Climate impact in India ‘irreversible’, says IPCC report
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.
Most of these impacts are irreversible and hence cannot be remediated even if greenhouse gas emissions decline dramatically, the Intergovernmental Panel on Climate Change (IPCC) has indicated in a report released Monday.
And not only will India be hotter, it will be more humid -- a worrying prospect to many people north of the Vindhyas who are discovering just how uncomfortable high so-called wet-bulb temperatures can be.
The report titled ‘Climate Change 2021: The Physical Science Basis’ released on Monday said heatwaves 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 factsheet indicates that sea surface temperature over the Indian ocean is likely to
increase by 1 to 2 degree Celsius when there is 1.5°C to 2°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 with “high confidence” although the Karakoram glaciers haven’t recorded any major retreating trend.
Snow-covered areas and snow volumes will continue to decrease during the 21st century, snowline elevations will rise and glacier mass is likely to decline further as emissions rise, it added. Rising global temperatures and more rain can increase the occurrence of glacial lake outburst floods (GLOFs) and landslides over morainedammed lakes, IPCC warned.
India has recently suffered a spate of flooding and landslide disasters in the high mountains of Uttarakhand and Himachal Pradesh. A GLOF on February 7 in Uttarakhand triggered flash floods in the Rishiganga and Dhauliganga valleys, sweeping away the Rishiganga hydel project and National Thermal Power Corporation’s Tapovan Vishnugad project. The disaster is feared to have killed over 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 . This the first time IPCC has released regional fact sheets. The Asia projection maps indicate annual mean temperatures will increase by 1-2°C relative to 1850-1900 period in case of 1.5° to 2°C global warming. There are likely to be 90 to 120 days in a year with maximum temperatures above 35°C in case of 1.5° to 2°C warming and over 180 days in case of 4°C warming. The impact of that on Indian agriculture could be catastrophic.
Marine heatwaves will continue to increase. Fire weather seasons will lengthen and intensify, particularly in North Asia regions. Mean surface wind speeds have decreased and will continue to decrease in central and northern parts of Asia.
Glacier run-off in the Asian high mountains will increase up to mid-21st century and subsequently run-off may decrease due to the loss of glacier storage, the report said. 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 with “high confidence”.
“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.
Impact on monsoon
As far as the monsoon is concerned, it 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. They are pollution particles which scatter solar radiation, although a few aerosol types can also absorb solar radiation thus having a cooling effect.
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°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, adding that they have “high confidence” in the projection.
There is strengthened evidence since IPCC’s fifth assessment report released in 2014 that 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°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.
“A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought, but the location and frequency of these events depend on projected changes in regional atmospheric circulation, including monsoons and mid-latitude storm tracks,” the report said.
Rainfall variability related to the El Niño–Southern Oscillation is projected to be amplified by the second half of the 21st century, it added.
Many regions are projected to experience an increase in the probability of compound events (ie different types of extreme events happening at the same time or one after the other). This can be particularly alarming for India, experts pointed.
Irreversible climate impact
The IPCC report has flagged that the climate crisis has caused certain impacts globally which are irreversible. Greenhouse gas emissions since 1750 have committed the global ocean to future warming, it said, adding that based on multiple lines of evidence, upper ocean stratification (vertical changes in sea water density), ocean acidification (decrease in ph value of oceans) and ocean deoxygenation (low oxygen zones in the oceans) will continue to increase in the 21st century. The rate at which these intensify will depend on emission trends.
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.
Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and for the Antarctic Ice Sheet.