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Tipping points of global warming

The Indian Express logo The Indian Express 19-10-2022 Amitabh Sinha
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While the world is worried about restricting global warming to within 1.5 degree or 2 degree Celsius, a new study has found that even the current level of average global temperatures -- about 1.1 degree Celsius higher than preindustrial times -- is enough to trigger catastrophic changes in several climatic systems. The study, published recently in Science journal, has warned that the thresholds for many of these systems could be crossed at the current levels of warming, setting off self-perpetuating changes that could put living beings at serious risk.

The research is an updated assessment of important climate tipping points, or the thresholds beyond which changes in the earth’s systems become uncontrollable and irreversible. Its findings could lead to a reassessment of global efforts to fight climate change, and are being widely discussed in scientific circles.

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Tipping points

The discussion on climate tipping points is not new, and several studies in the past 15 years have identified different tipping points such as the disintegration of Greenland ice sheet, a spontaneous reduction in Amazon forest cover, melting of glaciers, or softening of the permanently frozen grounds in the polar regions that have large amounts of carbon trapped in them.

Over the years, researchers have identified at least 15 tipping points, each correlated with different levels of temperature rise. The latest study has identified nine global and seven regional tipping points, and has re-assessed their dynamics and correlation with global warming.

Tipping points at work

Rising temperatures are causing largescale changes in these climatic systems. Glacial melt, thinning of Arctic ice, rise in sea-levels are all well-documented and visible changes. However, it is still possible, at least theoretically, to arrest these changes, or even reverse them over time. But once the tipping points are crossed, this possibility no longer exists. It is like the dam burst moment.

The process of change becomes self-perpetuating. It feeds into itself and accelerates the process. What is worse, it also feeds into and accelerates other linked processes.

The Greenland ice sheet, which is already melting, is a good example to illustrate this process. As it melts, the height of the ice sheet gradually reduces. In the process, a larger part of it gets exposed to warmer air. That is because air is warmer at lower altitudes than at higher altitudes. The exposure to warmer air expedites the process of melting. Once the tipping point is crossed, this becomes a self-sustaining and cyclic system. The system does not reverse even if the global temperatures stop rising.

Similar is the case with Amazon forests. These play a very important role in causing rains in the region. If deforestation continues unabated, there would be fewer and fewer trees, which would reduce rainfall, causing further stress on the trees. Once again, it develops into a self-perpetuating process.

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Several areas of the world remain frozen throughout the year. These are known as permafrost. Because they have remained in this state for centuries, they hold large amounts of carbon -- from plants and animals that died and decomposed over the years -- trapped in them. It is estimated that the permafrost layers hold as much as 1,700 billion tonnes of carbon, mainly in the form of carbon dioxide and methane. In comparison, the global emissions of carbon in a year are in the range of 40 billion tonnes.

The softening or melting of permafrost layers is already releasing some carbon into the atmosphere. This release of carbon is adding to the warming, which in turn is expediting the process of softening of permafrost layers. This too has a tipping point beyond which it would become a self-perpetuating cycle.

New findings

When the discussion on tipping points had first emerged about two decades ago, most of these were considered plausible only in warming scenarios exceeding 5 degree Celsius. But more recent information, including those presented by the Intergovernmental Panel on Climate Change (IPCC), suggest that most of these tipping points would be crossed between 1 and 2 degree Celsius temperature rise.

The latest study has presented evidence to suggest that some of these tipping points could be met even at the current levels of warming. It has shown that the present 1.1 degree Celsius warming was within the lower end of temperature ranges for at least five tipping points. It means that these self-perpetuating changes could possibly have already begun. For warming between 1.5 degree and 2 degree Celsius, six tipping points become “likely” and four more become “possible”, the study has said.

“Our assessment provides strong scientific evidence for urgent action to mitigate climate change. We show that even the Paris Agreement goal of limiting warming to well below 2°C and preferably 1.5°C is not safe as 1.5°C and above risks crossing multiple tipping points. Crossing these CTPs (climate tipping points) can generate positive feedbacks that increase the likelihood of crossing other CTPs,” the authors have said in the study.

Policy response

The findings of this study are expected to further amplify the voices asking for increase in efforts to restrict global warming. The sixth assessment report of the IPCC released earlier this year had said that global emissions of greenhouse gases needed to peak by 2025, and reduce by 43 per cent from current levels by 2030, if the 1.5 degree Celsius target was to be achieved. With the current level of efforts, the world is on the path to become more than 2 degree warmer by the year 2100.

However, it is unlikely that countries would significantly increase the ambition of their climate action in the next few years. If anything, the progress is only likely to slow down because of the impacts of the Ukraine war on the energy supply chains across the world.

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