Cold, hot or dry: Persistent weather extremes associated with decreased storm activity

December 11, 2015

"Less or less severe storms in the mid-latitudes, this at first sight seems to be good news - but unfortunately it isn't," says lead-author Jascha Lehmann. "These storms have a moderating effect on land temperatures as they bring maritime air from the oceans to the continents and a lack of them can thus favor extreme temperatures."

In the Northern Hemisphere mid-latitudes, much of the day-to-day weather variability is determined by the storm track regions located over the Atlantic and Pacific oceans. Here, weather systems, including storms, are generated and travel eastwards to the continents. In winter, storms bring air from the relatively warm oceans to the continents and thus have a warming effect. In summer, the effect reverses with winds bringing relatively cool and moist air from the sea. The authors show that a lack of such weather systems can thus favor more persistent heat and drought events in summer, and cold spells in winter.

"This summer a severe drought in China's northern bread basket region Liaoning threatened crop yields, while California has been experiencing a prolonged drought for no less than three consecutive years," says Lehmann. Comprehensive analysis of satellite weather data shows that these are indeed regions where significant reductions in storm activity are detected during the rainy season. In summer, storm activity calmed down over as much as 80 percent of the land area in the mid-latitudes. In winter the changes are more patchy, yet pronounced reductions are found over eastern US and large parts of Europe and Asia. This includes regions like New York and Chicago which suffered from record-breaking cold temperatures in recent winters.

These detected changes in mid-latitude storm tracks are likely linked to changes in the jet stream and planetary waves in the atmosphere. Such dynamical changes favor certain types of weather situations in some regions and others elsewhere. "Regional changes are mostly due to natural variability but on top of that we see this pronounced overall weakening in summer storm activity," says co-author Dim Coumou, "This is also something projected by climate models under future emission scenarios. However, the data so far is not sufficient to say whether the storm activity changes are caused by climate change - this has to be investigated further."

Although average summer storm activity decreases, the most intense winter storms are projected to increase in frequency under continued global warming. This could have severe implications for heavy rainfall events. Also, the most intense hurricanes and typhoons in the tropics are likely to increase under future warming because they're driven by rising ocean surface temperatures. In the Northern mid-latitudes, the main driver is the temperature difference between the warm equator and the cold Arctic; a difference that is shrinking because man-made warming is over-proportionate in the Arctic.

"Altogether our study highlights how sensitive regional weather conditions are to any changes in large-scale atmosphere dynamics," says Coumou. "This can have serious impacts for people on the ground."
Article: Lehmann, J., Coumou, D. (2015): The influence of mid-latitude storm tracks on hot, cold, dry and wet extremes. Nature Scientific Reports. [DOI 10.1038/srep17491]

For further information please contact:
PIK press office
Phone: +49 331 288 25 07
Twitter: @PIK_Climate

Potsdam Institute for Climate Impact Research (PIK)

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to