A new study out of Princeton University suggests that it may take much less carbon than previously thought to reach the global temperature that scientists deem as being unsafe. Evan if emissions come to a complete stop, the already existing carbon dioxide in our atmosphere is enough to warm our planet for hundreds of years.
The researchers simulated an Earth on which, after 1.8 trillion tons of carbon emissions entered the atmosphere, the emissions suddenly ceased. Scientists generally create these models of a screeching half of emissions to test the heat-trapping staying power of carbon dioxide. Within a millennium of this simulation, post-carbon emissions shutoff, the carbon itself faded steadily, with 40% absorbed by the Earth’s oceans and landmasses within 20 years and 80% absorbed by the end of 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.
After a century of cooling, the Earth warmed by 0.37 degrees Celsius during the next four hundred years as the ocean absorbed less and less heat. While the resulting temperature spike isn’t large, a little heat goes a long way in this scenario. Earth has only warmed by 0.85 degrees Celsius since pre-industrial revolution.
The Intergovernmental Panel on Climate Change estimates that global temperatures a mere 2 degrees Centigrade higher than pre-industrial times would dangerously harm with the climate system as well as earth’s ecosystems. To avoid that point would mean that humans would have to keep industrial emissions below one trillion tons of carbon, about half of which has already been put into the atmosphere since the dawn of industry.
The lingering warming effect the researchers found, however, suggests that the 2-degree point may be reached with much less carbon, says first author Thomas Frölicher, who conducted the work as a postdoctoral researcher at Princeton University.
The researcher’s conclusions contradict a scientific consensus that the global temperature would remain constant or decline if emissions were suddenly halted to zero. But previous research doesn’t take into account the gradual reduction in the oceans’ ability to absorb heat from the atmosphere, particularly the polar oceans, as noted by the author. Although carbon dioxide steadily dissipates, Frölicher and his co-authors were able to see that the oceans that remove heat from the atmosphere gradually take up less. Eventually, the residual heat offsets the cooling that occurred due to dwindling amounts of carbon dioxide.