Assessing Long Term Historical Air Temperature Records in the Estimation of Warming Trends for Use by Agricultural Scientists Globally

Plant breeders globally are presently handicapped by uncertain estimates of future increases in annual air temperatures. In particular, lack of location-specific estimates in the next 25 years is likely to hinder their attempts to incorporate specifically additional heat tolerance and pest resistance into new varieties in addition to the many other breeding and agronomic issues associated with global climate uncertainty which challenge agricultural scientists. Failure to adequately predict the likely future suite of challenging abiotic and biotic stresses to crops may render the new varieties needed for the coming generations to be less productive and with less effective longevity, bringing severe global consequences. In this paper we have made an attempt to provide estimates of the likely range of increases in annual average air temperature 25 years into the future across a wide range of locations. These were selected, essentially at random, but with provisos that the sites should be in areas suitable for cropping, and have had an uninterrupted, freely available data stream for at least 100 years. The sites showed great variability in likely temperature increases in 2039, from around a maximum increase equivalent to 4.5 oC per hundred years to a minimum of no change (1975-2013). There was also considerable variability when the time period over which the analysis was performed was changed from 1975-2013 to more historic or more recent periods. Approximately half of the sites analyzed for 1975-2013 project no significant future increase in air temperature. With longer data runs most sites showed at least modest increases in temperature, with the extreme case—Tbilisi in Georgia—requiring a return to 1881 before a significant increase was recorded. If a default period has to be selected then 1975-2013 remains the pragmatic option.

Keywords:

Crop breeding , Future air temperature forecasts , Uncertainty , Urbanization