According to experts, climate change could, in the worst case, lead to human extinction. An international team writes in the "Proceedings" of the US National Academy of Sciences ("PNAS") that up to now, too little has been known about such end-time scenarios and their probability. Under the heading "Climate Endgame: Exploring Catastrophic Climate Change Scenarios," the authors advocate more prudent risk management and more research into the worst-case scenarios of global warming. The world must start preparing for end-time scenarios caused by climate change.
"There is ample evidence that climate change could reach catastrophic proportions," write the scientists, including former and one current director of the Potsdam Institute for Climate Impact Research (PIK), Hans Joachim Schellnhuber and Johan Rockstrom. Despite 30 years of effort, human-caused greenhouse gas emissions have continued to rise. "Even discounting the worst-case scenario of climate change, the world is on track to experience a temperature increase of between 2.1 and 3.9 degrees by 2100."
Nevertheless, the consequences of a warming of 3 degrees have not yet been sufficiently investigated. The research focuses on scenarios in which the consequences of climate change are moderate. "Facing a future of accelerated climate change without considering the worst-case scenarios is naïve risk management at best and fatally foolish at worst," it said.
For climate researcher Niklas Höhne from Wageningen University, the worst-case scenario of extinction is still "relatively far away". "But before that there are gradations," said the expert, who was not involved in the article. "It is quite likely that whole parts of the country and countries are no longer habitable."
In their article, the researchers write about the expansion of areas with extreme heat - that is, an annual average temperature of over 29 degrees Celsius. Around 30 million people in the Sahara and on the Gulf Coast are currently affected. According to the team's modeling, two billion people could live in such areas by 2070.
This shows how complex climate impacts could be. "By 2070, these temperatures and the social and political consequences will directly affect two nuclear powers and seven high-security laboratories housing the most dangerous pathogens," says co-author Chi Xu of China's Nanjing University. "There is serious potential for catastrophic consequences."
The scientists therefore advocate including more complex relationships in future risk assessments. They warn of a "risk cascade" in which individual consequences of climate change trigger further problems. For example, heat and uninhabitable areas could lead to migration, social unrest and international conflicts.
"We are increasingly understanding the interaction and interactions between climate change and other areas such as biodiversity, the economy and food production," says Daniela Jacob, Director of the German Institute for Climate Services (GERICS), who was not involved in the article. "Now we are so far that we can collect this knowledge and thus generate important insights for the survival of the earth system."
The scientists write that the consequences of climate change are particularly dangerous with regard to tipping points. These threshold values are comparable to a cup on a table: If you push it towards the edge, nothing happens at first - until it reaches a tipping point where it crashes. For climate change this means something like: The melt in an ice region reaches a point where it can no longer be stopped. Once regions of ice have melted, the ice is gone for the time being. This is particularly dangerous when one tipping point leads to another.
According to the authors, the Intergovernmental Panel on Climate Change (IPCC) has not yet sufficiently dealt with the possible catastrophic consequences of climate change. None of the IPCC's 14 special reports deal with extreme or catastrophic climate change. According to the authors, they should be considered in the next report.
Jacob, who was lead author of an IPCC special report herself, also supports it. "I think that's right, because it does two things: On the one hand, a special report collects the state of knowledge on the subject. It shows whether we know enough or have gaps," she says. "And on the other hand, this analysis triggers research."
It is questionable whether such scenarios should be discussed outside of science. "It's a step too early for me," she says. "In dialogue with the public, you won't get any further with such end-of-the-day scenarios if you don't yet know exactly what can happen, when that could happen and what you have to do to prevent the worst."
Höhne, on the other hand, considers it important to educate people about worst-case scenarios. "We have to clearly communicate what the risks are. And on the other hand say: We still have it in our hands," says the researcher. "We know how to do it, we have the technologies and we know the political measures. It's not even expensive, it's even cheaper in the long run to do something about climate change."