Perilous Times and Climate Change
What's behind all the world's weather chaos?
By Brandon Miller, CNN Meteorologist
August 12, 2010 12:09 p.m. EDT
STORY HIGHLIGHTS
* Peshawar, Pakistan, saw six times the month average rainfall in
only 24 hours
* Moscow has experienced hottest temperatures in recorded history
* Area of high pressure over Russia forced part of jet stream south
to Pakistan
* Interaction between jet stream, seasonal monsoon currents could
have led to intense rainfall
(CNN) -- 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.
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).
Send your stories, video, photos of extreme weather
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.