IPCC report : “With warming, we are seeing that there are specially varying rainfall patterns of change that are projected over the future. There is intensification of the water cycle, which is going to affect the rainfall pattern. Precipitation is likely to increase in high latitude, but it is the Indian Monsoon that is expected to witness the change.”
That was Swapna Panickal from Pune’s Indian Institute of Tropical Meteorology (IITM) talking about the assessment of the Intergovernmental Panel on Climate Change (IPCC)’s report released on Monday.
Panickal is one of the authors of the report from the Working Group I – ‘Climate Change 2021: the Physical Science Basis’ – of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022. For the first time, it has provided a detailed regional assessment too. (AR6WGI)
The report provides new estimates of the chances of crossing the global warming level of 1.5 degree Celsius (C) in the next decades, and finds that unless there are immediate, rapid, and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5 degree C or even 2 degree C will be beyond reach.
“One of the main methodological improvements since the last IPCC report AR5 is that throughout this report, we have combined many different lines of evidence and we have not looked at observations and projections in isolation but all aspects of the climate system. The changes that we will see under the illustrative five scenarios of possible future emissions are based on combined lines of evidence observations, physical and theoretical understanding, different types of global and regional climate changes to models and the assessment from attributing changes to different drivers of climate systems,” said Associate Director, Environmental Change Institute, University of Oxford, Dr Friederike Otto.
All the land masses are divided into 11 regions and the regional factsheets are issued for different regions plus mountains and urban centres apart from coastal areas; all of which are an outreach product fully traceable to the AR6-WGI.
For the South Asia region, identified as SAS in the report, heatwaves and humid heat stress will be more intense and frequent during the 21st century (medium confidence) and both annual and summer monsoon precipitation will increase during the 21st century, with enhanced interannual variability (medium confidence).
For the uninitiated, the term ‘confidence’ is for the level of agreement between the global scientists for a particular issue; high is when majority or all of them agree, low means, when there is disagreement based on studies.
In case of Asian Monsoons, the report states that the South and Southeast Asian monsoon has weakened in the second half of the 20th century (high confidence) and the dominant cause of the observed decrease of South and Southeast Asian monsoon precipitation since the mid-20th century is anthropogenic aerosol forcing.
The dry-north and wet-south pattern of East Asian summer monsoon precipitation change results from the combined effects of greenhouse gases and aerosols (high confidence); in the near-term, South and Southeast Asian monsoon and East Asian summer monsoon precipitation will be dominated by the effects of internal variability (medium confidence) while in the long-term, South and Southeast Asian monsoon and East Asian summer monsoon precipitation will increase (medium confidence), the report said.
The temperature over South Asia too is a major factor. The observed mean surface temperature increase has clearly emerged out of the range of internal variability compared to 1850-1900. Heat extremes have increased while cold extremes have decreased, and these trends will continue over the coming decades (high confidence).
“Glaciers are declining, and permafrost is thawing. Seasonal snow duration, glacial mass, and permafrost area will decline further by the mid-21st century (high confidence),” the report stated. “Glacier runoff in the Asian high mountains will increase up to mid-21st century (medium confidence), and subsequently runoff may decrease due to the loss of glacier storage.”
Relative sea level around Asia has increased faster than global average, with coastal area loss and shoreline retreat. Regional-mean sea level will continue to rise (high confidence), it warned.
One of the report authors, scientist from Indian Institute of Tropical Meteorology, Pune, Dr Swapna Panickal said, “With warming, we are seeing that there are specially varying patterns of change that are projected over the future. There is intensification of the water cycle, which is going to affect the rain patterns. If you see globally, in high latitudes, the precipitation is likely to increase but it is projected to decrease over large parts of the Sub-tropics. And assessed that change in monsoon precipitation is expected.
For India and South Asia, the assessment of observed change in ‘hot extremes’ and the confidence in human contribution towards that change has increased, and so for heavy precipitation. However, the assessment for agricultural or ecological drought shows, ‘low in agreement’ change.
Explaining what ‘confidence’ here means, Otto said, all lines of evidence and attribution show that the frequency and intensity of heat waves has increased in the South Asia region and there have been attribution studies that say that one important driver of this increase is human induced climate change. But for agriculture and ecological droughts, there are quite a few studies but not from over the whole South Asia region. “They are on different geographical scales and some of them show an increase in the likelihood of intensity of this type of droughts, but others show decrease or no change. These studies don’t agree with each other and so there is not a single signal for the whole region but there are some signals on smaller parts of the region and the detailed assessment on that is in the underlying chapter, Otto said.
For the ‘High Mountain Asia’ the report said, “Rising temperature and precipitation can increase the occurrence of glacial lake outburst floods and landslides over moraine-dammed lakes (high confidence).”
For Coastal cities, it said, the combination of extreme sea level, increased by both sea level rise and storm surge, and extreme rainfall/river flow events will increase the probability of flooding (high confidence).
The most alarming projections, especially in view of India, are about the main factors that contribute to amplifying the warming of urban areas. The three main factors are: Urban geometry — Tall buildings close to each other absorb and store heat and reduce natural ventilation; Human activities — due to heat released from domestic and industrial heating or cooling systems, running engines, and other sources and materials that make up cities — these materials are very good at absorbing and retaining heat and then re-emitting that heat at night.
The IPCC report hopes that providing climate change impact region-wise with targeted information available to the respective governments can help them initiate and to act upon in time to plan and implement mitigative measures against the devastating impacts that humanity will witness if the global temperature rise is not kept in check below 1.5 degrees Celsius.