CO2 levels affect the length of the pollen season and the characteristics of the plans themselves, with some species shown to increase their pollen-producing capacity and even their toxicity. {5.6}

Ecology and Ecosystems

For at least the past 40 years, many species have been and are currently shifting the phenology (timing) of spring events in concert with warming temperatures. Examining 542 species of plants and 19 of animals, a large phenology (e.g., timing of blooming, egg laying, migrating) study of 21 European countries for the last 30 years of the 20th century found a total of 78% of species were shifting their spring phenology earlier and only 3% were shifting later. When combining all species showing change along with those in the same areas not showing a measurable change, species on average were found to change ~2.5 days per decade. Throughout the Northern Hemisphere the similar change was reported to be 2.3 days per decade. The magnitude of the change occurring only in those species showing a change on average was ~4 to ~5 days a decade. {5.7}

As the climate has warmed many species have been and are continuing to track this warming by shifting their ranges into areas that before warming were less hospitable due to cooler temperatures. Terrestrial species are moving toward the poles and up in elevation, while marine species are generally moving down to deeper waters. The average shift over many types of terrestrial species around the globe was about 6 km per decade. {5.7}

Historically, extinctions of most species have been found to be due to various stresses, such as land-use change, invasive species, and hunting, but now the vulnerability of many species to extinction is enhanced with the added stress placed upon them by climate change. Those species more prone to becoming in danger of extinction include those that have a maximum dispersal distance shorter than the distance to the closest “cool refuge” and those that are not a good colonizer and hence fail to become established in these cooler locations. {5.7}

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