James E. Hansen, the irrepressible NASA scientist who was among the first to sound the alarm about human-caused global warming, has roiled the scientific community again with a new scientific paper explicitly linking high concentrations of carbon dioxide and other heat-trapping gases to recent severe heat waves and drought.
My colleague Justin Gillis has a detailed article in Tuesday's Times on the study and the initial reaction to it.
In the paper, published in the prestigious Proceedings of the National Academy of Sciences, Dr. Hansen and two co-authors say that human activities â€" chiefly the burning of fossil fuels â€" have “loaded the dice,†making extreme weather events more frequent. They go further and say that the drought in the United States and the deadly heat wave in Russia, among other recent weather extremes, were direct consequences of this phenomenon.
While the vast majority of climatologist s believe that higher concentrations of carbon dioxide and other greenhouse gases make harsh weather more likely, most have so far been reluctant to attribute specific weather events to higher greenhouse gas levels.
This is a question that has vexed scientists and perplexed the public for years. Was global warming responsible for Hurricane Katrina and other powerful storms? Has the burning of coal and oil caused the historic heat waves that large parts of the United States are now suffering? How much of the weird weather so much of the world is now experiencing can be attributed to global warming, and how much to the natural variability of climate?
These are questions that have not only scientific implications but political consequences as well. If one believes â€" as President Obama does â€" that human activities are contributing to climate change, then it follows that people have an obligation to take steps to slow emissions a nd mitigate the impact. If one believes â€" as Mitt Romney now appears to â€" that recent weather phenomena are merely cyclical events, then an aggressive government response seems like a costly and ineffective solution.
These are core political questions that the candidates and the electorate will face this fall, even though so far we have not yet heard a vigorous public debate on them. The Times hopes to kick-start that discussion through its Agenda project.
Here and here are links to more detail from the Hansen study, with some fascinating visualizations of the spreading heat.
