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Using a simplified climate model, Randers and his colleague Ulrich Goluke projected changes to the year 2500 in two scenarios: the instantaneous cessation of emissions and the gradual reduction of the gases that heat the planet to zero by 2100.
Global warming will disrupt food supplies, slow global economic growth and may already be causing irreversible damage to nature, according to a UN report due this week that will put pressure on governments to act. Image: Wikimedia Commons.
PARIS – Even if humanity stopped emitting greenhouse gases tomorrow, the Earth will warm for centuries to come and the oceans will rise meters, according to a controversial modeling study released Thursday.
The natural drivers of global warming – more heat-trapping clouds, melting permafrost, and shrinking sea ice – already activated by carbon pollution, will gain their own momentum, Norwegian researchers reported in the journal Nature Scientific Reports.
“According to our models, humanity is beyond the point of no return when it comes to stopping the melting of permafrost using greenhouse gas cuts as a single tool,” said lead author Jorgen Randers, professor emeritus of climate strategy at the BI Norwegian Business School told AFP.
“If we want to stop this melting process, we have to do something extra, for example suck CO2 out of the atmosphere and store it underground, and make the Earth’s surface brighter.”
Using a simplified climate model, Randers and his colleague Ulrich Goluke projected changes to the year 2500 in two scenarios: the instantaneous cessation of emissions and the gradual reduction of the gases that heat the planet to zero by 2100.
In an imaginary world where carbon pollution is stopped at the flick of a switch, the planet warms over the next 50 years to around 2.3 degrees Celsius above pre-industrial levels, about half a degree above the target set in the 2015 Paris Agreement and it cools down a bit after that.
The surface of the Earth today is 1.2 ° C warmer than it was in the middle of the 19th century, when temperatures began to rise.
But beginning in 2150, the model causes the planet to gradually begin to warm up again, with average temperatures rising another degree over the next 350 years, and the sea level rising at least three meters.
In the second scenario, the Earth heats up to levels that would tear the fabric of civilization much more quickly, but it ends at roughly the same point at 2500.
‘TIP POINTS’
The main finding, disputed by leading climate scientists, is that several thresholds, or “tipping points”, have already been crossed in Earth’s climate system, triggering a self-perpetuating warming process. , as has happened millions of years ago. .
One of these factors is the rapid retreat of sea ice in the Arctic.
Since the late 20th century, millions of square kilometers of snow and ice, which reflect about 80 percent of the Sun’s radiative force back into space, have been replaced in summer by open ocean, which absorbs the same percentage.
Another source is the melting of permafrost, which contains twice as much carbon as is in the atmosphere. The third is the increasing amount of water vapor, which also has a warming effect.
The reactions of half a dozen leading climate scientists to the study, which the authors acknowledge is sketchy, varied dramatically, with some saying the findings warrant follow-up investigation and others rejecting it outright.
“The model used here … has not been shown to be a credible representation of the actual climate system,” said Richard Betts, director of climate impacts research at the University of Exeter.
“In fact, it is in direct contradiction to more established and extensively evaluated climate models.”
Mark Maslin, professor of climatology at University College London, also pointed to shortcomings in the model, known as ESCIMO, describing the study as a “thought experiment.”
“What the study draws attention is that reducing global carbon emissions to zero by 2050,” a goal championed by the UN and adopted by a growing number of countries, “is just the beginning of our actions to tackle climate change. “.
Even the most sophisticated models used in projections by the UN’s scientific advisory body, the IPCC, show that the temperature targets of the Paris climate pact cannot be achieved unless massive amounts of CO2 are removed from the atmosphere.
One way to do this is to plant billions of trees. Experimental technologies have shown that the suction of CO2 from the air can be done mechanically, but so far not on the required scale.
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