The Arctic’s changes due to human-induced global heating will result in countries at the Northern hemisphere’s mid-latitudes experiencing longer periods with severe heat and droughts over the summer months. This is what researchers from Potsdam Institute for Climate Impact Research discovered in a recent study. Most of Europe is included in the Northern Hemisphere’s mid-latitude countries (northern nations with a moderate climate). nord Scandinavia, most of the USA (except some northern sates or northern Alaska), and most of Canada (excl. Mongolia, the Far North, northern China and Mongolia, as well as most of Russia (excl. The far north, and the majority of Japan (excl. Its most southern island. Dim Coumou, the lead author of this study, and his colleagues published their results in Science (citations below). The Northern Hemisphere will see more extreme heat and drought during the summer months. According to Mr. Coumou, “When great air streams above us become disturbed by climate changes, it can have serious effects on the ground. You might think that reducing storm activity is a good thing. However, this decrease leads to greater persistence of weather system in the Northern Hemisphere Mid-Latitudes. “Storms carry moist and cool water from the oceans to continents, providing relief during periods of intense heat. Warm weather conditions are made to endure during periods of low activity, which can lead to heat buildup and drought. Other research has focused primarily on winter storms as they cause the greatest damage. Although the intensity and frequency of winter storms can vary depending on where they are located, the average storm activity in the colder months is stable. According to satellite and weather station observations, overall storm activity has declined in the summer months. Summer storms seem to be becoming less common, more intense or both. This team looked at synoptic winds and calculated the energy of their wind speeds. The energy is an indicator of how intense and frequent low- and high-pressure systems interact in the atmosphere. It has declined approximately one-tenth from 1979.. Jascha Lehmann, co-author, said that “unabated climate changes will likely further weaken summer circulation patterns, which could exacerbate the risk of heatwaves.” Climate simulations for next decade, the CMIP5, also show the same connection as what we observed in observations. “The recent high temperatures may have been a symptom of a new trend. The rapid warming observed in circulation could also be due to the Arctic’s rapid warming, according to researchers. Although global warming can be attributed to greenhouse gas emissions, the temperature rises in far northern regions due to faster heating from fossil fuels. The far northern regions of the globe that used to be covered with ice, but are now ice-free are more dark than white ice and reflect less sunlight into the space. Warmer water results in higher temperatures. The atmospheric temperature difference in the Northern Hemisphere’s cold polar regions and other parts of the Northern Hemisphere is reduced. Air motion can only occur if there is a temperature differential. The greater this difference, the faster the air moves. Researchers explained that a smaller difference means the jet stream weakens. This weakening could be linked to the decline in summer storm activity, according to researchers. According to Mr. Coumou, “Regardless of how we view the extreme heats, all evidence points in the same direction.” Heat extremes don’t just rise because the earth is warming, they also increase due to climate change affecting airstreams important for shaping weather. “We observed that weather becomes more consistent, which results in extreme heat on monthly timescales. The risk of heat waves with high impact is increasing.” Citation. Dim Coumou and Jascha Lehmann, “The weakening Summer Circulation in the Northern Hemisphere Mid-Latitudes.” Science. Publication online 12 February, 2015. DOI: 10.1126/science. 1261768.
