By Matt Owens July 30, 2014
It seems like the summer on the US East Coast has been unusually cold so far, but the truth is that it's only been cold compared to the recent dramatic warming caused by the rapidly rising greenhouse gas concentration in the atmosphere.
Everyone knows that "global warming" is supposed to "warm things up," but the temperature doesn't just rise uniformly across all times of the day and night or across all seasons, regions, and years. Consider, for example, that when the polar ice sheets start to collapse and send out armadas of icebergs across the ocean, that will lower temperatures far away from the North or South Poles.
Observations over the past several decades have continued to confirm that the diurnal temperature range (DTR) is narrowing around the world, which means that the difference between the high and low temperature of the day and night is becoming smaller. The daily lows are especially rising faster than the daily highs. The difference between winter and summer is also narrowing. And this trend is especially pronounced at the North Pole. This trend will continue as long as greenhouse gas levels remain elevated and out of equilibrium.
In the Washington, D.C. area, this year's “cold” summer is actually normal compared to the 60's, 70's, and most of the 80's. As for the “cold” winter, the same is pretty much true, although this past winter may have been somewhat more erratic than usual.
The animation above compares the daily low and high temperature record for the Washington Dulles temperature station over two different five year periods. The graph below shows daily mean temperatures, compressed into 7 day averages.