The graphic incorporates the latest information from the just–released IPCC report. Richard Millar, working with Myles Allen, provided the “guts” of the interactive graphic for future temperature rise, which are based on the high scenario in the IPCC report.

The foundation of this graphic is part of a new collaborative research effort between UCS, Oxford University, and others, which you’ll hear more about around the time of an upcoming American Geophysical Union meeting. For now, join Bill Gates and more than 125,000 others who have checked out past and future temperatures over their lifetimes.

How hot has it gotten over your lifetime? What about your grandparents? What about a child dear to you? Send me a comment about your personalized global warming metrics.

With today’s release of the Summary for Policymakers of Working Group I:  The Physical Science Basis, the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5) presents us with a very different opportunity to wrestle with our collective response to the slings and arrows of unabated carbon emissions on our warming planet. To be sure, the formal language of the IPCC is far less eloquent than Shakespeare’s, but the authoritative and cautiously-written climate science synthesis provokes us to confront profoundly important questions – questions that are hugely time-sensitive, not timeless.

Much media attention in the lead-up to the release has focused on questions over the pace of warming during the past decade. But the most fundamental questions that the IPCC can inform and motivate us to address are not about current changes, driven largely by past emissions – they are about how the emissions choices we make today and in the near future will affect the scale of warming and climate disruption that our generation imposes on generations to come.

Most often, the question gets framed as “will we stay below 2°C?”, that is, will we reduce emissions swiftly enough to keep global average surface temperatures from rising to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels? Signing the Copenhagen Accord in 2009, world leaders agreed to keep temperature increases resulting from heat-trapping emissions to less than 2° C, a target aimed at limiting dangerously disruptive climate impacts. A policy target informed by science, “2° C” is the formally codified benchmark, the line in the sand by which nations have agreed to measure our collective success in providing  generations to come with a secure climate future.

The IPCC’s Summary for Policy Makers (SPM) tells us that global average surface temperatures have risen about 0.85° C since 1900. It concludes that “cumulative emissions of CO₂ largely determine global mean surface warming by the late 21^st century and beyond” – in other words, the principal driver of long-term warming is total emissions of CO_2. And it finds that having a greater than 66% probability of keeping warming caused by CO₂ emissions alone to below 2° C requires limiting total further emissions to between 370-540 Gigatons of carbon (GtC).

At current rates of CO₂ emissions (about 9.5 GtC per year), we will hurtle past the 2° C carbon budget in less than 50 years. And this conservatively assumes that emissions rates don’t continue on their current upward trajectory of ~3 percent per year.

Future temperature change is projected comparing results of multiple global climate models using four “Representative Concentration Pathways (RCP’s)” – standardized scenarios of possible future concentrations of heat-trapping gases, aerosols, and other human drivers of climate change.

The SPM draws modest direct attention to some of the IPCC’s findings most relevant to the 2° C policy target. Table SPM2, for example, projects temperature changes to the end of this century (2081-2100) relative to a 1986-2005 baseline, rather than to the pre-industrial baseline upon which the 2° C target rests. But one can draw upon the information within the table’s footnote, which quantifies mean projected warming between 1850-1900 and 1986-2005 as 0.61° C to assess warming relative to pre-industrial levels more directly. More in-depth information will be forthcoming in Chapter 12 of the full report, due out next week.

Global carbon dioxide emissions are currently tracking above the highest concentration pathway (RCP8.5), a pathway that the IPCC projects will bring global average surface temperatures well above 2° C by mid-century and above 4° C by 2100. Only projections following the lowest concentration pathway (RCP2.6) result in a mean increase in global average temperatures below 2° C.

There are uncertainties around these temperature projections, of course. The SPM concludes that “global surface temperature change for the end of the 21^st century is likely to exceed 2 °C for RCP6.0 and RCP8.5 and more likely than not to exceed 2° C for RCP 4.5.” And, importantly “warming will continue beyond 2100 under all RCP scenarios except RCP 2.6”.

Can we transition swiftly to a pathway akin to RCP 2.6?  Doing so would require global carbon dioxide emissions reductions of 50% below 1990 levels by 2050 and may well require sustained globally net negative CO₂ emissions, i.e. net removal of CO₂ from the atmosphere in the second half of this century. Some have proposed that this might be achieved by both dramatically reducing carbon emissions, and coupling large-scale expansion of bioenergy with carbon capture and storage (CCS).

Beneath its cautious prose, the IPCC report firmly highlights the urgency of our challenge. The science itself does not prescribe specific actions. And the IPCC steers clear of assessing the relative likelihood that political will and policy choices will lead us to follow more closely along one concentration pathway or another. And yet – the IPCC report’s findings make clear that with each passing year of continued high emissions, the prospect of keeping temperatures from rising less than 2°C through emissions reductions alone will become ever more vanishingly small. They challenge us to both redouble efforts to aggressively reduce emissions and to begin the hard work of preparing now to manage the risks of a world that may warm well in excess of 2°C within this century.

Look for more insights from the IPCC Working Group II report (Impacts, Adaptation and Vulnerability) due out next March and the Working Group III report (Mitigation) slated for release in April.

The Intergovernmental Panel on Climate Change (IPCC) is poised to release the latest climate assessment “summary for policymakers” in Stockholm, Sweden, when they meet September 23 – 26, where these hot topics will be addressed.

Nearly all global indicators show “full speed ahead” for trends consistent with human-influenced climate change

Even as a car slows down to go over a “speed bump,” there is no question the car is still advancing down the road. Similarly, the global average surface temperature trend of late is like a “speed bump” and we would expect the rate of temperature increase to speed up again just as most drivers do after clearing the speed bump.

We keep getting questions about this air temperature trend that has more to do with where the excess heat is primarily going — the ocean — and the rate at which heat transfers to the deep ocean, as well as other factors that can temporarily offset the influence of heat-trapping gases. These include ocean cycles such as phases of the El Niño Southern Oscillation in the Pacific Ocean. Or tiny pollution particles as well as tiny particles emanating from volcanic eruptions that reflect sunlight.

More importantly, society tends to focus quite heavily on the surface temperature since that is where most of us live our daily lives. We know that is just one of the many ways we measure climate change. A look at the big picture shows a world that continues to face disruption from human-induced climate change.  Each indicator has a different period of length for rates of change that you can check out in these hyperlinks: ocean heat content, global sea level rise, global sea surface temperature,  global surface temperature, Arctic minimum sea ice extent, and reference glaciers cumulative mass.

Globally, many indicators show a comprehensive view that the climate system is changing: the ocean and atmosphere are warming, sea level is rising, snow and ice is diminishing – at unprecedented rates. Data source: EPA Indicators graphs with period of record available as of September 24, 2013. Table created for this post.

Look for the IPCC to place extreme events in context

Scientists have long understood that weather events spawn within a background state of conditions that climate change influences, such as seasonal sea surface temperature, ice extent, water vapor volume in the atmosphere, etc. The most extreme of these weather events can wreak havoc on communities that suffer exposure to such monstrous calamities. In a few days, look to the IPCC summary to shed light on the latest science.

Since the IPCC issued a special report on extreme events in 2012, we know that the observed historic record can only get us so far in our understanding since by definition these events are very rare. However, over just the past few years, the science has advanced to the point where models can simulate conditions surrounding similar extreme events. Unlike Earth, these can be investigated in ways that can increase confidence in the statistical outcomes regarding similar types of extreme events. Using such evidence, scientists declared that flooding conditions in Thailand in 2011 were from rains in the normal range. Unfortunately, the exposed communities had other risks that conspired to make such an event  a tragic disaster in Thailand. On the other hand, investigations into the severe Texas drought in 2011 and the historic storm surge from Hurricane Sandy that battered the U.S. East Coast around Halloween 2012 indicate that the severity of these events have links with a changing climate.

Community planners are doing what they can to incorporate climate change projections of the future to better prepare for even more extreme events going forward. Especially given the limited budgets of local communities, this focus by regional planners is a heroic public service. In many ways I think of these planners as the real “first responders” of the extreme events of the future.

An inside view of the IPCC

As science historian Spencer Weart pointed out in a previous post, it was established jointly under the auspices of the World Meteorological Organization and the United Nations Environmental Program in 1988 to assess “the scientific information that is related to the various components of the climate change issue…needed to enable environmental and socio-economic consequences of climate change to be evaluated”.

I was a co-lead author of the final chapter in the first assessment science report (1990), a reviewer during the second assessment (1995) and co-chair of Working Group II, which addressed climate impacts, adaptation, and vulnerability for the third assessment (2001).

As is often pointed out, the IPCC does not conduct original research. Its mission is to assemble experts who are asked to use their best scientific judgment to assess the status of scientific understanding across multiple facets of climate change science—including social science, as this understanding relates to climate impacts and vulnerabilities—and to consider the costs and benefits of climate mitigation and adaptation strategies. These experts then write the reports.

Who writes the IPCC reports?

Who are these experts? They are nominated by participating nations (more than a hundred nations participate) and relevant UN bodies. In the case of the assessment report I headed, we had over 1000 nominations for authors with full resumes (I read them all), and from these we carefully selected authors (~180) who had published relevant papers in the scientific literature. We later drew from this list for chapter review editors (~30), and used many others (>400) as reviewers.

Assessing implies much more than simply reporting what is in the published literature. A new, interesting, and provocative finding might, for example, be given less weight than a somewhat older more established finding. This in part explains the range of confidence that will be given to a particular summary statement about the state of scientific understanding relating to some aspect of climate change or climate impacts.

How have climate models from previous reports performed?

Models are an important component of an assessment since they can be used to make projections based upon recent trends and a plausible understanding of what is driving the trends. Some critics of the IPCC approach say that such model projections are not to be trusted and thus should not be used in the policy making process. But it is illustrative to examine some of the projections made in the 1990 assessment. By 20th century standards the 1980s had been an exceptionally warm decade. If the scientific consensus that this warming was due to the accumulation of greenhouse gases in the atmosphere, and that human activities (e.g.. combustion of fossil fuels and land use practices) were responsible for the rising atmospheric concentrations of greenhouse gases, then a business as usual scenario could result in several discernable changes in climate. Among these were the following: 1) surface warming that would be greater on land than on the ocean; 2) the highest rates of warming would occur at high latitudes in the Northern Hemisphere; 3) an increase in anomalous high- and decrease in anomalous low- temperature events; 4) an increase in precipitation at high latitude in winter, and 5) intense precipitation events increasing in many regions. In 1990 none of these were yet apparent with statistical significance, and yet today, two decades later, data for each are now convincing and these trends are accepted within the climate science community as further indications of human-caused climate change.

Changes in temperature, sea level, and northern hemisphere snow cover. Figure courtesy of the IPCC (AR4).

The rate of change in some aspects of climate has exceeded expectations of what could occur in a decade or several decades into the future. Significant among these are the loss of summer sea ice in the central region of the Arctic Ocean and the loss of ice from Greenland. The latter has played into underestimates of sea level rise. In part this is because recently observed rates of Greenland melt are higher than expected, and in part because unlike the thermal expansion component of sea level rise (a warmer ocean has a larger ocean volume) the relationship between global warming and the rate of melt for Greenland’s glacial ice (2 – 3 km thick) is not as easily quantified. Thus it is more difficult to project the future contribution of Greenland (and Antarctic) ice loss in scenarios for sea level rise. At the time of the third IPCC assessment (2001) it was thought unlikely that Greenland could by this time be losing ice as rapidly as it is.

There remains much to be learned about how global climate and regional manifestations thereof will play out as we move further and further into uncharted territory with greenhouse gases in the atmosphere accumulating at higher rates and reaching higher levels than at any time in the last million or more years. How are internal cycles in the ocean, such as the El Niño – Southern Oscillation, or the North Atlantic Oscillation being affected by warming-induced changes in atmosphere-ocean interactions? Over the past decade precision in measurements of ocean heat content have increased substantially. It is now clear that the oceans are holding 90% of the heat that is accumulating in the climate system as a result of anthropogenic activities. Moreover, ocean heat content has shown an unequivocal upward trend over the last decade, even while the rate of increase in atmospheric temperature has not increased as rapidly as it did during the prior decade. A slowing in the rate of increase in atmospheric temperature may also be partly due to unusual solar activity at this time. Relative to the past three decades of solar observations, at this point in the nominal eleven-year solar cycle the sun would be expected to be more active. Instead we are seeing what some experts are suggesting what might be the smallest cycle in a century.

Looking ahead, biggest uncertainty is still how much carbon we will burn

Climate change projections made by the IPCC will always be limited by an incomplete understanding of Earth’s climate, by unanticipated events like major volcanoes, and by surprises like an unusually weak solar maximum. But the historically cautious nature of the IPCC assessment process has led to a remarkably robust set of projections.

Still though, one of the largest uncertainties that climate scientists must contend with is that of future societal decisions regarding greenhouse gas emissions. Were the peoples and nations of the world to embark upon an aggressive campaign to dramatically reduce these emissions, two things are certain: future climate projections would be more reliable, and we would have much greater confidence in projections that the most costly impacts of future climate change, which might otherwise be expected, could be avoided.

In the last IPCC report in 2007, the sea level rise projections listed in the summary document did not include the full estimated contributions from changes in ice flow and melting of the two great ice sheets on the planet, Greenland and Antarctica. This led to erroneous speculation in media coverage that the projected sea level estimates were lower than previous reports. Hopefully the forthcoming report will be more explicit about all of the contributions to sea level rise – the fact is, snow and ice are rapidly melting and raising sea levels.

Snow and ice – a barometer of Earth’s climate

In the last two decades I’ve seen with my own eyes the rapid disappearance of many of the planet’s snow fields and the retreat of alpine glaciers. Unfortunately, my anecdotal observations are backed up by data and are clearly linked to global warming.

Over the last century, in the Sierra Nevada the surface area of glaciers has been decreasing and spring river runoff is lower. In Montana’s Glacier National Park over the same period the number of sizable glaciers has dropped from 150 to less than 25. In Wyoming, the 44 extant glaciers in the Wind River Range have decreased in area by almost half in the last four decades. And it’s not just confined to North America. Glaciers are in retreat worldwide – in Switzerland, in Peru, in New Zealand. If snow doesn’t endure through the summer, glaciers simply cannot grow. Snow needs to remain for multiple seasons for it to form into ice and become a moving glacier.

The disappearance of land-based snow and ice

Thermal expansion of the oceans now takes a back seat to the contribution from melting of land-based ice (which was not accounted for in previous projections of future sea level rise). Source: UCS (after Church et al., 2011)

What happens to our snow fields, our alpine glaciers, and our ice sheets truly matters. The melting and retreat of northern hemisphere snow and ice due to global warming is a concern for two major reasons. The first is that when land-based ice melts, sea level rises. The second is that removing snow and ice cover on land leaves behind a darker surface which increases the amount of sunlight that is absorbed at earth’s surface – a feedback that increases the original warming.

When land-based ice melts, sea level rises

For most of the last century, thermal expansion from simply heating up the ocean was the main contributor to the global rise in sea level. But that’s changed in the last two decades.

A recent study shows melting of land-based ice and the resulting runoff into the sea now accounts for twice as much sea level rise as thermal expansion does. More than half of the contribution from land-based ice is from melting of alpine glaciers and ice caps, while Greenland and Antarctica (both ice sheets) account for the rest.

NASA satellite images show the changing extent of snow and vegetation for the globe over the course of the year. The greatest seasonal changes occur in the northern hemisphere. To persist, alpine glaciers and ice sheets need snow to accumulate from year to year. Top left is the view looking down on the North Pole, top right is the South Pole. Source: IDV Solutions

Greenland – the inappropriately-named island that is one of only two major ice sheets on the planet (Antarctica being the other) – is also experiencing major melt events annually. In the years 2007, 2010, and 2012 surface melt area was extensive and record-breaking. This year Greenland is experiencing a melt season closer to the long-term average. Don’t be fooled by 2013, though – the Arctic is still warming at twice the pace of the rest of the globe, as noted in the recent State of the Climate in 2012 report by the American Meteorological Society.

IPCC report highlights link between warming and loss of snow and ice

The contribution to sea level rise from melting of land-based snow and ice will continue to increase while emissions and temperatures rise. Our current challenge is to reduce our emissions swiftly and deeply to avoid the worst impacts of climate change. The forthcoming IPCC report will be a stark reminder that it is time to heed the science and act. The snow-speckled meadows and the majestic peaks surrounded by glaciers are surely worth saving not only for the services they provide like water supply and habitat, but also for the sake of future generations.

Since the 1960s scientists had convened study groups and workshops on climate change, for example under the supervision of the U.S. National Academy of Sciences. These bodies would then issue dry reports. As a result, governments recognized that climate change was an important issue and accordingly, they increased spending for research. However, few governments adopted policies that would reduce emissions or increase capacity for adaptation.

25 years ago, a call to action

In 1988, the United Nations Environmental Programme (UNEP) and the World Meteorological Organization (WMO) convened a “World Conference on the Changing Atmosphere” in Toronto. This was a meeting by invitation, dominated by scientists. There were a few high-ranking government officials among the 300 attendees, but most countries were represented by relatively junior staff.

The Toronto conference’s report concluded that the changes in the atmosphere due to human pollution “represent a major threat to international security and are already having harmful consequences over many parts of the globe.” For the first time, a group of prestigious scientists called on the world’s governments to set strict, specific targets for reducing greenhouse gas emissions. Immediate action was needed, they said, to negotiate an “international framework convention” to set the terms for national legislation.

Creating a new, fully independent group to address climate change

Who would coordinate such an initiative? The conservative Reagan Administration might have been expected to oppose the creation of a prestigious body to address climate change. However, they feared still more strong pronouncements on environmental policy from independent scientists like those at the Toronto conference. The Reagan Administration, and some other governments, were also wary of control by the WMO or any other body that was part of the United Nations structure. Better, they concluded, to form a new, fully independent group under the direct control of representatives appointed by each government—that is, an intergovernmental body.

Responding to this pressure from the United States and others, in 1988 the WMO and UNEP collaborated in creating the Intergovernmental Panel on Climate Change (IPCC). Unlike earlier conferences, National Academy panels, and the like, the IPCC was in the hands of people who participated not only as scientists, but as official representatives of their governments. The IPCC was neither a strictly scientific nor a strictly political body, but a unique hybrid. It could issue reports only with the firm agreement of essentially all the world’s leading climate scientists plus the consensus of all participating governments without exception. Importantly, it would put policy options on the table, but would not make explicit policy recommendations.

Why the IPCC has authority on climate change

The IPCC’s constitution should have been (and perhaps was intended to be) a recipe for paralysis. Instead, the panel turned its procedural restraints into a virtue: whatever it did manage to say would have unimpeachable authority.

Experts contributed their time as volunteers, writing working papers that drew on the latest studies. These were debated at length in correspondence and workshops. The IPCC scientists, initially 170 of them in a dozen workshops, worked hard and long to craft statements that nobody could fault on scientific grounds. The draft reports next went through a process of peer review, gathering comments from virtually every climate expert in the world. It was much like the process of reviewing articles submitted to a scientific journal, although with far more reviewers. All this followed the long-established practices, norms and traditions of science. The scientists found it easier than they had expected to reach a consensus. This undertaking was the first of its kind in terms of breadth, and the exhaustive level of review and revision. The First IPCC Assessment report was released in 1990, with major reports since then every five to seven years.

Any conclusions had to be endorsed by a consensus of government delegates, many of whom were not scientists at all. The elaborate IPCC process, however, had educated many bureaucrats and officials about the climate problem, and most were ready to accept the scientific consensus and consider policy options based on it.

In the face of opposition from the immensely powerful fossil fuels industry and its many allies, the IPCC would issue what was arguably the most important policy advice any body has ever given; by 2001 it made it clear that avoiding the many risks of a changing climate would require nothing less than a dramatic shift in the energy sources upon which we rely. As a result, communities would face stark choices about their way of life as the climate changed around them. Governments are still divided on if, how and when to respond to climate change, but the IPCC has succeeded remarkably in fulfilling its declared purpose of providing advice that helps set the baseline for decision-making around climate change.