Thursday, 24 July 2008
When we discuss the impacts of climate change, most people have visions of melting glaciers, polar bears, and shifting dunes. These are serious problems, to be sure, but they seem for the most part to be something that will happen to someone else, far away.
Few people consider effects that will hit much closer to home. Take weeds, for example.
Lewis Ziska, an ecologist with the U.S. Department of Agriculture, wanted to understand how weeds are affected by a warmer world. Short on funds to expand his research lab, he hit on an ingenious solution:
"Then it occurred to Ziska that the complaints made by residents of nearby Baltimore about summer in their city — the exhaust-laden air and the way in which buildings and pavement soak up solar energy to create an abnormally warm “heat island” — could be put to good use. When he checked, he found that in fact the temperatures in Baltimore run 3 to 4 degrees Fahrenheit warmer on average than those of the surrounding countryside, and the concentration of CO2 in the local atmosphere (440 to 450 p.p.m., or parts per million by volume) is well above the current global average. This, coincidentally, matched almost exactly what the panel on climate change predicted for the planet as a whole 30 to 50 years in the future in its “B2 scenario,” a middle-of-the-road projection that envisions continuing greenhouse gas increases but also some success in abatement programs."
Ziska collected soil with weed seeds from an organic farm and created identical growing beds on the farm, in a nearby suburb with moderately higher temperatures and CO2 levels, and in the high-temperature, high-CO2 heat island. Then he let the weeds grow. The results over the next five growing seasons were breathtaking.
In nearly every case, Ziska found that weeds benefit much more from increased CO2 concentrations than do agricultural crops and domesticated plants. In the high-CO2 plot, the weeds grew much faster and up to twice as large as the weeds on the farm. Many were more resistant to common herbicides. And when trees eventually began growing on the untended plots, the high-CO2 plot was dominated not by oak and maple, but by stubborn invasive species like ailanthus and mulberry.
What's more, the weeds produced more pollen in a high-CO2 environment. When Ziska grew ragweed at the CO2 concentrations predicted for the end of the century, they produced twice as much pollen as they do today, and of a form more likely to cause allergic reactions. Poison ivy grew faster and produced a more intense form of rash-inducing oil. This means that climate change is bad news if you're an allergy sufferer, if you're a farmer, or if you simply enjoy having a weed-free lawn or vegetable plot. The future may look a bit brighter if you manufacture herbicides or produce anti-allergy medications, but it looks there will be more losers than winners. There are, of course, many other implications to the rise of the weeds, which I'll leave as an exercise for the reader.
The growth of weeds in a warmer world is rarely discussed, and yet the potential impacts on people, farmers, corporations, and local ecosystems is huge. And this is only one of many interlocking impacts.
My team at Carbon Clear spends a lot of time helping companies understand how climate change can affect their business over the coming years and decades. We do this in part to help our clients prepare for the future. But we also look at these impacts to help people understand that greenhouse gas emissions can impose a high price - both at home and abroad. Faced with massive global change, early action to reduce greenhouse gas emissions is often the most sensible investment we can make.