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Even if humanity stops emitting greenhouse gases tomorrow, the Earth will warm for centuries and the oceans will rise by meters, according to a controversial modeling study released Thursday.
Natural drivers of global warming – more heat-trapping clouds, melting permafrost and shrinking sea ice – already triggered by carbon pollution will take 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 by using greenhouse gas reduction as a single tool,” the lead author Jorgen Randers, professor emeritus of climate strategy at BI Norwegian Business School, told AFP.
“If we want to stop this fusion process, we have to do something more – for example, suck CO2 from the atmosphere and store it underground, and make the Earth’s surface brighter.”
Using a stripped-down climate model, Randers and his colleague Ulrich Goluke projected changes up to 2500 under two scenarios: the instant shutdown of emissions and the gradual reduction of gases that warm the planet to zero by 2100.
In a make-believe world where carbon pollution stops with the flip of the switch, the planet warms over the next 50 years to about 2.3 degrees Celsius above pre-industrial levels – about half a degree at above the target set in the 2015 Paris Agreement – and chills slightly after that.
The Earth’s surface is now 1.2 ° C warmer than it was in the mid-19th century when temperatures began to rise.
But from 2150, the planet begins to warm gradually again, with average temperatures rising another degree over the next 350 years and sea level by at least three meters.
In the second scenario, the Earth warms up to levels that would tear the fabric of civilization apart much faster, but end up at roughly the same point around 2500.
– ‘Tipping points’ –
The main finding – disputed by leading climatologists – is that several thresholds, or “tipping points”, of the Earth’s climate system have already been crossed, triggering a self-sustaining warming process, as has happened to millions of people. years in the past. .
One of these factors is the rapid retreat of sea ice in the Arctic.
Since the end of the 20th century, millions of square kilometers of snow and ice – which reflect about 80% of the Sun’s radiating force in space – have been replaced in summer by the great ocean, which absorbs the same percentage at the place.
Another source is the melting of permafrost, which contains twice as much carbon as the atmosphere. The third is the increased amounts of water vapor, which also has a warming effect.
The reactions of half a dozen leading climatologists to the study – which the authors recognize as schematic – varied widely, with some saying the findings deserved follow-up research, and others dismissing them outright.
“The model used here does not turn out to be a credible representation of the real climate system,” said Richard Betts, head of climate impact research at the University of Exeter.
“In fact, it is directly contradicted by more established and extensively evaluated climate models.”
Mark Maslin, professor of climatology at University College London, also pointed out the shortcomings of the model, known as ESCIMO, describing the study as a “thought experiment”.
“What the study draws attention to 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 not only the beginning of our actions to fight against 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 can only be met if massive amounts of CO2 are removed from the air. ‘atmosphere.
One way to do this is to plant billions of trees. Experimental technologies have shown that sucking CO2 out of the air can be done mechanically, but so far not on the scale required.
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