Temperature records over the past few years have impressively shown how quickly the window for limiting global temperature rise to 1.5 degrees Celsius above pre-industrial levels could close. A team of researchers with participation from Austria has now revised the estimates of the remaining CO2 budget. Their conclusion, published in the journal “Nature Climate Change”: If things continue as they have been for another six years, the goal will finally be history.
The most recent developments in recent years have also surprised many experts in a negative sense: the effects of the unprecedented increase in greenhouse gas concentrations in the atmosphere are taking effect much more quickly than was often expected. This year’s thermal anomalies, with sea temperatures well above the long-term average, the comparatively very hot summer and warm autumn in many regions of the world, and the highest daily global average temperatures recorded to date, illustrate this.
The US climate agency NOAA expects a probability of more than 99 percent that 2023 will be the world’s hottest year since records began. According to the EU’s climate change service Copernicus, average temperatures so far this year have been 1.4 degrees Celsius above pre-industrial levels. Study researchers have now asked how large the scope remains until the 1.5-degree threshold is exceeded more or less permanently, within which, according to experts, the negative effects of the climate crisis can at least be maintained within reasonable limits -lead authors Robin Lamboll of Imperial College London and Joeri Rogelj of the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, near Vienna.
Scope of CO2 budget halves
In their analysis, the scientists have now come to the conclusion that there is still a 50 percent probability that the increase will be limited to the 1.5 degree limit if humans emit just an additional 250 gigatons of CO2 from January 2023. This would mean that the fiscal space for CO2 would be halved compared to the latest estimates from the Intergovernmental Panel on Climate Change (IPCC) from the beginning of 2020.
This is mainly due to the fact that emissions have increased again since a brief decline as a result of the Covid-19 pandemic. The latest weather observations would also have a negative impact on budget estimates, according to a perspective paper on the work by Benjamin Sanderson of the International Center for Climate and Environmental Research in Oslo.
In other words, within this 250 gigaton margin, there are only about six years left in which CO2 can be emitted like this year, according to the newspaper. Scientists used as a reference value the approximately 40 gigatons of CO2 emissions that humans caused worldwide last year. For the 50 percent probability of remaining below the threshold of more than two degrees, the team, which also includes IIASA researchers Zebedee Nicholls, Christopher Smith, Jarmo Kikstra and Edward Byers, calculated a remaining budget of about 1,200 gigatons of CO2.
Various uncertainties
However, scientists emphasize in their work that this information is anything but immutable: a factor of uncertainty is the influence of emissions of other greenhouse gases, whose concentrations have also increased in recent decades.
It is also unclear how global warming will continue when net emissions are zero – that is, if no more greenhouse gases enter the atmosphere than are removed from it by nature or technical efforts. Sanderson points out here that, given the new numbers from Lamboll and colleagues, achieving net-zero emissions by mid-century, as politicians have often promised, would not be enough to prevent the 1.5-year limit from being exceeded. limit.
“The current study shows one thing above all: the 1.5 degree target will be very, very tight. It is almost irrelevant whether the budget will be achieved in six years – as in this study – or in ten years – with emissions remaining at same.” . as previously thought – it is sold out. In any case, it is extremely tight. And this is not a new discovery,” explained the head of the New Climate Institute in Cologne, Niklas Höhne, who was not involved in the study, to the German Science Media Center (SMC). But that doesn’t mean giving up. “So much for contrary. This shows that every ton of carbon dioxide saved is even more important because the budget is extremely tight.”
Service: The online study: https://doi.org/10.1038/s41558-023-01848-5; The perspective article: https://doi.org/10.1038/s41558-023-01846-7