As attitudes on climate change have evolved over the past two decades, much of the credit goes to the hard, sometimes contentious work of thousands of scientists who crafted pathbreaking scientific assessments under the auspices of the Intergovernmental Panel on Climate Change (IPCC) and other groups.
The work of the IPCC is now well-known—the organization shared the Nobel Peace Prize for 2007 with former U.S. Vice President Al Gore. But in the Robert C. Barnard  Environmental Lecture at AAAS on 1 October, climate specialist James J. McCarthy described the lesser-known mechanics of the assessment process and how the IPCC teams, in a succession of reports released in 1990, 1995, 2001 and 2007, hammered out increasingly tougher conclusions on the role of human activity in climate change.
“The IPCC has been a great instrument,” said McCarthy, who is Alexander Agassiz Professor of Biological Oceanography at Harvard University and current chairman of the AAAS Board of Directors. He said the rigor of the scientific assessments is persuasive and the deliberative process should be applied to new aspects of the climate debate, notably whether nations—in the absence of aggressive steps to reduce greenhouse emissions—may be forced to manipulate the climate by geo-engineering in order to counter global warming.
James J. McCarthy
“There clearly is a need for other kinds of assessments,” said McCarthy, who was co-chair of a working group for the 2001 IPCC report. He also served as one of the lead authors on the Arctic Climate Impact Assessment in 2004-2005 and was an author of the recent “Global Climate Impacts in the United States,” an assessment begun during the Bush administration and completed in June.
McCarthy spoke at the 10th Barnard Lecture, an annual forum for addressing current environmental problems. The lecture series is endowed by the international law firm of Cleary, Gottlieb, Steen and Hamilton to honor Barnard, the late counsel to the firm, for his contributions to environmental and public health law as well as his many years of service as a member of the selection committee for the AAAS Fellowships at the U.S. Environmental Protection Agency.
The IPCC assessments, starting with the first report in 1990, have helped prod governments to action on the climate change issue. Delegates at a United Nations conference in Rio de Janeiro in June 1992 adopted the U. N. Framework Convention on Climate Change, aimed at reducing the concentrations of heat-trapping greenhouse gases in the atmosphere.
A follow-on 1997 conference in Kyoto, Japan—meant to give the Rio accord more teeth—set legally binding targets and timetables for emissions reductions. The Kyoto Protocol, which came into force in 2005, has been ratified by 175 nations but not by the Unites States. Neither President Bill Clinton nor President George W. Bush submitted the Protocol to the U.S. Senate for ratification. Six months before the meeting in Kyoto, the Senate expressed strong opposition to an agreement that did not include meaningful participation by developing nations in the Protocol's binding commitments.
[Image courtesy of the United States Global Change Research Program]
Still, evidence of human-induced climate changes continues to grow, McCarthy said. Some of those changes, such as reductions in Arctic sea ice, are increasing at a faster rate than previously projected, according to the “Global Climate Impacts in the United States” report.
“We are headed to dangerous territory at breakneck speed,” McCarthy said, and the international efforts to understand and respond to the climate challenges are continuing. The parties to the Rio framework on climate change will convene in Copenhagen, Denmark, in December to wrangle over details of a potential successor to the Kyoto Protocol.
Again, the debate likely will be driven by the carefully drawn conclusions of international teams of scientists. Despite some climate skeptics in Congress and the chattering classes, McCarthy stressed that the IPCC has delivered what was asked of it: a considered weighing of the scientific evidence in a manner accessible to policy makers. Without such scientific spadework, he said, the Rio and Kyoto accords would not have been possible.
McCarthy is an experienced hand in the time-consuming scientific assessment process. As co-chair of Working Group II for the 2001 IPCC report, he helped shepherd a 1,032-page report on the likely consequences of climate change for ecological systems, economic well-being and human health.
The report included a 73-page technical summary and a 17-page summary for policy makers. There were 183 authors (drawn from more than 1,000 nominations) from 73 nations. There were 440 government and expert reviewers, as well as 33 independent review editors who served as the “judges” to ensure that the authors properly responded to questions and concerns from the reviewers.
During a four-day final plenary session, delegates from more than 100 nations joined authors of the report in Geneva to go over the content line-by-line, with the report displayed on a large screen where changes in the document were tracked. The review was done in English with simultaneous translation into five other languages. The subtleties of language and meaning were always a concern. “That was a period in which my beard went from red to gray,” McCarthy quipped. “It is an enormously taxing endeavor.” The final session wrapped up at 2:00 a.m.
The IPCC process has been sometimes misunderstood by media and politicians, according to McCarthy. In one congressional hearing, he said, a U.S senator told him: “You don't write these reports. They are written by U.N. environmental activists.” McCarthy begged to differ, noting that the reports are written by scientists directly involved with the research that supports the conclusions. During the review process, he said, “at no time was any change made that misrepresented the science.”
McCarthy credited the late Bert Bolin, a Swedish meteorologist and climate specialist, as the driving force behind the establishment of the IPCC. Bolin and others had seized upon a 1979 study by the U.S. National Academy of Sciences, “Carbon Dioxide and Climate—A Scientific Assessment,” as an important start in the effort to draw together what was then known about the complex interactions that drive climate. “It appears that the warming will ultimately occur,” the Academy report said cautiously. Regional climate changes “may well be significant,” it said, but the socioeconomic consequences “cannot yet be adequately projected.”
Four years later, another Academy report on “Changing Climate” considered possible impacts of a warming climate on sea levels, agricultural productivity, water availability and other factors. It also warned that there may be surprises and added: “In our calm assessments, we may be overlooking things that should alarm us.”
In the mid-1980s, the World Commission on Environment and Development warned that by the early 21st century, the average global temperature may have increased enough “to shift agricultural production areas, raise the sea level to flood coastal cities, and disrupt national economies.”
Such dire events have not yet come to pass, but the so-called Brundtland Report (named after the Commission's chair, Gro Harlem Brundtland) helped to raise the level of concern enough that the United Nations Environmental Program and the World Meteorological Organization jointly established the IPCC in 1988, with Bolin as chairman. The U.N. General Assembly asked the new intergovernmental panel to produce a report by 1990 on the quality of the evidence for human-induced climate change.
That first IPCC report (McCarthy was one of the authors) concluded that “emissions resulting from human activities are substantially increasing the atmospheric concentrations of greenhouse gases.” There was enormous debate within the group over the use of the word “substantially,” McCarthy said. The group also estimated that carbon dioxide from burning of fossil fuels was responsible for more than half of the enhanced greenhouse effect.
By 1995, the IPCC scientists concluded that “the balance of evidence suggests a discernible human influence on global climate.” A draft version of the report had used the word “appreciable” rather than “discernible,” McCarthy said. Why not go beyond the previous estimate of “more than half” and just use a numerical estimate such as 80%? he asked. Because, he said, “that would never get through the consensus process.”
Still, the IPCC was moving toward tougher language. In its 2001 report, the IPCC found that there is “new and stronger evidence that most of the warming over the last 50 years is attributable to human activities.” The lightning-rod word this time was “most.”
The 2001 report also found that the “potential for large-scale and irreversible impacts poses risks that have yet to be quantified.” But the IPCC started to move beyond warnings about future consequences of global warming to note that impacts already were being felt. “No longer can you say we'll wait and see,” McCarthy said. “We have to adapt right now.” And the longer the steps toward reducing greenhouse gases are put off, he said, the tougher it will be to adapt.
The IPCC's Fourth Assessment Report in 2007 was even more categorical. “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.” It gave 9 out of 10 odds that most of the observed increase in average global temperatures since the mid-20th century is due to the release of greenhouse gases by human activities.
The “unequivocal” statement had “a ring of compelling authority” to it, McCarthy said, and climate science was thrust into the public arena as never before. Researchers also were developing more sophisticated computer models that allowed projections of regional as well as global climate impacts, including heat waves, intense tropical storms and greater frequency of heavy rains.
The next IPCC assessment is due in 2014, and the work already is well underway. Over the years, participation in the organization has grown from 28 nations to more than 140. The question for the participants now is not whether climate change is unequivocal, McCarthy said. Rather, they must assess more directly the regional impacts of climate change and how to cope with them.
The work of the Arctic Climate Impact Assessment in 2004-2005 offers a glimpse of how such regional assessments can be carried out, McCarthy said. The study was backed by eight nations with Arctic territory and included input from six groups of indigenous peoples in the region. The assessment found widespread and consistent evidence for increases in land and ocean temperatures in the Arctic, reductions in seasonal sea ice and glacier volume, deeper thawing of permafrost and ecological disruptions such as the loss of spruce forests on Alaska's Kenai Peninsula due to spruce bark beetles that thrive in the warmer temperatures.
The recently released federal report on “Global Climate Change Impacts in the United States” also draws together a wealth of data on the possible effects of warming temperatures on nine regions in the United States and seven industrial sectors. It discusses what could happen with a “business as usual” approach, including the expected stresses on already overburdened water systems. The report underscores the importance of mitigation: reducing greenhouse emissions, producing and using energy more efficiently, using energy sources that do not emit carbon. Nations could begin serious mitigation today, without further research, McCarthy said.,, “What is lacking is resolve,” he said.
But no matter how aggressively heat-trapping emissions are reduced, the report notes, “some amount of climate change and resulting impacts will continue due to the effects of gases that already have been released.” That means adaptation must go hand in hand with mitigation. Such adaptations could include farmers switching to crops better suited to warmer growing conditions, companies relocating businesses away from coastal areas vulnerable to sea-level rise, and municipalities altering zoning and building codes so that fewer structures are placed in harm's way from flood, fires and other extreme events.
But McCarthy said scientists also must be prepared to study more radical methods of adaptation, such as use of fine particles in the atmosphere to reflect some sunlight back to space. “We may reach a point,” he suggested, “where we're going to be so desperate that we will need to look critically at various geoengineering approaches. There's a lot of literature popping up on this now. And I think it's an area where assessments [like those of the IPCC] for geoengineering options will be critically needed.”