Many believe that points of no return in our Earth system, such as the disappearance of the Amazonian jungle and the ice sheet in western Antarctica, are unlikely. A team of authors reviewed the evidence that points of no return could be passed and proposed solutions to the problems.
Politicians, economists, and even some natural scientists tend to believe that the points of no return in our Earth system, such as the disappearance of the Amazon jungle and the ice sheet in western Antarctica, are unlikely and poorly understood. However, now there are more and more indications that these events are much more likely than it seemed earlier, that they have serious consequences and are closely related to a variety of biophysical systems. As a result, the world is threatened with long-term and irreversible changes.
In this article, we analyze the evidence that points of no return can be passed, identify knowledge gaps, and suggest solutions. We investigate the consequences of such large-scale changes, find out how quickly they can occur, and if we can somehow control it.
In our opinion, taking into account such tipping points helps to establish that we have a climate emergency and to intensify calls for urgent action to prevent climate change, which are being made today by everyone: schoolchildren and scientists, cities and entire countries.
The Intergovernmental Panel on Climate Change (IPCC) put forward the idea of such tipping points 20 years ago. At that time, "large-scale disruptions" in the climate system were considered probable only if global warming exceeded 5 degrees Celsius above pre-industrial levels. The information summarized and presented in the last two IPCC special reports (published in 2018 and in September of this year) suggests that points of no return can be passed even with a warming of 1-2 degrees.
If countries fulfill their commitments to reduce greenhouse gas emissions (and there are great doubts about this), global warming will be at least 3 degrees Celsius. This is despite the fact that the 2015 Paris Agreement aims to limit warming to well below 2 degrees. Some economists, assuming that climatic points of no return are very unlikely (albeit catastrophic), suggest that 3 degrees of warming is optimal in terms of cost and benefit. But if such tipping points seem more likely, then the “best” recommendations for cost-benefit models are the same as in the latest IPCC report. In other words, warming needs to be limited to 1.5 degrees Celsius. And this requires extraordinary measures.
THE DISAPPEARANCE OF ICE
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We believe that some points of no return in the Earth's cryosphere are dangerously close, but reducing greenhouse gas emissions can still slow down the inevitable accumulation of negative consequences and help us adapt.
Studies of the past ten years show that the coast of the Amundsen Sea in the western part of Antarctica, indented by the bays, may have already passed this point of no return. The “overlapping line” where ice, ocean and rocky base meet, is relentlessly receding. Model research shows that when this sector disappears, it can disrupt the stability of the rest of the ice sheet in West Antarctica like a domino effect. This will lead to a rise in sea level by three meters over time from several centuries to a millennium. Studies show that such large-scale destruction of the ice cover in the western part of Antarctica has occurred repeatedly in the past.
The latest evidence indicates that some of the land ice in the east of Antarctica in the Wilkes Basin is also unstable. Simulations suggest that this could raise sea levels by another four meters in a little more than a century.
Greenland's ice cap is melting at an accelerated rate. If the melting process crosses a certain threshold value, then in several thousand years the sea level will rise by another seven meters. Further, as the height of the ice cover decreases, it melts even more, opening the surface to meet the increasingly warm air. The models created show that with a warming of one and a half degrees, the Greenland ice cap is doomed to disappear, and this may happen as early as 2030.
Thus, it is possible that we have already forced future generations in the coming millennia to live at a sea level rise of about 10 meters. However, we can still change this time frame. The rate of melting depends on the amount of warming beyond the point of no return. At a warming of 1.5 degrees, this could take 10,000 years. If it exceeds 2 degrees, it will take less than 1,000 years. Scientists need more observational data to determine if the ice is reaching a critical point. They need better models based on past and present data to determine how soon and how quickly the ice sheet will break.
But whatever the data suggests, practical action is needed to slow sea level rise. This will help people adapt, and among other things, gradually move large, low-lying settlements to other places.
Another important incentive to limit the temperature rise to 1.5 degrees is that other points of no return can be passed at lower global warming. Recent IPCC models predict a series of sharp temperature shifts from one and a half to two degrees Celsius, some of which will be associated with melting sea ice. Such ice is already rapidly decreasing in the Arctic, and this suggests that with a warming of two degrees, this region has a 10 to 35% chance of almost completely freeing from ice in the summer.
THE BOUNDARIES OF THE BIOSPHERE
Climate change and human activities can trigger disruptive changes of varying scales in a range of ecosystems in the biosphere.
Heat waves in the oceans have resulted in massive coral bleaching and the loss of half of the coral from the shallow waters of Australia's Great Barrier Reef. This is terrible, but it is predicted that 99% of tropical corals could disappear if the average global temperature rises by two degrees Celsius. It is caused by the link between ocean warming, acidification and pollution. This will be a huge loss to marine biodiversity and deprive many people of their livelihoods.
Points of no return in the biosphere not only weaken our life support systems, but can also trigger dramatic emissions of carbon into the atmosphere. This will further intensify climate change and reduce the remaining emission reductions.
Deforestation and climate change are upsetting the balance in the Amazon Basin, home to the world's largest humid jungle and home to one in ten known animal species. Estimates regarding the point of no return in the Amazon vary widely. Someone says that the turning point will come when 40% of the forests will be cut down, while others call the figure 20%. Since 1970, the region has lost about 17% of its forests. The rate of deforestation changes with changes in policy. Determining the point of no return requires models in which deforestation and climate change are interacting forces. They also need to include information on fires and climate as interacting mechanisms, and consider the whole picture as a whole.
Warming in the Arctic is happening twice as fast as in the world as a whole, and the taiga of the subarctic zone is becoming more vulnerable. Warming has already caused large-scale imbalances among insects, and an increase in the number of fires has led to the death of North American boreal forests, which could turn some regions from carbon sinks to carbon source. Permafrost throughout the Arctic begins to thaw irreversibly, releasing carbon dioxide and methane, which are about 30 times stronger than CO2 over a century.
Scientists need to develop their understanding of the observed changes in large ecosystems, as well as where new points of no return may arise. It is necessary to more accurately determine the amount of existing carbon stocks and the possible volumes of CO2 and methane emissions.
The remaining global emissions budget for a 50 percent chance of staying within 1.5 degrees of warming is only about 500 gigatons of CO2. Emissions in the permafrost zone can take an estimated 20% (100 gigatons of CO2) from this budget, and this is without methane from deep permafrost and without underwater marine hydrates. If the forests are close to the point of no return, then their disappearance in the Amazon basin will lead to the release of another 90 gigatons of CO2, and the destruction of the taiga will give 110 gigatons of carbon dioxide. With global CO2 emissions of more than 40 gigatons per year, the budget may already be exhausted.
GLOBAL CASCADE EFFECT
In our view, a clear emergency will arise if we approach the global cascading effect of such tipping points, which will bring the world into a new climatic “greenhouse” state and become less livable. A reciprocal reaction between the ocean and atmospheric circulation can occur, or reverse effects, which will increase the level of greenhouse gases and global temperatures. Or, global points of no return may be the result of a reciprocal cloud formation.
We argue that cascading effects can be widespread. Last year, researchers analyzed 30 types of changes in climate regime and ecological systems, from the disappearance of the ice cap in the western part of Antarctica to the transformation of selva into savannah. This analysis showed that passing points of no return in one system increases the risk of the same passing in other systems. Such connections were found in 45% of possible interactions.
In our opinion, examples of this have already begun to appear. For example, the melting of sea ice in the Arctic leads to an increase in regional warming, and the warming in the Arctic and the melting of Greenland is causing the influx of fresh water into the North Atlantic Ocean. This has resulted in a 15% slowdown since the mid-20th century in the Atlantic meridional overturning circulation, which contributes greatly to the transport of heat and salt by the ocean. Rapid melting of the ice sheet in Greenland and further slowing of the Atlantic meridional overturning circulation could disrupt monsoon seasons in West Africa, causing drought in the African Sahel. A slowdown in this circulation could also drain the Amazon, disrupt monsoon cycles in East Asia and raise temperatures in the Southern Ocean, which will accelerate the melting of Antarctic ice.
Paleostatistics show that global tipping points may have triggered phenomena such as the onset of cyclical ice ages 2.6 million years ago, as well as changes in their amplitude and frequency about a million years ago. Simulation can hardly create such an imitation. Regional points of no return occurred repeatedly during the last ice age 80-10 thousand years ago (especially at its end) (Dansgaard-Eschger oscillations and Heinrich events). This does not directly apply to the present interglacial period, but such events highlight that the Earth's system has repeatedly entered an unstable state under the influence of relatively weak forces caused by changes in the Earth's orbit. Now we are straining this system very strongly, since the concentration of CO2 in the atmosphere and global temperatures are growing faster and stronger,than during the last glacier retreat.
The content of CO2 in the atmosphere today is the same as it was last observed about four million years ago in the Pliocene. And it is rapidly increasing, approaching the level that was last about 50 million years ago in the Eocene. Then temperatures were 14 degrees higher than in pre-industrial times. It is very difficult to simulate this "greenhouse" state of the Earth using climate models. One possible explanation is that such models overlook the key point of no return. This year, a model study was published that indicates that the abrupt decay of stratocumulus clouds, releasing about 1,200 ppm CO2, could lead to global warming of about eight degrees.
Early results from the latest climate models for the IPCC Sixth Assessment Report show that the climate is much more sensitive and vulnerable (defined as the temperature response to a doubling of CO2 in the atmosphere) than in previous models. There will be new results, and further research is needed, but we believe that even these preliminary results indicate that a global point of no return is possible.
To solve these problems, we need models that take into account a richer set of connections and relationships in the Earth system. And we need data from the present and from the past for these models to work. If these models help us better understand past abrupt climate change and its greenhouse state, there will be greater confidence in their ability to predict the future.
Some scientists argue that the arguments about the possibility of global points of no return are purely hypothetical. But we adhere to the following position. Given the enormous consequences and irreversible nature of the points of no return, any serious risk assessment must take into account the facts, however limited our understanding of those facts. It would be irresponsible to make a mistake in this case.
If destructive cascading phenomena can occur, and the global point of no return cannot be ruled out, then this is a threat to the existence of civilization. Again, no cost benefit analysis will help us. We must change our approach to the climate problem.
ACT IMMEDIATELY
In our opinion, the data on the points of no return indicate that we are in a global emergency. The risks and severity of this situation cannot be overstated.
We argue that the time remaining for intervention to prevent the point of no return is already approaching zero, and the response time to achieve zero emissions is at best 30 years. Thus, we could already lose control over the points of no return, and we cannot prevent them. The consolation is that the rate of accumulation of damage after the point of no return, and hence the risks from it, we can still keep under control to a certain extent.
The resilience of our planet and its ability to recover is in great trouble. The answer to this should be not just words, but also actions of the entire world community.