Some Cool Logic Required for Climate Change in South Dakota

At the Capital Journal in Pierre, South Dakota, the newspaper has begun a series on climate change with an article entitled "Cool logic for a heated debate."

Some statements in this piece:

'The biggest trend we're seeing is warming in winter, and then our overnight lows throughout the year are not as low,' state climatologist Dennis Todey at South Dakota State University said. 'It simply isn't getting as cold anymore overnight.'

In other words, some of the effects Arrhenius had expected are visible in places such as South Dakota.

'The average spring freeze is getting earlier and our average fall freeze is getting later,' Todey said.

Director Mark Anderson of the U.S. Geological Survey's South Dakota Water Science Center in Rapid City said scientists agree on the trends.

'What we're seeing is a general warming trend, but the technical or most significant warming would be winter minimum temperatures. The easiest way to say it is, it's just not getting as cold at night in the wintertime as it used to,' Anderson said.

Or to think of it another way: Prairie artists of the future may find fewer occasions on which to paint another 'Thirty Below.'

The state's average temperatures vary each year, but the most significant increase in average temperature has been in the past 30 to 40 years. Over time, Todey said, the state has warmed by 2 to 3 degrees.

Some cool logic indeed is needed to address these issues.

We will start with the statement that, for the state, "the most significant increase in average temperature has been in the past 30 to 40 years."

In contrast, there has been absolutely no statistically significant increase in South Dakota's average temperature during the past 30 years.  The trend isn't even remotely close to statistically significant.  Similarly, there has been no significant trend in the state's average temperature over the last 40 years.

During the last 30 years, there is almost a perfect non-correlation in the state's wintertime minimum temperature, and over the past two decades, there is nearly a significant declining trend toward colder winter minima.

The average wintertime temperature actually has a negative correlation toward cooling – not warming – during the last three decades.  The last 20 years nearly has a statistically significant cooling trend.  How is that consistent with "the biggest trend we're seeing is warming in winter"?  On the balance of probabilities, the state's average winter temperatures have been declining for a few decades.

Apparently "[p]rairie artists of the future may find fewer occasions on which to paint another 'Thirty Below.'"  In the Rapid City climate sub-region, there have only been two days that reached -30º F since records began in 1942: one each in 1990 and 1996.  Rather, it looks as if they have become more common over time.

For the Aberdeen climate sub-region, there is no significant trend in -30º F days per year since records began in the early 1900s.  Not even a hint of a trend – in fact, non-parametric trend analyses lean towards more per year, not fewer.  Certainly over the last three decades the correlation is positive (i.e., more "thirty below," not fewer).

No significant trend in -30º F days for the Huron climate region over the past century, nor in the Sioux Falls area.

Thirty-below days were never common in the state, and their historical sparseness means there appears to be no clear relationship to anthropogenic climate change.

Then there is this claim:

'The average spring freeze is getting earlier and our average fall freeze is getting later,' Todey said.

No, it is not.  There is nothing close to a significant trend in the growing season length (i.e., the length of time between the spring freeze and fall freeze) over the last century in any of South Dakota's climate sub-regions, nor since 1970.  During the last three decades, all of South Dakota's climate sub-regions exhibit correlations toward shorter growing seasons, not longer.  This is the complete opposite of what is claimed in the Capital Journal article.

And then there is this claim:

Scientific data also indicates South Dakota has been getting wetter, according to the findings in a national study and state experts. That, too, is climate change, and scientists say it may be related to a warmer atmosphere that can carry more moisture, though they do not understand why some areas are receiving more rain while others are getting less.

'We are clearly seeing changes towards more precipitation around the state and the whole upper Midwest,' said Todey. While precipitation is highly variable -- from one year to the next there may be increases or decreases in overall precipitation -- looking at historical data reveals the state has become wetter over time.

'It's generally been going on for about the last 80 years,' Todey said. But South Dakota is not alone. The same effect is happening in North Dakota, Minnesota, Iowa and Nebraska, Todey said.

Cherry-picking 101.  The last 80 years?  You mean starting in the depths of the great drought of the 1930s (1934 to be exact)?  Here is the annual precipitation in South Dakota since records began in 1895.  Does it look reasonable to start a precipitation trend analysis in the mid-1930s?

There is no significant trend since records began in 1895, nor since 1970, nor over the past three decades.

The same conclusion is reached by looking at the state's drought index.  No sign of a significant trend toward increasing wet or dry conditions since records began 120 years ago, or since 1970, or since 1984.

Good science journalism presents all the details to the public and helps them make an informed and accurate conclusion.

After looking at all the details in an objective manner, the conclusion is that the climate of South Dakota is simply not changing in the excessively simplified manner as described in this Capital Journal article.

If you experience technical problems, please write to