The scale of climate change is ‘unprecedented’, says UN report
Human-induced climate change is already affecting many weather and climate extremes in every region of the world on a scale that is unprecedented over the past 2,000 years, according to a UN scientific study.
The latest report by scientists working for the Intergovernmental Panel on Climate Change (IPCC) reveals that evidence of human influence on extreme weather such as heatwaves, heavy rain, droughts, and tropical cyclones has strengthened.
It adds that any changes due to past and future greenhouse gas emissions are “irreversible” for centuries to millennia, especially changes in the ocean, ice sheets and the global sea level.
Each of the last four decades has been successively warmer than any decade that preceded it since 1850. On average, the global surface temperature from 2001 to 2020 was 0.99°C higher than from 1850 to 1900 and was 1.09°C higher from 2011 to 2020 than from 1850 to 1900, with larger average increases over land (1.59°C) than over the ocean (0.88°C).
It adds that, since 1750, increases in greenhouse gas concentrations of carbon dioxide, methane, and nitrous oxide are “unequivocally caused by human activities”.
The report highlights that global surface temperature will continue to increase until at least the mid-century and that global warming of 1.5°C and 2°C will be exceeded during the 21st century unless “deep reductions” in carbon dioxide and other greenhouse gas emissions take place over the next few decades.
It says that increased global warming will lead directly to changes in the climate system, which include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation (rain, snow and sleet), droughts in some regions, and the number of intense tropical cyclones, as well as reducing Arctic sea ice, snow cover and permafrost.
We are also more like to experience changes in the global water cycle, which will become increasingly variable, with more severe wet and dry events.
It points out that human influence is “very likely” the main driver of the global retreat of glaciers since the 1990s and the decrease in the Arctic sea ice area between 1979 and 1988 and 2010 and 2019.
It says that human influence is also very likely to have contributed to reduced spring snow cover in the Northern Hemisphere since 1950 and the surface melting of the Greenland ice sheet over the past 20 years.
Reducing climate change
Looking to the future, the report suggests that limiting human-induced global warming to a specific level requires reducing CO2 emissions so that they reach at least net zero, together with strong reductions in other greenhouse gas emissions.
It adds that strong, rapid, and sustained reductions in methane emissions would also restrict the warming effect that would come about from declining aerosol pollution and would lead to improved air quality.
Commenting on the scientists’ findings, United Nations Secretary-General António Guterres said: “This week’s IPCC climate report is a code red for humanity. Only if we combine forces immediately, can we avert a climate catastrophe. There is no time for delay and no room for excuses. We need to act now.”
The report comes ahead of the 2021 UN Climate Change Conference of the Parties – known as COP26 – which takes place in Glasgow from 31 October to 12 November 2021.