- It is not possible to say that a single storm or heat wave is a direct consequence of climate change, says Erik Kjellström, professor of climatology at SMHI. 

- But global warming is making certain weather events more common and often more intense. 

In the past year, the extreme weather events have replaced each other. Droughts and forest fires have ravaged both Australia and California. Siberia has had temperatures well above normal during the first half of the year, which affected the ice cover in the Arctic, which was record low in July. Japan and China have been hit by severe floods during the summer. 

The link between these events and climate change has been questioned, including by Australian politicians. Droughts and fires are not uncommon in the country, on the contrary. 

China is also regularly hit by floods and Siberia has had warm periods in the past. It is therefore not easy to distinguish between what is a normal, albeit unusual, weather event, and what is due to global warming. But in some cases it works, for others it does not, according to Erik Kjellström. 

- You can use both weather observations and different climate models to calculate the probability that a certain weather event will occur. 

The method is called "extreme event attribution" and earlier this year, using this type of calculation, researchers were able to establish that the risk of the high temperatures that led to the fires in Australia and the record heat in Siberia increased significantly due to climate change.

- The conditions for the type of heat wave that led to the fires in Australia are about twice as large in today's climate, compared to how it was at the beginning of the 20th century, according to the climate models, says Erik Kjellström. 

He believes that the methods are relatively accurate, but can be even better. For example, the climate models in the study tend to underestimate the increase in heat waves in Australia, where observations indicate that the risk has even increased tenfold since the beginning of the 20th century.

This type of research is also important to be able to better predict the extreme weather in the future. In Sweden, continued global warming will produce more and more intense heat waves, while winters will be shorter and the risk of extreme cold snaps will decrease, according to Erik Kjellström. 

- We will also see heavier rainfall and increased risk of drought.