A new study, published in the journal Scientific Reports, directly links climate change caused by human activity to the phenomena behind recent increases in extreme weather, such as heatwaves, flooding, and droughts. While it has long been suspected that climate change could cause extreme weather, only recently have scientists begun to link specific events to the results of climate change.

The new study focuses on extreme weather caused by changes to “planetary waves” – patterns of wind, including the jet stream, that normally moves eastward in patterns throughout the northern hemisphere. The study examines how changes in these waves have led to long-term drought in California, heatwaves in Russia, and severe flooding in Pakistan in 2010.

In response to temperature changes, the waves normal eastward movement can be interrupted, stopping entirely. This can leave regions with the same weather patterns for long periods. What would normally be a few hot days can turn into a severe heat wave, and heavy rains can become persistent, leading to floods. Weather patterns like this have occurred more frequently in recent decades, but linking specific weather events to climate change has been difficult.

The new study uses climate modeling and observations to show that the conditions necessary to halt the movement of planetary waves are becoming increasingly common as a result of climate change.

The study’s lead researcher, Professor Michael Mann from Pennsylvania State University, said “Human activity has been suspected of contributing to this pattern before, but now we uncover a clear fingerprint of human activity.”

Another researcher involved in the study, Kai Kornhuber, from Germany’s Potsdam Institute for Climate Impact Research, explained:

“We looked into dozens of different climate models, as well as into observational data, and it turns out that the temperature distribution favoring planetary wave stalling increased in almost 70% of the simulations.”

Wind patterns such as the waves rely on temperature differences between the poles and equatorial regions. Climate change has been heating the Arctic much faster than the tropics, shrinking this temperature gap. Land has also warmed faster than ocean areas.

Professor Stefan Rahmstorf, also with the Potsdam Institute, explained why the drastic changes in the Arctic matter for the entire world:

“It is not just a problem of nature conservation or polar bears, it is about a threat to human society that comes from these rapid changes. This is because it hits us with increasing extreme events in the highly populated centers in the mid-latitudes. It also affects us through sea level rise, which is hitting shores globally. So these changes that are going on in the Arctic should concern everyone.”

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