United Nations's Intergovernmental Panel on Climate Change (IPCC) in its sixth assessment report, Climate Change 2021: The Physical Science Basis, has assessed climate change, its implications and potential future risks, alongside adaptation and mitigation options.
The report has been prepared by the scientists of the Working Group-I and the remaining two parts of the said report would be released in 2022.
Key Highlights:
1- Average surface temperature is expected to touch 2 degree Celsius by the mid-21st century without a sharp reduction of emissions. The global surface temperature was 1.09°C higher between 2011-2020 than between 1850-1900.
2- CO2 concentrations are highest in at least two million years and much of it is human-induced. Humans have emitted around 2,400 billion tonnes of CO2 since the late 1800s.
3- Sea level rise has tripled since 1971. The Arctic Sea ice is the lowest in 1000 years. During the 21st century, the littoral areas will face coastal erosion, frequent and severe flooding in low-lying areas due to continued sea-level rise. About half the sea level rise is due to thermal expansion.
4- Every 0.5-degree Celsius rise in global warming will increase hot extremes, high precipitation and drought. It will further debilitate Earth’s carbon sinks present in plants, soils, and the ocean.
5- Increased heat extremes and decreased cold extremes have been observed and will continue over the coming decades.
6- The report further predicts a change in the freezing level of mountains and retreat in snowlines over the coming decades, causing a change in the water cycle, precipitation patterns, inundations across the Himalayas.
Findings for India
1- As the IPCC report predicts that global warming will lead to a rise in temperature in every part of the world, the extent of temperature rise may vary across the world, causing heatwaves in many parts. These heatwaves are being called extreme heatwaves for India as they will be hotter as compared to the heatwaves in the past.
2- The report also highlights the monsoon patterns across the world. It predicts that pluvial floods are set to increase across South Asia. India will not only have to predict excessive rainfall due to erratic monsoons but will also have to outline areas experiencing extreme drought.
3- Furthermore, the report underlined that snowcaps in the Himalayas will show rapid melting in the coming decades.
4- The Indian Ocean which includes the Arabian Sea and Bay of Bengal has warmed faster than the global average. The sea surface temperature over the Indian ocean is likely to increase by 1-2 degrees Celsius over the next 20 years.
The Government of India has welcomed the report. It stated that the developed nations have contributed the most to rising global temperatures and therefore institute faster and swifter curbs on their carbon emissions.
Summary of the report
A. The current state of climate
Human-induced climate change is affecting the world. The scale of recent climate changes and the present state of many aspects of the climate system are unprecedented for thousands of years.
Improved information on climate processes, paleoclimate evidence and the response of the climate system to increasing radiative constraining give the best gauge of equilibrium climate sensitivity of 3 degrees Celsius, with a smaller range compared to the previous assessment report by IPCC.
B. Possible climate futures
The report indicates that the global surface temperature will continue rising until at least the mid-century under all emissions scenarios considered. It pressed red alert on global warming of 1.5-2 degree Celsius which is expected to exceed during the 21st century subject to deep reductions in CO2 levels and GHGs emissions in the coming decades.
Much of the changes in the climate system become larger in direct relation to increasing global warming such as rising frequency and intensity of hot extremes, marine heatwaves, heavy precipitation, agricultural and ecological droughts in some regions, the proportion of intense tropical cyclones and reductions in Arctic sea ice, snow cover and permafrost.
The continued global warming is projected to intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.
Increasing CO2 emissions will eventually reduce the effectiveness of the ocean and land carbon sinks at slowing the accumulation of CO2 in the atmosphere. The changes due to the past and future greenhouse gas emissions are irreversible for centuries to millennia, especially 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 at the regional level with little effect on centennial global warming. These are important to consider in planning for the full range of possible changes.
With the increased global warming, each region will experience concurrent and multiple changes in climatic impact drivers. These climatic impact drivers would be more widespread at 2 degree Celsius as to 1.5 degree Celsius global warming and even more widespread and/or pronounced for higher warming levels.
D. Limiting future climate change
Linking 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 GHG 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 GHG emissions lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios.
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.
About IPCC Assessment Reports
IPCC publishes assessment reports every few years, with the first one being published in 1990. The fifth climate report was published in 2014 ahead of the climate change conference in Paris.
The IPCC Assessment Reports by three working groups of scientists are as follows:
1- Working Group-I: The group deals with the scientific basis for climate change.
2- Working Group-II: This group deals with the likely impacts, vulnerabilities and adaptation issues.
3- Working Group-III: The group of scientists in this group deals with actions that can be taken to fight climate change.