Tipping Points That Would Turn The Earth Into A Hothouse For Thousands Of Years Could Be Frighteningly Close

The loss of sea ice is the best known feedback mechanism from global warming, but others could matter more in the long run. Florida Stock/Shutterstock

Most of these feedbacks operate on a longer time scale, over which they could easily tip us into a “hothouse world” where sea levels rise by 15 meters (50 feet) and many areas become incapable of supporting human life.

Crucially, the paper notes, most of these forces are almost impossible to stop once they get started. Although these threats have been considered before individually, the authors focused on the neglected aspect of how they could interact.

“The real concern is these tipping elements can act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over,” Steffen said in a statement.

Tipping points that could occur at small increases above pre-industrial levels (yellow) could trigger others (orange), which in turn feed into the most extreme possibilities (red). Steffen et al./PNAS

The paper notes that the burning of fossil fuels is far from the only human activity that can make these tipping points more likely. For example, tropical rainforests benefit from being surrounded by other rainforests. Chop some down and there is less rain for nearby forests, increasing the danger of dry-season fires.

The authors admit our knowledge of the temperatures at which these tipping points will be crossed is poor, and in some cases, the rate of warming is as important as the absolute amount. Nevertheless, they argue we can't be confident of keeping the Earth in a stabilized temperature state if temperatures rise by 2ºC (3.6ºF) compared to pre-Industrial levels. Terrifyingly, we are already halfway there.

When the Earth's temperature is at a low point in this chart, it takes something powerful to push it out. If we take the wrong path, this could send us into an almost unchangeable hothouse. Steffen et al./PNAS


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