September 30, 2023

Science – Heat, drought, heavy rain – Extreme weather is on the rise – Knowledge

Potsdam (dpa) – Heat warning in southern Europe, floods in the USA, heavy rains in Japan – this summer people in many regions of the world suffer from bad weather and its consequences. According to studies, such events are becoming more frequent, which does not surprise scientists.

“For decades, climate researchers have been warning about increased heat, drought and resulting fires, as well as torrential rains and floods from global warming caused by greenhouse gas emissions,” says Stefan Ramstorff of the Potsdam Institute for Climate Impact Research (PIK). “The predictions come many years ago, as the measurement data show.”

Rahmstorf explains that extreme weather conditions have been steadily increasing for decades. This trend could continue. “The same extremes that have been increasing for decades will continue to increase until the world achieves carbon neutrality.” In the future, events that did not happen in the recent past may occur.

Many of the phenomena are easy to explain: “Higher temperatures increase drought because soil and vegetation dry out more quickly due to greater evaporation if it doesn’t rain a lot,” Ramstorff explains. But not only dehydration is the result of heat. “Higher temperatures also lead to more intense precipitation because warmer air can absorb more water vapor and then the rain will fall.” According to a study published in the journal Climate and Atmospheric Science, the number of precipitation records has risen sharply. On average, one in four standard daily precipitation events can be attributed to climate change.

Quick action is required

Met summer has already set several records this year: According to the European Union’s climate change service Copernicus, June has never been as warm as this year since records began. According to local authorities, Canada is experiencing the worst wildfire season in its history. The global average temperature for several days in July was higher than the previous record set in 2016, according to Climate Reanalyzer data from the American University of Maine.

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In Ramstorf’s view, it’s important to act — and quickly. He explains that it is important to avoid the unmanageable through rapid climate protection and at the same time adapt as much as possible to the inevitable part of climate change. In the Paris Agreement, countries agreed to limit global warming to 1.5 degrees if that was possible. But Ramstorff fears he will miss that goal. “As long as the use of fossil energy remains subsidized, self-imposed climate targets are ignored, for example in the transport sector, and effective free measures such as a general speed limit are not used, there can be no talk of serious efforts towards 1.5 degrees.”

Does climate change affect the jet stream?

Europe is affected more than other mid-latitude regions by warming. “This is due to a more frequent and persistent occurrence of a double-jet weather pattern, as is the case now,” Rahmstorf explains.

The jet stream is a ribbon-like field of strong winds about ten kilometers high that wraps around the Earth over northern latitudes. A double jet stream splits into two branches. As a result, the layers of the jet stream last longer and, according to a study by PIK, cause more frequent heat waves in Western Europe.

The rippling jet stream can also form large swells around the globe. If these remain over an area and do not move further around the Earth, unfavorable weather conditions can also settle there for a long time. Climate researcher Kai Kornhuber of the Center for Climate Research and the German Society for Foreign Relations said that there is currently a discussion underway to what extent climate change contributes to amplifying this phenomenon.

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Long periods of heat are possible

What is certain is that the Arctic is currently warming faster than the regions along the equator, so the difference in temperatures is getting smaller. However, Kornhuber explained that this divergence is a major driver of the large-scale winds. Therefore, its reduction may be an additional reason for the slower mid-latitude atmospheric circulation and the longer persistence of extreme weather events in the region.

In general, it appears that weather patterns are also becoming more consistent regionally — that is, the heat wave is lasting longer, Kornhuber says. Interactions between heat and drought can become more intense, especially in areas of extreme drought. Kornhuber stressed that “the main undisputed reason for the increase in the occurrence of heat waves is the warming of the atmosphere due to the increase in the concentration of greenhouse gases.”

According to the latest data from the World Weather Organization (WMO), atmospheric concentrations of greenhouse gases carbon dioxide, methane and nitrous oxide have reached new highs in 2021. There is concern that ecosystems on land and oceans could absorb less carbon dioxide. So far, they have stored some carbon dioxide. In some land areas of the world, the transition from the sink of carbon dioxide to the source is already underway, for example in parts of the Amazon rainforest.

Climate researchers: factors other than global warming

Ocean temperatures are also showing extreme values ​​this summer. In general, this is also due to “an increase in greenhouse gases in our atmosphere,” says Ramstorff. Because of the water’s heat storage capacity, just over 90 percent of the extra energy captured went into the ocean. “That’s why there have been regular new heat records out there for decades.”

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According to the “Climate Reanalyzer” data, the average surface temperature of the seas has been at a record high since March: each day is the warmest on record. Measurements began 40 years ago. In the past few days, the temperature has been about 0.8 degrees higher than the average for the same period from 1982 to 2011.

Rahmstorf hypothesizes that many other factors are contributing to the increase in addition to global warming. This also includes El Niño, which causes surface temperatures to rise in the tropical Pacific Ocean. El Niño is a natural phenomenon that occurs every few years. It can exacerbate the consequences of climate change because it has an additional warming effect. Depending on the region of the world, El Niño causes more heat and drought or more floods.

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