Guest essay by Eric Worrall
Warmer winters are now a bad thing…
Winter crops may cause unintended warming, study says
A new study shows that fields with crop cover showed significantly warmer winter temperatures than fields with no cover or just short stubble.
Author: Cory Reppenhagen
Published: 11:02 AM MST January 5, 2019
Updated: 6:54 PM MST January 5, 2019
Farmers grow crops or leave dying vegetation in their fields over the winter. A new study from the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, shows they may be causing unintended climate warming.
“When they stick out above the snow, they can warm winter temperatures,” Danica Lombardozzi, a plant ecophysiologist with NCAR, said.
Lombardozzi headed this new study that showed warming caused by crop cover absorbing high amounts of sunlight. She used computer modeling to find that fields with crop cover showed significantly warmer winter temperatures than fields with no cover or just short stubble.
“On average, that increased air temperature by 5.5 degrees Fahrenheit or 3 degrees Celsius. A significant temperature rise,” Lombardozzi said.
The abstract of the study;
Cover Crops May Cause Winter Warming in Snow‐Covered Regions
D. L. Lombardozzi G. B. Bonan W. Wieder A. S. Grandy C. Morris D. L. Lawrence
First published: 12 September 2018
Cover crops, grown between cash crops when soil is fallow, are a management strategy that may help mitigate climate change. The biogeochemical effects of cover crops are well documented, as they provide numerous localized benefits to farmers. We test potential biogeophysical climate impacts of idealized cover crop scenarios by assuming that cover crops are planted offseason in all crop regions throughout North America. Our results suggest that planting cover crops increases wintertime temperature up to 3 °C in central North America by decreasing albedo in regions with variable snowpack. Cover crops with higher leaf area indices increase temperature more by decreasing broadband albedo, while decreasing cover crop height helped to mitigate the temperature increase as the shorter height was more frequently buried by snow. Thus, climate mitigation potential must consider the biogeophysical impacts of planting cover crops, and varietal selection can minimize winter warming.
Plain Language Summary
Planting cover crops is an agricultural management technique in which crops are grown in between cash crop seasons when the soil would otherwise be fallow. Cover crops provide many local benefits to farmers and can increase carbon storage in soils. In this study, we test how planting cover crops in all agricultural regions in North America can change wintertime temperatures. Model simulations suggest that cover crops can warm winter temperatures up to 3 °C in regions with variable winter snowpack, such as central North America. Planting cover crop varieties that are less leafy or get buried under the variable snowpack can help to minimize winter warming. Our study suggests that the climate mitigation potential of cover crops may be offset in these regions if cover crop varieties are not carefully selected.
My question – why didn’t someone try to get some field measurements? I mean you can understand in some cases it would be difficult to set up a field study, but in this case taking field measurements would have been trivial; ask farmers for their temperature data. A polite request to farmers interested in the study not to plant some of their monitored fields with winter cover crops would have completely avoided the need to rely on models.