Commentary: We are waiting anxiously for a huge climate science report

WINNIPEG, Canada: On Monday (Aug 9), the Intergovernmental Panel on Climate Change (IPCC) will release its most comprehensive report on the science of climate change since 2013. It will be the first of four reports released under the IPCC’s latest assessment cycle, with subsequent reports coming in 2022.

Over the past eight years, climate scientists have improved the methods they use to measure different aspects of climate and to model (or project) what might happen in the future. They’ve also been monitoring the changes that have developed right before our eyes.

This updated assessment comes three months before world leaders gather in Glasgow, Scotland, to find ways to avoid the worst effects of climate change and renew their commitments to reduce greenhouse gases. It also comes amid another year of severe heat waves, droughts, wildfires, flooding and storms.

The report will provide policymakers with the best possible information regarding the physical science of climate change, which is essential for long-term planning in many sectors, from infrastructure to energy to social welfare. Here are five things to look for in the new report.

1. HOW SENSITIVE IS THE CLIMATE TO INCREASING CARBON DIOXIDE?

Atmospheric carbon dioxide (CO2) levels are higher now than they have been in 800,000 years, reaching 419 parts per million (ppm) in May 2021. Average global temperature rises with each increase in atmospheric CO2 concentration, but how much it rises depends on many factors.

Climate scientists use models to understand how much warming occurs when CO2 concentrations double from pre-industrial levels – from 260 ppm to 520 ppm – a concept called “climate sensitivity”. The more sensitive the climate, the faster greenhouse gas emissions must be curbed to stay below 2 degrees Celsius.

Older climate models estimated that a doubling of atmospheric CO2 would lead to a temperature increase of 2.1 to 4.7 degrees Celsius.

The latest set of climate models, called CMIP6, broadened the range to 1.8 to 5.6 degrees Celsius, meaning the climate is at least as sensitive to doubling of carbon dioxide as previous models showed, but may, in fact, be even more sensitive.

The range is influenced by uncertainties in a number of climate factors, including water vapour and cloud cover, and how they will increase or decrease the effects of warming.