The weather has been crazy: floods, drought, wildfires, tornadoes. Is climate change to blame? Is it here to stay? Here are some of the most recent insights from online blogs and media to explain what is going on.

Climate, ice and weather whiplash

from Yale Forum on Climate Change and the Media

Peter Sinclair’s video brings together Rutger’s Jennifer Francis and Weather Underground’s Jeff Masters to explain weather whiplash: why we have been having periods of persistent bad weather.

As Arctic sea ice melts, the Arctic becomes warmer. A lesser temperature differential between the polar and the tropical regions weakens the Polar Jet Stream. The Jet Stream essentially keeps polar and tropical weather patterns separate. When it weakens, two things happen. One: it becomes more wavy. That allows more extreme weather to move further north and south. Two: the Jet Stream tends to get stuck in place, so the weather pattern gets blocked. This is why we are seeing more persistent droughts, persistent rain, persistent winter cold than we are used to. Watch the video for a more in-depth explanation with weather maps.

Why are we having such bad weather?

Greg Laden’s blog refers to Sinclair’s video and goes on to explain more about how the Polar Jet Stream works. He also discusses what constitutes “bad weather”, and delves further into the connection with global warming. Although these extremes could be part of a larger pattern of variation, he concludes that our climate has more likely shifted to a “new normal.” Superstorms such as Hurricane Sandy are part of this standard.

How climate change may reshape tornado season

Scientists are not as certain what effect climate change will have on the frequency and destructiveness of tornadoes. Henry J. Enton in The Antlantic Cities gives an outline of what causes tornadoes and explains why the outcome is difficult to predict. Global warming will increase moisture in the atmosphere, which favours tornadoes, but reduce wind shear, which may cancel out the effect.

Low tornado numbers and low tornado deaths, May 2012-April 2013

U.S. tornado statistics to not indicate increasing frequency. The U.S. Severe Weather Blog looked at numbers of tornadoes in 12-month periods going back to 1954, and numbers of fatalities back to 1875. No trend is evident. In fact May 2012-April 2013 showed the lowest number of tornadoes and the second-lowest number of tornado deaths.

So we can expect more severe weather in persistent patterns, but tornadoes may or may not be part of the forecast.