Implication for India: Glacial retreat, cyclones and intense heat

Many of these are irreversible and cannot be remediated even if greenhouse gas emissions decline dramatically, the Intergovernmental Panel on Climate Change (IPCC) has indicated in a report released on Monday.
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.(AFP) PREMIUM
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.(AFP)
Updated on Aug 10, 2021 02:40 AM IST
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ByJayashree Nandi, Hindustan Times, New Delhi

Here’s a quick list of what a warming world means for India: glacial retreat in the Hindu Kush Himalayas; compounding effects of sea-level rise and intense tropical cyclones leading to flooding; an erratic monsoon and intense heat stress.

Many of these are irreversible and cannot be remediated even if greenhouse gas emissions decline dramatically, the Intergovernmental Panel on Climate Change (IPCC) has indicated in a report released on Monday.

And not only will India be hotter, it will be more humid.

The report titled Climate Change 2021: The Physical Science Basis released on Monday said heat waves and humid heat stress will be more intense and frequent during the 21st century over South Asia.

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.

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.

Rising global temperatures and more rain can increase the occurrence of glacial lake outburst floods (GLOFs) and landslides over moraine-dammed lakes, IPCC warned.

India recently suffered a spate of flooding and landslide disasters in the high mountains of Uttarakhand and Himachal Pradesh. A snow-ice avalanche on February 7 in Uttarakhand triggered flash floods in the Rishiganga and Dhauliganga valleys, killing at least 200 people.

Heat extremes have increased while cold extremes have decreased, and these trends will continue over the coming decades over Asia, according to the report. Annual mean temperatures in Asia will increase by 1-2 degree C relative to 1850-1900 period in case of 1.5 to 2 degree C global warming. There are likely to be 90 to 120 days in a year with maximum temperatures above 35 degree C in case of 1.5 to 2 degree warming and over 180 days in case of 4 degree C warming. The impact oof that on Indian agriculture could be catastrophic.

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, IPCC has said.

“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, and it will contribute to more frequent and severe coastal flooding in low level areas and coastal erosion. Along with this, extreme sea level events that were previously seen once in a hundred years, could also happen every year by the end of the century,” said Swapna Panickal, IPCC author and climate scientist from Indian Institute of Tropical Meteorology.

The ministry of environment, forest and climate change said on Monday that it welcomes the IPCC report, which “vindicates India’s position” on differentiated action needed by developed and developing countries. “Developed countries have usurped far more than their fair share of the global carbon budget. Reaching net zero alone is not enough, as it is the cumulative emissions up to net zero that determine the temperature that is reached. This has been amply borne out in the IPCC report. It vindicates India’s position that historical cumulative emissions are the source of the climate crisis that the world faces today... India’s cumulative and per capita current emissions are significantly low and far less than its fair share of global carbon budget,” a ministry statement said.

Union environment minister Bhupendra Yadav also said in a tweet that the report was a clarion call for the developed countries to undertake immediate emission cuts and decarbonise their economies.

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.

At the global scale, extreme daily rainfall events are projected to intensify by about 7% for each 1 degree C of global warming. Extreme rainfall events are defined as the daily precipitation amount over land that was exceeded on average once in a decade during the 1850–1900 reference period.

The proportion of intense tropical cyclones (categories 4-5) and peak wind speeds of the most intense tropical cyclones are projected to increase at the global scale with increasing global warming.

Rainfall variability related to the El Niño–Southern Oscillation (ENSO) is projected to be amplified by the second half of the 21st century, it added. The Indian monsoon is affected by ENSO.

Many regions are projected to experience an increase in the probability of compound events (i.e different types of extreme events happening at the same time or one after the other). This can be particularly alarming for India, experts pointed.

“2 degree C global warming has serious implications due to possible increases in extreme weather events like heat waves, heavy precipitation, intensification of tropical cyclones, etc. Also, the variability of climate will increase suggesting dry becomes drier and wet becomes wetter. Another worrying fact is that we should expect compounding extreme weather events. For example, drought followed by heat waves. A flood followed by another flood. We have not documented this very well,” said M Rajeevan, former secretary, ministry of earth sciences.

Irreversible climate impacts

The IPCC report has flagged that the climate crisis has caused certain impacts globally which are irreversible. Mountain and polar glaciers will continue melting for decades or centuries, the IPCC said with ‘very high confidence’ implying that Himalayas in India and neighbouring countries could be facing irreversible changes.

It is also certain that global mean sea level will continue to rise over the 21st century. In the longer term, sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and will remain elevated for thousands of years even if warming is limited to 1.5 degree C, the report said.

“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. Very strong increase in heat waves, heavy rainfall events, further melting of glaciers can be expected. Sea level rise will cause flooding when tropical cyclones hit. These impacts are here and will not go away,” said Friederike Otto, associate director, Environment Change Institute, University of Oxford during a media briefing on Sunday.

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Tuesday, December 07, 2021