'It may be too late': Reducing greenhouse gas emissions might not stop global warming, claims climate scientist



Researchers believe that oceans' increasing inability to absorb heat could push temperatures up even if carbon dioxide emissions were shut off

Temperatures may even stabilise at even higher levels

Carbon dioxide reductions necessary to prevent dangerous warming may have been underestimated, it's been claimed



Many scientists believe that global warming will come to an end if, some day, humans succeed in stopping greenhouse gas emissions into the atmosphere.



It would, they say, be hotter on Earth than before industrialisation, but nonetheless temperatures would not rise.



However, this strongly held notion has been challenged by climate physicist Thomas Frölicher.



Doomed? New research suggests that the Earth's temperature may continue to rise even if carbon dioxide emissions were reduced to zero

He argues that it is very possible that the Earth’s atmosphere could continue to warm for hundreds of years even after emissions of greenhouse gas carbon dioxide have been halted.



What’s more, temperature levels may stabilise at an even higher level at a later stage.



He said: ‘In the long term, the temperature increase could be 25 per cent greater than assumed today.’



Also, Frölicher’s study, conducted at Princeton University, 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 per cent absorbed by Earth's oceans and landmasses within 20 years and 80 per cent soaked up at the end of the 1,000 years.



Hot debate: The new research claims that the heat-absorbing capacities of the polar oceans have been overestimated

WHY SHUTTING OF CARBON DIOXIDE EMISSIONS MAY NOT STOP WARMING

The idea that global warming can be halted by reducing carbon dioxide emissions to zero has been challenged by a leading climate scientist. He has argued that how efficiently oceans can absorb heat from the atmosphere may have been overestimated and that the Earth's temperature could rise by 0.37C even if carbon dioxide levels drop to nothing. This is because, a new study argues, the oceans reach a saturation point, after which they cannot take in any more heat.

What's more, the amount humans need to reduce carbon dioxide emissions by to prevent reaching the accepted danger level of a two Celsius rise may have been underestimated. The consensus is that once 1,000 billion tonnes of carbon dioxide has been pumped into the atmosphere, global temperatures will rise by an average of two Celsius and the environment potentially irreparably damaged. Humans have already put 500 billion tonnes of carbon dioxide into the skies. However, the study claims that the two Celsius danger level may be reached sooner - by the time just 750 billion tonnes is released.



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 planet warmed by 0.37 degrees Celsius (0.66 Fahrenheit) during the next 400 years as the oceans 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 Intergovernmental Panel on Climate Change estimates that global temperatures a mere two degrees Celsius (3.6 degrees Fahrenheit) higher than pre-industrial levels would dangerously interfere with the climate system.



To avoid that point would mean humans have to keep cumulative carbon dioxide emissions below 1,000 billion tons of carbon, about half of which has already been put into the atmosphere since the dawn of industry.



The Princeton University research suggests that even if carbon dioxide emissions came to a sudden halt, the carbon dioxide already in Earth's atmosphere could continue to warm our planet for hundreds of years.



The researchers found while carbon dioxide steadily dissipates, the absorption of heat by the oceans decreases, especially in the polar oceans such as Antarctica. This effect has not been accounted for in existing research.



And the lingering warming effect the researchers found suggests that the two-degree point may be reached with much less carbon.



‘If our results are correct, the total carbon emissions required to stay below two 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 two degrees would require keeping future cumulative carbon emissions below 250 billion tons, only half of the already emitted amount of 500 billion tons.’



The researchers' work contradicts a scientific consensus that the global temperature would remain constant or decline if emissions were suddenly cut to zero.



But previous research did not account for a gradual reduction in the oceans' ability to absorb heat from the atmosphere, particularly the polar oceans, Frölicher said.



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.



The researchers showed that the change in ocean heat uptake in the polar regions has a larger effect on global mean temperature than a change in low-latitude oceans, a mechanism known as ‘ocean-heat uptake efficacy.’



‘The regional uptake of heat plays a central role. Previous models have not really represented that very well,’ Frölicher said.



‘Scientists have thought that the temperature stays constant or declines once emissions stop, but now we show that the possibility of a temperature increase can not be excluded,’ Frölicher said. ‘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.'