IPCC’s findings, put forth in over 3,949 pages of analysis from over 14,000 scientific papers, holds up the mirror on how human influence alone has caused the present crisis and there is no getting away from future warming of at least 1.5 degrees Celsius in the next 10 to 20 years.
IPCC’s report is based on robust science with attribution studies that clearly link human influence to extreme weather events; paleoclimatic data that help understand how climatic changes in the 21st century are different from the past; and advanced models which tell us how once-in-50-year heat extremes will jump by 8.6 times at 1.5 degrees Celsius warming.
This is why most findings and projections in the IPCC report are “high confidence”. Coming ahead of the United Nations (UN) Climate negotiations in November, world leaders can be squarely blamed for catastrophe if they fail to collectively respond to IPCC’s report.
HT lists five key takeaways from the IPCC report which make it “code red for humanity”.
Why one cannot doubt IPCC’s projections anymore
IPCC’s sixth assessment report on Climate Change 2021: The Physical Science Basis is the most updated science on climate crisis. IPCC is highly confident of its findings because observational capabilities have vastly improved since the AR5 cycle in 2014.
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The AR6 has used several recently instigated satellite measurement techniques — for example, high-vertical-resolution profiles of temperature and humidity in the upper troposphere and stratosphere from the early 2000s using global navigation satellite systems, which provide estimates of most recent atmospheric warming. There are improved measurements of ocean heat content, warming of the land surface, ice sheet mass loss, and sea level changes.
Developments in the latest generation climate and Earth system models, which include representation of physical, chemical and biological processes, have led to better simulation of climate crisis indicators.
IPCC has also used reconstruction of past climate trends from paleoclimatic archives. Paleoclimatology is the study of ancient climates, prior to the widespread availability of instrumental records according to National Oceanic and Atmospheric Administration. Various evidence from the environment is studied for this such as skeletons of tropical coral reefs, glaciers and ice caps, laminated sediments from lakes etc.
One of the most interesting features of IPCC report is however attribution. The attribution of extreme weather events to human influence (including greenhouse gas and aerosol emissions and land-use changes) has substantially advanced. This basically means that the scientific community can now attribute extreme precipitation, droughts, tropical cyclones etc to human influence.
Some recent hot extreme events would have been extremely unlikely to occur without human influence on the climate system, the IPCC said. A few events, for example, extreme rainfall events in the United Kingdom (UK), heat waves in Australia, or Hurricane Harvey that hit Texas in 2017, have been heavily studied.
Many highly impactful extreme weather events have not been attributed, particularly in the developing world where studies are generally lacking. “Scientists at IPCC are no longer coy about telling us clearly that climate change is caused by human activities. In fact, they go as far as to ‘attribute’ climate change to specific extreme weather impacts. This is important because till now we have only been able to understand climate change impacts in terms of the increased frequency of such events in the world. But now, we know with greater certainty the role of climate change in, say, the extreme heat event in Canada or wildfire in Greece or the floods in Germany. No more ifs or buts,” said Sunita Narain, director general, Centre for Science and Environment in a statement.
Fossil fuel emissions have already irreversibly impacted the planet
Each of the past four decades has been warmer than any decade that preceded it since 1850.
Global surface temperature in the first two decades of the 21st century (2001-2020) was 0.99 degrees Celsius higher than 1850-1900 and global surface temperature was 1.09 degrees Celsius higher in 2011–2020 than 1850–1900 or the pre-industrial period. “It is likely that well-mixed greenhouse gas (GHG) emissions contributed to a warming of 1 degrees Celsius to 2 degrees Celsius, other human drivers, principally aerosols, contributed a cooling of 0.0 degrees Celsius to 0.8 degrees Celsius,” the IPCC report said. It added that it was extremely likely that human influence led to global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area between 1979–1988 and 2010–2019; changes in rainfall patterns, seal level rise and warming.
The report has also flagged that the climate crisis has caused certain impacts globally which are irreversible and will continue to affect us in future. Greenhouse gas emissions since 1750 have already committed the global ocean to future warming including 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) — this will continue to increase in the 21st century. The rate at which these intensify will depend on emission trends.
Mountain and polar glaciers will also continue melting for decades or centuries, the IPCC said with “very high confidence”. Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and for the Antarctic Ice Sheet. It is also certain that global mean sea level will continue to rise over the 21st century.
IPCC has also attributed all of these changes to human influence without mincing words. The basic physics underlying the warming effect of greenhouse gases on the climate has been understood for more than a century, and our current understanding has been used to develop the latest generation climate models. Like weather forecasting models, climate models represent the state of the atmosphere on a grid and simulate its evolution over time based on physical principles. They include a representation of the ocean, sea ice and the main processes important in driving climate and climate change. Results consistently show that such climate models can only reproduce the observed warming when including the effects of human activities, in particular the increasing concentrations of greenhouse gases, IPCC explained.
IPCC warns of extremely rare but catastrophic events for the first time
For the first time, IPCC has also warned of some high impact events which are unlikely but if they do occur, they will be catastrophic. Low likelihood, high-impact outcomes may arise from a series of very large volcanic eruptions that could substantially alter the 21st century climate trajectory compared to SSP-based Earth system model projections that the IPCC has considered. IPCC considers five socioeconomic pathways (SSPs) which are essentially possible paths of growth human societies could follow over the next century.
These are events whose probability of occurrence is very low but whose potential impacts on society and ecosystems are very high. To better inform risk assessment and decision making, such low likelihood outcomes are described as they may be associated with very high levels of risk, the report said.
Even at levels of warming within the very likely range, global and regional low-likelihood outcomes might occur, such as large changes in rainfall patterns, additional sea level rise associated with collapsing ice sheets, or abrupt ocean circulation changes. For example, the Atlantic Meridional Overturning circulation (AMOC), which also influences the southwest monsoon, is unlikely to experience an abrupt collapse before 2100. “If it were to occur, it would very likely cause abrupt shifts in regional weather patterns and water cycle…the probability of these low-likelihood outcomes increases with higher global warming levels.”
With increasing global warming, some very rare extremes and some compound events (multivariate or concurrent extremes) with low likelihood in past and current climate will become more frequent, and there is a higher chance that events unprecedented are recorded.
India is facing a unique situation due to air pollution particles
It is very likely that anthropogenic aerosols weakened the regional monsoon circulations over South Asia, East Asia and West Africa during the second half of the 20th century, thereby offsetting the expected strengthening of monsoon rains in response to global warming. The present trends in monsoon rains are dominated by the effect of aerosols.
Anthropogenic aerosols are nothing but air pollution particles which scatter solar radiation. They decrease evaporation and have a cooling effect on surface temperatures. The aerosols are masking the effect of global warming on rise in monsoon rain and surface temperatures.
When asked if air pollution over the South Asian region including India is reducing the severe effects of climate crisis, R Krishnan, Director, Centre for Climate Change Research at Indian Institute of Tropical Meteorology and IPCC author said: “Air pollution has huge implications for health, monsoon and air quality. So, I will not say they are good for us.” It is, however, certain that when the impact of aerosols wane, the surface temperature will spike further and monsoon rains will increase in quantity. Hot extremes will increase and erratic rains with a rise in extreme rainfall events and flooding will continue in the meantime, IPCC has said.
Is India ready for more extremes?
Heatwaves and humid heat stress will be more intense and frequent during the 21st century all over South Asia. The IPCC has simulated what are these heat extremes.
For example, one in ten-year heat extreme events already occur 2.8 times globally in the present. They will increase to 4.1 times in 1.5 degrees Celsius global warming and 5.6 times in 2 degrees Celsius global warming. Once in 50-year heat events are occurring 4.8 times in 50 years and will occur 8.6 times in 1.5 degrees Celsius warming and 13.9 times at 2 degrees Celsius warming. The challenge of heat and humidity extremes are already being felt but will spike very rapidly in the next 10 to 20 years because it is very likely that the world will warm by 1.5 degrees Celsius above pre-industrial levels in the next 20 years.
“The global projections will also apply for India. We are already seeing a rise in extremes but they will go up further in coming years which is certain,” Krishnan explained during a media briefing.
Globally, also, for 1.5°C of global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons as well as changes in precipitation patterns affecting flooding and drought occurrences. At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the World Meteorological Organisation (WMO) said responding to the IPCC report.
“The extreme heat we have witnessed in 2021 bears all the hallmarks of human-induced climate change. British Columbia in Canada recorded an incredible temperature of 49.6°C – breaking all previous records – as part of an intense and extensive heatwave in North America.
Fires in North America stoked by heat and drought have sent plumes of smoke across the Atlantic. In recent days, we have seen devastating fires in Turkey and Greece amid an intense and long-lasting heatwave in the Mediterranean. Siberia – a region traditionally associated with permafrost – has once again seen huge wildfires after exceptional heatwaves, fires and low Arctic sea ice in 2020,” said WMO Secretary-General Petteri Taalas.
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