If the excesses of the holidays get you down, you're not going to like the modeling results that Canadian climate researchers are reporting this week in Nature Geoscience. It looks like the carbon dioxide cocktail we are brewing in the atmosphere will leave us with a hangover that won't quit.
Scientists have been warning for some time now that, because CO2 lives so long in the air, its impact on global temperatures will be felt long after we curb the emissions of fossil fuels, which most researchers see as the cause of global warming.
It is a prospect that is almost too gloomy to contemplate. Once in the atmosphere, CO2 stays up there for many centuries, scientists say. Some of it begins mixing with the ocean or the land vegetation after a few hundred years, and some of it stays up there practically forever. Climate specialists use phrases like "irreversible on human timescales" to describe our predicament.
An international team of researchers reported two years ago in the Proceedings of the National Academy of Sciences that "the climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop." On a global scale, "atmospheric temperatures do not drop significantly" for a millennium.
Now comes a Canadian team led by Nathan P. Gillett of the University of Victoria who describe modeling results of a scenario that assumes carbon dioxide emissions stop completely in 2100. According to their simulation, "ongoing regional changes in temperature and precipitation are significant" during the following 1,000 years even as global average temperatures remain fairly constant.
"Moreover, our projections show warming at intermediate depths in the Southern Ocean that is many times larger by the year 3000 than that realized in 2100. We suggest that a warming of the intermediate-depth ocean around Antarctica at the scale simulated for the year 3000 could lead to the collapse of the West Antarctic Ice Sheet, which would be associated with a rise in sea level of several meters."
If this long-delayed warming response of the Southern Ocean shows up in other climate model simulations, it could change some thinking about a leading geoengineering strategy proposed to curb Antarctic ice melt. Injecting aerosols into the stratosphere to cast a cooling chemical parasol over the planet "would be ineffective for several centuries," the authors say, if the melting is the result of ocean warming.
IMAGE: From the Canadian Earth System Model, simulations show a slight cooling of the Northern Hemisphere and warming of the Southern Ocean around Antarctica. The top panel depicts changes in near-surface air temperatures between 1855 and 2105. Lower panel simulates temperature changes between 2105 and 2995. Courtesy Nature Geoscience