The Importance of Nightly Minimum Temperatures

Everyone talks about what the “high for today” will be when looking at weather forecasts for the next few days. While this is important, seldom do people consider what the “low for tonight” may be, but the lows are just as essential as the highs. Nightly minimum temperatures, just like daily maximum temperatures, have both significant ecological and agricultural impacts, as well as effects on public health.

First, consider the ecological impacts. An increase in the lowest minimum temperature in winter may permit the eggs of insects, such as the Southern Pine Beetle, to survive winters in regions where colder temperatures in the past prohibited survival (Ayres et al. 2011).  This invasive species has already invaded the New Jersey Pinelands, and threatens to do considerably more damage. It is hypothesized that the reason for the invasion is at least in part a function of warmer extreme minimums. This rise in lowest minimum may also help facilitate cold-tolerance for non-invasive species, such as the bark beetle found in the western conifer forests of United States and Canada, meaning these bark beetles would be able to live throughout the winter season with an increase in cold tolerance (Bentz et al. 2010). This winter survival of species is enough to change an ecosystem.

Minimum temperatures affect agriculture as well. Hatfield et al. (2011) reports that plant respiration rates actually slow down as minimum temperatures increase above an optimum level; meaning that overall crop yield will be reduced. In another study, Hatfield and Prueger (2015) have shown that the effects of increased minimum temperatures have decreased the ability of maize to efficiently produce grain. The decreased crop yield due to these temperatures could have devastating effects on world hunger.

Finally, human and public health is also an important function of minimum temperatures, one example being the rise of heat waves in the hot summer months. A summer increase in the minimum temperatures may be indicative of greater heat stresses being placed on individuals or families without air conditioning at night, especially during heat waves. This detrimentally impacts the ability of sensitive populations to recover from previous daytime heat, as they are not able to cool down at night. Pollen season could also be affected as well. A study published by Zhang et al. (2015) shows that allergenic pollen season timing and levels in the US are partially associated with the number of Frost Free Days (FFD), where FFD is defined as the interval between the last frost day each spring and first frost day each fall. The rise of minimum temperatures in the fall and winter could possibly increase the FFD, which might affect pollen season length.

For more information, and some real analyzed data on the topic of minimum temperature extremes, the Office of the New Jersey State Climatologist has a short study on their website, specifically using COOP stations in New Jersey. Find it here!

As always, for more great articles on our changing climate, be sure to visit here!

References
Ayres, Matthew P., Sharon J. Martinson and Nicholas A. Friedenberg, 2011: Southern pine beetle ecology: populations within stands, Southern Pine Beetle II. General Technical Report., 140, 75-89.
Bentz, Barbara J., Jacques Regniere, Christopher J. Fettig, E. Matthew Hansen, Jane L. Hayes, Jefferey A. Hicke, Rick G. Kelsey, Jose F. Negron, and Steven J. Seybold, 2010: Climate Change and Bark Beetles of the Western United States and Canada:  Direct and Indirect Effects, BioScience, 60, 603-613.
Hatfield, Jerry L., Kenneth J. Boote, Bruce A. Kimball, Lewis H. Ziskz, Roberto C. Izaurralde, 2011: Climate Impacts on Agriculture: Implications for Crop Production, Publications from USDA-ARS / UNL Faculty. 1350.
Hatfield, Jerry L., John H. Prueger, 2015: Temperture extremes: Effect on plant growth and development, Weather and Climate Extremes, 10, 4-10.
Zhang, Yong, Leonard Bielroy, Zhongyuan Mi, Ting Cai, Alan Robock, and Panos Georgopoulous, 2015: Allergenic pollen season variations in the past two decades under changing climate in the United States, Global Change Biology, 21, 1581-1589.

©2018 Meteorologist Joey Fogarty