The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) on the physical basis of climate change has been released today after more than three years of work by over 230 climate researchers. This is the long-awaited update to the last large assessment report (AR5), which was published eight years ago in 2013. I was a coordinating lead author of the chapter on weather and climate extremes. Additional researchers from ETH Zurich contributed to other chapters as well: Erich Fischer was an author on the chapter on global climate projections, and Martin Wild worked on the chapter on the Earth's energy budget, climate feedbacks and climate sensitivity. To sum up, the evidence in the report clearly shows that climate change is no longer a vague threat in the future: it is happening here and now, and our consumption of fossil fuels is chiefly responsible for this phenomenon.
Unprecedented events
My research areas are weather and climate extremes, and I’ve never received as many requests for my expertise as over the past several weeks. The recent extreme climate events that occurred across the northern hemisphere – from heatwaves and fires in Canada, Greece and Turkey to heavy precipitation and floods in Switzerland and Germany – have endangered the population and left people feeling shaken.
There have always been extreme weather events, of course, but evidence of observed changes in extremes has mounted since AR5. As global warming increases, these changes will worsen, with more regions being affected, and with weather extremes increasing in intensity and frequency in the affected regions. In other words, extreme unprecedented weather events will continue to occur. Terms like “a once in a century storm” will become obsolete.
What particularly worries me is that we will also see increases in compound events resulting from the combination of different changes in the climate system. With polar ice melting, for example, sea levels will rise. At the same time, episodes of heavy precipitation are becoming more frequent. Taken together, both phenomena will cause more flooding in coastal areas. Hot and dry conditions are also occurring simultaneously more often, which significantly increases the risk of fires.
Human-induced climate change
Our conclusions in the latest IPCC report also show that we can more clearly attribute these extreme events to human-induced climate change than was the case when AR5 was published. Some heat waves observed over the past few years would have been extremely unlikely
to occur without human influence on the climate system, for instance.
