Those of us who detest the recent anthropogenic increases in carbon dioxide, nitrous oxide, methane and other pollutants cannot deny that increases in temperature, carbon dioxide levels and precipitation can increase plant productivity. Ask any Alaskan farmers about their increases in crop yields in recent years.
A fascinating map from the Office of the State Climatologist at Texas A&M University shows the vast changes in precipitation across the US in the last 118 years (from 1895 to 2013).
In the last 100 years, change in precipitation has been the most influential climate factor affecting the US. While all locations in general have seen increased precipitation annually over the last 100 years, the largest increases are occurring in Michigan, Mississippi and New England.
Precipitation intensity also has increased, resulting in more precipitation occurring in larger events. These events often are detrimental to agricultural production, leading to increased soil erosion, flooding and other structural damage. The increases in precipitation and in-field flooding in recent years also have led to installation of more subsurface drainage tile.
Historic temperature changes have been less pronounced and more seasonal. The most widespread temperature trend in the is generally warmer winters, especially over the last 30 years. The overall warmer trend has not eliminated colder winters (such as 2013–14). The trend has simply reduced their likelihood and severity.
Warming winters impact the growing season length and winter-kill of insects. Warmer winters do not reduce certain insect populations effectively and allow insects to overwinter further north, creating an easier path for migrating insects — both beneficial insects and pests — to be reintroduced.
While the overall summer temperature trend is flat, there are differences in trends between maximum and minimum temperature. Average maximum temperatures are primarily flat. Average minimum temperatures are consistently rising during the summer and throughout the year.
The warmer temperatures are increasing growing season length. While still quite variable, frost-freeze dates are changing in the spring (earlier) and fall (later). Throughout the 20th century, the overall climate shifts have lengthened the growing season by 9-10 days or more. Agriculture has adapted to this, utilizing longer-maturity varieties and the extended growing season to create higher yielding crops. The largest impact of this change has been in northern areas of the Corn Belt where a lack of heat and shorter seasons have historically been limiting factors to production.
Increased precipitation and changes in cropping system practices have increased the amount of moisture in the atmosphere. Change in atmospheric moisture content has been attributed to cropping changes, such as conversion of pasture/range to row crop and transfer away from wheat to corn/soybean rotation. The causes of overall increases in dew point still are being studied. Regardless of the causes, higher dew points create more humid conditions overall. The dew point increase likely contributes to the rising overnight minimum temperature trend.
The changes we have seen in climate have some beneficial impacts on agriculture. Plants grow faster when more carbon dioxide is present in the atmosphere and when more rainfall is present and when night time temperatures are increased.
We need to be much more subtle in our discussion of climate change lest the climate change deniers say we are just ignorant and blind. When we deny the positive effects of climate change, the deniers can rightfully say: “Climate change? Bah, humbug.”