Periodically, Earth Observatory answers reader questions on this blog. Here’s a recent note from Manny J of New York City:
“I recall that starting on May 15, 2013, the cold did not leave [New York]. In fact, it still felt like winter because it refused to warm up. Then came June 2013, with the sky overcast each and every day, with the humidity very high, hardly any sun except for an occasional peeping through. In fact as of June 30, 2013, there was no summer as summer used to be. The weather pattern was such that I had never seen anything like it. Do you know why?”
We asked Gavin Schmidt, deputy chief of NASA’s Goddard Institute for Space Studies (GISS) and a NYC resident, what he thought:
“The seasonal weather pattern in any particular location is very sensitive to the chaotic dynamics in the atmosphere. Our ability to attribute those changes to either ocean temperature patterns or external drivers is quite limited, and so we can’t provide an answer that can satisfactorily address this question. Things that we can say are caused (statistically) are generally on larger spatial scales and longer time scales.”
In recent years, many readers have asked Earth Observatory if a particular spell of crazy weather is a result of global warming. As Gavin pointed out and many others have explained, weather events and climate are different things. Climate is what you expect to happen, and weather is what actually happens on a day-to-day, week-to-week time scale. There is inherent chaos and unpredictable variability in weather. Climate, on the other hand, is a matter of trends and long views. What might the season or year look like when compared to the averages of many years? Is it getting warmer or cooler, wetter or drier? Can that be explained by some physical process?
Above: temperature anomalies for June 2013, as calculated by NASA GISS
There were heat waves, cool spells, and weird weather long before anyone spoke of global warming. And global warming and climate change are not linear, everywhere-the-same patterns. But there is growing evidence that weather extremes are becoming more extreme, the unusual is becoming more usual — and global climate change is a key reason. The Intergovernmental Panel on Climate Change recently published a report on climate extremes, which is also summarized well by Climate Central.
As we explained in a feature story earlier this spring, the behavior of storms is growing more erratic. Other research has shown that heat waves have become more frequent and more likely to break records. This video below shows how the number of deviations from normal — the number of extreme heating or cooling events — has shifted toward more extreme highs and fewer lows.
While Manny and other New Yorkers had an unorthodox June, much of the rest of the United States and the world baked. According the NOAA National Climatic Data Center and meteorologist-blogger Jeff Masters of Weather Underground, June 2013 was the fifth warmest June on record. July 2013 also was shaping up to be quite hot just about everywhere.