A climate change may lengthen the UK pollen season and potentially make pollen concentrations higher. It’s possible that climate change can lead to changes in the strength of pollen. The UK is also facing a threat from changes in the geographical distribution of allergenic plants, due to climate change, with invasive species such as ambrosia being on the watch list. A single ragweed plant can produce a billion grains of pollen per season and its pollen causes strong allergic reactions.