Climate change is a serious threat. It is a crisis that alarmingly still receives more lip service than actual action. The current state of climate change—and its consequent effects—is perilous.
The recently released UN IPCC (United Nations Intergovernmental Panel on Climate Change) Working Group 1 report “is a code red for humanity,” says UN Secretary General António Guterres. He further adds that “greenhouse gas emissions from fossil fuel burning and deforestation are choking our planet and putting billions of people at immediate risk. Global heating is affecting every region on Earth, with many of the changes becoming irreversible.”
New climate model simulations; analyses of data from paleoclimate archives; and peer-reviewed studies point to a clear trend of increased human influence in the warming of the atmosphere, ocean and land. Since 1970, global surface temperature has increased faster than in any other 50-year period over the last 2,000 years.
Greenhouse gas (GHGs) emissions have increased since 1750 – a leading contributor to global warming. Meanwhile, there has been a cooling influence—although not an environment friendly ally—due to usage of aerosols. Each of the past four decades were incrementally warmer than any earlier period since 1850.
Exhibit 1: History of global temperature change and causes of recent warming
The report highlights that human activity is the primary contributor to receding glaciers globally since the 1990s, and the decrease in Arctic Sea ice, and its thickness levels, between 1979-1988 and 2010-2019. The Arctic Sea’s ice expanse, in 2020, was at its least in the past 1,000 years. Such massive reductions in glacier and ice sheets sound an ominous warning – that global mean sea levels have also shot up drastically. It increased by 0.20 m between 1901 and 2018.
Increased human influence led to rise in CO2 emissions resulting in increased acidification and heating of the ocean surface. In 2019, CO2 concentration levels were higher than at any time in at least 2 million years. Likewise, methane and nitrogen oxide levels were at their highest in 80,000 years. Compounding the ill effects are declining oxygen levels in many oceanic regions since the mid-20th century. This has led to migration trends being observed in marine organisms over the past two decades.
Exhibit 2: Assessed contributions to observed warming in 2010–2019 relative to 1850–1900
Due to the surge in CO2 levels, weather and climate patterns too have been impacted, and especially so due to human activity. “Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.
Heatwaves have become more frequent and severe across most land masses since the 1950s, while the frequency and intensity of cold waves have reduced. Most land masses have also witnessed frequent and intense precipitation since the 1950s. Meanwhile, some regions experienced droughts due to increased land evapotranspiration.
Exhibit 3: Synthesis of assessed observed and attributable regional changes
Temperatures will only rise further
“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” said Valérie Masson-Delmotte, IPCC Working Group I Co-Chair. Five emission scenarios have been used by the report to project possible future climate patterns. Across all listed scenarios, global surface temperatures will continue to rise until at least the mid-century. Global temperatures will exceed 2°C by end-21st century unless there are active reductions in CO2 and GHGs concentration levels.
Exhibit 4: Future anthropogenic emissions of key drivers of climate change and warming contributions by groups of drivers for the five illustrative scenarios
Even considering a very low GHG emissions scenario, global surface temperatures will be higher by 1.0-1.8°C between 2081 and 2100 as compared with the 1850-1900 period. Meanwhile, the global warming level of 2°C will be exceeded within the 21st century under the high and very high GHG emissions scenario, when compared to the decades between 1850–1900.
Exhibit 5: Changes in global surface temperature
Land surfaces will continue to become warmer by 1.4-1.7 times in comparison to ocean surfaces. The Arctic, meanwhile, will become two times warmer than the global surface temperature. With every additional 0.5°C of global warming, the frequency and intensity of heatwaves, precipitation, agricultural and ecological droughts will increase in certain regions such as the mid-latitude and semi-arid regions. These areas will register even warmer temperature – about 1.5 to 2 times the rate of global warming.
Exhibit 6: Projected changes in the intensity and frequency of hot temperature extremes over land, extreme precipitation over land, and agricultural and ecological droughts in drying regions
The global water cycle will continue to intensify with increases in global temperatures. Regions with warmer climate may face very wet and very dry weather depending on regional atmospheric changes, including monsoon and storm tracks. Countries in South and Southeast Asia, East Asia and West Africa are expected to receive increased monsoon precipitation in the mid- to long-term scenario.
Amid an increasing CO2 emissions scenario, the ocean and land carbon sinks will become less effective in slowing the accumulation of CO2 in the atmosphere. The rate at which land masses and oceans absorb CO2 emissions will decrease in the second half of the 21st century.
Exhibit 7: Cumulative anthropogenic CO2 emissions taken up by land and ocean sinks by 2100 under the five illustrative scenarios
Changes in the ocean, ice sheets and global sea levels, caused due to past and future GHG emissions, will remain irreversible for centuries to millennia. Mountain and polar glaciers will continue to melt. By 2100, the global mean sea level will have risen by 0.28 to 0.55 m in comparison to 1995-2014 levels.
Exhibit 8: Selected indicators of global climate change under the five illustrative scenarios
Limit the climate crisis
Limiting cumulative CO2 emissions is one possible way of containing human influenced global warming. But this will require global CO2 emissions to be reduced to net zero, including strong reductions in other GHG emissions. In addition, stemming the use of aerosols will arrest aerosol emissions, leading to better air quality and reduced warming effects.
There is a clear link between CO2 emissions and global warming. Each 1,000 GtCO2 of cumulative CO2 emissions is likely to cause an increase of 0.27-0.63°C in global surface temperatures.
Exhibit 9: Near-linear relationship between cumulative CO2 emissions and the increase in global surface temperature
Lowering global CO2 emissions to net zero is critical towards stabilising CO2-induced global surface temperature increases. Anthropogenic CO2 removal (CDR) is effective in removing CO2 from the atmosphere, which is then stored in reservoirs. CDR removal is critical in achieving global net zero emissions, resulting in lower atmospheric CO2 concentration and reversed ocean surface acidification. If CDR is achieved and sustained, CO2-induced surface temperature increases can be gradually reversed.
Mr Zhai reiterated that, “Stabilising the climate will require strong, rapid and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions.” A failure to heed the climate change clarion call can lead to catastrophic consequences.