According to a controversial modeling study published on Thursday, even if humanity stopped the emission of greenhouse gases yesterday, the Earth would warm up for centuries to come and the oceans would have to rise by meters.
The natural drivers of global warming – clouds trapped in excess heat, melting permafrost, and shrinking sea ice – that are already in motion from carbon pollution, will take on their own momentum, researchers from Norway told in the journal Nature Scientific report.
“According to our model, humanity is beyond the point-of-return when it comes to preventing melting of parafrost using greenhouse gas reductions as a single tool,” says author Jorgen Randers, one of the Climate Strategies in BI Professor Emeritus Norwegian Business School, told AFP.
“If we want to stop this melting process, we have to do something other than that – for example, sucking CO2 from the atmosphere and storing it underground, and making the Earth’s surface brighter.”
Using the stripped-down climate model, Randers and collaborator Ulrich Goluke estimated shifts up to 2500 under two scenarios: immediate cessation of emissions, and gradual reduction of planet warming gases to zero by 2100.
In a fictional world where carbon pollution ceases with a switch, the planet is about 2.3 degrees Celsius warmer than pre-industrial levels over the next 50 years – about half a degree above the target set in the 2015 Paris Agreement – and beyond. A little cool.
When temperatures began to rise in the mid-19th century, the Earth’s surface is 1.2C warmer today.
But in the model starting in 2150, the planet is slowly warming up again, with average temperatures climbing another degree over the next 350 years, and sea levels rising at least three meters.
Under the second scenario, the Earth heats up to levels that tear the fabric of civilization more quickly, but ends up at around 2500 at the same point.
Basic Search – Contested by leading climate scientists – is that many thresholds, or “tipping points” in the Earth’s climate system have already been exceeded, leading to a self-perpetuating process of warming, as has happened millions of years before in the past.
One of these drivers 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kilometers of snow and ice – which represents about 80 percent of the sun’s radiation power back into space – has been replaced by the open sea in summer, which instead absorbs the same percentage.
Another source is the thawing of the pumafrost, which holds twice as much carbon in the atmosphere. The third is increasing the amount of water vapor, the effect of which is also hot.
Responses from half a dozen prominent climate scientists to the study – which the authors acknowledge is planned – varied rapidly, with some saying that the follow-up to the findings merits research, and others dismiss it out of hand.
“The model used here .. has not shown a reliable representation of the actual climate system,” said Richard Bates, head of climate impacts research at the University of Exeter.
“In fact, this is directly contradicted by more established and largely evaluated climate models.”
Mark Maslin, a professor of climate science at University College London, also pointed out the shortcomings in the model, calling the study a “thought experiment”.
“Whether the study draws attention to reducing global carbon emissions by 2050” – a goal by the United Nations and embraced by a growing number of countries – is “just the beginning of our actions to combat climate change.”
Even the more sophisticated models used in the estimates of the IPCC, the scientific advisory body of the United Nations, suggest that the Paris Climate Treaty temperature targets cannot be reached unless massive amounts of CO2 are removed from the atmosphere is.
One way to do this is to plant billions of trees. Experimental technologies have shown that the removal of CO2 from air can be done mechanically, but not yet at the required scale.
© Agence France-Presse