For the past three years, CONSTRAIN researchers have worked with hundreds of experts from across the world to deliver the Intergovernmental Panel on Climate Change (IPCC) report, which examines the physical science basis of climate change.
Many of the changes they have observed in the climate are unprecedented in thousands, if not hundreds of thousands of years. Some of the changes already set in motion, such as continued sea level rise, are irreversible over hundreds to thousands of years.
But according to the report, which numbered seven CONSTRAIN experts among its authors, strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change, with global temperatures stabilising within 20 to 30 years.
Like many others, CONSTRAIN Principal Investigator and Coordinating Lead Author of the chapter on the Earth’s energy budget, climate feedbacks, and climate sensitivity, Professor Piers Forster, spent the past fortnight in a virtual approval session to agree the final document.
Professor Forster said: “The bad news is that a low level of future warming can now be ruled out.
“But the good news is that if the world can substantially reduce emissions in the 2020s and get to net-zero CO2 emissions by 2050, temperature rise can still be limited to 1.5°C.”
The 1.5°C target was established by the Paris Agreement in 2015, committed to by nearly 200 nations.
Though some progress has been made, the authors of the latest report are clear: unless there are immediate, rapid and large-scale reductions in emissions, the 1.5°C target will be out of reach.
Of the negotiation process, Professor Forster said: “It’s been quite strange negotiating with 190 counties or so from your kitchen, interrupted by parcel deliveries and children.”
CONSTRAIN’s Amanda Maycock, Bjørn Samset, Joeri Rogelj, Johannes Quaas, Thorsten Mauritsen, Jochem Marotzke and Jean-Louis Dufresne were also Lead or Coordinating Lead Authors on chapters covering topics ranging from carbon cycles and feedbacks to near-term changes in the climate.
Cutting edge science
The IPCC is the leading world body for assessing the science related to climate change, its impacts and potential future risks, and possible response options.
This is the first major assessment of the latest science since 2013. It draws on multiple lines of evidence, including computer models, physical observations, and theoretical understandings.
Under all scenarios examined in the report, global surface temperature will continue to increase until at least 2050. Unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades, global warming of 2°C will be exceeded during the 21st century.
With every additional increment of global warming, weather extremes like heatwaves, heavy rainfall, and drought, many of which are already being experienced across parts of the world, will become more intense and frequent. This will have widespread impacts on all aspects of human society, from agriculture to transport.
Informing global policy
This report is released ahead of the much-anticipated COP26 negotiations in Glasgow in November, and the findings have particular significance for decision-makers.
“The focus must now be on maximizing near term action at COP26” said Professor Forster.
“We need to reduce emissions as fast as possible and achieve global net-zero as soon as possible to limit the risks of the feedbacks that we don’t yet have a clear enough picture on.”
COP26 will bring together Heads of State, climate experts and campaigners to agree coordinated action to tackle climate change. Today’s report will put further pressure on securing ambitious and tangible outcomes from the negotiations.
“This report is a reality check,” said IPCC Working Group I Co-Chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”
The report released today is the first in a series of three reports that make up the IPCC Sixth Assessment Report (AR6). The Working Group II and Working Group III reports on climate impacts, adaptation and vulnerability, and mitigation of climate change, are due for release in February and March 2022 respectively. A final Synthesis Report is scheduled for September 2022.
The IPCC Sixth Assessment Report, Climate Change 2021: The Physical Science Basis, is now available online.
CONSTRAIN will be providing further information on key climate science concepts discussed in the IPCC report in the run-up to COP26.