An example of regional climate is the extraordinary dust bowl years of the 1930s. Much of the central U.S. experienced record high temperatures and exceptional droughts. In fact many of the all-time temperature records for individual states occurred during this time. This was at a time when the global climate was cooler. A regional warming of that magnitude today would be unbearable.
The record for South Carolina is 111 degrees on three different dates, twice in 1925 and once in 1954. However, it was also quite hot and dry for South Carolina during the 1930s.
These are examples of extremes in weather and can be set at any time, but what about the climate. How has the local climate changed? We can examine this by looking at the data set from Columbia, SC.
I looked at changes in the average annual temperature and average annual precipitation by looking at the 30-year moving average with help from meteorologist Scott Ryan. The National Weather Service calculates the climatological norms every ten years. However, by looking at the moving average you are looking at how the climate is changing every year and can easily see the trends.
|Average Annual Temperature for Columbia, South Carolina. Image Credit: Scott Ryan.|
It should be noted that when you are looking to the global data sets you may be looking at 5 or 11-year moving averages and this is a 30-year moving average. Thus you can not compare the two.
The 30-year moving average smooths out a lot of the variability. How does it compare to the annual temperature?
|The Annual Temperature vs The Average Annual Temperature for Columbia, SC. The purple line is the average annual temperature while the black line is the annual temperature. Image Credit: Scott Ryan.|
The same type of analysis can be done with the average annual precipitation.
|The Average Annual Precipitation for Columbia, SC. Image Credit: Scott Ryan.|
More variability can be seen in the yearly precipitation.
|The Annual Precipitation vs The Average Annual Precipitation for Columbia, South Carolina. The purple line is the average annual precipitation while the black line is the annual precipitation. Image Credit: Scott Ryan.|
Our climate is most definitely getting warmer and drier. No matter how you analyze the data, you get the same conclusion. Furthermore, we are seeing this warming trend in all seasons of the year (seasonal data is not shown here). The past two summers have been the hottest on record.
The more disturbing trend is that we are moving toward a drier climate. We have seen an increasing number of droughts and their intensity is increasing as well. Yet, we are also seeing an increasing number of extreme rainfall events. Eight of the heaviest rainfall events have occurred since 1958 even as the climate has been drying. What is happening is that when we see significant rainfall it tends to be quite heavy, then we can go long periods without much rain.
What might be causing this change in climate? What does this tell us about the future? I will cover those topics in a later post.