Is the record-shattering heatwave that has been blamed for the death of thousands in Russia somehow related to the devastating flooding in Pakistan? Are these disasters happening more frequently — and are they a result of global warming? Sometimes these connections can clearly be observed and understood. At other times they are more complex, taking place across time scales much longer than we are able to observe.
photo: AP Photo/Mikhail Metzel
Muscovites will long remember the summer of 2010 as the hottest and most extreme weather summer in the city’s long history. The all-time temperature record was set, and re-set, five different times during a two-week span from late July to early August. In that period the temperature climbed above 30 degrees Celsius (87 degrees Fahrenheit) for 29 consecutive days (and still counting). In addition to the extreme heat, which reached up to 39 degrees Celsius (102 degrees Fahrenheit) on multiple days in a city that averages an August high of 22 degrees Celsius (72 degrees Fahrenheit), the capital was shrouded in a thick layer of smoke from area wildfires. The combination of extreme heat and lack of rainfall left western Russia vulnerable to wildfires, which burned out of control southeast of Moscow.
Nearly 4,000 kilometers (2,485 miles) away in Pakistan, monsoon rains fell with an intensity that had never before been observed. Peshawar, a city in northern Pakistan 140 km (87 miles) west of the capital Islamabad, received six times the monthly average rainfall in only 24 hours. Heavy rain has continued to occur throughout Pakistan since the initial heavy downpour on July 29, and the flooding has impacted an estimated 14 million people, killing over 1,300 at time of writing. Though these disasters are different and vary by great distances, they could have both been the result of a large area of high pressure centered over western Russia.
The high pressure, also known as a “blocking high,” can influence weather patterns over great distances by altering the jet stream. The jet stream is an area of fast-moving air that occurs high in the atmosphere, at an altitude roughly where commercial airliners cruise, and it acts like a highway for storms. As the name suggests, a “blocking high” is exceptionally strong and blocks the jet stream, which forces the jet stream to move around it. These scenarios normally last for a couple of days, but can last for weeks, as we have seen in Russia. Areas under the high pressure will see drought and heat, as seemingly endless days of sun bake the earth. As the jet stream is continually forced around the high pressure zone, flooding can result from areas that see storms continually move over the same areas.
We saw this in Central Europe last week, as storm systems that could not advance into Eastern Europe and Russia continued to rain over parts of Germany and Poland, causing flooding. The area of high pressure that has been parked over western Russia for the last several weeks also forced part of the jet stream south to Pakistan, an area where it normally would not be found during mid-summer. An interaction between the jet stream and the seasonal southwest monsoon currents over southeast Asia could have led to the intense bursts of rainfall experienced there.
So what caused this area of high pressure in western Russia to be so strong and last for so long?
As we continually stress, one extreme weather event, or even a series of weather events, is not caused by global warming or climate change. Weather extremes such as floods or heat waves happen every year, all over the globe. Many climate scientists believe, however, that these events will become more common, as the Earth warms because of global warming. Others will point to more distinct and shorter-scale cycles such as El Nino and La Nina, which commonly lead to extremes in weather around the globe. So, while we can tie many of these global weather disasters together around a common meteorological trigger, we cannot say for certain if climate change is helping to pull that trigger, or perhaps loading the gun more frequently.
One thing is for sure: as global weather disasters will continue to happen, and our knowledge and coverage of them continues to improve, we will continue to question if they are related, and what is really causing them.