The term “Hothouse Earth” refers to a potential future scenario where human-caused climate change leads to extreme conditions that are difficult to reverse. This concept was coined by Johan Rockström and others in a 2018 paper, indicating that if global temperatures exceed a critical threshold, such as 2°C above pre-industrial levels, it could trigger self-reinforcing feedback loops that accelerate climate warming, resulting in a state of sustained extreme warming and rising sea levels. The Hothouse Earth scenario emphasizes the importance of understanding the complex interactions between climate systems and the potential irreversible nature of climate change.

In the new study, ‘The risk of a hothouse Earth trajectory‘ scientists concluded that the globe is closer than previously believed to a “point of no return,” beyond which it will be impossible to halt global warming.

A chain reaction of additional tipping points and feedback loops could result from ongoing global warming. In contrast to the 2-3C temperature increase the world is already on track to achieve. The chain of events lock the planet into a new and terrible “hothouse Earth” environment. Additionally, the temperature would differ greatly from the temperate conditions of the previous 11,000 years, when human civilization as a whole flourished.

The Guardian: At just 1.3C of global heating in recent years, extreme weather is already taking lives and destroying livelihoods across the globe. At 3-4C, “the economy and society will cease to function as we know it”, scientists said last week, but a hothouse Earth would be even more fiery.

The public and politicians were largely unaware of the risk of passing the point of no return, the researchers said. The group said they were issuing their warning because while rapid and immediate cuts to fossil fuel burning were challenging, reversing course was likely to be impossible once on the path to a hothouse Earth, even if emissions were eventually slashed.

It was difficult to predict when climate tipping points would be triggered, making precaution vital, said Dr Christopher Wolf, a scientist at Terrestrial Ecosystems Research Associates in the US. Wolf is a member of a study team that includes Prof Johan Rockström at the Potsdam Institute for Climate Impact Research in Germany and Prof Hans Joachim Schellnhuber at the International Institute for Applied Systems Analysis in Austria.

“Crossing even some of the thresholds could commit the planet to a hothouse trajectory,” said Wolf. “Policymakers and the public remain largely unaware of the risks posed by what would effectively be a point-of-no-return transition. “It’s likely that global temperatures are [already] as warm as, or warmer than, at any point in the last 125,000 years and that climate change is advancing faster than many scientists predicted.”

It is also likely that carbon dioxide levels are the highest they have been in at least 2m years. Prof Tim Lenton, an expert on tipping points at the University of Exeter in the UK, said: “We know we are running profound risks on the current climate trajectory, which we can’t rule out could turn into a trajectory towards a much less habitable state of the climate for us.

However, we don’t need to be heading towards a hothouse Earth for there to be profound risks to humanity and our societies – these will already be upon us if we continue to 3C global warming.”

The evaluation summarized current research on climate feedback loops and 16 tipping elements and was published in the journal One Earth. The Amazon rainforest, sub-Arctic forests and permafrost, mountain glaciers, polar sea ice, the Greenland and Antarctic ice sheets, and the Atlantic meridional overturning circulation (Amoc), a network of ocean currents that significantly affects the world’s climate, are among the tipping elements.

According to the experts, permafrost, mountain glaciers, and the Amazon rainforest all seem to be on the verge of tipping, suggesting that it may already be occurring in Greenland and west Antarctica.

The Guardian: “Research shows that several Earth system components may be closer to destabilising than once believed,” they concluded. “While the exact risk is uncertain, it is clear that current climate [action] commitments are insufficient.”

Prof William Ripple, at Oregon State University, US, who led the analysis, said: “The Amoc is already showing signs of weakening, and this could increase the risk of Amazon dieback. Carbon released by an Amazon dieback would further amplify global warming and interact with other feedback loops. We need to act quickly on our rapidly dwindling opportunities to prevent dangerous and unmanageable climate outcomes.”

Scientists warned in 2018 of the prospect of a hothouse Earth. In this scenario, global temperature stays significantly above the 4C rise of current worst-case climate scenarios for thousands of years, driving a huge rise in sea level that drowns coastal cities. The scientists said then that the “impacts of a hothouse Earth pathway on human societies would likely be massive, sometimes abrupt, and undoubtedly disruptive”.

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Quick AI summary: A study in One Earth reviewing 154 peer-reviewed studies suggests that human-modified landscapes require at least 20% to 25% (semi-)natural habitat per square kilometer to maintain essential ecosystem functions supporting human well-being. The research indicates that five critical Nature’s Contributions to People (NCPs) nearly disappear if this habitat falls below 10%, a level currently seen in roughly two-thirds of all human-modified lands.

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