The news on climate change seemed bad enough in 2007, when the Intergovernmental Panel on Climate Change (IPCC) announced in their fourth assessment report that "warming of the climate system is unequivocal," that humans were "very likely" to blame, and that if we keep pumping greenhouse gases into the atmosphere, climate will "very likely" change much more than it did in the 20th century. But researchers reported today that, in the 2 years since the report was released, the news has gotten even worse.
Climate scientist Chris Field of Stanford University relayed the first bit of bad news to a sober audience during his talk, "What is New and Surprising since the IPCC Fourth Assessment." According to a paper his group published in the Proceedings of the National Academy of Sciences in 2007, humans are now pumping out climate-warming gases nearly three times faster than the IPCC authors anticipated in their worst-case scenario. Specifically, Field described how carbon emissions had been increasing at 0.9% per year through the 1990s, but accelerated to 3.5% per year growth between 2000 and 2007.
Why the disparity?
The acceleration, it turned out, was mostly due to economic growth in quickly developing economies, particularly China, and the move toward burning coal, which produces more CO2 per unit of energy than any other fossil fuel. But before Americans feel too smug, he reminded the U.S. that it still emits far more CO2 per capita than China.
Sea-level rise is also looking more ominous. Climate researcher Anny Cazenave of the Centre National d'Etudes Spatiales in Toulouse, France, followed Field's presentation with news that sea level is now rising twice as fast as it had been for the last half-century. In 2007, the IPCC had reported that sea level had been rising 1.7 mm per year since the 1960s. Cazenave described precise measurements of sea level from orbiting satellites that show average sea levels rising 3.35 millimeters per year from 1993 through 2008.
The odd thing is that sea level is not rising for the same reasons it was just a few years ago. Sea level rises because warming ocean water expands, and it rises because more water from glaciers and ice sheets melt into the sea. For reasons that Cazenave says are not understood, water stopped expanding, perhaps temporarily, a few years ago. But sea level kept rising, which means that the water had to come from land. Sure enough, by cross-checking measurements of ice lost from ice sheets and glaciers, the researchers showed that whereas melting land ice accounted for just 40% of sea level rise between 1993 and 2003, it now accounts for 80%.
In a comment that could sum up the whole session, Field said, "I don't think there's anything here that should be taken as reassuring."