In 2012, 93 percent of natural catastrophes were weather-related disasters. The United States was seriously affected: it accounted for 69 percent of overall losses and 92 percent of insured losses due to natural catastrophes worldwide ~ World Watch Institute
America has some of the wildest weather on the planet, and it turns out those extremes – which run from heat waves and tornadoes to floods, hurricanes and droughts – carry a heavy price tag ~ theguardian
The mega-storm that generated the massive cyclonic system that passed over the central U.S (from May 18th through May 20th) spawned many storm systems and severe tornadoes. In Oklahoma, it took less than 1 hour for a thunderstorm system to develop into a full-blown 3 km diameter tornado of the highest size/strength (EF5). As you know, this tornado caused total devastation along a swath greater than 30 km long and about 3 km wide in the southern part of the city. Two schools and a hospital were destroyed resulting in heavy loss of life.
The actual tornado tracked through the most built up part of the city and had a length of 6.22 km (Image 2). As bad as this was, if the tornado had tracked further north by about 10 km, the path length through the built-up part of the city would have been about 28 km and likely would have resulted in four times more damage.
The high altitude jet stream guided this storm directly over Oklahoma City and was a key ingredient responsible for the extremely rapid development of the tornado witnessed. Unfortunately, the location, strength, waviness, and behavior of the jet stream is changing as a result of rapid climate change. You can get use to more “Climate Bomb” extreme weather events – there is nothing to be surprised about here.
Greenhouse gas emissions from humans have warmed the planet since about 1850; the warming rate has stepped up a notch over the past several decades, and even more so now with ‘feedbacks’ kicking in big time.
There is less snow cover on the land over northern Canada, northern Eurasia and Siberia, and there is less sea ice over the Arctic Ocean. The snow and ice reflects greater than 80% of the incoming light from the sun back into space keeping these areas colder. With less snow the dark land is uncovered and with less sea ice the dark ocean is uncovered. These both reflect much less light; only about 20% and 10% respectively. The rest is absorbed and heats the ground and sea. The melting ground is releasing methane; the warming sea heats the sea floor and that warming releases more methane. Thus, parts of the high Arctic are warming at 5 to 6 times the average global rate. The equator temperature does not change as much (even seasonally the change is only about 3°C over the year). Thus, the temperature gradient between the equator and Arctic is greatly reduced.
By basic physics and meteorology, this reduced equator-pole temperature difference slows the west to east wind component. Fast jet streams circle the earth from west to east; as they slow they become much wavier and travel much more northward and southward. Regions north of the wavy jets are cold and dry (air source is cold Arctic) while regions south of the wavy jets are hot and moist (air source is equatorial marine regions). The jet is thus an intersection of these two different types of air masses (with cold fronts and warm fronts, respectively). The large local temperature gradients give rise to large pressure gradients resulting in extreme (and very unstable) weather regions.
Since the wave troughs carry cold air very far south and the wave crests carry warm moist air far north, the frontal temperature gradients are larger under climate change then they were before and thus the storm magnitudes are now larger. That’s why I wrote earlier that we shouldn’t be surprised.
Global warming also brings greater ocean evaporation and warmer air can carry more water vapor – in fact, in the last 3 decades or so there has been a 4% increase in atmospheric humidity. When this water vapor condenses to forms clouds, energy is released. Greater energy in the atmosphere thus fuels more violent storms, and Climate Bombs are born.
The Oklahoma tornado is just another example of the global ‘weirding‘ that we are seeing. Our reference frame is the “old climate”, but now the equator-polar temperature gradients are smaller, but the local frontal temperature gradients are larger. In our “new climate” (in which there is much less sea ice in the Arctic) this type of tornado will be much more probable – at least while we abruptly transition from the “old” to the “new” and unfamiliar climate.
Our future is a world with much warmer global temperatures. Paleoclimate records show temperature rises of 6 to 10°C within two decades have occurred many times in the past over Greenland; in one case the rise was 16°C. I see no reason why this will not occur again.