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Even if humanity stops emitting greenhouse gases tomorrow, the Earth will warm up for centuries to come and oceans will rise by meters, according to a controversial modeling study released Thursday.
Natural factors of global warming – more heat-trapping clouds, permafrost melting and sea ice shrinkage – already set in motion by carbon pollution will gain momentum, Norwegian researchers reported in the journal Nature. Scientific reports.
“According to our models, humanity is beyond the tipping point when it comes to stopping permafrost melting by using greenhouse gas cuts as the only tool,” lead author Jorgen Randers, emeritus professor of climate strategy at the BI Norwegian Business School, he 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 colleague Ulrich Goluke predicted changes up to the year 2500 in two scenarios: the instantaneous cessation of emissions and the gradual reduction to zero of global warming gases by 2100.
In a fictional world where carbon pollution stops with a flick of the switch, the planet warms up over the next 50 years to about 2.3 degrees Celsius above pre-industrial levels – about half a degree above the target set in Paris Agreement of 2015 – and cools down slightly later.
The Earth’s surface today is 1.2 ° C warmer than it was in the mid-19th century, when temperatures began to rise.
But starting in 2150, the model causes the planet to gradually warm up again, with average temperatures rising another degree over the next 350 years and sea levels 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 end up at roughly the same point by 2500.
Points of no return
The main discovery – disputed by leading climate scientists – is that various thresholds or “critical points” have already been exceeded in the Earth’s climate system, triggering a self-sustaining warming process, as has happened millions of years in the past.
One such factor 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 radiative force in space – have been replaced in the summer by the open ocean, which absorbs the same percentage.
Another source is the thawing of permafrost, which holds twice as much carbon in the atmosphere. The third is the increase in the 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 as schematic – have varied widely, with some saying the findings warrant follow-up research, and others a priori rejecting it.
“The model used here … has not proved a credible representation of the real climate system,” said Richard Betts, head of climate impact research at the University of Exeter.
“Indeed, it is directly contradicted by more established and widely evaluated climate models.”
Mark Maslin, a 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 supported by the UN and embraced by a growing number of countries – “is just the beginning of our actions to addressing climate change “.
Even the most sophisticated models used in projections by the United Nations scientific advisory body, the IPCC, show that the temperature targets of the Paris climate pact cannot be achieved unless huge 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 extraction of CO2 from the air can be performed mechanically, but so far not to the required scale.
© Agence France-Presse
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