After a long drought in many parts of the Northern Hemisphere, there is more news about extreme precipitation. At the end of last week, heavy rains caused flooding in parts of Germany and Austria. In the Himalayas, monsoon rains do not stop, which is why more than 800 people have died in Pakistan alone. On August 22, the state of Texas in the United States declared a state of emergency due to bad weather.
Is climate change to blame?
The explanation quickly comes from different angles: Blame it on global climate change. But is it really so? “Extreme weather has always been and will always be,” says climate researcher Schukje Filip of the Royal Netherlands Meteorological Institute (KNMI). “Climate change could affect their intensity and frequency.”
But is this impact really as serious as the media, politicians and eco-activists say it is? “Often global warming does play a role. in extreme weather conditionsbut this effect is usually not systematic and often flattens out,” says climate expert Friederike Otto of King’s College London. Otto and Philip are part of the World Weather Attribution (WWA) international research team. to what extent global warming on the planet affects individual extreme weather conditions.
To do this, scientists from WWA use the same meteorological models that are used in the preparation of weather forecasts. They are based on physical basic components that determine the weather and climate. With their help, explains Otto, it is possible to simulate the composition of the atmosphere – both with and without all the greenhouse gases emitted in the process of human life. That is, in the state in which the atmosphere was, according to modern data, before the period of industrialization in the world.
By comparing the two models, scientists calculate how changes in the atmosphere affect the frequency and intensity of certain weather patterns. This study seeks answers to questions about how certain natural disasters are related to global warming. Fact-checking DW provides answers to basic questions.
Is climate change causing rain and heat
“Extreme weather conditions that lead to catastrophes are always the result of many factors,” says Otto. In addition to natural causes, there are also factors that depend on the person. For example, in the case of floods caused by heavy rains, among other things, large-scale deforestation and soil compaction, as well as global warming, are an important cause. So climate change is not the only factor causing extreme weather.
How strong the link between climate change and natural disasters depends on what it is, Otto explains: “When it comes to floods and droughts, in these cases global warming often plays a minor role compared to other factors.”
Climate change alone cannot cause heavy rainfall, but it creates the preconditions for more rainfall. “A warmer atmosphere absorbs more moisture, which leads to more rain,” Philip continues. “But when and where it rains depends on many factors.”
At extreme temperatures global warming effect, according to Philip, is felt directly. This does not lead to extreme precipitation, but in a warm atmosphere, the heat periods are even stronger, but the cold phases are milder. Therefore, the lack of crops in Northern India and Pakistan this year is a direct consequence of climate change, Otto emphasizes.
The impact of climate change is the same everywhere
“The impact of climate change varies from region to region,” Philip points out. “Even similar weather extremes can have different effects in different locations.” This makes the comparison between the flooding in western Germany in the Ara Valley last July and KwaZulu-Natal in southern Africa this April obvious. In Africa, floods have killed 435 people and left thousands homeless. In Belgium and Germany, more than 220 people have died as a result of flooding after heavy rains.
According to the WWA research team, a flood of the magnitude of the Arskaya Valley would, for an atmospheric situation around 1900, be a 500-year event. This means that in a region of the same area between the Alps and the North Sea, at the average temperatures of the time, such precipitation should have been expected on average about every half century.
Due to climate change, this probability has increased by 1.2-9 times: in today’s climate, floods like the Arsky one should be expected every 56-400 years. At the same time, they may be 3-19 percent stronger than they were 120 years ago. In the South African province of KwaZulu-Natal, climate change has doubled the likelihood of an extreme rainfall like this April’s since 1900. And their intensity has become 4-8 times higher than it would be without climate change.
On the one hand, uncertainties regarding the impact of climate change on extreme weather conditions vary in scale. This, scientists say, is due to the fact that the area of flooded areas in South Africa is many times larger than the affected valleys in Belgium and Germany. The smaller the area, the more difficult it is to give accurate estimates. On the other hand, it is clear that the impact of global warming on heavy rainfall in South Africa is less than in Central Europe.
Can disasters be predicted?
A serious and accurate weather forecast can only be made a few days in advance. Uncertainty about the actual weather situation grows exponentially as you look to the future. The weather is literally too chaotic to make accurate daily forecasts over a longer period of time, explains Otto.
“But what we can predict and calculate very well anyway is the frequency of certain weather conditions and temperature or precipitation thresholds,” says Otto. With rising temperatures in many places around the world, weather patterns that could cause floods, droughts and other anomalies are becoming more likely, according to WWA forecasts.