T.Those warning signs are glowing red. California’s wildfires were definitely exacerbated by the effects of global heating. A study published in July warns that the Arctic is undergoing an “accidental weather reversal” that could lead to dramatic changes. If to draw this point, on 14 September it was reported that a huge ice shelf in northeastern Greenland had detached itself, wrapped in hot water from below.
On the same day, a study of satellite data revealed growing cracks and crevices in the ice shelves protecting two of Antarctica’s largest glaciers – indicating that the shelves could also break, causing the glaciers to open and melt, causing Sea level rises. The loss of ice is already following our poor-condition scenarios.
These developments show that the harmful effects of global warming are mounting, and there should be an urgent need to take immediate action to cut greenhouse gas emissions. But the case for emissions cuts is actually much stronger. That’s because scientists are increasingly concerned that the global atmosphere could create something completely new out of its current state – one that has no experience dealing with humans. Many parts of the earth system are unstable. Once reduced, it can fall and stimulate a domino-like cascade.
Tipping point
We have known for years that in many parts of the climate there are so-called tipping points. This means that like soft pressure, slow and steady warming, they can make large changes, which are completely incompatible with the trigger. If we hit any of these tipping points, we have no practical way to prevent the consequences that could come.
The Greenland ice sheet is an example of a tipping point. It has enough ice to raise the global sea level by seven meters, if it all melts. And that fugitive is likely to melt.
Ricarda Winkelman of the Potsdam Institute for Climate Impact Research in Germany says that the top surface of ice sheets is slowly shrinking. The result is familiar to anyone who has walked in the mountains. “If we climb a mountain, the temperature around us gets warmer.” As the ice sheet shrinks, the surface temperature rises higher, leading to more melting. “It’s one of those self-reinforced or accelerated feedbacks.”
We don’t know exactly how much temperature Greenland will pass through its tipping point and start an unpleasant melting. One study estimates that it will only take 1.6C warming – and we have already warmed the planet 1.1C since the end of the 19th century.
This fall will take centuries, which is a bit comfortable, but such a fall is hard to stop. Maybe we can quickly cool the planet below the 1.6C threshold, but that’s not enough, as Greenland will melt uncontrollably. Instead, Winkelman says, we have to give things more cooling – it’s not made clear by how much. Tipping points that behave like this are sometimes described as “reversible”, which is confusing; In reality they can be reversed, but it takes a bigger push than the one that set them up in the first place.
In 2008, researchers at the University of Exeter, led by Timothy Lenton, identified the key “tipping elements” of the climate. Along with the Greenland ice sheet, the Antarctic ice sheet is also at risk of an unstoppable collapse – such as the Amazon rainforest, which can die back and be replaced with meadows.
A particularly important tipping element is the vast ocean current known as the Atlantic Meridian Overthrown Circulation (AMOC), which carries cold Arctic water toward the warm equator and carries the equator toward the Arctic. AMOC has collapsed in the past and many scientists fear it is on the verge of collapse again – an event that was featured in a 2004 film (ridiculously exaggerated and accelerated) Paramdivas. If the AMOC collapses, it will change the weather patterns around the world – leading to colder climates in Europe, or at least lower temperatures, and changes when and where monsoon rains fall in the tropics. For the UK, this could mean the end of most arable farming, according to a paper Lantern and a paper published in January.
Dombinos tumbling
In 2009, another study took the idea further. What if the tipping elements are connected to each other? That would mean setting one up could lead to another departure – or even releasing a cascade of dramatic changes, spreading throughout the world and reshaping the world we live in.
For example, the melting of the Greenland ice sheet is releasing huge amounts of cold, fresh water into the North Atlantic. This weakens the AMOC – so it is clearly possible that if Greenland passes its tipping point, the resulting melt will push the AMOC beyond its own threshold.
“These are the exact same principles that we know happen on tiny scales,” says Catherine Sudding of the University of Colorado, who studies similar shifts in ecosystems. The main point is that processes exist that can amplify small initial changes. This could be true on a meadow or the scale of an entire planet.
However, the tipping point cascade is very difficult to emulate. In many cases the feedback goes both ways – and sometimes one tipping point makes it less likely that another will be triggered, not more. For example, AMOC brings warm water from the equator to the North Atlantic, contributing to the melting of Greenland. So if the AMOC collapses, that northward flow of hot water will stop – and Greenland’s ice will be less likely to collapse. Depending on which greenland or AMOC hits its tipping point first, the resulting cascade will be very different.
More than that, dozens of such links are now known, and some of them cover huge distances. Lanton says, “The melting of a sheet of ice at one pole raises the sea level, and the increase at the opposite pole is the greatest. “Say you’re melting Greenland and you’re raising sea levels under the ice sheets of Antarctica.” It sends more hot water around Antarctica. “You’ll weaken those ice shelves.”
“Even if the distance is quite far, the big dominoes can still help the next one,” Winkleman says.
In 2018, Juan Rocha of the Stockholm Resilience Center in Sweden and his colleagues mapped all known links between tipping points. However, Rocha says the power of interconnections is still largely unknown. This, combined with the total number of them and the interactions between the climate and the biosphere, means that it is very difficult to predict the Earth’s overall response to our greenhouse gas emissions.
Inside the hothouse
The most worrying possibility is that closing one tipping point could release many others, pushing the Earth’s atmosphere into a new state that has not been experienced for millions of years.
Before humans existed, the earth had an “ice house” atmosphere, meaning that there is permanent ice on both poles. But millions of years ago, the weather was in a “hothouse” condition: there was no permanent polar ice, and the planet was many degrees warmer.
If it has happened before, can it happen again? In 2018, researchers including Lanton and Winkelman explored this question in a much-discussed study. They wrote that the Earth system could reach a planet close to the threshold which could lock it in a very fast way to many hot conditions – hothouse earth. The threshold of fear at current rates of warming will only be decades away.
Lenton says the jury is still out on whether this global threshold exists, let’s see how close it is, but it’s not something that should be dismissed.
“The strongest evidence of these moments for me is based on the idea that we could be committed to a ‘waithouse’ rather than a hothouse,” says Lenton. “We can see the ice sheet collapsing. This will lead to a world that has a Northern Hemisphere.” There is no ice and much less than Antarctica, and sea levels are 10 to 20 meters high. “Such an increase would be enough to swamp many coastal megacities, unless they are protected. Will also be moderated by, which will also weaken the Indian monsoon and disrupt the West African one.
Winkleman’s team studied a similar scenario in a study published online in April, which has not yet been peer-reviewed. They mimicked interactions between Greenland and the West Antarctic ice sheet, the AMOC, the Amazon rainforest, and El Ni બીજીo, another major meteorological system known as the Southern Oscillation. They discovered that two ice sheets were likely to stimulate the cascade, and the AMOC then spread the effect worldwide.
What to do
Everyone who studies tipping point cascades agrees on two main points. The first is that it is crucial not to be discouraged by the severity of the risks; It is still possible to avoid beating Domino’s. Second, we should not wait for accurate knowledge of where the tipping points are – which has proved difficult to determine, and will not come until it is too late.
Rocha compares it to smoking. “Smoking causes cancer,” he says, “but it’s very difficult for a doctor to figure out how many cigarettes you need to smoke to get cancer.” Some people are more sensitive than others, depending on factors ranging from heredity to the level of air pollution where they live. But this does not mean that it is a good idea to eat chicken with your lungs while continuing to smoke. “Don’t smoke for long periods of time, because you’re committed to something you don’t want to do,” says Rocha. The same logic applies to climate dominoes. “If that happens, it’s really expensive and hard to recover, so we’re not going to break that threshold.”
“I think the precautionary principle is the best step forward for us, especially when we’re dealing with a system when we know there’s a lot of feedback and interconnections,” Suding agrees.
“These are their risks that we are playing into their potential effects,” says Lenton. “In order to clean up fossil fuels as quickly and as quickly as possible, and to sort out some sources of greenhouse gases, such as food and land use, we have to release ourselves,” says Lenton. He insisted that the tipping point for two great ice sheets could be well between 1s and 2cm warming.
“We don’t really need a climate explanation for Paris,” Winkleman says. In the 2016 agreement, most countries pledged to limit warming to 1.5 to 2C, although US President Donald Trump has since chosen to pull the US out of it. Winkleman argues that 1.5C is the right target, as it takes into account the existence of tipping points and offers the best chance of avoiding them. “For some of those tipping elements,” he says, “we’re already in that dangerous area.”
Cutting greenhouse gas emissions is not a surprising or original solution. But red flashes are our best chance to stop the warning signs.
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