Even if CO2 emissions stopped, global warming would continue for centuries

A new study led by Princeton University suggests that even if we were to cut all carbon dioxide (CO2) emissions today, the Earth would continue getting warmer for hundreds of years.

This finding is contrary to current thinking on global warming, say the researchers, because it does not correctly take into account regional effects on the ocean’s ability to absorb heat.

First author Thomas Frölicher conducted the investigation as a postdoctoral researcher in Princeton’s Program in Atmospheric and Oceanic Sciences. He says:

“The regional uptake of heat plays a central role. Previous models have not really represented that very well.”

CO2 emissions need to be cut by much more

Writing in a recent online issue of the journal Nature Climate Change, the team suggests we may need to cut CO2 emissions by a lot more than previously thought to stop global temperatures reaching unsafe levels.

Estimates from the Intergovernmental Panel on Climate Change (IPCC) suggest a global temperature only 2 deg C (3.6 deg F) higher than it was in pre-industrial times would interfere dangerously with climate systems.

To avoid this, cumulative emissions would have to stay under 1,000 billion tons of carbon, about double the amount already shed into the atmosphere since industry began.

Dr. Frölicher, now a researcher at the Swiss Federal Institute of Technology in Zurich, explains the impact of their new findings:

“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.”

“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.”

The study’s findings contradict the current consensus which says global temperature would stay the same or even fall if CO2 emissions were suddenly to drop to zero.

But Dr. Frölicher says previous studies have not accounted for the gradual decline in the ocean’s ability to absorb heat from the atmosphere, particularly near the poles.

He and his colleagues suggest when you take this into account, although CO2 would gradually dissipate if emissions stopped abruptly, the oceans that take up heat from the atmosphere are able to do this less and less as time goes on.

Eventually, the residual heat offsets the cooling that occurs from gradually dissipating CO2.

The reason lies in the difference in “heat uptake efficacy” between polar oceans and low-latitude oceans. This was first proposed in a 2010 paper by co-author Michael Winton, a researcher at Princeton’s National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory (GFDL).

CO2 emissions

If CO2 emissions suddenly stopped completely, the CO2 already in the Earth’s atmosphere could carry on warming the planet for hundreds of years. While CO2 dissipated, the oceans’ absorption of heat would decrease, especially near the poles.

A temperature increase cannot be excluded

Dr. Frölicher:

“Scientists have thought that the temperature stays constant or declines once emissions stop, but now we show that the possibility of a temperature increase cannot be excluded.”

“This is illustrative of how difficult it may be to reverse climate change – we stop the emissions, but still get an increase in the global mean temperature.”

On 10 November 2013, Market Business News announced a report that suggests worldwide carbon emissions slackened for the first time in 2012.