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Saturday, September 25, 2021

Explained: Clearest picture of climate

The latest IPCC report, while flagging the same concerns as previous ones, is now backed up by more data than ever. The human contribution to rising temperatures is clearer, and the 1.5°C warming closer.

Written by Amitabh Sinha | Pune |
Updated: August 13, 2021 3:02:24 pm
A man pushes a scooter through floodwaters in Xinxiang in central China's Henan Province, Monday, July 26, 2021. (AP Photo/Dake Kang, File)

More intense and frequent heat-waves, increased incidents of extreme rainfall, dangerous rise in sea-levels, prolonged droughts, melting glaciers — there is little in the latest report of the Intergovernmental Panel on Climate Change (IPCC) that it has not flagged earlier. Except, perhaps, the fact that 1.5°C warming is much closer than was thought earlier, and inevitable.

But the 4,000-page document, the first part of the Sixth Assessment Report, released on Monday, contains mountains of fresh evidence to support what IPCC has been warning of for decades, so that IPCC can make those same statements with far greater confidence, and higher accuracy. As Valerie Masson-Delmotte, co-chair of IPCC’s Working Group-I that produced today’s report, put it, scientists now have much better clarity about what was happening to the Earth’s climate.

“We have the clearest picture of how the Earth’s climate functions, and how human activities affect it. We know, better than ever, how the climate has changed in the past, how it is changing now, and how it will change in the future,” she said after the release of the report.

An example of that is the confidence with which IPCC is now saying that the rise in global temperatures was a direct result of human activities. In the previous assessment reports, the IPCC had said that human activities were “likely”, or “most likely” behind the rising temperatures. The latest report says it was “unequivocal” that this was indeed the case.

This might appear to be a minor quibble over semantics, but a large amount of evidence is required to force such a shift. And the certainty with which such statements can be made often is key to convincing governments to decide their course of action.

From extreme to common

The crux of the report is not in the headline statements that mostly contain the averaged, or mean, values of prediction ranges. The real worries lie in the extremities of those predictions.

One of the headline statements of the latest report is that the 2°C warming is likely to get exceeded by the end of this century unless immediate and deep reductions in greenhouse gas emissions are initiated immediately. What gets masked in this statement is the fact that in the business-as-usual, or worst-case, scenario, the temperature rise by the end of the century would exceed even 4°C.

This is important because the worst impacts of climate change are projected to get manifested in extreme events — rainfall, drought, heat-waves, cyclones and others — and the frequency of such events is expected to rise sharply. In a way, extreme events would no longer also remain rare. They are likely to get normalised very soon.

“The increases in temperature, rainfall, or other factors like glacier melting that are reported in the assessment (report), are mainly averages. But averages often mask the extremes. In a 2°C warmer world, for example, not every day would be 2°C warmer than pre-industrial times. Some days can be 6°C to 8°C, or even 10°C, warmer. That is how global warming will manifest at the local levels,” said Bala Govindasamy, Professor at the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science, Bengaluru, who contributed to the IPCC report.

“Similar is the story with rainfall, or sea-level rise, or other changes that are predicted for the future. I would, therefore, say that we must be most worried about the extremes. Also, extremes are the most compelling reason for (governments to initiate) more ambitious climate action,” said Govindasamy.

Govindasamy said the frequency of extreme events would soon result in a shift in the mean values that might already be at alarming levels now.

Impacts already being felt

A key message that scientists keep on repeating is that the adverse impacts of climate change does not begin after a threshold – 1.5°C or 2°C rise in temperatures – is reached. The impacts projected at 2°C of warming would be present at 1.5°C as well, and are being witnessed even now. But they begin to get worse as the warming increases.

“With every additional amount of global warming, we will see greater changes in the climate. Every additional half degree of warming will cause increase in the intensity and frequency of hot extremes, heavy precipitation and drought. At 2 degrees of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and human health. At a global scale, extreme daily rainfall events would intensify by about 7% for each additional degree Celsius of global warming,” Masson-Delmotte said.

What else is new

While the IPCC has for several years been calling for far greater climate action in the immediate term, it has, for the first time now, also tried to answer how long it would be before the benefits of immediate action begins to show fruits. This is a crucial issue confronting governments – whether any visible and tangible results of emission cuts are possible in the near term.

The Sixth Assessment Report has not answered this question comprehensively but suggested that the results of ambitious emission reductions might begin to show over time scales of 10 to 20 years.

A new element in the sixth Assessment report is the discussion over “compound events”, two or more climate change-induced events happening back to back, triggering each other, or occurring simultaneously. A recent event in Uttarakhand, involving heavy rainfall, landslides, snow avalanche, and flooding, is a good example of a compound event.

Glacial lake bursts, a familiar occurrence in the Himalayan region, is also an example of a compound event, accompanied as it is with heavy rainfall and flooding. Compound events can be several times deadlier. If occurring together, they feed into each other, aggravating each other’s impacts. If occurring one after the other, they give little time for communities to recover, thus making them much more vulnerable.

“Many regions are projected to experience an increase in the probability of compound events with higher global warming. In particular, concurrent heatwaves and droughts are likely to become more frequent,” the report says.

“With increasing global warming, some very rare extremes and some compound events with low likelihood in past and current climate will become more frequent, and there is a higher chance that events unprecedented in the observational record occur,” the report says.

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