(Image source: NASA)
Over the past week, temperatures have been building throughout Central Siberia. A broad swath of heat pushed thermometers into the upper 70s to upper 80s (with isolated spots showing 90+ degree readings, Fahrenheit) in a broad region stretching from Siberia’s forests all the way to the Arctic Coast. These heatwave conditions set off more than a score of large fires that raged through both Arctic forest and across broad areas of tundra. The largest of these fires covered areas up to 1000 square miles and numerous smoke plumes were visible from satellite, some of which stretched more than 800 miles in length. A larger pall of smoke from this region covered areas of North-Central Russia, the Arctic Coast and sections of Europe more than 2,000 miles away.
You can view these fires and related smoke plumes in the NASA Aqua Satellite image provided by Lance-Modis above.
The scorching Arctic heat wave and massive burning has been set off, once again, by a high amplitude northward bulge in the polar Jet Stream and related ‘heat dome’ high pressure system resting just beneath the bulge. As you can see in the below image, provided by the California Regional Weather Service, this particular heat bulge extends past the 80 degree North Latitude line, nearly reaching the North Pole. This extraordinary upward sweep in the Jet has completely compromised the polar vortex, allowing hot air to build far north and pass deep into the Arctic Ocean environs.
(Image source: California Regional Weather Service)
Arctic coastal temperatures usually average less than 50 degrees Fahrenheit at this time of year, but the region beneath this Arctic heat dome has averaged about 15-20 degrees hotter over the past week. Further south, where the tundra fields and arboreal forests of Siberia lay, temperatures have been even warmer with highs stretching into the middle and upper 80s and even lower 90s in some isolated locations. The added heat and the occasional thunderstorm that will typically form under such highly unusual Arctic conditions enhances the chance of wildfires. Now, after a week of such conditions, more than a score of large fires rage.
(Image source: Arctic Weather Maps)
Unfortunately, forecasts call for hot conditions to persist over this region of the Arctic at least until Saturday. Then, the heat dome and related Jet Stream bulge is predicted to slowly shift toward Europe, bringing heat, dryness and related risk of wildfires along with it.
This particular heat wave is the most recent of many to plague the Arctic during 2013. Large Arctic regions from Siberia, to Europe, to Canada to Alaska experienced periods of extreme heat where temperatures rose 10, 15, 20 degrees or more (Fahrenheit) above average. The added heat and evaporation in one region appeared to aid in the formation of record floods in another with both Europe and Canada experiencing some of their worst floods on record.
Strange changes to the Jet Stream and the water cycle driving these extreme events are directly related to human-caused global warming. In the first instance, human-caused warming has set off a series of events that have caused a major erosion of Northern Hemisphere sea ice. Since 1979, more about 50% of sea ice extent and 80% of sea ice volume has been lost. Since the 1900s, more than 60% of sea ice extent has melted away. The sea ice, which tends to lock cold air in the Arctic, is thus dramatically weakened. The result is that more warm air tends to pool in the Arctic. As this happens, the temperature difference between the North Pole and temperate regions lessens. This loss of differential causes the Jet Stream to slow down. As the Jet Stream slows, it tends to move more like a lazy river, creating big loops, large high amplitude waves and numerous cut off flows. The net result is that weather systems move more slowly, causing weather patterns to persist over longer periods.
The high amplitude waves that have tended to form in the Jet Stream also result in warmer air being transported toward the North Polar region. In the case of the current Siberian heatwave and wildfires, this is exactly what is happening. What we have seen, this summer, is a ring of very hot conditions developing in the higher Latitude regions from about 60 degrees North to about 80 degrees North. This is the zone where much of the extreme Arctic heating has emerged.
This second factor, added atmospheric heat, causes greater evaporation to occur, especially in regions where the heat is most intense. On average, the global hydrological cycle, which is the net rate at which water evaporates and then comes back to the Earth in some form of precipitation, increases its intensity by 8% for each degree Celsius of warming. Currently, average global temperatures are about .8 degrees Celsius hotter than the 1880s average. So the rate at which water evaporates and the rate at which it falls from the skies as rain and snow has increased by more than 6%. In the hot regions under the Jet Stream bulges and related heat dome high pressure systems this means far more intense soil drying and risk of wildfires. In the wet regions of cut off lows and down-slopes in the polar Jet Stream this means more intense rainfall events.
In essence, this is how human caused global warming is helping to drive extreme weather events now. And the current Siberian heatwave and related wildfires is just one case in point.