What if all emissions of man-made greenhouse gases were stopped completely? Researchers are trying to understand the development with a model calculation. First of all, there would be an effect that would further aggravate the situation.
Even if all man-made emissions that affect the climate were stopped immediately, global warming could reach 1.5 degrees with a probability of around 42 percent. This is the result of a new simulation study. The researchers also found that an immediate stop in emissions would initially even be accompanied by faster warming because the cooling effect from aerosols from the burning of coal, oil and natural gas would be lost; only after a few years would the global temperature drop. The study by a group led by Michelle Dvorak from the University of Washington in Seattle has been published in the journal “Nature Climate Change”.
The researchers emphasize that they want to look at two aspects of climate change separately:
For this reason, Dvorak and colleagues assumed for their simulations that all man-made climate-relevant emissions would have stopped abruptly at the beginning of 2021. In this way, they calculated that if emissions were not reduced to zero until 2029, the probability of exceeding the 1.5 degree limit increases to 66 percent.
With the help of the computer model “FaIR”, which was developed by experts for the radiation balance of the earth, the scientists created time series of 39 gases and short-lived drivers of climate change. It was concluded that stopping emissions immediately would result in rapid global warming to nearly 1.5 degrees, because: “Tropospheric aerosols produced by burning fossil fuels and burning biomass have atmospheric lifetimes of days to weeks and practice currently exerts a strong net cooling effect on climate (a negative radiative forcing).” With this cooling effect gone, rapid warming would occur before reductions in greenhouse gases lowered the temperature.
So far, climate researchers have focused on the effect that would arise from the absence of the greenhouse gas carbon dioxide (CO2). Because CO2 breaks down very slowly in the atmosphere, the CO2 concentration would remain high for a long time and the temperature would hardly change. Methane, on the other hand, is broken down in 10 to 20 years and other greenhouse gases are not as long-lived as CO2. Stopping emissions of these substances would therefore result in a gradual reduction in the average global temperature.
As in the United Nations Sixth World Climate Report (IPCC), the reference period to which the temperature changes refer is the period 1850 to 1900. Dvorak’s team calculated that from 1850 to 2019, humans emitted 2290 billion tons of CO2 into the atmosphere have fired. After a further 1080 billion tons from January 2021, the 1.5 degree limit will be reached, after 1980 billion tons the two degree limit. Amplification effects such as increased methane emissions from the thawing permafrost are not taken into account in the climate model, so the warming can also be higher.
Jochem Marotzke, Director at the Max Planck Institute for Meteorology in Hamburg, describes the study as “very well done”. He was the coordinating lead author of the Sixth World Climate Report and therefore knows the background very well. Simulations like the ones in this study would have been viewed with suspicion a few years ago, says Marotzke. “Today we know that these simulations with fairly simple models are very well suited for predicting the temperature development.”
The study is also of interest to Elmar Kriegler from the Potsdam Institute for Climate Impact Research, although the Sixth World Climate Report already takes into account the dynamics shown in the study. Kriegler was a co-author of several reports by the Intergovernmental Panel on Climate Change. The study shows that it will be very difficult to keep global warming below 1.5 degrees. Even if the long-term goal of not exceeding the 1.5-degree threshold can be achieved, it is to be expected that this threshold will be “overshot” for a few years. However, more political measures than before are required: “Efforts to curb climate change will be a struggle for every tenth of a degree”.
