Veggie farmers lower the surface temperature, but they’re not a climate cure-all

Posted at 3:17 PM, Jul 02, 2019
and last updated 2019-07-02 17:17:51-04

Your mom may have told you to eat your veggies because they are good for you, apparently they are good for our climate in the short term too.

A new study in Tuesday’s Global Change Biology finds that irrigated farms in the Central Sands region of Wisconsin that grow vegetables, significantly cool the local climate. That’s compared to rain-fed farms and forests that are nearby.

Near surface maximum temperatures on these farms were cooler by one to three degrees Fahrenheit on average, while increasing minimum temperatures up to four degrees Fahrenheit. Daily, the irrigated farms see a three to seven degree smaller range in temperatures compared to other land use. That’s consistent throughout the year.

With an increasingly warmer world, lower temperatures may sound like good news for farms, but its tempered by the fact that these farms also have generally higher minimum temperatures, compared to forest areas and rain fed farms. Soil on these farms can hold heat that is released at night, slightly raising the minimum temperature.

This study is the first to find a connection between irrigated farms in the Midwest and an altered climate. A temperature difference has been shown in drier regions, like in California, but it wasn’t clear if this would be true for more humid climates like Wisconsin’s.

Scientists figured this out by installing temperature and humidity sensors throughout a 37 mile part of the region that is east of the Wisconsin river and encompasses 1.75 million acres in the state. The scientists took measurements for 32 months between 2014 and 2016.

The scientists think these farms were cooler because the water that evaporates through the crops acts a bit like how your sweat can cool you down.

These lower temperatures can impact heat sensitive plants and pests. The temperature difference should be taken into account for future forecasts as this difference is often overlooked and that might be particularly important in this region that has seen a rapid expansion of irrigated agriculture.

Irrigation may be having a positive impact in the short term, but in light of the climate crisis, the cooling probably won’t be enough to compete with the predicted regional warming trend. In other words, farmers shouldn’t think they can plant their way out of the climate crisis by irrigating vegetables.

“Farmers in irrigated regions may experience more abrupt temperature increases that will cause them to have to adapt more quickly than other groups who are already coping with a warming climate,” says Christopher Kucharik. Kucharik works with the Nelson Institute and the UW-Madison agronomy department.”It’s that timeframe in which people have time to adapt that concerns me.”

If greenhouse gas emissions continue to increase at a high rate, climate models predict that the average surface temperature could increase 4.7-8.6º F above 1986–2005 levels by the end of this century.

Irrigated farming generates greenhouse gases like any kind of farming does. Agriculture and forestry together contribute about 9.4% of US greenhouse gas emissions, as of 2016. That doesn’t make it the biggest sector to add to the climate crisis, industry and transportation are the biggest greenhouse gas generators at 29.1% and 28.5% respectively, but agriculture is an energy intense sector of the economy as it accounts for 1% of US production, but emits 10% of US greenhouse gases in 2016, according to the US Department of Agriculture.

A lower surface temperature due to irrigation may also give farmers the wrong impression that they should not be adapting their farming practices to account for climate change. Earlier studies have shown that happens when farmers don’t feel the extreme highs and lows.

These are aspects of agriculture that will likely be mentioned in August when the next report is due out from the IPCC, or Intergovernmental Panel on Climate Change, the United Nations body for assessing the science related to climate change.