Bengaluru: In yet another alarm over climate change, a group of scientists have warned that the Earth is headed to a “global tipping point” if the ongoing crisis is allowed to continue on its current path.
Tipping points are reached when particular impacts of global warming go beyond a critical level.
In their article published in the journal Nature, the scientists have said “we are an existential threat to civilisation” and “in a state of planetary emergency”.
The researchers have laid out nine primary tipping points that are reaching alarming levels of danger: the melting of the Arctic sea ice, West Antarctic ice sheet, East Antarctic ice sheet and Greenland ice sheet; permafrost; slowdown in Atlantic circulation; loss of coral reefs, Amazon rainforest, and boreal forest in the Arctic region.
The latest warning comes just weeks after 11,000 scientists from 153 countries declared a state of global climate emergency urging for immediate and drastic action to curb global warming.
Tipping points
The concept of tipping points was introduced by the United Nations’ Intergovernmental Panel on Climate Change (IPCC) several years ago. Until very recently, it was thought that these tipping points in the climate system were considered likely to be touched only if global temperatures exceeded beyond 5°C above pre-industrial levels.
However, the latest two IPCC Special Reports from 2018 and 2019 suggested that these tipping points could be exceeded even between 1 and 2 °C of warming beyond pre-industrial levels.
The 1°C barrier has already been breached.
In the best case scenario, despite the Paris Agreement goals to curb the rise of temperatures to 2 °C, the planet is expected to be a degree hotter by the end of the century. If warming is allowed to continue at the present rate, the planet is likely to cross the 3 to 4 °C mark by 2100.
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Ice tipping points
Among the nine tipping points to consider, the researchers stress on ice collapse.
The 2019 IPCC report indicated that the Amundsen Sea embayment of West Antarctica might have already passed a tipping point as ice retreats rapidly. The report also said that the East Antarctic ice sheet at the Wilkes Basin is also unstable.
Models predict the two are expected to add 3 to 4m rise in sea level by next century.
Furthermore, the melting itself is accelerating. Models suggest that the Greenland ice sheet, in the Arctic region of the world, could completely collapse when temperatures cross 1.5 °C of warming — as predicted by the 2019 IPCC report. This is expected to occur in a decade, by 2030.
In their Nature article, scientists explain that the rate of melting depends on the magnitude of warming above the tipping point. At a 1.5 °C rise, sea level could rise to 10m over 10,000 years. But at 2 °C rise, the same could take place in less than 1,000 years.
By the end of this century, many coastal cities are expected to go under water including Chennai, Mumbai, New York City, and Shanghai.
Loss of coral reefs
Over 25 per cent of all known marine life depend directly or indirectly on coral reefs, which span only 1 per cent of the ocean floor. They are the primary habitat for over 4,000 species of fish and thousands of other animals.
Heat waves in the ocean have already led to coral bleaching and over 50 per cent loss of corals in Australia’s Great Barrier Reef.
The Nature researchers state that if temperatures cross 2°C, owing to interactions between warming, ocean acidification, and pollution, 99 per cent of tropical corals are projected to be lost.
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The Atlantic circulation slowdown
Excessive melting of Arctic sea ice is dumping freshwater into oceans, especially North Atlantic. This has contributed to a 15 per cent slowdown of the Atlantic Meridional Overturning Circulation (AMOC), a key part of global heat and salt transport by the ocean.
Rapid melting of the Greenland ice sheet and further slowdown of the AMOC could destabilise the West African monsoon, the scientists said in Nature. This could trigger drought in Africa and change monsoon patterns in India.
A slowdown in the AMOC could also dry the Amazon, disrupt the East Asian monsoon and cause heat to build up in the Antarctic Ocean, which could accelerate Antarctic ice loss.
Releasing carbon
Trees and forests, along with ice, act as carbon sinks and trap carbon dioxide. With the Arctic warming at least twice as quickly as the global average, several sources of trapped carbon are starting to release it back into the atmosphere.
The melting of permafrost is a contributor, releasing methane as well as carbon dioxide into the air. It further releases diseases trapped in the ice, such as anthrax.
New evidence shows the raging fires in the boreal forests are already releasing massive quantities of carbon dioxide into the atmosphere.
Similarly, deforestation is threatening Amazon, whose tipping point could lie as low as 20 per cent of the forest cover. Currently, we have lost 17 per cent of the rainforest since 1970.
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Evidence from the past
The article explained that the Earth has seen such conditions in the past, where the planet slipped into excessive heating and then into ice age. These cycles occurred through natural climate change over thousands and millions of years as the Earth and sun changed in their orbit.
“Now we are strongly forcing the system, with atmospheric CO2 (carbon dioxide) concentration and global temperature increasing at rates that are an order of magnitude higher than those during the most recent deglaciation,” said the scientists.
Today, the carbon dioxide concentration in the atmosphere is already at what it was 4 million years ago, and climbing towards levels that were last seen 50 million years ago. Back then, the global temperatures were 14°C higher than they were in pre-industrial times.
“If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilization,” said the scientists.
They stated that no amount of economic cost–benefit analysis is going to help humanity survive unless it urgently changes its approach to tackling the climate crisis that is already here.
“The evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute,” the scientists concluded.
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