Planet crosses 1.5°C global warming limit

France, Jan. 12: A milestone has been reached: 2024 was the warmest year ever recorded and the past two years were the first to exceed a 1.5°C temperature increase compared with pre-industrial levels, the European Union's Copernicus climate observatory announced on January 10. 

The news is symbolic. Since 2015, the Paris Agreement has aimed to keep rising global temperatures below this limit in order to reduce the impacts of human-driven climate change.

In the treaty, such an increase is referred to as a long-term climate trend – the average temperature would have to remain above the 1.5°C threshold for 20 to 30 years for the limit to be officially considered exceeded. But the figures for 2024 – which recorded a 1.6°C increase overall – have raised fears that the target may now be altogether unattainable.

“Today the 1.5 degree goal is practically ancient history already,” said Jochem Marotzke, climatologist and oceanographer at the Max-Planck-Institute for Meteorology in Hamburg, Germany. “Anyone who continues to say the world can stay below that limit is delusional. We have to face reality and adapt to increasing warming.”

But, is there a way to turn back the clock and return to a more liveable climate? Faced with the failure to keep global temperatures below 1.5°C, is it possible to overstep that limit and then reverse the trend?

This idea of reversible overheating, known as an “overshoot”, is increasingly referenced by some politicians and scientists. It is even part of scenarios modelled by the UN’s Intergovernmental Panel on Climate Change (IPCC).

But as reassuring as the concept may sound “it would entail many risks and its implementation today remains highly uncertain”, says Carl-Friedrich Schleussner, researcher at the International Institute for Applied Systems Analysis, and author of a study evaluating short- and long-term overshoot scenarios.

The first issue is that to bring down the global thermostat, billions of tonnes of CO2 would have to be captured in the atmosphere. For the world to even achieve carbon neutrality – a perfect balance between the carbon that is emitted and absorbed – it would first have to counteract unavoidable residual emissions, such as those generated by agriculture, and historical emissions. 

To reduce the global temperature by 0.1°C the study estimates that at least 150 billion tonnes of CO2 would need to be absorbed, equivalent to four years of global emissions.

But such quantities would be extremely difficult to achieve. Aside from extensive reforestation to recreate natural carbon sinks, it would only be possible through geoengineering such as carbon capturing plants or even the much-maligned solar geoengineering – a method of cooling the earth by reflecting sunlight back into space.

Such methods are still developing, often contested and expensive. They require large reserves of energy, water and land and could have unexpected long-term effects. 

For comparison, today only 2 billion tonnes of CO2 are eliminated per year by human efforts, mainly reforestation, 2 million of which are permanently eliminated by more technological solutions.

The quantities of CO2 that need to be stored could also turn out to be even greater than predicted. Scientists regularly warn of the risk of “hidden” warming, a scenario in which temperatures would continue to rise even after carbon neutrality had been achieved.

“And even if we could achieve this huge technological challenge, it still might not be enough,” says Schleussner. (AFP)