Climate change skeptics obsess about the immense uncertainties that plague climate modeling. It’s not, however, all a matter of mysterious physics and chemistry. Human behavior — in this case our boundless capacity to ignore grave danger — poses the greatest challenge. No order of scientific progress nailing down the links that regulate Earth’s climate will enable certain projections of climate change over the next century because it is human behavior that controls the most powerful element: emissions of greenhouse gases such as CO2 and methane.

Today scientists with the international Global Carbon Project are releasing an updated accounting of CO2 emissions, and they far exceed the best guesses of human behavior by the Intergovernmental Panel on Climate Change (IPCC). “Emissions in 2007 were at the high end of’ those used for climate projections in the last [IPCC] report,” says Global Carbon Project participant Corinne Le Quéré, an environmental chemist at the University of East Anglia.

Emissions from burning fossil fuels and cement manufacturing — the largest sources of anthropogenic CO2 — continue to increase rapidly (see graph above); in 2007 they were now 38% higher than in 1990. In total, emissions drove up the atmospheric concentration of CO2 by 2.2 parts per million last year, compared with 1.8 ppm in 2006. At the end of 2007 CO2 was at 383 ppm — the highest concentration during the last 650,000 years and probably during the last 20 million years according to the Global Carbon Project. 

At the same time the oceans, which in past acted as a buffer to absorb excess CO2, are saturating. Le Quéré, who coauthored a report last year in Science that the Antarctic Ocean had already saturated, calls it a dangerous combination: “If this trend continues and the natural sinks weaken, we are on track towards the highest projections of climate change.”

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