Climate Change, Pollen and Allergy Season
October 14, 2014; 6:41 AM
Pollen grains are used by plants for fertilization and reproduction, but in humans, pollen can cause respiratory problems like hay fever and asthma. Most of the pollen that triggers allergic reactions comes from trees, weeds and grasses. One single ragweed plant can produce one million pollen grains in a day and ragweed pollen has been reported to travel up to 400 miles out at sea and two miles up in the air! Rising temperatures and changes in precipitation can affect the growth and distribution of allergenic plants and pollen distribution worldwide. Climate change can impact human respiratory health both directly by promoting or aggravating respiratory diseases and indirectly by increasing the exposure to triggers or risk factors for respiratory disease. The National Climate Assessment and recent scientific publications summarize the effects of climate change on pollen and allergenic plants:
Warmer air temperatures and a higher number of frost-free days have advanced the start time of plant growth and the start time of pollen production, leading to an earlier and longer pollen season. For example, ragweed pollen season has increased 13-27 days at latitudes above 44°N in North America.
Increased levels of carbon dioxide have led to enhanced photosynthesis, making pollen-producing plants bigger. Larger plants have been reported to produce more pollen, which contains a greater amount of allergenic proteins.
Warming temperatures have contributed to a change in the spatial distribution of pollen. Ragweed, a rare type of pollen for the United Kingdom, has been reported at record levels for the first time in the East Midlands as of September of 2014. Ragweed doesn't survive in this area because of the cool climate, but milder autumns and delays in the first frost may be changing this.
Earlier start and peak of the pollen season has been more pronounced in species that flower early in the year. Plants in urban areas have been reported to flower earlier than those in rural areas, with earlier pollination of about two to four days.
The number of people suffering from asthma is growing in the United States and worldwide. Asthma prevalence has increased in the United States from 7.3 percent in 2001 to 8.4 percent in 2010. The scientific community believes that climate change could be a plausible contributor to the rise in asthma.
The following figure shows the increased duration of ragweed pollen season, courtesy of the National Climate Assessment.