WASHINGTON, D.C. – As Congress wrangles over climate legislation in the nation's capitol, a new report by the National Research Council suggests that decisions made now about cutting atmospheric carbon dioxide may lock in climate changes for centuries.
Climate Stabilization Targets draws its conclusions from the "extreme persistence" unique to carbon dioxide among the major agents that warm the planet.
Methane, black carbon on ice and snow, as well as aerosols can affect global warming in the coming decades. But CO2, which accounts for more than half of the current impact on the Earth's climate, is the key driver of long-term warming. According to the report:
"Carbon dioxide flows in and out of the ocean and biosphere in the natural breathing of the planet, but the uptake of added human emissions depends on the net change between flows, occurring over decades to millennia."
While some aspects of future climate impacts are hard to quantify, the report says recent advances in climate research can be employed with a new measure of confidence in making policy choices – particularly in the realm of future wildfires, sea level rise, summer heat and precipitation trends.
The report lists several key impacts tied to degrees of global warming, which are predicted to decrease rainfall in the American Southwest, the Mediterranean and southern Africa by 5 to 10 percent for each 1.8 degrees Fahrenheit rise in temperatures.
Similar warming could bring less streamflow to river basins in the Arkansas and Rio Grande, and lower crop yields for corn in the U.S. and Africa, and wheat in India. Other parts of the world would see more precipitation.
The report, released Friday, gives estimates of the average temperature increases that would be likely if CO2 were stabilized in the atmosphere at various target levels. However, the report does not recommend any particular targets.
Setting these levels, the report notes, is a policy choice rather than strictly a scientific one, based on how much risk or damage to people and nature that policy-makers find acceptable.
Deep Cuts Needed
Whatever target reductions are ultimately determined, the report says, they must be swift and dramatic.
"Carbon emissions during this century will essentially determine the magnitude of eventual impacts and whether [the new geologic era] is a short-term, relatively minor change from the current climate or an extreme deviation that lasts thousands of years."
The science puts atmospheric concentrations of CO2 at the highest level in at least 800,000 years. That could double or nearly triple by the end of the century depending on future emissions, leading to even greater global consequences.
The amount of heat-trapping carbon that human activities create already far exceeds what oceans and other natural systems can remove. Keeping emissions rates the same not only won't maintain the climatic status quo, the concentration of CO2 in the atmosphere would increase, much like the water level in a bathtub when water is coming in faster than it is draining, according to the report.
Reductions of more than 80 percent of peak global emissions would be required to stabilize carbon dioxide concentrations for a century or so at any chosen target level. Nor does stabilizing CO2 mean that temperatures will stabilize immediately, it notes.
"Even after the CO2 level stabilizes, the warming would continue to grow in the following decades and centuries, reaching a best-estimate global "equilibrium" warming ... Waiting to observe impacts before choosing a stabilization target would therefore imply a lock-in to about twice as much eventual crop loss, rainfall changes, and other impacts that increase with warming."
The NRC report was sponsored by the Energy Foundation and the U.S. Environmental Protection Agency.
(Photo: Jan Brons)