The Intergovernmental Panel on Climate Change (IPCC), long regarded as the single most trustworthy source of information on climate science, states unequivocally that Earth's climate is warming rapidly and that we're now more than 90 percent certain that human activities have caused most of the observed warming in recent decades. The research behind these findings, published in the IPCC's landmark 2007 report, is rock-solid science. In recognition of the importance and excellence of the IPCC's work in bringing climate science to the attention of policy makers and the public, the group shared half of the 2007 Nobel Peace Prize.
Everybody at the U.N. Framework Convention on Climate Change (UNFCCC) negotiations, which took place last month in Bali, Indonesia, was aware of the IPCC's latest conclusions. These negotiations are an annual event, and the Bali meeting attracted more than 10,000 people, including a large press corps and many stakeholders from the energy industry and environmental interest groups. I attended representing a group of 200 climate science experts who went to inject some quantitative scientific substance into the negotiations.
Climate science is now able to provide significant predictive power, meaning the IPCC report can link specific concentrations of greenhouse gases with the associated climatic consequences. How much sea level will rise or how much temperatures will change does depend on how much humanity allows greenhouse gas amounts to increase. Yet, what is said publicly by the negotiators almost never refers to the science in this way. Thus, the term "dangerous" in the UNFCCC objective of preventing dangerous anthropogenic interference with the climate system remains unqualified.
As a veteran observer of these difficult negotiations, I was reminded of the dark days of an earlier environmental crisis, the human-caused depletion of the stratospheric ozone layer, dramatized by the creation of an ozone hole over Antarctica. In the mid-1980s, frustrated by the lack of progress in reaching an agreement to end the manufacture of the chemicals that caused the problem, a prominent U.S. atmospheric scientist, F. Sherwood Rowland, who would later share the Nobel Prize in chemistry, told a journalist, "What's the use of having developed a science well enough to make predictions, if in the end, all we're willing to do is stand around and wait for them to come true!"
Today, I feel exactly the same way about the procrastination and posturing that too many governments have substituted for meaningful action to limit global warming. The statements attributed to the United States, especially by Paula Dobriansky, who headed the U.S. delegation, and James Connaughton of the White House Council on Environmental Quality, have been widely reported, and have clearly caused offense to many countries. But I don't want to single out the United States. China was notably unwilling to accept any restrictions on its greenhouse gas emissions, and several other countries followed or welcomed the U.S. lead. The struggle to have major countries agree to specific targets and timetables has been unsuccessful so far.
Meanwhile, the rate at which humankind is emitting greenhouse gases into the atmosphere continues to increase every year. Only a sharp reversal of this trend offers hope of stabilizing the amount of these gases in the atmosphere and limiting climate change.
The international group that I represented in Bali went to publicize "The 2007 Bali Climate Declaration by Scientists." Signatories of this document include many leaders of the climate science research community whose excellence and expertise are beyond doubt. They include Nobel laureate Paul Crutzen; National Academy of Sciences members Robert Dickinson, Kerry Emanuel, Stephen Schneider, and Carl Wunsch; quite a few lead authors and coordinating lead authors of the IPCC Fourth Assessment Report; and several heads of major research institutions. But we each signed the declaration representing only ourselves, not the IPCC, our employers, or any other organization.
"The 2007 Bali Climate Declaration by Scientists" had the immediate goal of asking the negotiators to reach an agreement limiting global warming to 2 degrees Celsius (3.6 degrees Fahrenheit) above the preindustrial temperature. Global warming is simply a symptom or measure of the magnitude of climate change, and 2 degrees Celsius is widely thought to be a low enough reasonable consensus estimate to prevent dangerous climate change. In fact, the European Union and other countries have already formally adopted this limit.
What actions are needed to ensure that the 2 degree Celsius target isn't exceeded? This is where climate science has a key role to play. While we cannot know safe greenhouse gas concentrations or emission limits exactly--just as medical science cannot specify a precise value as a safe limit on, say, cholesterol--the science summarized in the 2007 IPCC report does provide excellent quantitative guidance.
The IPCC, which is mandated to be policy-neutral, cannot make policy recommendations. However, once a policy maker accepts 2 degrees Celsius above preindustrial levels as a target upper bound on allowable warming, then the IPCC report describes approximately what the limit must be for greenhouse gas concentration, in what year carbon dioxide emissions must peak before declining, and what percentage reduction in emissions is needed. (The information is succinctly summarized in table SPM.5 in the Working Group III Summary for Policymakers, and is repeated as table 5.1 in the Fourth Assessment Synthesis Report.)
Taking a 2-degree-Celsius limit on global warming as the goal, the Bali declaration states, "Based on current scientific understanding, this requires that global greenhouse gas emissions need to be reduced by at least 50 percent below their 1990 levels by the year 2050. In the long run, greenhouse gas concentrations need to be stabilized at a level well below 450 parts per million. In order to stay below 2 degrees Celsius, global emissions must peak and decline in the next 10 to 15 years, so there is no time to lose. As scientists, we urge the negotiators to reach an agreement that takes these targets as a minimum requirement for a fair and effective global climate agreement."
The outcome of the Bali meeting was deeply disappointing, but not surprising. The science cannot make a subjective judgment on how much warming is acceptable, or say in what ways society should stabilize greenhouse gas concentrations. Those are political judgments. In the end, after much bitterness, the negotiators reached an agreement to continue negotiating over the next two years, but they didn't come close to agreeing on the substance of such an agreement. It's true that many international agreements took quite a few years to materialize. It's been 10 years since the Kyoto meeting. What's clear scientifically, however, is that time is running out. If an agreement isn't possible in the next 2, 3, or 4 years, it may be too late to prevent serious climatic consequences.
At subsequent climate negotiations, the important question will be whether governments are willing to implement and enforce an effective agreement to halt the rapid rise in atmospheric carbon dioxide and other pollutants that cause global warming. My personal view is that governments, especially democratically elected ones, will respond to the will of their people. And what will it take to make large numbers of people increase the priority that they now give to this issue? Perhaps it will take some sudden, shocking, and unambiguous climate event such as the destabilization of a large part of the Greenland ice sheet and a sharp increase in sea level. The ozone hole would be a parallel case historically. It would be a pity if we needed to wait for that, which is like waiting to have a heart attack rather than heeding a physician's warnings about cholesterol and weight. In climate science as in medical science, prevention is better than a cure, but not everybody is wise enough to act early.
Governments and businesses worldwide, and ultimately, humankind as a whole, will determine what actions will be taken. Climate science, however, is able to provide highly useful input to this policy-making process. Making wise climate policy includes taking sound climate science into account. The future depends on it.