Green Grass
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It's springtime, and the land is greening up across America, even on the high, cool plains of eastern Colorado. It might look nice, but it's a sign of trouble brewing on the prairie.. Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is The Weather Notebook.

A warmer climate appears to be helping some unwanted plants to grow at the expense of the native grasses that support thousands of cattle, and a lot of farmers, too. A new study by Colorado State University indicates that a warmer atmosphere is to blame, but it's apparently the milder nights, not the hotter days, that are causing the problem. The research team analyzed temperatures and plant growth at the Pawnee National Grasslands, about 100 miles northeast of Denver. They found that the average daytime highs there have gone up about two and a half degrees (Fahrenheit) since 1970. However, the nighttime lows have risen roughly five degrees. As a result, there's now a longer time between the last freeze and the first warm afternoon of spring. This gives a plants that don't need warm afternoons to get growing in the spring, a head start. So different plants are taking over the native grasses.

Most of these plains are covered by blue grama, a native grass that cattle fancy. But lately, the warmer spring nights appear to be giving a head start to competing plants that cattle don't eat, prairie pepperweed and Russian thistle. If blue grama continues to get pushed out with these warmer spring nights, it could spell trouble for cattle ranchers across the high plains.

Thanks today to contributing writer Bob Henson. Our show's Senior Editor is Jay Allison and our engineer is Sean Doucette. Thanks to Subaru and the national Science foundation.