The weather had a lot to offer this year: from icy winter and raging tropical storms to extreme heat, drought and forest fires to torrential rain and muddy floods, it was all there. 2023 isn't even over yet, and forecasts and breaking news about heat records from the past twelve months are already abounding. Researchers agree that the year trumped all previous measurements – at least when it came to temperatures. It won't just go down in history as the hottest year on record. It is said to have been hotter than it has been for 125,000 years.
Only climate scientists are not entirely sure exactly what role climate change has played in all the extreme weather events. “To say that extreme weather events are fundamentally becoming more frequent due to climate change would not be correct,” says the website of the Helmholtz Institute’s climate initiative.
Whether man-made climate change was responsible for the devastating forest fires in Greece and Canada or for the violent floods in China, Libya and Eastern Europe? It depends, say attribution researchers like Ben Clarke from the Grantham Institute for Climate Change and the Environment at Imperial College in London, who study exactly such questions. The weather is simulated in different scenarios using different climate models - firstly in a hypothetical atmosphere without human influence and under current conditions with increased greenhouse levels.
What does this mean for the climate year 2023? An overview of the most extreme weather events:
Never in the history of weather records has it been as hot as on July 6, 2023: the global average temperature was 17.08 degrees Celsius. The first temperature records were reported particularly by countries in southern Europe; the Italian capital Rome was among the front runners. According to calculations, the summer of 2023 has broken all previously measured temperature records.
This is what science says: This year's heat records would never have been set without anthropogenic climate change, according to Ben Clarke, with the weather phenomenon El Niño also playing a role (read more about this here). "Our study found that the extreme heat waves that hit Europe and North America in July have become 2 to 2.5 degrees Celsius hotter due to climate change." According to several scientific studies, the middle and east of North America, central and southern Europe, western and central Asia and southern Africa are particularly affected.
Dry river beds or low water levels in rivers put the French authorities on alert in the spring: no rain for 30 days, the soil was still suffering from last year's drought, it was said. In some regions of the country, water conservation measures were imposed before it could even get really hot. It was also far too dry for the time of year in Germany. Media wrote about a “winter drought”.
This is what science says: The German Weather Service differentiates between four different types of drought:
Globally, countries and regions are affected to varying degrees. Droughts occur when there is too little rain. Climate change can make them worse. "Our studies have found that long-term droughts in the Horn of Africa and western Asia have become much more intense due to climate change," says Clarke.
In 2023, there was no continent that was not affected by severe forest fires. There was such a fire in the Canadian province of Quebec in June that the smoke spread across the border and enveloped the US metropolis of New York in an orange haze. In Australia, the fire brigade fought gigantic bush fires, there were blazes in the lower third of Africa, as well as in parts of Asia and Latin America. In Europe, the fire on the Greek island of Rhodes in particular caused a stir: 20,000 people had to be brought to safety and several nature reserves were destroyed.
This is what science says: When it comes to forest fires, researchers mostly agree that climate change itself does not cause fires. But he favors them. Experts speak of “fire weather”. Drought, little or no rainfall and high temperatures ensure there is enough fuel. But only human carelessness or lightning strikes cause fires (you can read more about this here).
Studies show that the risk of forest fires has increased massively, particularly in the western United States and Canada, the Mediterranean region, the Amazon, Southeast Asia and Australia. The reason for this is global warming and drought. According to the world climate report, the forest fire season lengthened by almost 19 percent between 1979 and 2013. By 2050, the frequency of fires is expected to increase by almost 20 percent compared to the turn of the millennium.
The year got off to a chaotic start in the USA: storms raged across California, Alabama and Nevada, bringing heavy snow and rain for weeks. In some regions it rained more in 50 days than in twelve months. For the first time in decades, California authorities warned of blizzards. The US President had to declare a state of emergency for the states of California and Alabama. At least 15 people died as a result of the storms.
In February, Cyclone “Freddy” roared across the Indian Ocean and the east coast of Africa. The island of Madagascar as well as the countries of Malawi and Mozambique were affected. Meteorologists call "Freddy" the longest-lived hurricane ever recorded. It lasted from early February to mid-March and claimed more than 1,400 lives.
This is what science says: Winter storms and hurricanes could occur less frequently due to global warming, but could be more violent, according to climate researcher Clarke. The connection between climate change and storms is particularly well documented for the North Atlantic: "Because of climate change, it is expected that strong hurricanes such as Katrina in 2005 and Maria in 2017 will increase not only with increased amounts of precipitation, but also with more extreme wind speeds," says the scientist.
According to a study in the specialist magazine "Pnas", hurricanes of strength three to five increased fivefold between 1979 and 2017. At the same time, they have lost speed within 60 years and are therefore becoming slower.
However, there is hardly any reliable knowledge for the tropical regions because there is a lack of weather data. However, researchers are observing that the paths of tropical storms in the western Pacific are shifting northward, "which may lead to extreme conditions in areas where this has not been the case in the past," explains Clarke.
In August, heavy rains washed away parts of Austria and Slovenia. The situation in Libya was particularly bad: two dams in the African country could not withstand the floods. The floodwaters poured towards the coastal town of Darna. More than 5,000 people died. The disaster was triggered by storm Daniel in the eastern Mediterranean. Greece, Turkey and Bulgaria were also affected. The Libyan government spoke of the heaviest rains in 40 years.
This is what science says: The role that climate change plays in wet extreme events has not yet been conclusively clarified. According to meteorologists and climate scientists, more data is needed for this. According to climate researcher Clarke, it is clear that increased temperatures will make rainfall more intense, "because a warmer atmosphere can absorb more water." Climate change could therefore have increased the extent of rainfall in Eastern Europe, for example.
Extreme heat and drought were followed by severe flooding in China. Thousands of people from several provinces had to be evacuated. The capital Beijing was also affected.
This is what science says: "While heavy rainfall is often the main cause of flooding, human factors such as land use and infrastructure can make it worse," explains climate researcher Clarke. According to scientists, some floods, for example in the Ahr Valley, would have occurred even without global warming because the soil in the region is predominantly sealed and can no longer absorb the water.
However, whether climate change itself increases the risk of flooding is controversial in research. According to analyzes by the Intergovernmental Panel on Climate Change, heavy rainfall is expected to occur more frequently in East Asia, for example, due to global warming. Other studies on the floods in China show that long-lasting heavy rains are replaced by shorter extreme events with flash floods. "It is therefore more likely that the extreme flooding experienced by China in 2023 was exacerbated by climate change, but the evidence is still relatively weak and depends on the type of rainfall events involved," Clarke said.
However, it is very likely that the flood risk will increase on all continents in the coming years. Because climate change is drying out the soil and precipitation can no longer be absorbed as well or at all.
Not all weather events can be explained by climate change. Nevertheless, science knows that it causes heat waves and makes many other extreme events more likely. In addition, global warming influences how strong a hurricane or forest fire is "and can lead to results that would not have been possible without it," summarizes climate researcher Clarke.
There are currently 70 different models in which weather and climate changes with different conditions are simulated, sometimes up to 200 times. However, there is not a suitable model for all weather events. Heat waves and heavy rain are easier to study because their background is less complicated than storms or forest fires.
The attribution researcher Friederike Otto sums up in an interview: "Ultimately, you cannot make any statements about a once-in-a-century event based on 100 years of observations alone. (...) We (need) more data in order to be able to do statistics on extreme events. "
Sources: Climate Initiative Helmholtz Institute, IPCC, Science Media Center, "Spectrum of Science", "Nature Climate Change", German Weather Service, Carbon Brief, IPCC, "Pnas"