Monday, July 16, 2012

Climate "Cycles" and Utah

Dr. Robert Gillies is the State Climatologist for Utah and appeared on KSL's Sunday Edition this past weekend to discuss climate change.  You can link to the video here.  Skip the NBC report at the beginning and go to Rob's discussion, which starts at about 2:50.

Rob does a nice job responding to reviewer comments and the question about weather simply being cyclical.  Questions at the weather–climate interface are difficult to answer.  Weather does not equal climate.  Heat waves and cold waves are part of the natural system.  But the statistics of heat and cold waves are changing.  Warm days and nights are becoming more common, cold days and nights less common.  Rob deals with this issue with the following response:
"...One has to realize that here in the west, our climate is highly variable so, for example, last year was cold and wet and now we have see-sawed to very warm and dry and that's part of the natural variability.  What you've got to look at is how trends occur over time, say since the 1950s or even earlier than that.  So when people say this is cyclical, yes it is, that is part of climate, but now we have very distinct evidence from NASA and NOAA and from many other agencies around the world that are showing that the mean temperature of the planet has increased and it has increased quite dramatically."
What Rob is describing is clearly evident if we look at the state average spring (March to May) temperature from 1895-2012.  I have picked these three months as warmth this spring contributed to the drought conditions that presently exist in the state.

Utah mean spring temperature (Source: NCDC)
The first thing to notice is that this spring was about 3ºF warmer than the long-term 20th century average.  That being said, there were springs in the early 20th century (1934 and 1910) that were warmer.   In other words, the temperatures experienced in Utah this spring were within the range of natural variability even many decades ago.

Note, however, how the frequency of warm springs has increased in the past few decades.  Springs with temperatures above the long-term 20th century average are far more frequent.

So, indeed there are cycles.  However, there is a clear shift in the frequency of the temperature variability toward higher values.

Perhaps we will take a look at 1934 in a future post.

1 comment:

  1. Yeah, I'd love to see a post on 1934! (Or on that one freakishly cold spring, either 1917 or 1918.)