News•March 27, 2013

Climate Change is Increasing Seasonal Allergies

Each spring, blooming flowers and trees are a hallmark of the season’s warmer weather. But their pollen is aggravating for people suffering from seasonal allergies, and can be downright dangerous for people with asthma. In fact, around this time each year, web searches soar for things like “pollen,” “allergies,” and “Claritin.” And this year is no different. During the past few weeks, Google web searches for “pollen” have been rising, as illustrated in the interactive graphic below.

Click here for a high resolution static version

Allergy related Google search trends show how the timing of allergy season varies from year to year, depending largely on spring weather. Years with mild winters, like 2007, 2010, and 2012, saw searches for “pollen” peak earlier and higher than other years. Those big spikes can give us a glimpse of what allergies will be like in the future. As climate change brings spring earlier and earlier, we can expect that seasonal allergies — and the web searches they inspire — will only worsen.

In fact, there is evidence that warmer temperatures have already begun to affect pollen seasons, causing them to start earlier and last longer. A 2011 study from the U.S. Department of Agriculture showed that since 1995, the ragweed pollen season has grown longer — as much as 13-to-27 days longer — across much of the U.S. In the spring, pollen from flowering trees causes most allergies, and already trees are blooming days, or even weeks, earlier now than they did several decades ago.

Not every year will have an earlier pollen season than the one before, since the variability of weather patterns will bring surprises, such as this year’s ongoing cold and snowy March. That is clear when you look at Google trends. In 2012, January-March temperatures were the warmest on record for the U.S., and the allergy season hit hard and early. By comparison, this year, the pollen season has been delayed. But studies looking over decades of plant growth and pollen trends show that, overall, the trend will be toward earlier and longer pollen seasons.

And climate models predicts that over the next several decades spring will continue to creep forward, particularly in northern regions of the U.S., which are likely to see more dramatic winter and spring warming trends, which will extend the length of pollen seasons even more.

And it’s not just the warming temperatures and earlier onset of spring that are affecting pollen production. All the CO2 being added to the atmosphere by burning fossil fuels is also compounding the problem. CO2 helps stimulate plant growth, and several recent studies have shown that when plants are exposed to more CO2, they tend to produce more pollen.

In combination, more pollen and longer pollen seasons are more than just an inconvenience. According to the National Climate Assessment, the pollen-related affects of climate change can “diminish productive work and school days.” And for anyone already suffering from seasonal allergies, their misery doesn't need any more company.