highlight in our study, Pfeffer et al. [2008] used a specifically prescribed velocity scaling to examine potential worst-case values for sea level rise. The Pfeffer et al. paper did not produce “projections” of sea level rise so much as a look at the limits that ice sheet dynamics might place on sea level rise. It is reasonable to comment on how our observations compare to the prescribed velocity values that Pfeffer et al. used. They lay out two scenarios for Greenland dynamics. The first scenario was a thought experiment to consider sea level rise by 2100 if all glaciers double their speed between 2000 and 2010, which is plausible given the observed doubling of speed by some glacier. The second experiment laid out a worst-case scenario in which all glacier speeds increased by an order of magnitude from 2000 to 2010, based on the assumption that greater than tenfold increases were implausible. The first scenario results in 9.3 cm sea level rise from Greenland dynamics (this does not include surface mass balance) by 2100 and the second scenario produces 46.7 cm sea level rise by 2100. The observational data now in hand for 2000-2010 show speedup during this period was ~30% for fast-flowing glaciers. While velocities did not double during the decade, a continued speedup might push average velocities over the doubling mark well before 2100, suggesting that the lower number for sea level rise from Greenland dynamics is well within reason. Our results also show wide variability and individual glaciers with marked speedup and slowdown. In our survey of more than 200 glaciers, some glaciers do double in speed but they do not approach a tenfold increase. Considering these results, our data suggest that sea level rise by 2100 from Greenland dynamics is likely to remain below the worst-case laid out by Pfeffer et al.

By adding our observational data to the theoretical results laid out by Pfeffer et al., we are ignoring uncertainties of the other assumptions of their experiment, but refining their velocity estimates. The result is not a new estimate of sea level rise but, rather, an improved detail for increasing accuracy. Indeed, a primary value of our study is not in providing an estimate of sea level rise, but in offering the sort of spatial and temporal details that will be needed to improve others’ modeling and statistical extrapolation studies. With just ten years of observations, our work is the tip of the iceberg for developing an understanding of long-term ice sheet behavior. Fortunately, our study provides a wide range of spatial and temporal coverage that is important for continued efforts aimed at understanding the processes controlling fast glacier flow. The record is still relatively short, however, so continued observation to extend the record is of critical importance.

In the same Science issue as our study, two perspective pieces comment on the challenges of ice sheet modeling [Alley and Joughin, 2012] and improving predictions of regional sea level rise [Willis and Church, 2012]. Clearly, all three of the papers are connected, as much as in pointing out where we need to learn more as in indicating where we have already made important strides.

Alley, R. B., and I. Joughin (2012), Modeling Ice-Sheet Flow, Science, 336(6081), 551-552.
IPCC (2007), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al., Eds., Cambridge University Press, ppp 996.
Moon, T., I. Joughin, B. Smith, and I. Howat (2012), 21st-Century Evolution of Greenland Outlet Glacier Velocities, Science, 336(6081), 576-578.
Pfeffer, W. T., J. T. Harper, and S. O’Neel (2008), Kinematic constraints on glacier contributions to 21st-century sea-level rise, Science, 321(000258914300046), 1340-1343.
Straneo, F., G. S. Hamilton, D. A. Sutherland, L. A. Stearns, F. Davidson, M. O. Hammill, G. B. Stenson, and A. Rosing-Asvid (2010), Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland, Nature Geoscience, 3(3), 1-5.
van den Broeke, M., J. Bamber, J. Ettema, E. Rignot, E. Schrama, W. Van De Berg, E. Van Meijgaard, I. Velicogna, and B. Wouters (2009), Partitioning Recent Greenland Mass Loss, Science, 326(5955), 984-986.
Willis, J. K., and J. A. Church (2012), Regional Sea-Level Projection, Science, 336(6081), 550-551.

Yamalian yawns

gavin — Fri, 11 May 2012 10:55:00 +0000

Steve McIntyre is free to do any analysis he wants on any data he can find. But when he ladles his work with unjustified and false accusations of misconduct and deception, he demeans both himself and his contributions. The idea that scientists should be bullied into doing analyses McIntyre wants and delivering the results to him prior to publication out of fear of very public attacks on their integrity is ludicrous.

By rights we should be outraged and appalled that (yet again) unfounded claims of scientific misconduct and dishonesty are buzzing around the blogosphere, once again initiated by Steve McIntyre, and unfailingly and uncritically promoted by the usual supporters. However this has become such a common occurrence that we are no longer shocked nor surprised that misinformation based on nothing but prior assumptions gains an easy toehold on the contrarian blogs (especially at times when they are keen to ‘move on’ from more discomforting events).

So instead of outrage, we’ll settle for simply making a few observations that undermine the narrative that McIntyre and company are trying to put out.

First of all, it should be made clear that McIntyre’s ~~FOI~~ EIR requests on the subject of Yamal are not for raw data, nor for the code or analysis methodology behind a published result, but for an analysis of publicly available data that has not been completed and has not yet been published. To be clear, these requests are for unpublished work.

Second, the unpublished work in question is a reconstruction of regional temperatures from the region of Yamal in Siberia. Regional reconstructions are generally more worthwhile than reconstructions from a single site because, if there is shared variance, the regional result is likely to be more robust and be more representative – and that makes it more valuable for continental and hemispheric comparisons. The key issues are whether all the trees (or some subset of them) share a common signal (are they mostly temperature sensitive? are some localities anomalous? etc.). It isn’t as simple as just averaging all the trees in a grid box or two. The history of such efforts follows a mostly standard path – local chronologies are put together, different ‘standardisation’ techniques are applied, more data is collected, wider collations are put together, and then regional reconstructions start to appear. Places that are remote (like Yamal) have the advantage of a lack of local human interference, and plenty of fossil material, but they are tricky to get to and data collection can be slow (not least because of the political situation in recent decades).

UK FOI (and EIR) legislation (quite sensibly) specifically exempts unpublished work from release provided the results are being prepared for publication (or are incomplete). So McIntyre’s appeals have tried to insinuate that no such publication is in progress (which is false) or that the public interest in knowing about a regional tree ring reconstruction from an obscure part of Siberia trumps the obvious interest that academics have in being able to work on projects exclusively prior to publication. This is a hard sell, unless of course one greatly exaggerates the importance of a single proxy record – but who would do that? (Oh yes: YAD06 – the most important tree in the world, The global warming industry is based on one MASSIVE lie etc.). Note that premature public access to unpublished work is something that many people (including Anthony Watts) feel quite strongly about.

Worse, McIntyre has claimed in his appeal that the length of time since the Briffa et al (2008) paper implies that the regional Yamal reconstruction has been suppressed for nefarious motives. But I find it a little rich that the instigator of a multitude of FOI requests, appeals, inquiries, appeals about inquires, FOIs about appeals, inquiries into FOI appeals etc. is now using the CRU’s lack of productivity as a reason to support more FOI releases. This is actually quite funny.

Furthermore, McIntyre is using the fact that Briffa and colleagues responded online to his last deceptive claims about Yamal, to claim that all Yamal-related info must now be placed in the public domain (including, as mentioned above, unpublished reconstructions being prepared for a paper). How this will encourage scientists to be open to real-time discussions with critics is a little puzzling. Mention some partial analysis online, and be hit immediately with a FOI for the rest…?

The history of this oddity (and it is odd) dates back to McIntyre’s early obsession with a reconstruction called the “Polar Urals” Briffa et al. (1995). This was a very early attempt at a local multi-proxy reconstruction, using a regression of both tree-ring widths and densities. McIntyre has previously objected to observations that 1032 was a particularly cold year in this reconstruction (though it was), that the dating of the trees was suspect (though it wasn’t), and that no-one revisited this reconstruction when reprocessed chronologies became available. [Little-known fact: McIntyre and McKitrick submitted a comment to Nature complaining about the dating issues in 1995 paper around Dec 2005/Jan 2006, which was rejected upon receipt of Briffa's response (which was an attachment in the second tranche of CRU emails). Neither this submission, the rejection (for good cause), nor the Polar Urals dating issue have been mentioned on Climate Audit subsequently.]

Around this point, McIntyre got the erroneous idea that studies were being done, but were being suppressed if they showed something ‘inconvenient’. This is of course a classic conspiracy theory and one that can’t be easily disproved. Accusation: you did something and then hid it. Response: No I didn’t, take a look. Accusation: You just hid it somewhere else. Etc. However, this is Keith Briffa we are talking about: the lead author of Briffa et al, (1998)(pdf) describing the “inconvenient” divergence problem in some tree ring density records, a subject that has been described and taken up by multiple authors – Jacoby, D’Arrigo, Esper, Wilson etc. Why McIntyre thought (thinks?) that one single reconstruction was so special that people would go to any lengths to protect it, while at the same time the same people were openly discussing problems in reconstructions across the whole northern hemisphere, remains mysterious.

Similarly, McIntyre recently accused Eric Steig of suppressing ‘inconvenient’ results from an ice core record from Siple Dome (Antarctica). Examination of the record in question actually demonstrates that it has exceptionally high values in the late 20th Century (reflecting the highest temperatures in at least the last 700 years, Mayewski et al.), exactly counter to McIntyre’s theory. McIntyre made these accusations public “a couple of days” – his words – after requesting the data, since apparently university professors have nothing more pressing to do than than respond instantly to McIntyre’s requests. In short, you have to give McIntyre what he wants within 48 hours or he will publicly attack your integrity. Unsurprisingly, no apology for that unjustified smear has been forthcoming.

So on to Yamal. The original data for the Yamal series came from two Russian researchers (Rashit Hantemirov and Stepan Shiyatov), and was given to CRU for collation with other tree-ring reconstructions (Briffa, 2000). As a small part of that paper, Briffa reprocessed the raw Yamal data with the regional curve standardisation (RCS) technique. The Russians published their version of the chronology with a different standardization a little later (Hantemirov and Shiyatov, 2002). McIntyre is accusing Briffa of ‘deception’ in stating that he did not ‘consider’ doing a larger more regional reconstruction at that time. However, it is clear from the 2000 paper that the point was to show hemispheric coherence across multiple tree ring records, not to create regional chronologies. Nothing was being ‘deceptively’ hidden and the Yamal curve is only a small part of the paper in any case.

Another little appreciated fact: When McIntyre started to get interested in this, he asked Briffa for the underlying measurement data from Yamal and two other locations whose reconstructions were used in Osborn and Briffa (2006). In May 2006, Briffa politely replied:

Steve these data were produced by Swedish and Russian colleagues – will pass on your message to them
cheers, Keith

Briffa was conforming to the standard protocol that directs people to the originators of data series for access to the underlying data, as opposed to the reconstructions which had been archived with the paper. McIntyre expressed great exasperation at this point, which is odd because in email 1548, McIntyre is quoted (from Sep 26, 2009 (and note the divergence in post URL and actual title)):

A few days ago, I became aware that the long-sought Yamal measurement data url had materialized at Briffa’s website – after many years of effort on my part and nearly 10 years after its original use in Briffa (2000).

To which Rashit Hanterminov responds:

Steve has an amnesia. I had sent him these data at February 2, 2004 on his demand.

Thus at the time McIntyre was haranguing Briffa and Osborn, McIntyre had actually had the raw Yamal data for over 2 years (again, unmentioned on Climate Audit), and he had had them for over 5 years when he declared that he had finally got them in 2009 (immediately prior to his accusations (again false) against Briffa of inappropriate selection of trees in his Yamal chronology).

Back to the main story. Of course, regional reconstructions are a definite goal of the dendro-climatology community and Briffa and colleagues have been working on these for years. Some of those results were published in Briffa et al (2008) as part of a special issue on the boreal forest and global change. Special issues come with deadlines, and as explained in a submission to the Muir Russell inquiry, a regional Yamal reconstruction putting together multiple sources of tree ring data was indeed ‘considered’ but wasn’t finished in time. McIntyre’s claim of deception comes from a strained reading of the MR submission (it is actually quite good reading). In response to extended (and yet again false) accusations from Ross McKitrick in the Financial Post:

Between these [two other reconstructions] we had intended to explore an integrated Polar Urals/Yamal larch series but it was felt that this work could not be completed in time and Briffa made the decision to reprocess the Yamal ring-width data to hand, using improved standardization techniques, and include this series in the submitted paper [Briffa et al., 2008].

Subsequently, in response to the issues raised by McIntyre, we explored the use of additional ring-width data local to the Yamal sub-fossil data. This work established the general validity of the published Yamal chronology information, albeit with significant statistical uncertainty, including during the medieval time and the late 20th century. [Refers to the online Oct 2009 response]

…

We still intend to publish an extended review paper that will compare and contrast features of the different published (and unpublished) versions of various regional composite chronologies in northern Eurasia and the effect on the character of climate reconstructions of calibrating them using different regression techniques.

So, Briffa et al did consider a regional reconstruction and are indeed working on it for publication, and it didn’t get into the 2008 paper due to time constraints. Clear, no?

However, a little later on in the submission, there is this paragraph:

(From McKitrick):

Thus the key ingredient in most of the studies that have been invoked to support the Hockey Stick, namely the Briffa Yamal series, depends on the influence of a woefully thin subsample of trees and the exclusion of readily-available data for the same area.

McKitrick is implying that we considered and deliberately excluded data from our Yamal chronology. The data that he is referring to were never considered at the time because the purpose of the work reported in Briffa (2000) and Briffa et al. (2008) was to reprocess the existing dataset of Hantemirov and Shiyatov (2002).

(my highlights).

This is clearly a response to McKitrick’s unjustified accusations, and in using the reference to the 2008 paper is a little contradictory to the paragraphs above which were much more explicit about the background and purpose of the 2008 paper. However, to take a slight mis-statement in a single sentence, when copious other information was being provided in the same submission, and accusing people of deliberate deception is a huge overreach. Were they trying to deceive only the people who hadn’t read the previous page? It makes no sense at all. Instead, McIntyre conflates the situation at the time of the 2000 paper with the very different situation around 2008 in order to paint a imaginary picture of perfidy.

The one new element this week is the UK ICO partial ruling on McIntyre’s appeal for access to the (still unpublished) regional Yamal reconstruction. For reasons that are as yet unclear (since the full ICO ruling has not yet been issued), the list of components from which the regional reconstruction might be built were released by UEA. All of this data is already public domain. And of course, since Briffa et al have been working on regional reconstructions since prior to the 2008 paper it is unsurprising that they have such a list. McIntyre then quotes an email from Osborn sent in 2006 in support of his claim that the reconstructions were finished at that point, but that is again a very strained reading. Osborn only lists the areas (and grid boxes) in which regional reconstructions might be attempted since “most of the trees lie within those boxes”. It makes no statement whatsoever about the work having already been done.

McIntyre’s subsequent insta-reconstruction from the list is apparently the ‘smoking gun’ that the results are being withheld because they are inconvenient, but if any actual scientist had produced such a poorly explained, unvalidated, uncalibrated, reconstruction with no error bars or bootstrapping or demonstrations of common signals etc., McIntyre would have been (rightly) scornful. Though apparently, scientists are supposed to accept his reconstruction at face value. The irony is of course that the demonstration that a regional reconstruction is valid takes effort, and needs to be properly documented. That requires a paper in the technical literature and the only way for Briffa et al to now defend themselves against McIntyre’s accusations is to publish that paper (which one can guarantee will have different results to what McIntyre has thrown together). In the meantime, they can’t discuss it online or defend themselves because the issue with the FOI appeal is precisely their ability to work on projects prior to publication without being forced to go public before they are finished.

Finally, a couple of observations regarding the follow-through from Andrew Montford and Anthony Watts. Montford’s summary is an easier read than anything McIntyre writes, but it is clear Montford’s talents lie in the direction of fiction, not documentary work. All of his claims of “why paleoclimatologists found the series so alluring”, or that the publication “must have been a severe blow”, or “another hockey stick” was “made almost to order to meet the requirements of the paleoclimate community” and other accusations are simply products of his imagination. He also makes up claims, that for instance, McIntyre asking Briffa for the Yamal data “was, as expected, turned down flat” (not true – the actual response was given above) and he imagines even more ‘deceptions’ than McIntyre. Since he assumes the worst of the people involved, everything he sees is twisted to conform to his prior assumptions – if there is an innocent explanation, he expends no time considering it. As for Watts, the funny thing is that he immediately thinks that Michael Mann needs to answer these accusations, and attempts a twitter campaign of harassment when Mike, rightly, points out that Yamal doesn’t actually impact that much and, in any case, it has nothing to do with him at all. Watts is clearly a cheerleader for the ‘Blame Mike First’ campaign, so maybe his next post will be on why Mike is responsible for the Greek bank default (have you seen those bond yield curves?!?).

It should also go without saying that sometimes life gets in the way of work, and suggestions that academics have to work on issues according to a timetable dictated by hostile and abusive commentators is completely antithetical to the notion of free inquiry or the inevitable constraints of real life. McIntyre is of course free to do any analysis he wants, but he has no right to demand that other people do work for him under fear of highly public false accusations of dishonesty. We can nonetheless look forward to more of these episodes, mainly because they serve their purpose so well.

References

K.R. Briffa, V.V. Shishov, T.M. Melvin, E.A. Vaganov, H. Grudd, R.M. Hantemirov, M. Eronen, and M.M. Naurzbaev, "Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia", Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 363, 2008, pp. 2269-2282. DOI.

K.R. Briffa, P.D. Jones, F. Schweingruber, S. Shiyatov, and E. Cook, "Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia", Nature, vol. 376, 1995, pp. 156-159. DOI.

K.R. Briffa, F.H. Schweingruber, P.D. Jones, T.J. Osborn, I.C. Harris, S.G. Shiyatov, E.A. Vaganov, and H. Grudd, "Trees tell of past climates: but are they speaking less clearly today?", Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 353, 1998, pp. 65-73. DOI.

P.A. Mayewski, K.A. Maasch, J.W.C. White, E.J. Steig, E. Meyerson, I. Goodwin, V.I. Morgan, T. van Ommen, M.A.J. Curran, J. Souney, and K. Kreutz, "A 700 year record of Southern Hemisphere extratropical climate variability", Annals of Glaciology, vol. 39, 2004, pp. 127-132. DOI.

K.R. Briffa, "Annual climate variability in the Holocene: interpreting the message of ancient trees", Quaternary Science Reviews, vol. 19, 2000, pp. 87-105. DOI.

R.M. Hantemirov, and S.G. Shiyatov, "A continuous multimillennial ring-width chronology in Yamal, northwestern Siberia", The Holocene, vol. 12, pp. 717-726. DOI.

T.J. Osborn, "The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years", Science, vol. 311, 2006, pp. 841-844. DOI.

The legend of the Titanic

rasmus — Thu, 03 May 2012 06:39:29 +0000

It’s 100 years since the Titanic sank in the North Atlantic, and it’s still remembered today. It was one of those landmark events that make a deep impression on people. It also fits a pattern of how we respond to different conditions, according to a recent book about the impact of environmental science on the society (Gudmund Hernes Hot Topic – Cold Comfort): major events are the stimulus and the change of mind is the response.

Hernes suggests that one of those turning moments that made us realize our true position in the universe was when we for the first time saw our own planet from space.

NASA Earth rise

He observes that

[t]he change in mindset has not so much been the result of meticulous information dissemination, scientific discourse and everyday reasoning as driven by occurrences that in a striking way has disclosed what was not previously realized or only obscurely seen.

Does he make a valid point? If the scientific information looks anything like the situation in a funny animation made by Alister Doyle (Dummiez: climate change and electric cars), then it is understandable.

Moreover, he is not the only person arguing that our minds are steered by big events – the importance of big events was even acknowledged in the fiction ‘State of Fear‘.

A recent paper by Brulle et al (2012) also suggests that the provision of information has less impact than what opinion leaders (top politicians) say.

However, if the notion that information makes little impact is correct, one may wonder what the point would be in having a debate about climate change, and why certain organisations would put so much efforts into denial, as described in books such as Heat is on, Climate Cover-up, Republican war on science, Merchants of doubt, and The Hockeystick and Climate Wars. Why then, would there be such things as ‘the Heartland Institute’, ‘NIPCC’, climateaudit, WUWT, climatedepot, and FoS, if they had no effect? And indeed, the IPCC reports and the reports from the National Academy of Sciences? One could even ask whether the effort that we have put into RealClimate has been in vain.

Then again, could the analysis presented in Brulle et al. be misguided because the covariates used in their study did not provide a sufficiently good representation of important factors? Or could the results be contaminated by disinformation campaigns?

Their results and Hernes assertion may furthermore suggest that there are different rules for different groups of people: What works for scientists doesn’t work for lay people. It is clear from the IPCC and international scientific academies that climate scientists in general are impressed by the increasing information (Oreskes, 2004).

Hernes does, however, acknowledge that a background knowledge is present and may play a role in interpreting events, which means that most of us no longer blame the gods for calamities (in the time before the enlightenment, there were witch hunts and sacrifices to the gods). The presence of the knowledge now provides a rational background, which sometimes seems to be taken for granted.

Maybe it should be no surprise that the situation is as described by Hernes and Brulle et al., because historically science communication hasn’t really been appreciated by the science community (according to ‘Don’t be such a scientist‘) and has not been enthusiastically embraced by the media. There is a barrier to information flow, and Somerville and Hassol (2011) observe that a rational voice of scientists is sorely needed.

The rationale of Hernes’ argument, however, is that swaying people does not only concern rational and intellectual ideas, but also an emotional dimension. The mindset influences a person’s identity and character, and is bundeled together with their social network. Hence, people who change their views on the world, may also distance themselves from some friends and connect with new people. A new standpoint will involve a change in their social connections in addition to a change in rational views. Events, such as the Titanic, Earth rise, 911, and Hurricane Katrina influence many people both through rational thought and emotions, where people’s frame of mind shifts together with their friends’.

What do I think? Public opinion is changed not by big events as such, but by the public interpretation of those events. Whether a major event like hurricane Katrina or the Moscow heat wave changes attitudes towards climate change is determined by people’s interpretation of this event, and whether they draw a connection to climate change – though not necessarily directly. I see this as a major reason why organisations such as the Heartland are fighting their PR battle by claiming that such events are all natural and have nothing to do with emissions.

The similarity between these organisations and the Titanic legend is that there was a widespread misconception that it could not sink (and hence its fame) and now organisations like the Heartland make dismissive claims about any connection between big events and climate change. However, new and emerging science is suggesting that there may indeed be some connections between global warming and heat waves and between trends in mean precipitation and more extreme rainfall.

References

R.J. Brulle, J. Carmichael, and J.C. Jenkins, "Shifting public opinion on climate change: an empirical assessment of factors influencing concern over climate change in the U.S., 2002–2010", Climatic Change. DOI.

N. Oreskes, "BEYOND THE IVORY TOWER: The Scientific Consensus on Climate Change", Science, vol. 306, 2004, pp. 1686-1686. DOI.

R.C.J. Somerville, and S.J. Hassol, "Communicating the science of climate change", Physics Today, vol. 64, 2011, pp. 48-. DOI.

Unforced variations: May 2012

group — Tue, 01 May 2012 20:23:45 +0000

New open thread for this month: misrepresentations of wind farm impacts on local climate? Clouds and contrarians? or whatever…

Unlocking the secrets to ending an Ice Age

group — Sat, 28 Apr 2012 11:25:12 +0000

Guest Commentary by Chris Colose, SUNY Albany

It has long been known that characteristics of the Earth’s orbit (its eccentricity, the degree to which it is tilted, and its “wobble”) are slightly altered on timescales of tens to hundreds of thousands of years. Such variations, collectively known as Milankovitch cycles, conspire to pace the timing of glacial-to-interglacial variations.

Despite the immense explanatory power that this hypothesis has provided, some big questions still remain. For one, the relative roles of eccentricity, obliquity, and precession in controlling glacial onsets/terminations are still debated. While the local, seasonal climate forcing by the Milankovitch cycles is large (of the order 30 W/m²), the net forcing provided by Milankovitch is close to zero in the global mean, requiring other radiative terms (like albedo or greenhouse gas anomalies) to force global-mean temperature change.

The last deglaciation occurred as a long process between peak glacial conditions (from ~26-20,000 years ago) to the Holocene (~10,000 years ago). Explaining this evolution is not trivial. Variations in the orbit cause opposite changes in the intensity of solar radiation during the summer between the Northern and Southern hemisphere, yet ice age terminations seem synchronous between hemispheres. This could be explained by the role of the greenhouse gas CO₂, which varies in abundance in the atmosphere in sync with the glacial cycles and thus acts as a “globaliser” of glacial cycles, as it is well-mixed throughout the atmosphere. However, if CO₂ plays this role it is surprising that climatic proxies indicate that Antarctica seems to have warmed prior to the Northern Hemisphere, yet glacial cycles follow in phase with Northern insolation (“INcoming SOLar radiATION”) patterns, raising questions as to what communication mechanism links the hemispheres.

There have been multiple hypotheses to explain this apparent paradox. One is that the length of the austral summer co-varies with boreal summer intensity, such that local insolation forcings could result in synchronous deglaciations in each hemisphere (Huybers and Denton, 2008). A related idea is that austral spring insolation co-varies with summer duration, and could have forced sea ice retreat in the Southern Ocean and greenhouse gas feedbacks (e.g., Stott et al., 2007).

Based on transient climate model simulations of glacial-interglacial transitions (rather than “snapshots” of different modeled climate states), Ganopolski and Roche (2009) proposed that in addition to CO2, changes in ocean heat transport provide a critical link between northern and southern hemispheres, able to explain the apparent lag of CO2 behind Antarctic temperature. Recently, an elaborate data analysis published in Nature by Shakun et al., 2012 (pdf) has provided strong support for these model predictions. Shakun et al. attempt to interrogate the spatial and temporal patterns associated with the last deglaciation; in doing so, they analyze global-scale patterns (not just records from Antarctica). This is a formidable task, given the need to synchronize many marine, terrestrial, and ice core records.

The evolution of deglaciation

By analyzing 80 proxy records from around the globe (generally with resolutions better than 500 years) the authors are able to evaluate the changes occurring during different time periods in order to characterize the spatial and temporal structure of the deglacial evolution.

Shakun et al. confirm Ganopolski’s and Roche’s proposition that warming of the Southern Hemisphere during the last deglaciation is, in part, attributable to a bipolar-seesaw response to variations in the Atlantic Meridional Overturning Circulation (AMOC). This is hypothesized to result from fresh water input into the Northern Hemisphere (although it is worth noting that the transient simulations of this sort fix the magnitude of the freshwater perturbation, so this doesn’t necessarily mean that the model has the correct sensitivity to freshwater input).

The bi-polar seesaw is usually associated with the higher-frequency abrupt climate changes (e.g., Dansgaard-Oeschger and Heinrich events) that are embedded within the longer, orbital timescale variations. However, numerous studies have indicated that it also sets the stage for initiating the full deglaciation process. In this scenario, the increase in boreal summer insolation melts enough NH ice to trigger a strong AMOC reduction, which cools the North at the expense of warming the South. The changes in Antarctica are lagged somewhat due to the thermal inertia of the Southern Ocean, but eventually the result is degassing of CO2 from the Southern Ocean and global warming. In particular, CO₂ levels started to rise from full glacial levels of about 180 parts per million (ppm), reaching 265 ppm 10,000 years ago (or ~2.1 W/m² radiative forcing), and with another slow ~15 ppm rise during the Holocene.

Figure 1: Simplified schematic of the deglacial evolution according to Shakun et al (2012). kya = kiloyears ago; NH = Northern Hemisphere

The evolution of temperature as a function of latitude and the timing of CO2 rise are shown below (at two different time periods in part a, see the caption). There is considerable spatial and temporal structure in how the changes occur during deglaciation. There is also long-term warming trend superimposed on higher-frequency “abrupt climate changes” associated with AMOC-induced heat redistributions.

Figure 2: Temperature change before increase in CO₂ concentration. a, Linear temperature trends in the proxy records from 21.5–19 kyr ago (red) and 19–17.5 kyr ago (blue) averaged in 10° latitude bins with1σ uncertainties. b, Proxy temperature stacks for 30° latitude bands with 1σ uncertainties. The stacks have been normalized by the glacial–interglacial (G–IG) range in each time series to facilitate comparison. From Shakun et al (2012)

What causes the CO₂ rise?

The ultimate trigger of the CO₂ increase is still a topic of interesting research. Some popular discussions like to invoke simple explanations, such as the fact that warmer water will expel CO₂, but this is probably a minor effect (Sigman and Boyle, 2000). More than likely, the isotopic signal (the distribution of ¹³C-depleted carbon that invaded the atmosphere) indicates that carbon should have been “mined’ from the Southern ocean as a result of the displacement of southern winds, sea ice, and perturbations to the ocean’s biological pump (e.g., Anderson et al., 2009).

This view has been supported by another recent paper (Schmitt et al., 2012) that represents a key scientific advance in dissecting this problem. Until recently, analytical issues in the ice core measurements provided a limitation on assessing the deglacial isotopic evolution of ¹³C. Because carbon cycle processes such as photosynthesis fractionate the heavy isotope ¹³C from the lighter ¹²C, isotopic analysis can usually be used to “trace” sources and sinks of carbon. A rapid depletion in ¹³C between about 17,500 and 14,000 years ago, simultaneous with a time when the CO₂ concentration rose substantially, is consistent with release of CO₂ from an isolated deep-ocean source that accumulated carbon due to the sinking of organic material from the surface.

Figure 3: Ice core reconstructions of atmospheric δ¹³C and CO₂ concentration covering the last 24 kyr, see Schmitt et al (2012)

Skeptics, CO₂ lags, and all that…

Not surprisingly, several people don’t like this paper because it reaffirms that CO₂ is important for climate. The criticisms have ranged from the absurd (water vapor is still not 95% of the greenhouse effect, particularly in a glacial world where one expects a drier atmosphere) to somewhat more technical sounding (like criticizing the way they did the weighting of their proxy records, though the results aren’t too sensitive to their averaging method). There’s also been confusion in how the results of Shakun et al. fit in with previous results that identified a lag between CO₂ and Antarctic temperatures (e.g., Caillon et al., 2003).

Unlike the claims of some that these authors are trying to get rid of the “lag,” Shakun et al. fully support the notion that Antarctic temperature change did in fact precede the CO₂ increase. This is not surprising since we fully expect the carbon cycle to respond to radical alterations to the climate. Moreover, there is no mechanism that would force CO₂ to change on its own (in preferred cycles) without any previous alterations to the climate. Instead, Shakun et al. show that while CO₂ lagged Antarctic temperatures, they led the major changes in the global average temperature (including many regions in the Northern Hemisphere and tropics).

It is important to realize that the nature of CO₂’s lead/lag relationship with Antarctica is insightful for our understanding of carbon cycle dynamics and the sequence of events that occur during a deglaciation, but it yields very little information about climate sensitivity. If the CO₂ rise is a carbon cycle feedback, this is still perfectly compatible with its role as a radiative agent and can thus “trigger” the traditional feedbacks that determine sensitivity (like water vapor, lapse rate, etc). Ganopolski and Roche (2009), for example, made it clear that one should be careful in using simple lead and lags to infer the nature of causality. If one takes the simple view that deglaciation is forced by only global ice volume change and greenhouse feedbacks, then one would be forced to conclude that Antarctic temperature change led all of its forcings! The communication between the NH and Antarctica via ocean circulation is one way to resolve this, and is also supported by the modeling efforts of Ganopolski and Roche. This also helps clear up some confusion about whether the south provides the leading role for the onset or demise of glacial cycles (it apparently doesn’t).

A number of legitimate issues still remain in exploring the physics of deglaciation. For instance, the commentary piece by Eric Wolff references earlier deglaciations and points out that solar insolation may have increased in the boreal summer during the most recent event, but was still not as high as during previous deglacial intervals. It will be interesting to see how these issues play out over the next few years.

References

P. Huybers, and G. Denton, "Antarctic temperature at orbital timescales controlled by local summer duration", Nature Geoscience, vol. 1, 2008, pp. 787-792. DOI.

L. Stott, A. Timmermann, and R. Thunell, "Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming", Science, vol. 318, 2007, pp. 435-438. DOI.

A. Ganopolski, and D.M. Roche, "On the nature of lead–lag relationships during glacial–interglacial climate transitions", Quaternary Science Reviews, vol. 28, 2009, pp. 3361-3378. DOI.

J.D. Shakun, P.U. Clark, F. He, S.A. Marcott, A.C. Mix, Z. Liu, B. Otto-Bliesner, A. Schmittner, and E. Bard, "Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation", Nature, vol. 484, 2012, pp. 49-54. DOI.

D.M. Sigman, and E.A. Boyle, , Nature, vol. 407, pp. 859-869. DOI.

R.F. Anderson, S. Ali, L.I. Bradtmiller, S.H.H. Nielsen, M.Q. Fleisher, B.E. Anderson, and L.H. Burckle, "Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2", Science, vol. 323, 2009, pp. 1443-1448. DOI.

J. Schmitt, R. Schneider, J. Elsig, D. Leuenberger, A. Lourantou, J. Chappellaz, P. Kohler, F. Joos, T.F. Stocker, M. Leuenberger, and H. Fischer, "Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores", Science, vol. 336, 2012, pp. 711-714. DOI.

N. Caillon, "Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III", Science, vol. 299, pp. 1728-1731. DOI.

Another well-deserved honor: Oeschger medal awarded to Michael Mann

group — Tue, 24 Apr 2012 13:10:36 +0000

As many will have already heard, our colleague, RC co-founder and friend Michael Mann will receive the Oeschger medal from the European Geosciences Union this week in Vienna. We are delighted to announce this and to congratulate Mike.

Hans Oeschger was a Swiss scientist originally trained as a nuclear physicist. His name is well known in climate science, especially because of his discovery, with Willi Dansgaard, of the Dansgaard-Oeschger events (the rapid climate changes during the last glacial period, first observed in Greenland ice cores). He was even better known in the radiocarbon research community as famously having developed one of the first instruments (the “Oeschger counter”) for measuring carbon-14. This paved the way for determining the age of very small organic materials, including samples from deep-sea sediment cores, which eventually led to the validation of the Milankovitch theory of ice ages. Oeschger and his colleagues in Bern were the first to measure the glacial-interglacial change of atmospheric CO₂ in ice cores, showing that atmospheric concentrations of CO₂ during the glacial period was 50% lower than the pre-industrial concentration, a result predicted by Arrhenius nearly a century earlier. Oeschger may thus be credited with work that was critical to validating two of the most important theories in science: the role of CO₂ in climate change, and the role of changes in the earth’s orbit. Oeschger was also an accomplished musician, and was known to join colleagues in playing chamber music at the International Conference on Radiocarbon.

Oeschger left rather large shoes to fill, and it is a great honor for Mike Mann to win an award bearing Oeschger’s name. Most everyone will probably assume that the award is for Mike’s well known “hockey stick” work. No doubt this is part of it, but the Oeschger award has never been given simply for the publication of one study, but rather for a career’s-worth of outstanding achievements. Most of the previous medalists are a good deal more senior than Mike Mann, and include paleoceanographer Laurent Labeyrie, limnologist Francoise Gasse, ice core pioneers Dominique Raynaud and Sigfus Johnsen and number of other major names in the climate and paleoclimate research, including RC’s own Ray Bradley.

Mike’s work, like that of previous award winners, is diverse, and includes pioneering and highly cited work in time series analysis (an elegant use of Thomson’s multitaper spectral analysis approach to detect spatiotemporal oscillations in the climate record and methods for smoothing temporal data), decadal climate variability (the term “Atlantic Multidecadal Oscillation” or “AMO” was coined by Mike in an interview with Science’s Richard Kerr about a paper he had published with Tom Delworth of GFDL showing evidence in both climate model simulations and observational data for a 50-70 year oscillation in the climate system; significantly Mike also published work with Kerry Emanuel in 2006 showing that the AMO concept has been overstated as regards its role in 20th century tropical Atlantic SST changes, a finding recently reaffirmed by a study published in Nature), in showing how changes in radiative forcing from volcanoes can affect ENSO, in examining the role of solar variations in explaining the pattern of the Medieval Climate Anomaly and Little Ice Age, the relationship between the climate changes of past centuries and phenomena such as Atlantic tropical cyclones and global sea level, and even a bit of work in atmospheric chemistry (an analysis of beryllium-7 measurements). Mike’s earliest work, as a physicist, involved studying the behavior of liquids and solids, and trying to understand phenomena such as the structural ordering of high temperature superconductors. In the earth sciences, he has published on topics as varied as the recovery from the KT-boundary mass extinction event and the factors driving long-term changes in the volume of the Great Salt Lake. He has studied and published on the impacts of historical and projected climate change on everything from the behavior of the Asian Summer Monsoon, to Atlantic Hurricanes, to rainfall patterns in the U.S. And for those interested in the hard-nosed statistics by which a scientist’s productivity gets measured, a quick check on the ISI web site will tell you that he has an “H Index” of 40 (that means that 40 of his papers have been cited at least 40 times), more than twenty of his papers have over 100 citations each, and two have over 700. Those are high numbers by any comparison.

But back to the hockey stick. Mike has weathered some rather intense scrutiny and criticism over the years, mostly over the details of a paper nearly 15 years old. Yet the basic conclusions of the “hockey stick” remain, and indeed have been strengthened by subsequent work. Most will be aware, for example, that the conclusion that the past few decades are likely the warmest of the past millennium — i.e. the conclusion of the best-known of Mike’s papers in Nature and Geophysical Research Letters –has never been seriously challenged. But well beyond the simple fact of having been right, Mike’s work was seminal, like Oeschger’s, in playing a pivotal role in launching an entirely new field of study. Although some earlier work along similar lines had been done by other paleoclimate researchers (Ed Cook, Phil Jones, Keith Briffa, Ray Bradley, Malcolm Hughes, and Henry Diaz being just a few examples), before Mike, no one had seriously attempted to use all the available paleoclimate data together, to try to reconstruct the global patterns of climate back in time before the start of direct instrumental observations of climate, or to estimate the underlying statistical uncertainties in reconstructing past temperature changes. Since Mike’s pioneering work (starting in 1995), hundreds of papers have adopted the basic approach he pioneered, and numerous PHD projects have been launched to try to improve upon it. Methods have improved of course, and no doubt will improve further (paleoclimate reconstruction using weather forecast data assimilation methods is the latest and most promising recent development). That Mike is a co-author on many of the latest and most innovative publications in this area — with dozens of different people — attests to the groundbreaking nature of his work.

We look forward to seeing Mike’s award lecture in Vienna, and we offer our heartfelt congratulations to a well-deserved honor. And while we are at it, we should congratulate Mike in advance for his election as a Fellow of the American Geophysical Union; that honor will be bestowed this fall in San Francisco.

Finally, we would be remiss to not mention that Mike has spent much of the past few months touring and lecturing on his experiences as an accidental and reluctant public figure in the debate over human-caused climate change, as detailed in his recent book The Hockey Stick and the Climate Wars: Dispatches from the Front Lines.

P.S. For those at EGU, you should also check out glaciologist Ian Joughin’s award lecture (Wednesday evening) for the Agassiz medal, for his important work in documenting and understanding the acceleration of Antarctica and Greenland’s glaciers.