Even more frequent and severe: heavy precipitation and heat waves

On August 9, the Intergovernmental Panel on Climate Change presented the first part of its latest comprehensive analysis of the global climate to the public. In it, a core team of 234 experts from 66 countries - including five from Switzerland - reviewed the state of knowledge on the scientific basis.

Greenhouse gases and temperatures continue to rise

Since the last status report in 2013, greenhouse gases in the atmosphere have continued to rise. From 2013 to 2019, average concentrations of CO2 increased by nearly 5 percent, methane by 3.5 percent and nitrous oxide (N2O) by 2.5 percent. "The report shows that atmospheric CO2 concentrations in 2019 were 47% higher than at the beginning of industrialization and higher overall than at any time in the last 2 million years," said Gian Kasper Plattner of the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and lead author of the IPCC report.

According to data, the global surface temperature between 2011 and 2020 was on average about 1.1 degrees Celsius higher than in pre-industrial times (1850 to 1900). The frequency and intensity of heat waves and extreme precipitation have increased since 1950. The main cause of these trends is human-induced climate change, according to the IPCC. "For some of the recently observed heat waves, it is extremely unlikely that they would have occurred in this way without human influence," says Sonia Seneviratne, a professor at ETH Zurich, and coordinating lead author of the chapter on changes in weather and climate extremes.

Warming of less than 1.5 degrees Celsius now hardly achievable

Global temperatures will continue to rise until the middle of this century. How much the rise will be depends on continued emissions. "Only if carbon dioxide emissions fall sharply already in the next few years and reach net zero by mid-century can global warming be limited to below 1.6 degrees Celsius with more than 50 percent probability and most likely below 2 degrees," says Erich Fischer of ETH Zurich and lead author of the IPCC report.

In the most pessimistic emissions scenario considered in the report, on the other hand, the temperature would increase by about 4.5 degrees, and in extreme cases by up to 5.7 degrees, according to the report. Even with a warming of just 1.5 degrees, heavy precipitation or heat waves would become more frequent in most regions and reach intensities of unprecedented magnitude. Each additional half degree increases the frequency and intensity of heat extremes, heavy precipitation, and agricultural and environmental droughts. Increased global warming is also leading to further melting of Arctic sea ice, glaciers and permafrost, decreasing snow cover and rising sea levels.

More weather extremes likely in Switzerland

The IPCC report emphasizes that land masses are generally warming more strongly than the global average and that the occurrence of weather extremes varies from region to region. Switzerland is also affected by this, it says. "Heat waves, heavy precipitation and agricultural and environmental droughts will increase in frequency and intensity in west-central Europe, and therefore also in Switzerland, as global warming increases," Seneviratne says.

Already irreversible changes today

In order to keep climate change to a minimum, according to the IPCC scientists, a reduction in CO2 emissions to net zero and a strong reduction in other greenhouse gases is essential. For example, methane emissions must also be reduced rapidly and substantially. The more rapid the reduction, the more warming and its consequences can be minimized, he said. "Certain changes, however, such as the rise in sea level or the melting of the ice sheets, are already irreversible for hundreds or thousands of years," says Plattner. Glacier retreat will also continue for decades, according to the IPCC report, even if global temperatures stabilize. In terms of risk assessments and planning adaptation measures, he says it's important to keep in mind that natural fluctuations in the climate system can regionally dampen or accelerate the effects of climate change in the short term, by up to a decade or two. "In the longer term, however, these fluctuations cannot compensate for warming," Fischer says.

Source: SCNAT

More IPCC information from:

• Erich Fischer, ETH Zurich, lead author: 2_AR6_Erich_Fischer_E
• Sonia I. Seneviratne, ETH Zurich/EPFZ, Coordinating Lead Author: 3_AR6_Sonia_Seneviratne_E
• Gian-Kasper Plattner, WSL, IPCC Lead Author Chapter 1: 4_AR6_Kasper_Plattner_E