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. On August 9, 2021 the IPCC released the first part of its sixth assessment report (AR6). The two remaining parts would be released next year.
The IPCC assessment reports have been extremely influential in directing the dialogue and action on climate change. The First Assessment Report led to the setting up of the UN Framework Convention on Climate Change, the umbrella agreement under which international negotiations on climate change take place every year. The Second Assessment Report was the basis for the 1997 Kyoto Protocol that ran till last year, and the Fifth Assessment Report, which came out in 2014, guided the Paris Agreement.
The first part of AR6, which presents scientific evidence for climate change, says that global temperatures had already risen by about 1.1 degree Celsius from pre-industrial times, a reference to the period between 1850 and 1900, and warns that a 1.5 degree Celsius warming was likely to be achieved before 2040.
The stated objective of the 2015 Paris Agreement, the international architecture to fight climate change, is to limit temperature increase to within 2 degree Celsius from pre-industrial times, hopefully within 1.5 degrees Celsius itself. Scientists say a temperature rise beyond 2 degree Celsius would result in catastrophic and irreversible changes that would make it difficult for human beings and other species to survive.
In a stark warning to world leaders, the 42-page summary for policy makers titled: Climate Change 2021: The Physical Science Basis drafted by 234 scientists from 66 countries warned that global warming of 1.5°C relative to 1850-1900 levels would be definitely exceeded under intermediate, high and very high emission scenarios and will be “more likely than not to be exceeded” even when countries agree to switch to net zero emissions by 2050.
A net zero emission target implies that all human-caused greenhouse gas (GHG) emissions are balanced out by removing GHGs from the atmosphere in a process known as carbon removal.
The sixth assessment report says that even if very wide-ranging and ambitious cuts in greenhouse gas emissions are initiated immediately, the temperature rise was expected to cross 1.5 degree Celsius, and reach 1.6 degree Celsius, before being reined back to 1.5 degrees Celsius.
Limiting the temperature rise to 1.5 degree Celsius, or even 2 degree Celsius, would be “beyond reach”, unless “immediate, rapid and large-scale” reductions in greenhouse gas emissions takes place, the report says.
The report says that there was now “unequivocal” evidence to say that global warming was being caused by human activities. It says “multiple lines of evidence” now supports this.
The world may have lost the opportunity to keep global warming under 1.5 degrees Celsius (°C) above pre-industrial levels. The 1.5°C global warming threshold is likely to be breached in the next 10 to 20 years (by 2040) in all emission scenarios, including the one where carbon dioxide (CO2) emissions decline rapidly to net zero around 2050, the intergovernmental panel on climate change (IPCC) said.