The prevalence of allergy in the world is increasing. While there are a number of factors involved, including the Hygiene Hypothesis, one appears to be climate change. As global temperature and CO2 levels rise, plant pollination cycles have become longer and more intense, with record pollen counts becoming routine. This was seen in the U.S. where record temperatures went hand-in-hand with record pollen counts, and with that, record allergy suffering.
Besides expanding the pollen season, increasing temperatures also change the botanic landscape, increasing the distribution of allergenic plants across a wider geographic area. Ragweed was fairly uncommon in Europe until recently when it experienced significant growth and now causes severe pollen counts in countries such as the Ukraine.
While warm temperatures and high CO2 are ideal growing conditions for all plants, allergenic plants, such as grasses and weeds, are the fastest growing and most adaptable so they will receive the most benefit. The success of these plants will mean increased symptoms among those living with allergies.
Besides plants, the warming climate will also have an impact on the distribution of insects, especially allergenic ones such as wasps and fire ants. With the extended warm seasons, wasps are coming out earlier and staying out longer, increasing the chances that allergic patients will encounter them. In addition, the distribution of fire ants appeared to be limited to the southern U.S. due to the freezing of the ground in the northern states. However, as the country gradually warms, less and less of this ground will experience extensive freezing, clearing the way for their upward expansion.
Since climate change is a very complex topic with uncertain strategies for prevention and improvement, it is difficult to make conclusive statements on this topic. However, the patterns that are emerging suggest there is a significant relationship, which means more people will likely become allergy sufferers seeking treatment in the future.