Introduction

In the last post https://rpubs.com/dgolicher/summer_temperatures I looked at the rather intriguing hint of negative slopes for temperatures recorded from North American central and mid west meteorlogical stations since 1970. This trend is the opposite of that found in most other regions. in order to show this more clearly I extracted all the stations with a significant (p<0.05) regression coeficient and produced raster surfaces using simple inverse distance weighted interpolation. The method was repeated for winter (December, January, February), spring (March, April, May), summer (June July August) and autumn (September, October, November)

Maps

Spring

Summer

Autumn

Winter

Interpretation

The result requires some independent verification, preferably through the use of more meteorological stations. One possible explanation for the apparent mid west anomaly is that regression takes the average daily maximums for each season for the years since 1970. During this period the extensive cereal farms in the region have undergone some changes in farming practices. More fertilizer is applied and crop yields have increased. It is interesting that the trend is not apparent in the autumn months, after harvest, and is only weakly shown in the winter. The most noticeable difference occurs during the growing season. There is at least a hint that the regional climate has altered very slightly as a result of increased greening and more evapotranspiration during the growing season. The phenomemon requires further research.