TIME Magazine

Climate Change: Case Closed

Posted Friday, Feb. 02, 2007 The debate on global warming is over.

That's the ultimate message from the report released in Paris today by the Intergovernmental Panel on Climate Change (IPCC), the U.N. body of leading researchers charged with analyzing climate science and producing the final word on what is happening — and will happen — to our planet. IPCC scientists now say that it is "very likely" that global warming is chiefly driven by the buildup of carbon dioxide (CO2) and other greenhouse gases caused by human activity, and that dangerous levels of warming and sea rise are on the way.

Those two words — the product of 2,500 scientists, 130 nations and 6 years of work — translates into a certainty of over 90%, up from the 66% to 90% chance the panel reported in its last major climate change assessment in 2001. That might not seem like a big difference, but in science, especially in a field as rapidly developing as climate studies, 90% is as good as it gets. The new report effectively completes a scientific revolution that began at the end of the 19th century, when a Swedish geochemist named Svante Arrhenius first proposed that CO2 released into the atmosphere by burning fossil fuels could change the planet's climate. "The message of this report is that the time for sitting on the fence is finished," says Robert Watson, chief scientist at the World Bank and a former chair of the IPCC. "Now is the time for action."

Action will need to be quick and substantial. The IPCC estimated that should the concentration of carbon dioxide reach twice the pre-industrial level of 280 parts per million, temperatures could rise between 3.2 to 7.1 degrees (Fahrenheit) — with a more than 1 in 10 change of far greater warming. Sea levels could rise between 7 and 23 inches. Heat waves and droughts will become more intense and longer-lived. Though the new IPCC assessment doesn't go into the social impacts of climate change, past studies indicate that the changes predicted will have a profound effect on humanity. Even if we were somehow able to end all greenhouse gas emissions today the world would continue to warm, thanks to the gases we've already added to the atmosphere — which now has a higher level of carbon than at any time over the past 650,000 years. "We're already committed to future changes," said Susan Solomon, a U.S. climatologist and co-chair of the new IPCC assessment.

That means that we will have to learn to live with global warming; indeed, considering that British meteorologists say the world's 10 hottest years since 1850 have occurred over the past decade, we're already living with it. The IPCC report will likely continue to shift the focus to the need to adapt to climate change, coupled with further attempts to slow the growth of greenhouse gas emissions. Governments must prepare for a world very different from the one we live in today: one where current coastal settlements could be swamped, where refugee camps could be filled by people fleeing the effects of global warming. "We will have to adapt, and we have a long way to go," says Eileen Clausen, the president of the Pew Center on Global Climate Change. "I think the IPCC report might help push that."

Perhaps the scariest thing about the IPCC report is that it is, by the nature of its composition, probably conservative. The final review, which took place this week in Paris, is painstakingly bureaucratic; the IPCC received 30,000 comments from scientists around the world as the report evolved through numerous drafts. Only the most-solidly backed facts — and often the least controversial ones — survived the winnowing process. The report itself offers a range of different estimates for temperature change and sea level rise, corresponding to different "emissions scenarios" that map out possible human responses over the coming century. The 3.2-to-7.1-degree prediction is a relatively optimistic one, which assumes quick adoption of more energy efficient technologies and a global population that peaks at mid-century. If energy-hungry China and India continue to grow rapidly (China may supplant the U.S. as the world's biggest carbon emitter before 2010) there's no guarantee that will happen.

Many scientists are already criticizing the IPCC report for being too conservative, especially on the question of sea level rise. The new assessment actually predicts a lower rise than what was forecast in the 2001 report, though it doesn't take into account some of the most recent research on rapid glacier melting. (The IPCC set a December 2005 cutoff date for the submission of scientific research to the new assessment.) A paper published in Science yesterday argued that sea levels today are already rising faster than the 2001 IPCC assessment predicted. At the same time, the new report's conclusion that warming will more likely than not increase the intensity of tropical storms is considered too liberal by some climate scientists.

It should be no surprise that arguments and questions still remain — good luck getting 2,500 scientists to agree on what to order for dinner, let alone come to a single conclusion on massively complicated climate science. But it would be a mistake, as skeptics have done, to point to the remaining disputes as evidence that a broad consensus still hasn't been reached on the science behind climate change. The new IPCC assessment is that consensus; as United Nations Environment Programme head Achim Steiner pointed out, "attention now shifts from whether human activity is linked to climate, to what on earth we are going to do about it."

Science has answered the first question; the next will be left to us. At the Paris press conference held to mark the release of the IPCC assessment, one journalist tried to get Solomon to say what the world should do about global warming. She would not take the bait. "It is my personal scientific approach to say that it is not my role to communicate what should be done," she said. "I believe that is a societal choice." Whatever happens over the next century, we can't say we weren't warned.