Even If emissions are halted, carbon dioxide could warm earth for centuries

Science 2.0: ...Because carbon dioxide emissions persist for a long time, even a sudden halt today means the carbon dioxide already in Earth's atmosphere could continue to warm our planet for hundreds of years, according to a numerical model which suggests that it might take a lot less carbon than previously thought to reach the global temperature scientists deem unsafe.

The researchers simulated an Earth on which, after 1,800 billion tons of carbon entered the atmosphere, all carbon dioxide emissions suddenly stopped. Scientists commonly use the scenario of emissions screeching to a stop to gauge the heat-trapping staying power of carbon dioxide. Within a millennium of this simulated shutoff, the carbon itself faded steadily with 40 percent absorbed by Earth's oceans and landmasses within 20 years and 80 percent soaked up at the end of the 1,000 years.

By itself, such a decrease of atmospheric carbon dioxide should lead to cooling. But the heat trapped by the carbon dioxide took a divergent track on their computer.  In a numerical model, while carbon dioxide steadily dissipates, the absorption of heat the oceans decreases, especially in the polar oceans such as off of Antarctica (above). This effect has not been accounted for in existing research. Photo courtesy of Eric Galbraith, McGill University.

After a century of cooling, their model of the planet warmed by 0.37 degrees Celsius (0.66 Fahrenheit) during the next 400 years as the ocean absorbed less and less heat. While the resulting temperature spike seems slight, a little heat goes a long way here. Earth has warmed by only 0.85 degrees Celsius (1.5 degrees Fahrenheit) since pre-industrial times.

...The lingering warming effect the researchers found, however, suggests that the 2-degree point may be reached with much less carbon, said first author Thomas Frölicher, who conducted the work as a postdoctoral researcher in Princeton's Program in Atmospheric and Oceanic Sciences under co-author Jorge Sarmiento, the George J. Magee Professor of Geoscience and Geological Engineering.

"If our results are correct, the total carbon emissions required to stay below 2 degrees of warming would have to be three-quarters of previous estimates, only 750 billion tons instead of 1,000 billion tons of carbon," said Frölicher, now a researcher at the Swiss Federal Institute of Technology in Zurich. "Thus, limiting the warming to 2 degrees would require keeping future cumulative carbon emissions below 250 billion tons, only half of the already emitted amount of 500 billion tons."...

A 17th century painting by Jan Porcellis, "Shipping in Stormy Seas"