If emissions continue to increase at the current rate, climate change could mean the end of the world. At least the world as we know it. It doesn’t have to be like this. But it is also not unlikely: According to the Intergovernmental Panel on Climate Change (IPCC), temperatures worldwide could rise by 2.5 to 4.5 degrees if the CO2 content in the atmosphere doubles. To date, it has increased by 50 percent compared to pre-industrial times.

Whether the collapse really occurs depends on the actions of humanity today. But what if we fail to limit greenhouse gas emissions?

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There is too little research on this compared to the risk involved. Says an international team led by Luke Kemp from the University of Cambridge. Your article, which appeared in the magazine “PNAS” on Monday, outlines an answer to the question of how to deal with this research gap and what could happen in the worst case.

The quintessence of the results: By 2070, two billion people could be living in areas with extreme heat and annual temperatures averaging 29 degrees. The affected regions were among the most densely populated and politically vulnerable in the world.

Currently only 30 million people in the Sahara and on the Gulf Coast live under similar temperature conditions. For comparison: the global average temperature is 13 degrees.

Heat is also a major threat to the food supply. The researchers warn that the world’s breadbaskets could collapse with increasing probability. For example, four degrees more globally would lead to 86 percent crop failures in the four most important corn-growing regions.

Hotter and more extreme weather could also fuel new epidemics as wildlife habitats shift or shrink and there is closer contact with humans. Climate change could amplify other threats, such as inequality, disinformation, or the violation of planetary boundaries.

One possible future the paper highlights are “warm wars,” in which technologically upgraded superpowers fight over dwindling carbon budgets and huge experiments designed to deflect sunlight and lower global temperatures.

Even without a worst-case scenario, the current course points the world to a temperature rise of between 2.1 and 3.9 degrees by 2100, the article recalls current calculations. If all commitments under the Paris Agreement for 2030 are implemented, it will be 1.9 to 3 degrees.

All long-term commitments and targets combined could result in 1.7 to 2.6 degrees of warming. “Even these optimistic assumptions lead to dangerous paths of the Earth system,” the authors write.

Studies on how climate change could trigger a domino effect or major crises have been sparse, it said. There is the IPCC special report on extreme events and disasters from 2012, the World Bank report “Turn down the heat” from 2014 or the EU project “High-End Climate Impacts and Extremes” (Helix) from 2017.

The non-fiction book “Our Final Warning” describes that with global warming of more than six degrees, the survival of humanity itself is in question.

But in order to better understand the risks, the team led by risk expert Kemp proposes a research agenda based on the four horsemen of the apocalypse in the Bible: The dangers of famine, extreme weather, conflicts and epidemics should be examined more closely.

There is also an urgent need to better understand the potential tipping points within the “greenhouse Earth”: from the methane released as the permafrost thaws to the loss of forests.

According to the article, a high risk potential lies in dwindling cloud cover. The resulting feedback is still poorly understood.

However, simulations would indicate that the stratocumulus cloud cover could be lost abruptly at possible CO2 concentrations in the year 2100. An additional global warming of eight degrees would then be possible.

For the IPCC, the paper suggests a special report on catastrophic climate change. The team defines this as a population decline of 25 percent and high economic and cultural losses. “Fourteen special reports have been published so far. None covered extreme or catastrophic climate change,” the authors regret.

In any case, the IPCC focuses very much on 1.5 and two degree scenarios. Why? One reason is the goals of the Paris Agreement. In addition, while complex risk assessments are more realistic, they are also more difficult.

A third reason is a climate science culture of “siding with the least drama” – to avoid being seen as alarmist. Geophysicist Bill McGuire (Twitter) recently said on the occasion of the publication of his book “Hothouse Earth”: “I know a lot of people who work in climate science who say one thing in public but something completely different in private. In trust, they are all much more afraid of the future we face, but they will not admit it publicly. “But the world needs to know how bad it could get in order to tackle the crisis.

As lead author Kemp puts it: “We know that the rise in temperature has a ‘fat tail,’ which means a wide range of less likely but potentially extreme consequences,” he said. “Remaining blind to worst-case scenarios is naïve at best and deadly stupid at worst,” he says.

However, no extreme emission scenarios are needed for this, but a focus on risks with low probability and high impact, contradicts Carl-Friedrich Schleussner from Humboldt University.

The fact that climate research neglects high risk scenarios is not correct anyway. “By far the most scientific studies examine climate impacts in the event of extreme warming scenarios.” Fortunately, these can no longer be regarded as realistic.

However, it is true that the risks of climate change are currently being considered in “an otherwise idealized and conflict-free world”. “The reality is different. In 2022 and unfortunately probably also for a long time in the 21st century,” said Schleussner, who was not involved in the study.

The researchers around Luke Kemp are aware that their warnings are not necessarily helpful to society because bad news often has a paralyzing effect. This is what climate communication research has shown. However, the authors of the study hope that an analysis of the extreme consequences of climate change could also stimulate action and awaken resilience.

“We need to incorporate irreversible and potentially catastrophic risks from human-caused climate change into our planning and actions,” said co-author Johan Rockström, director of the Potsdam Institute for Climate Impact Research. He cites the death of the Amazon rainforest and the accelerating melting of the Greenland ice sheet as examples of systems that are rapidly shifting from cooling sinks to sources of warming.

“This means that we cannot be satisfied with just looking at averages. We also need to consider non-linear high risks. It is crucial to calculate the catastrophes in order to avoid them,” Rockström directs the view of a future that is not so dystopian same: inaction,” climate scientist Katharine Hayhoe tweeted.