Clearest picture of climate - IPCC AR6 August 2021

The UN Secretary-General António Guterres described the IPCC's latest climate report as “a code red for humanity.”

 Clearest picture of climate - IPCC AR6 August 2021

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• Code Red: Man has created a serious problem for himself, if we believe what the latest IPCC report indicates. It is titled "Climate Change 2021: The Physical Science Basis" (a 4000 pages document).
• Core message: The IPCC, in its Sixth Assessment Report (AR6), estimates that under all growth scenarios, the planet’s warming level will touch 1.5 degree Celsius. It shows that emissions of greenhouse gases (GHGs) from human activities are responsible for approximately 1.1 degree Celsius of warming since 1850-1900. Averaged over the next 20 years, global temperature is expected to reach or exceed 1.5 degree Celsius above normal range. The UN Secretary-General António Guterres described the report as “a code red for humanity.”
• What will worsen: More intense and frequent heat-waves, increased incidents of extreme rainfall, dangerous rise in sea-levels, prolonged droughts, melting glaciers — are situations that IPCC has warned earlier too, and does so again. The fact that 1.5°C warming is much closer than was thought earlier, and inevitable, is the new alarm.

1. The report is the first part of the Sixth Assessment Report, and contains mountains of fresh evidence to support what IPCC has been warning of for decades
2. IPCC claims scientists now have much better clarity about what was happening to the Earth’s climate
3. They now 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
4. An example: the confidence with which IPCC is now saying that the rise in global temperatures was a direct result of human activities. Earlier the IPCC would say 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.

• From extreme to common: The real worries lie in the extremities of those predictions. A headline statement 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. So, in the business-as-usual, or worst-case, scenario, the temperature rise by the end of the century would exceed even 4°C.

1. 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.
2. 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.
3. Similar is the story with rainfall, or sea-level rise, or other changes that are predicted for the future. Extremes are the most compelling reason for (governments to initiate) more ambitious climate action.

• Impacts already being felt: Scientists are clarifying that adverse impacts of climate change do 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 now. But they begin to get worse as the warming increases. Every additional half degree of warming will cause increase in the intensity and frequency of hot extremes, heavy precipitation and drought.
• How much time to rectify: 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.
• Compound events: These are 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.

1. 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.
2. 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.

• Indian Ocean: The Indian Ocean which includes the Arabian Sea and Bay of Bengal has warmed faster than the global average, the IPCC said with “very high confidence.” Its oceans fact sheet indicates that sea surface temperature over the Indian ocean is likely to increase by 1 to 2 degree C when there is 1.5 degree C to 2 degree C global warming. For a country with a 7,516 km-long coastline, and an agricultural and rural economy still dependant on annual monsoon rains, that’s bad news.

1. In high mountains in Asia, which includes the Himalayas, snow cover has reduced since the early 21st century, and glaciers have thinned, retreated, and lost mass since the 1970s, the IPCC said, although the Karakoram glaciers haven’t recorded any major retreating trend.
2. Rising global temperatures and more rain can increase the occurrence of glacial lake outburst floods (GLOFs) and landslides over moraine-dammed lakes, IPCC warned.
3. Marine heat waves will continue to increase. And sea levels around Asia in the North Indian Ocean have increased faster than the global average, with coastal area loss and shoreline retreat. The regional-mean sea level will continue to rise. About 50% of the sea level rise is due to the thermal expansion. Also, Indian Ocean region is warming at a higher rate that means the relative sea level can also increase over the regions. Hence, the coastal regions will see the sea level rise through the 21st century.

• Impact on monsoon: The monsoon has weakened in the second half of the 20th century mainly due to aerosols from human activity. Atmospheric aerosols are suspended liquid, solid, or mixed particles with highly variable chemical composition and size distribution. Though in the near term (the next 20 years) South and Southeast Asian monsoon and East Asian summer monsoon rains will be dominated by the effects of aerosols and internal variability, in the long-term, monsoon rain will likely increase. At 1.5 degree C global warming, heavy precipitation and associated flooding are projected to intensify and be more frequent in most regions in Africa and Asia, the report said. The global water cycle will continue to intensify as global temperatures rise, with rainfall and surface water flows projected to become more variable and unpredictable within seasons.
• Summary: Some of the changes are locked in — these include increase in sea level rise, melting of glaciers and thawing of permafrost. In India, the increase in heat waves is masked by aerosol emissions; if these are cut down, further increases in heat waves are likely. 

 

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