Scientists from Switzerland, India, the Netherlands, France, the United States of America and the United Kingdom, collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of the low soil moisture, both at the surface and the root zones for most crops.

Main findings

• Heat and low rainfall in West-Central Europe had far reaching impacts on a variety of sectors including human health, energy, agriculture, and municipal water supply. It was exacerbated by e.g. poor water infrastructure and leakages, and it came at a time when food and energy prices were already high resulting in compounding social and economic impacts.
• In this study, we particularly focus on the dry soils which caused severe economic and ecological impacts across the Northern Hemisphere (excluding the tropical regions) and were particularly severe in West-Central Europe. We therefore focus on these two regions, North-Hemisphere extratropics and West-Central Europe, to analyse the agricultural and ecological drought from June to August 2022.
• Observation-driven land surface models show that very low summer surface and root-zone soil moisture, such as observed in 2022, happens about once in 20 years in today’s climate in both regions.
• While the magnitude of historical trends vary between different observation-based soil moisture products, all agree that the dry conditions observed in 2022 over both regions would have been less likely to occur at the beginning of the 20th century.
• To determine the role of climate change in these observed changes, we combine the observation-based datasets with climate models and conclude that human-induced climate change increased the likelihood of the observed soil moisture drought events. The change in likelihood is larger in the observation-based data compared to the models.
• We also assessed the role of climate change in temperature and rainfall in these regions and found that the strong increase in high temperatures is the main reason for the increased drought.
• Combining all lines of evidence we find for West-Central Europe that human-induced climate change made the 2022 root zone soil moisture drought about 3-4 times more likely,  and the surface soil moisture drought about 5-6 times more likely.
• For the Northern Hemisphere extratropics, human-induced climate change made the observed soil moisture drought much more likely, by a factor of at least 20 for the root zone soil moisture and at least 5 for the surface soil moisture, but as is usually the case with hard to observe quantities, the exact numbers are uncertain.
• The models analysed also show that soil moisture drought will continue to increase with additional global warming, which is consistent with projected long-term trends in climate models as reported e.g., in the IPCC AR6.

Using the same methods usually used in WWA’s rapid attribution studies, researchers from Imperial College London and Oxford University found that the extreme rainfall that hit Japan during Typhoon Hagibis in October 2019 was made about 67% more likely by human-caused climate change.

In an additional step the scientists calculated what the monetary consequences of this increase in rainfall are and found that roughly $4 billion of the $10 billion damage in insured losses caused by the rainfall can be attributed to climate change.

There are not many studies attributing economic damages to climate change, so the methodology is less established. Similar studies have calculated the financial damage attributable to climate change in particular extreme events, using the same methodology as in this study, for example a study of Hurricane Harvey, which hit Texas in 2017, found that $67 billion of the damage could be attributed to climate change. This is the first study, for any extreme weather event in Japan, to calculate the damage attributed to climate change, and may underestimate the influence of climate change as observed extreme rainfall in Japan has increased by more than climate models simulate.

The results reflect the growing economic burden Japan – and other countries – already face from climate change and will increasingly experience if emissions are not rapidly eliminated: the “costs of inaction”. The study looks at how much climate change increased the damage from just one extreme event, but as temperatures rise Japan is being hit by a growing number of extreme heat waves and heavy rainfall events.

The current Siberian heat has contributed to raising the world’s average temperature to the 2nd hottest on record for the period January to May. Using published scientific methods we looked at a large region spanning most of Siberia, inclusive of the area affected by the prolonged six-month heat and the town of Verkhoyansk that recorded the record daily temperature for the Arctic region. We analysed the average temperatures between January and June 2020 for the large region, as well as the hottest maximum daily temperature in June 2020 for Verkhoyansk. We found in both cases that this event would have effectively been impossible without human-induced climate change.

Main findings

• The results showed with high confidence that the January to June 2020 prolonged heat was made at least 600 times more likely as a result of human-induced climate change.
• We note that even with climate change, the prolonged heat was a very rare event expected to occur less than once every 130 years.
• The results for the town of Verkhoyansk show that the record breaking June temperatures were also made much more likely (upwards of many thousands of times), though there is less confidence in this result.
• Combining the values from the models and weather observations shows that for the large region the same six-months hot spell would have been at least 2 degrees Celsius cooler had it occurred in 1900 instead of 2020. For Verkhoyansk, maximum June temperatures increased due to climate change by at least 1 degree compared to 1900.
• By 2050 the Siberian region could expect to have temperatures increase by at least 2.5 degrees compared to 1900, but this increase could be as high as 7 degrees.
• This would correspond to an additional warming of at least 0.5 degrees and possibly up to around 5 degrees by 2050 compared to today.

Background

Siberia can normally expect to have a series of low and high pressure systems moving over the region allowing warmer and cooler air to affect the weather. However, a strong jet stream in the 2019-2020 winter led to very warm conditions which caused ice and snow to melt and in turn increased the warming with darker surfaces absorbing more heat. Overall, the 6 months from January to June 2020 were more than 5 degrees Celsius warmer than average (1981–2010) over the study region (see Figure 1). This extremely hot period led to local heat records being broken, including at the Verkhoyansk weather station which recorded 38 degrees Celsius on 20 June. The Russian Meteorological Service said that this measured temperature was the highest ever recorded beyond the Arctic circle, with the World Meteorological Organization carrying out its own research to verify this.

This has resulted in a range of natural and human disasters leading President Putin to declare a state of emergency, as reported in the media including The Guardian, Reuters and The New York Times. Siberian forests have been experiencing wildfires because of the hot, dry conditions that have extended across thousands of miles, and led to the release of 56 Megatons of CO2 in June. Those areas not affected by the fires have become a breeding ground for large swarms of Siberian silk moths that feed on the trees making them more prone to fire. Fish are swimming deeper in the oceans looking for cooler water making it harder to catch them with current equipment, whilst people on the land have reported an increase in physical and mental conditions as a result of the increased and prolonged heat. The melting of the permafrost has caused infrastructure to collapse leading to fuel leakages and resulting environmental disasters. In addition, the melting could lead to the release of trapped methane gas, a potent greenhouse gas, into the atmosphere.

Heatwaves and hot spells can be defined in a large number of ways and there is not one “right” definition but depending on the impacts different definitions will be appropriate. For this study we used two definitions:

• the large region over Siberia which experienced prolonged higher than normal temperatures over the first 6 months of 2020, and
• the weather station in the town of Verkhoyansk that measured a maximum temperature of 38 degrees Celsius on 20 June.

For the large region we analysed average temperatures over 6 months while looking at maximum June temperatures for the single weather station. The large regional definition is relevant for most impacts whereas the temperature record at an individual place can help people understand their local changing climate. From a scientific point of view it is always useful to compare different ways to define an event in order to assess how much the results depend on the exact definition. In this case we found for both extreme events (prolonged six-month heat and record daily temperature in June 2020 in Verkhoyansk) that human-induced climate change played a very large role. While we are very confident that the large-scale prolonged event would have been essentially impossible without climate change, our confidence for the daily record at the individual weather station is much lower. This is due to better data being available and the increased robustness achieved from averaging climate models over large regions.