Climate Change: Food & Weeds

Climate Change: Food & Weeds

by Renée Harber

Farmers have always been at the mercy of the weather, but in a world of extremes, where drought, heat-waves, and monstrous thunderstorms have become so much more common, growing a profitable crop will be just that much more challenging. This is where it hits the rest of us too. It’s that old supply and demand thing. When the crops die or produce less food, or it costs more money to grow that food, then the price at the grocery store will go up accordingly.

The effects of climate change on food crops are expected to vary depending on the specific crop, and on the interplay between temperature, CO2 and water availability. In some cases, the crop might actually benefit from the warmer temperatures, and higher CO2 concentrations, as long as there is adequate water. But, that’s a big if. Water is expected to be in shorter supply than it already is. And, what grows well in drought conditions?

Weeds, of course, are some of nature’s best opportunists. They are what they are simply because of their ability to capitalize on a given situation, however inhospitable that situation happens to be. They tolerate extremes of drought that would cause the average zucchini plant to dissolve into dust. They reproduce so quickly and abundantly that they put rabbits to shame. In the plant world, weeds are overbearing, impertinent…downright obnoxious. So, given their propensity for taking advantage of the situation, what might they do in a drier, hotter, more extreme climate?

Scientists have found some interesting, if not entirely surprising results. It turns out that weeds not only benefit from higher temperatures, but from higher CO2 concentrations as well. A researcher with the USDA measured the growth of Canada Thistle under current atmospheric CO2 levels versus levels from the early 1900s. Those plants grown in today’s CO2 concentrations were twice the size of those grown under 1900 conditions. And, what can we expect with the CO2 levels predicted to occur in another 50 years? Well, the thistles toughened up to the point where they barely responded to herbicide (RoundUp) sprays.

In addition to tougher, faster growing weeds, we might also need to contend with the northward expansion of invasive weed species. The spread of invasive weeds is never a positive, but it’s particularly ominous when one compares farming in warmer regions of the US with say the mid-west. Studies show that soybean farmers in the southern US lose on average about 64% of their crop due to weeds, while northern farmers lose only about 22%. Such a significant further reduction in yield would be a big loss to our food system, which is dependent on soybeans for oil and animal feed, as well as for the tofu, soy milk and edamame that many of us enjoy.

In general, it looks like weeds will be even more competitive in a warmer world!

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