The rising incidence of allergic diseases is a popular topic these days. The WHO estimates that 300 million people currently have asthma and 250,000 people die annually. This increase in asthma prevalence and severity over recent decades presents a significant challenge to public health. Pollen is an important trigger of some types of asthma, and both pollen quantity and season depend on climate and weather variables. Over the same period as the global rise in asthma, there have been considerable increases in atmospheric carbon dioxide concentration and global average surface temperature. Greater concentrations of carbon dioxide and other greenhouse gases result in higher temperatures and may increase pollen quantity and induce longer pollen seasons. Ozone, particulates, vehicle emmissions, and other pollutants have risen also. Pollen allergenicity can also increase as a result of these changes in climate. Exposure in early life to a more allergenic environment may also provoke the development of other atopic conditions, such as eczema and allergic rhinitis. Although the causes of allergy and asthma is complex, the recent global rise in these problems could be an early health effect of climate change. The problem is likely to worsen in the future according to scientists.