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Locking In Our Future

By Douglas Fischer, Daily Climate editor

Welcome to the Anthropocene.

Decisions made today about planet-warming emissions will influence climate impacts not just for decades but for centuries and perhaps even millennia, a panel from the National Academy of Sciences warned Friday.

Given the longevity of carbon dioxide and other greenhouse gases in the atmosphere, these scientists said, these decisions effectively lock humanity in for a range of impacts, some of which can be "very severe."

"Emissions of carbon dioxide from the burning of fossil fuels have ushered in a new epoch where human activities will largely determine the evolution of Earth's climate," the scientists wrote.

"Actions taken during this century will determine whether the Anthropocene climate anomaly will be a relatively short term and minor deviation from the Holocene climate, or an extreme deviation extending over many thousands of years."

The 242-page report was sponsored by the Energy Foundation - a partnership of major foundations interested in clean energy - and the U.S. Environmental Protection Agency and was chaired by Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration. 

It attempts to quantify the impacts of various emissions targets, estimating changes in precipitation, stream flow, wildfires, crop yields and sea-level rise that can be expected with different degrees of warming. It also quantifies the average temperature increases expected if carbon dioxide were stabilized in the atmosphere at different levels.

Per one degree Celsius rise in temperature (or 1.8ºF), the report found:

  • Five percent to 10 percent less rainfall in the Mediterranean, southern Africa and southwest North America.
  • Five percent to 10 percent less stream flow in major river basins, including the Arkansas River and the Rio Grande.
  • Five to 15 percent lower yields of some crops, including corn and wheat in the United States and Africa.
  • Three percent to 10 percent increase in heavy rain storms across most land areas
  • A two-fold to four-fold increase in area burned by wildfire in parts of western North America.

"There are a lot of lags in the climate system," Solomon said Friday during a press briefing. "Not only are we committing to future impact, but we're committing to impacts that are bigger than we anticipated at the time we emitted them."

The report highlights recent scientific progress in the understanding how global warming affects precipitation patterns, heat waves, stream flow, sea ice retreat, crop yields, coral bleaching, and sea level rise. "This increased confidence provides direct scientific support for evaluating the implications of different stabilization targets," the authors noted.

What's notable, however, is the permanence of the change. Carbon dioxide hangs in the air for centuries. "It gives new weight to decisions we make," said Katherine Hayhoe, a climate researcher at Texas Tech University, who was also an author of the report.

"I know it could affect my health and that it could even affect my children. But what we don't consider is that it could affect our great-great-great-great grandchildren for generations to come."

Solomon compared it to diet: "If I knew that every pound of cheesecake that I ate would give me a pound that could never be lost, I think I would eat a lot less cheesecake."

Average temperatures across the globe have risen about 1.6ºC, or 0.9ºF, since the 1880s and today are rising about half a degree Celsius per decade, or 0.3ºF, according to various assessments. The atmospheric concentration of carbon dioxide stands today at about 390 parts per million, the highest in 800,000 years and about 35 percent higher than pre-industrial levels.

Depending on emissions rates, today's level could double or nearly triple by the end of this century, greatly amplifying human impacts on climate, the report said.

And while that carbon is leading to impacts that are, in some instances, already being felt, scientists warn that the more pernicious - and significant - impact comes from the lag time associated with pumping that carbon skyward.

Higher cumulative carbon emissions result in both a higher peak warming and a longer duration of warming. The duration is particularly critical, the report said, because an extended warming period offers more time for Earth systems that respond very slowly - such as the deep oceans and the great ice sheets - to assert themselves, even very long after anthropogenic emissions have ceased.

Once the Greenland ice sheets and the Arctic summer ice cap go, in other words, humanity may not see them again for thousands of years, no matter how radically industrial emissions are cut, the scientists warned.

"The sea level rise implications of the Anthropocene could lead to major changes in the geography of the Earth over the coming millennia," the scientists wrote.  "Widespread coastal inundation would be expected if anthropogenic warming of several degrees is sustained for millennia; while these slow changes allow time for adaptation, they are essentially irreversible."

While the report laid out a number of different scenarios based on emissions targets, the authors took pains to avoid any recommendations. Choosing an emissions target is ultimately a political decision, not a scientific one, the scientists said.

Even if the stakes are high.

"You have to view climate change as a very personal risk analysis," Solomon said. "Some people might feel differently about the risk of big numbers than others."

DailyClimate.org is a nonprofit news service that covers climate change. This work by The Daily Climate is licensed under a Creative Commons Attribution-No Derivative Works 3.0 United States License.

For more information on The National Academies' findings see Climate Stabilization Targets: Emissions, Concentrations, and Impacts Over Decades to Millennia (2010).