World Weather Attribution

The Stormy Month of January 2018 over Western Europe

Several major storms pounded Western Europe in January 2018, generating large damages and casualties. The two most impactful ones, Eleanor and Friederike, are analyzed here in the context of climate change. Strong winds associated with such storms are observed to have become less frequent in the past four decades. Models show a different signal, with no significant change in their frequency until now and a slight increase in the future. By analyzing a number of climate simulations, we conclude that human-induced climate change has had so far no significant influence on storms like the two studied. However, all simulations indicate that global warming could lead to a marginal increase (0-20%) of the probability of extreme hourly winds until the middle of the century. These trends do not account for the other factors, such as roughness, aerosols, and decadal variability, that contributed to the observed reduction in probability.

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Trends in Weather Extremes

Twenty years ago, the trend in annual mean global mean temperature became detectable. Ten years ago, robust regional seasonal mean temperature trends similarly started to emerge.  Nowadays, we can see trends even in weather extremes. Studying these trends is an essential step in the extreme event attribution procedure we use at WWA. Over the years, we have collected a fair number of results in these analyses and other articles. In this article, I take a step back and consider global long-term meteorological station data for hot, cold, and wet extremes, and share some thoughts on tropical cyclones and droughts. I make no claims for completeness; there is a lot of literature on this that I do not know.

Continue reading on WWA >> or on Climate Lab Book.


Cold Waves in North America Are Not As Cold Now As a Century Ago

Over the last week of 2017 and first week of 2018, a cold wave gripped the northeastern U.S. and southeastern Canada, with temperatures over 18ºF (10ºC) colder than is typical at this time of year over this area, setting records at many sites. We show that the temperature of North American cold waves has increased substantially over the last century due to global warming. So, although this cold spell would not have been unusual before global warming, it is now a relatively rare event in any one region. The chance of a cold wave anywhere in North America is much larger than in this specific location. We do not find any evidence for an intensification of these types of cold waves due to the Arctic warming faster than the midlatitudes. On the contrary, they seem to be warming faster than the winter mean as the Arctic air coming south is less cold now.

Read the full analysis here.


Climate Change Fingerprints Confirmed in Hurricane Harvey’s Record-Shattering Rainfall

Scientists with World Weather Attribution (WWA) find that human-caused climate change made the record rainfall that fell over Houston during Hurricane Harvey roughly three times more likely and 15 percent more intense.  WWA is releasing the findings of its new analysis regarding the role of human-induced climate change on Hurricane Harvey’s devastating rains that is published in the peer-reviewed journal, Environmental Research Letters (ERL). The findings are being released jointly with the American Geophysical Union (AGU) in a joint press release and at a press conference on Wednesday, December 13 at 2:30 p.m. CT at the annual AGU Fall Meeting in New Orleans.  The paper can be found on our website and in Environmental Research Letters.