Why Does Climate Change Cause Extreme Weather? The Polar Vortex & Global Warming Explained (2014)

Published on Feb 18, 2014

The 2014 North American cold wave is an extreme weather event affecting parts of Canada and the United States east of the Rocky Mountains, extending as far south as Central Florida, and Northeastern Mexico. An Arctic cold front, initially associated with a nor'easter on January 2, tracked across Canada and the United States, resulting in heavy snowfall. Temperatures fell to unprecedented levels due to the front, and consequently low temperature records were broken across the U.S., leading to business, school, and road closures, as well as mass flight cancellations. Records of meteorological data have been kept by the National Weather Service since it was established in 1870. Altogether more than 200 million people were affected, in an area ranging from Rocky Mountains to the Atlantic Ocean and extending south to include roughly 187 million residents of the Continental United States.

Research on a possible connection between individual extreme weather events and long-term anthropogenic climate change is new and the topic of scientific debate. Prior to the events of January 2014, several studies on the connection between extreme weather and the polar vortex were published suggesting a link between climate change and increasingly extreme temperatures experienced by mid-latitudes (e.g., central North America). This phenomenon can be understood to result from the rapid melting of polar sea ice, which replaces white, reflective ice with dark, absorbent open water (i.e., the albedo of this region has decreased). As a result, the region has heated up faster than other parts of the globe. With the lack of a sufficient temperature difference between Arctic and southern regions to drive jet stream winds, the jet stream may have become weaker and more variable in its course, allowing cold air usually confined to the poles to reach further into the mid latitudes.

This jet stream instability brings warm air north as well as cold air south. The patch of unusual cold over the eastern United States was matched by anomalies of mild winter temperatures across Greenland and much of the Arctic north of Canada, and unusually warm conditions in Alaska. A stationary high pressure ridge over the North Pacific Ocean kept California unusually warm and dry for the time of year, worsening ongoing drought conditions there.


There has been long ongoing debate about a possible increase of tropical cyclones as an effect of global warming. However, as of March 2012, the latest IPCC report on extreme events SREX states that "there is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities." Increases in population densities increase the number of people affected and damage caused by an event of given severity. The World Meteorological Organization and the U.S. Environmental Protection Agency have in the past linked increasing extreme weather events to global warming, as have Hoyos et al. (2006), writing that the increasing number of category 4 and 5 hurricanes is directly linked to increasing temperatures. Similarly, Kerry Emanuel in Nature writes that hurricane power dissipation is highly correlated with temperature, reflecting global warming. Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high CO2 conditions, are more intense than under present-day conditions. Thomas Knutson and Robert E. Tuleya of the NOAA stated in 2004 that warming induced by greenhouse gas may lead to increasing occurrence of highly destructive category-5 storms. Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-projections of global warming. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific. The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the warming and moistening atmospheres, and the model-projected increases in Atlantic wind shear.