Decrease in global Diurnal Temperature Range (DTR) poses potential impacts to human health, agriculture and natural environment
New research confirms that a significant decrease has occurred in the DTR, the difference between the daily maximum and daily minimum temperature, recorded globally since the mid-20th Century. The reduction in global DTR, resulting from daily minimum temperatures warming faster than daily maximum temperatures, is an indicator of shifts caused by climate change.
The pair of studies, published in the Journal of Geophysical Research and highlighted in Nature Climate Change and EOS, are important due to the specific implications for both human health and agriculture associated with decreased DTR. The research was led by Professor Peter Thorne of Maynooth University’s Department of Geography in partnership with many international collaborators.
The decrease in DTR has significant ramifications for our society. Research has shown that, despite Ireland’s temperate climate, our mortality rates are affected by temperature. In heat waves, it is not the daily maximum temperature that proves dangerous, rather it’s when the minimum temperature at night does not go low enough to allow the body to recover. Similarly, crops and livestock require low minimum temperatures in order to recover from excessive daytime temperatures. With the agri-food sector worth an estimated €24 billion, changes in such aspects of the thermal climate could have extremely significant consequences for Ireland’s economy.
Commenting on his findings, Professor Thorne observed: “A change in an area’s DTR alters the thermal stress on local ecology and places pressure on the overall resilience of its natural environment.”
Despite being one of the 27 main indices defined by numerous world bodies for the detection of climate change, it has been over a decade since changes in DTR globally have been assessed in a standalone study and the Intergovernmental Panel on Climate Change (IPCC) reported in 2013 that there was only medium confidence in our knowledge on worldwide trends.
The complete lack of dedicated studies, since the earlier 2007 IPCC report when it was identified as a key uncertainty, may be partially attributable to significant gaps in global records. Estimates are far easier to establish in Europe, North America, Asia, and Australia where there have historically been far more weather stations than in Africa, South America, India, Antarctica, or Greenland. This study takes advantage of substantively improved basic records arising from the International Surface Temperature Initiative, chaired by Professor Thorne, and new and revised assessment algorithms to present a more comprehensive analysis of global DTR patterns.
The evidence supports the conclusion that most global land areas analysed have experienced significant warming of both maximum and minimum temperature extremes since 1950. In that period, daily minimum temperatures rose by 0.24°C per decade while daily maximum temperatures rose by 0.19°C per decade. With daily minimum temperatures rising faster than daily maximum temperatures, DTR has decreased by 0.04°C per decade since the mid-20th Century with Europe experiencing a greater decrease in DTR than either North America or Australia.
There are practical reasons behind the relative neglect of DTR by climatologists. Meteorological records have been carried out at weather stations as far back as the late 18th Century regionally and the late 19th Century globally. Efforts have been made for at least three quarters of a century to collate and assess these records; however, in many places historical observations of minimum and maximum temperatures, which, in the pre-automatic weather station era, required separate instruments, may not exist. Therefore, many of the historical analyses have been limited to a consideration of changes in average temperatures, which are more complete.
Discussing the relative data sparsity, Professor Thorne noted: “There is low confidence in trends and multi-decadal variability in DTR prior to the mid-twentieth century, because of current data sparsity in the digitized records. However, it is likely that considerable pre-1950 data exists, which could be shared and / or rescued and used in future analyses. In weather stations all over the world, there are countless records that have never been digitised. There are many reasons for this, the most obvious of which is cost; however, this is not an insurmountable problem and at next month’s international climate conference to be held at Maynooth University we will be exploring some innovative and exciting approaches that could see these records become widely available for researchers in the coming years.”