Sixth Assessment Report - IPCC

• 10 Aug 2021

On 9th August 2021, the Inter-governmental Panel on Climate Change IPCC released the first part of its sixth assessment report (AR6) titled ‘Climate Change 2021: The Physical Science Basis’. The two remaining parts would be released next year.

• The report was released by one of the three Working Groups of IPCC - intended to assess scientific, technical and socio-economic information concerning climate change.
• Working group 1 published The Physical Science Basis of Climate Change, which said that, if greenhouse gas emissions are halved by 2030 and net zero by 2050, global warming can be stopped.
• The report's 234 authors built on more than 14,000 scientific papers to create a 3,949 page report, which was then approved by 195 governments. The summary for policymakers was drafted by scientists and agreed to line-by-line by governments.

Headline Statements from the Summary for Policymakers

A.The Current State of the Climate

• It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
• The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.
• Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).
• Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C, with a narrower range compared to AR5.

B.Possible Climate Futures

• Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.
• Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
• Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
• Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.
• Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

C.Climate Information for Risk Assessment and Regional Adaptation

• Natural drivers and internal variability will modulate human-caused changes, especially at regional scales and in the near term, with little effect on centennial global warming. These modulations are important to consider in planning for the full range of possible changes.
• With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers would be more widespread at 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.
• Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment.

D.Limiting Future Climate Change

• From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.
• Scenarios with low or very low greenhouse gas (GHG) emissions (SSP1-1.9 and SSP1-2.6) lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios (SSP3-7.0 or SSP5-8.5). Under these contrasting scenarios, discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years, and over longer time periods for many other climatic impact-drivers (high confidence).

Regional Fact Sheet - Asia

Common Regional Changes

• 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).
• Marine heatwaves will continue to increase (high confidence).
• Fire weather seasons will lengthen and intensify, particularly in North Asia regions (medium confidence).
• Average and heavy precipitation will increase over much of Asia (high to medium confidence).
• Mean surface wind speeds have decreased (high confidence) and will continue to decrease in central and northern parts of Asia (medium 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).
• 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).

Asian Monsoons

• The South and Southeast Asian monsoon has weakened in the second half of the 20th century (high confidence). The dominant cause of the observed decrease of South and Southeast Asian monsoon precipitation since 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).
• In the long-term, South and Southeast Asian monsoon and East Asian summer monsoon precipitation will increase (medium confidence).

Tibetan Plateau (TIB)

• Over most of the Hindu Kush Himalayan region, snow cover has reduced since the early 21st century, and glaciers have retreated and lost mass since the 1970s. The Karakoram glaciers have remained either in a balanced state or slightly gained mass. During the 21st century, snow-covered areas and snow volumes will decrease in most of the Hindu Kush Himalayan, and snowline elevations will rise and glacier volumes will decline (high confidence).
• A general wetting across the whole Tibetan Plateau and the Himalaya is projected, with increases in heavy precipitation in the 21st century.

Southeast Asia (SEA)

• Future warming will be slightly less than the global average (high confidence).
• Observed mean rainfall trends are not spatially coherent or consistent across datasets and seasons (high confidence). Rainfall will increase in northern parts and decrease in the Maritime Continent (medium confidence).
• Compound impacts of climate change, land subsidence, and local human activities will lead to higher flood levels and prolonged inundation in the Mekong Delta (high confidence).
• Although there has been no significant long-term trend in the overall number of tropical cyclones, fewer but more extreme tropical cyclones have affected the region.
• So far, five assessment reports have been produced, the first one being released in 1990. The fifth assessment report had come out in 2014 in the run up to the climate change conference in Paris.

IPCC & Assessment Reports

• Every few years, the Inter-governmental Panel on Climate Change (IPCC) produces assessment reports that are the most comprehensive scientific evaluations of the state of earth’s climate.
• Set up in 1988 by the World Meteorological Organisation (WMO) and the UN Environment Programme (UNEP), the IPCC does not itself engage in scientific research. Instead, it asks scientists from around the world to go through all the relevant scientific literature related to climate change and draw up the logical conclusions.
• So far, five assessment reports have been produced, the first one being released in 1990. The fifth assessment report had come out in 2014 in the run up to the climate change conference in Paris.
• The IPCC reports are created by three working groups of scientists:
  • Working Group-I deals with the scientific basis for climate change.
  • Working Group-II looks at the likely impacts, vulnerabilities and adaptation issues.
  • Working Group-III deals with actions that can be taken to combat climate change.