If it seems to you allergy sufferers that you're reaching for Kleenex and hay fever pills earlier and earlier each spring to ward off sneezing fits, you may be right.
A panel of climate scientists and plant physiologists said Tuesday that higher temperatures and carbon dioxide levels are linked to longer and more intense pollen production.
"What we're seeing with additional warming and earlier springs is that the trees are flowering earlier and producing more pollen," said Lewis Ziska, a research plant physiologist with the U.S. Department of Agriculture.
There are three seasonal sources of pollen that trigger allergies: trees in the spring, grass and weeds in the summer and ragweed in the fall.
Ziska said increases in carbon dioxide levels since the early 1900s have probably doubled pollen production in ragweed, which he studies. The effects are even more pronounced in urban areas, he said.
Compared with rural areas, cities act as heat sinks -- they're 2 to 3 degrees warmer -- and contain about 20% more carbon dioxide.
"What we have found is the average ragweed in a city environment is producing about 10 times as much pollen as the average ragweed plant growing out in the country," Ziska said.
Also, in the last 15 to 20 years the average ragweed season has been longer, even in northern latitudes.
Ragweed plants growing in Southern Canada are now experiencing 21 more days of flowering than they were back in the 1990s, Ziska said.
Ziska and his fellow panelists were convened by the Union of Concerned Scientists to speak about warmer and earlier spring seasons.
Todd Sanford, a UCS climate scientist, said average temperatures in the U.S. have increased by about 1.5 degrees since record keeping began in the 1880s. More than 80% of that warming has occurred since 1980, he said.
"In the contiguous United States, spring has been warming faster than both summer and fall since the late 1800s," Sanford said. "Over the same time period, the month of March has warmed by just over 2 degrees Fahrenheit."
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