Princeton University- led research was published in the journal Nature Climate Change The report concludes 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 study suggests that it might take a lot less carbon than previously thought to reach the global temperature scientists deem unsafe.
The simulation shows a serious fading in the polar oceans’ ability to remove surplus heat.
Credit: Antarktika, Wikimedia Commons via Climate News Network
The scientists simulated a planet where emissions continue to grow to 4 times the pre-industrial levels (1800 billion tons released into the atmosphere) and then stop the emissions altogether. They found that in this case the carbon would be absorbed by forests, grasslands, algae, coral and shells etc., and that after a time the planet would begin to cool for approximately a century but would begin to warm again and go on warming for centuries afterwards.
Oceans Influence dims
That is because although what scientists call “radiative forcing” – CO2 traps infra-red radiation and keeps the Earth’s temperature up – would begin to ease, the polar oceans that play such a powerful role in the climate machine would become less efficient at removing the surplus heat.
The logic of all this rests on the reasoning that life on Earth for the last 10,000 years has continued comfortably with a particular ratio of CO2 to other gases in the atmosphere. To increase carbon levels significantly – and this has already begun to happen – would therefore disturb this comfortable equilibrium, and then trigger a very long period of uncertainty.
Frölicher and colleagues found that 40 percent of the extra carbon in the atmosphere would have been soaked up within 20 years, and 80 percent within 1,000 years. This would of course affect temperatures.
First, as the carbon dioxide levels reached a maximum, the world would warm sharply and then, after 15 or 20 years, start to cool. The cooling could continue for a century
.
Little time left.
But in the simulation, after the initial 100-year cooling-off period the Earth started to warm again. It went on warming for 400 years, by 0.37°C. This doesn’t sound much – but the Earth has already warmed by 0.85°C over pre-Industrial averages.
The world’s governments have collectively agreed that it would be good if the rise in average global temperatures could be halted at 2°C, and they have accepted in principle – serious concerted action has yet to be agreed – that with 500 billion tons of CO2 already released into the atmosphere, the safe limit should be 1,000 billion. But this now looks less plausible.
“If our results are correct, the total carbon emissions required to stay below 2°C of warming would have to be three quarters of previous estimates, only 750 billion tons of carbon,” said Frölicher. “Thus, limiting the warming to 2°C would require keeping future cumulative carbon emissions below 250 billion tons, only half of the already emitted amount of 500 billion tons.”
The study is a simulation and there is much research to be completed before predicting this doomsday scenario.
“This is illustrative of how difficult it may be to reverse climate change – we stop the emissions but we still get an increase in the global mean temperature,” says Frölicher.
Photograph by Hsuan Tang