DTE analyses data put out by climatologist & weather historian Maximiliano Herrera
A woman giving water to her pet. Photo: China Xinhua News / Twitter
Extreme heat has besieged nearly the entire northern hemisphere and some regions in the southern hemisphere this year, according to media reports.
Some 33 countries across five continents — Asia, Africa, South America, Europe and North America witnessed simultaneous heatwaves since July 14, 2022.
The heatwaves have broken temperature records in all these countries and caused widespread wildfires in many regions.
Down To Earth analysed the data put out by Maximiliano Herrera, an independent climatologist and weather historian, on the microblogging website Twitter. Herrera regularly updates extreme temperature records on his website and collaborates with Weather Underground, a public weather observation network, now owned by IBM.
The heatwaves in many countries such as Spain, China, US, Canada, Russia, Iran, Turkmenistan, Morocco, Paraguay and Argentina are still ongoing as of July 28.
For instance, China, especially its southeast region, is undergoing its second heatwave spell in July. Around 900 million people in the country are currently living under some kind of heat warning, according to state-run China Xinhua News Agency.
The first heatwave spell was between July 5-July 17 and the second began July 23 and will last till the first week of August, according to a report by Global Times, the country’s government-run media outlet.
The second heatwave of July is more widespread than the first, according to China Meteorological Administration.
Between July 15 and July 26, as many as 51 weather stations across China broke their all-time temperature records, according to another Global Times report.
The temperature records have been broken in 71 weather stations across China, said Xinhua News Agency. The heatwaves in southeast China have been occurring for seven weeks now, said Herrera.
Within Asia, there are also ongoing heatwaves in Russia, Iran and Turkmenistan. But in the past two weeks, Uzbekistan, Tajikistan, Kazakhstan, Turkey and Taiwan have also suffered from blistering heat.
The city of Al Hoceima in Morocco on the Mediterranean coast in north Africa reached a maximum temperature of 41 degrees Celsius (°C) July 26, which is the joint highest ever recorded in the city. On the same day, there were two active heatwaves in the United States (US). The first was between Oklahoma and Kansas and the second was between Oregon and Washington.
In Canada, the town of Lytton in the British Columbia region had broken the country’s all-time temperature record of 49.6°C in June 2021.
The year 2022 recorded a temperature of 42°C on July 27, showing that last year’s event was not just a freak accident, but the region is warming in general and has become prone to heatwaves.
On the other side of the equator, there are unusual winter heatwaves in Paraguay and Argentina. Paraguay recorded its highest July temperature July 25.
The northern part of Argentina is experiencing extreme heat while the southern part is freezing, simultaneously showing two extremes within the country.
In Europe, there are ongoing heatwaves in Spain. At the same time, many eastern European countries such as Romania, Macedonia, Bulgaria, Slovakia, Hungary and Croatia have suffered from heat in the last few days.
In the past two weeks, a total of 19 European countries have experienced heatwaves and in most of them, monthly or all-time temperature records have been broken.
The most severe heatwaves have been in the United Kingdom (UK), France and Spain.
Almost all weather stations in the UK broke their temperature records July 18 and July 19, with Coningsby in the eastern UK recording the country’s highest temperature at 40.3°C July 19.
Two other stations in London also crossed the 40-degree mark on the day, with London’s Heathrow airport becoming the first station to make the cut.
The primary reason for these simultaneous and devastating heatwaves, at least in the northern hemisphere, is a phenomenon known as planetary wave resonance.
Planetary waves, also generally known as Rossby waves, get set up in the atmosphere due to the increasingly wavy nature of the Arctic Jet Stream.
The Arctic Jet Stream is a band of fast-flowing winds above the Arctic region that is becoming wavier due to the region’s warming.
Scientists have said the Arctic is warming at anywhere between two to four times the rate as the rest of the world, with parts of it close to Norway, warming at seven times than the rest of the world.
Rossby waves can occur in any fluid. They appear in the Earth’s oceans as well as the atmosphere.The atmospheric Rossby waves occur due to Earth’s geography.
They help transfer heat from tropical regions to polar regions, bring back cold air and balance the heat in the atmosphere.
“The slow motion of these waves often results in fairly long, persistent weather patterns,” according to the US’ National Oceanic and Atmospheric Administration.
These waves can sometimes get stuck in certain wind patterns in the northern hemisphere, leading to their amplification known as resonance and hence causing simultaneous extreme weather events.
“We have had resonance conditions for a planetary wave with wave number 7 during the past week, with large wave amplitudes. This lead to simultaneous heatwaves in different areas of the northern hemisphere”, said Stefan Rahmstorf, head of Earth System Analysis at Potsdam Institute of Climate Impact Research, Germany, on Twitter.
Several studies show that these wave resonance events are increasing due to global warming, he further added.
Warming in the Arctic region is believed to be the reason behind the meanderings of the jet stream.
“Arctic warming is affecting the meanderings of the jet stream. Since the jet stream is like a referee between the warm sub-tropical air and the cold polar air, the meanderings create multiple centres of warm blobs and cold blobs”, said Raghu Murtugudde, a climate scientist at the University of Maryland.
These meanderings are related to the coriolis effect and vorticity, which increase from low to high latitude, he added.
The coriolis effect is a force acting on the winds in the atmosphere due to Earth’s west to east rotation and vorticity is any twisting motion of winds in the atmosphere.
“The air pushed north is pulled back and air pushed south is pulled back north by the Coriolis and vorticity imbalance. Thus these meanderings are the Rossby waves. The cold blobs go unnoticed because they bring nice weather, but the warm blobs wreak havoc for populations that are not so used to heatwaves,” Murtugudde explained.
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