The collapse of the Amazon forests, the melting of the glaciers and frozen lands, the death of the coral reefs - these are some of the factors that may lead to irreversible changes * some of them are occurring at an alarming rate
By David Armstrong McKay, researcher in the field of earth system resilience, Stockholm University
Continued emission of greenhouse gases may cause climatic tipping points. These are self-sustaining changes in the climate system, which will cause devastating changes, such as sea level rise, even if all emissions end.
The first big assessment of the year 2008 It identified nine parts of the climate system that are sensitive to change, including ice sheets, ocean currents and large forests. Since then, huge advances in climate modeling and a flood of new observations and records of ancient climate change have given scientists a much better picture of these fundamentals. Additional additions were also proposed, such as the freezing zone in the Arctic Circle (permanently frozen ground that may release more carbon if it thaws).
Estimates of the levels of warming at which these elements could tip the scales have been advanced since 2008. The collapse of the West Antarctic ice sheet was previously considered a risk when warming would reach 3 to 5 degrees Celsius above the Earth's pre-industrial average temperature. Now it counts Already possible at current warming levels.
in the new assessment Our After the last 15 years of research, my colleagues and I have found that we cannot rule out five tipping points that are occurring now, when global warming is about 1.2 degrees Celsius. Four of those five become more likely as global warming exceeds 1.5 degrees Celsius.
These are sobering conclusions. However, not all the news coverage Catch the nuances of our research. So here is the real meaning of our findings.
Unclear threshold values
We synthesized the results of more than 200 studies to estimate the warming threshold of each reference element. The best estimate was either one that many studies converged on or that a particular study judged to be particularly reliable. For example, records of past ice sheet retreats and modeling studies indicate that the Greenland ice sheet is likely to collapse beyond 1.5°C. We also estimated the minimum and maximum threshold at which collapse is possible: Greenland model estimates range from 0.8°C to 3.0°C.
In this range, the bias becomes more likely as warming increases. We defined the tip as possible (but still unlikely) when warming is above the minimum but below the best estimate, and as probable if the warming is above the best estimate. We also judged how confident we were in each estimate. For example, we are more confident in our estimates of the collapse of the Greenland ice sheet than those of the sudden thawing of frozen ground.
This uncertainty means that we do not expect four climate tipping points to occur in the first year in which global temperatures reach 1.5 degrees Celsius above the pre-industrial average (which climate scientists say could happen in the five years the next few years), or even when the average temperatures over several years reach 1.5 degrees Celsius above the pre-industrial level at some point in the coming decades. Instead, every fraction of a degree makes the bias more likely, but we can't be sure exactly when the bias becomes inevitable.
This is especially true for the Greenland and West Antarctic ice sheets. While our assessment indicates that their collapse becomes likely inevitable beyond 1.5°C, the ice sheets are extremely massive and thus change very slowly. The collapse will take thousands of years, and the processes driving it will require continued warming to stay above the threshold for several decades. If warming returns below the threshold before the process kicks in, it might that ice surfaces will temporarily exceed their threshold without collapsing.
For some other turning points, the change is expected to be more diffuse. We estimate that both tropical coral reef death and the sudden thawing of permafrost are possible at the current level of warming. But the threshold varies between reefs and patches of permafrost. both are already happening In some places, but in our estimation, these changes become much more common in a similar period beyond 1.5 degrees Celsius.
Elsewhere, small parts of the Amazon and boreal forests may overturn and move first to a savanna-like state, bypassing a more catastrophic turn in the entire forest. Results Unpublished models indicate that the reference of the AmazonA miracle may occur in several regions with varying levels of warming rather than as one big event.
The Amazon cannot collapse from forest to pasture all at once. Parallax/shutterstock
There may also be no well-defined threshold for some other peak components. Ancient climate records indicate that ocean currents in the North Atlantic could change dramatically from strong, as they are today, to weak as warming and melting freshwater from Greenland disrupts their flow. Current models It is pointed out that the threshold for the collapse of the Atlantic circulation depends on the speed at which the warming increases along with other factors that are difficult to measure, which makes it very uncertain.
into the danger zone
There are signs that some tipping points are already approaching. Years of drought have caused parts of the Amazon to be less durable against fires and exhaust more carbon from what they absorb.
The leading edge of several retreating glaciers in West Antarctica is found Only a few kilometers away From the unstoppable retreat. Early warning signals in climate monitoring data (such as larger and longer fluctuations in the amount of glaciers melting each year) indicate that stability is already being undermined in parts from the Greenland ice sheet and the Atlantic current circulation.
These signals cannot tell us exactly how close we are to tipping points, only that destabilization is underway and a tipping point may be approaching. The most we can be sure of is that every fraction of additional warming will destabilize these components and make the initiation of self-feeding changes more likely.
This strengthens the argument for the need for significant cuts in emissions in line with the Paris Agreement's goal of stopping warming at 1.5 degrees Celsius. Compliance with this agreement will reduce the chances of causing several climatic turning points - even if we cannot rule out that some of them will be reached soon.
For an article in The Conversation
More of the topic in Hayadan:
