Rapid, effective climate action is needed to stop global warming. But when would the positive effects of such measures be felt in concrete terms?
Climate scientists have now investigated this using model simulations. The result: If we were to move towards the strict two-degree climate protection target around the world later this year, this would have a direct impact on the climate system. However, due to the sluggish reaction of the global climate and the large natural fluctuations, these effects could only be felt in a few decades at the global mean temperature.
The Earth’s climate system is slow to respond to changes because many buffers make its response very sluggish. An extreme case is the Pacific deep sea, which only now reflects the climate cooling of the “little ice age” in the 16th century – with a few centuries delay. Warming due to rising greenhouse gas levels in the atmosphere is also not immediately noticeable.
In 2014, researchers calculated that the carbon dioxide emitted by mankind will only develop its maximum greenhouse effect after about ten years. However, this effect will last for at least a century. The greenhouse gases emitted today therefore have the potential to influence the climate of our grandchildren. “Anthropogenic climate change can be compared to a tanker ploughing through the waves at full throttle,” explains author Bjorn Samset of the Center for International Climate Research in Norway. “If you go backwards at full force, it will still take some time before you realize that the ship is going slower.”
Inertia and variable at the same time
In the context of climate protection, this raises the question of when the first positive effects of, for example, drastic emission reductions would emerge: “If we were to significantly reduce a greenhouse gas today with considerable resources and with a lot of goodwill from the public, when could we see the benefits in the form of reduced climate change?” says Samset and his colleagues. As they explain, this question is far from trivial. In addition to the inertia of the climate system, its natural fluctuations also play a role. They mask the long-term trend and therefore make it difficult to clearly identify a development, whether positive or negative. The effect of anthropogenic climate change can therefore only be statistically demonstrated when looking at longer periods of time. “Just as it took us some time to prove global warming, we also need a lot of patience before we can determine whether our climate action has the desired effect,” Samset said.
He and his colleagues have now examined in more detail how long this might take. For this, they assumed as a basic scenario a world that is heading for a warming of around 2.6 degrees in 2100, which corresponds to the RCP climate scenario of 4.5. Then they simulated how much the global mean temperature would change in 2100 if individual emissions such as CO2, methane, nitrous oxide, or soot were stopped completely this year, if they were to be reduced by five percent per year, or if the two-degree target of the Paris climate agreement were to be pursued. In addition, the researchers determined when, for the first time, the global mean temperature could be proven to be a difference from the basic scenario.
Clear signal from 2033 at the earliest
The simulations showed that even if we stopped all CO2 emissions today, we would not be able to demonstrate the positive effect of this measure until 2033 at the earliest. By 2100, however, this would at least avoid a degree of warming. Climate protection in line with the Paris climate agreement would even take until 2047 to see the first clear effects, the scientists report. For other greenhouse gases such as methane or nitrous oxide, the delay would be even greater. Only a reduction in soot emissions would be noticeable a little faster: from about 2028. “The effects of the emission reductions can be compared with those of social distancing during the corona pandemic: they work from day one, but because of the incubation period, it takes some time to see the effect on the infection numbers,” explains Samset. “In the same way, any reduction in greenhouse gas emissions will result in less heat being absorbed, but it will take some time before we can measure that.”
This means that even successful climate protection will not be noticeable at first. Both global temperatures and weather extremes will continue to rise. This can be a problem for the acceptance of the measures and the communication of their necessity, as Michael Brüggemann, Professor of Communication Science at the University of Hamburg, comments on the study: “The fact that climate change develops over decades and centuries, but the attention span of media publics does not extend beyond a few days, is at the heart of the communication problem of climate change.” , he says. “We must act today so that humanity is better off much later. This requires a lot of responsibility.”
