The IPCC process encapsulates both the promise and the problem of global consensus on climate change. Under its aegis, 2,500 scientists from around the world have reviewed the voluminous research on climate change in order to assess its impact now and in the future. Their conclusions were then reviewed by officials from over 100 countries some less convinced than others of the science behind global warming to produce a document politically acceptable to the governments of the world. The search for diplomatic consensus necessarily waters down the findings of the scientists, although such consensus is a prerequisite for effective global action.
The IPCC had concluded in February that greenhouse gas emissions from human activity were "very likely" the chief driver of global warming, and Friday's report dealt with its human and ecological impact. But clashes between scientists and political officials over its wording almost prevented the report from being published on schedule. Countries such as China, Russia and the U.S. reportedly pushed to water down the IPCC's predictions, while the scientists whose work formed the backbone of the report fought back in an all-night session preceding Friday's release.
Though some scientists angrily denounced the IPCC report as a hobbled compromise even then, its predictions make frightening reading. The IPCC concludes that global warming has almost certainly triggered changes in the Earth's ecosystem that have already been felt in increased drought, shrinking glaciers and changing seasons, and these effects are expected to intensify. Freshwater stored in glaciers and snow cover will be lost, while rainfall will increasingly come in destructive deluges, reducing the water supply to one-sixth of the humanity with the teeming masses dependent on the melt water from the Himalayas particularly hard hit.
Some 20-30% of plant and animal species are at risk of extinction if global temperatures rise in line with median projections, while by 2080, many millions of people living along coastlines will face an annual flood risk. As Camille Parmesan, a professor of integrative biology at the University of Texas, put it, "We're going into a realm the world has not seen for a very long time."
The IPCC expects climate change to bring "increased deaths, disease and injury due to heat waves, floods, storms, fires and droughts," with most of the pain being borne by the poor, tropical countries already on the edge of environmental disaster. In Africa by 2020, between 75 and 250 million people are expected to suffer from increased water shortages resulting from climate change, and attempting to adapt could consume as much as 10% of the GDP of African nations. In poorly nourished Central and South Asia, crop yields could decrease 30% by 2050. "The poorest of the poor are going to be the worst hit," said IPCC Chairman Rajendra Pachauri. "People who are poor are least able to adapt to climate change."
In the short term, some of the northern, industrialized countries may actually benefit. Canada, Russia and parts of the U.S. will for a time experience shorter winters and bumper harvests. But the already arid southwestern U.S. could become a permanent dust bowl, while Australia will see intensified droughts and agricultural decline throughout the country's populated south and east.
So great is the potential human toll of global warming that some economists believe that the focus of global efforts should be less on eliminating carbon emissions than on the urgent challenges of adapting to climate change, such as preparing new sources of water or planning for the movement of millions of environmental refugees. Others argue that while such preparations are a matter of urgency because of the warming trend already in motion, at the same time, if carbon emissions continue to rise, so will temperatures, intensifying the crisis. But there's broad agreement on the economic logic of immediate global action, says Robert Watson, the chief scientist for the World Bank and a former chair of the IPCC: "The cost of mitigation will be less than the cost of inaction."
While the challenges are clearly daunting, some scientists complained in the wake of February's IPCC report that sensationalist media coverage painting an inevitable and apocalyptic picture of climate change paralyzes rather than galvanizes the public. But the unwritten word behind the IPCC's dire predictions, and its source of hope, is if. If we can limit and later eliminate carbon emissions, if we can make a rapid transition to cleaner energy, if we help poorer nations adapt to the changes underway, then the worst consequences will be averted. But that can only happen if we act globally.