The known impact of climate change
Documented evidence of the biological impact of climate change
How can we be sure that a change in the environment is actually the result of climate change?
Because the Earth’s climate cannot be deliberately altered, the best evidence is generally association – when the observed impact corresponds to a period of climate change. This association can be strengthened if:
- other possible causes can be eliminated
- a plausible mechanism exists to explain the link to the climate.
Climate-linked changes have been seen in a wide range of biological systems – from the blooming of spring flowers to the nest building of birds. Some of the best-documented cases use data collected over many years, often not for climate change purposes:
Drosophila robusta (fruit fly)
Analysis of data going back to 1946 shows that the distribution of ‘warm’ and ‘cool’ genotypes in the north-east of the USA is changing – genotype frequencies in New York populations in 2002 were close to those seen in Missouri, nearly 1,000 miles (1,600 km) further south, in 1946.
Sachem skipper butterfly
This butterfly (Atalopedes campestris) has spread from California to Washington state (420 miles) in just 35 years – in one particularly warm year it moved 75 miles northward.
This Californian bay is a small region where northern species of fish (which are found up to Alaska) and southern species (seen in Mexico) overlap. A comparison of sites surveyed in 1931 and in the 1990s found that numbers of nearly all southern species had increased while those of nearly all northern species had decreased.
A study of 171 forest plant species at different elevations (0 to 2,600 metres) in western Europe found that the optimum altitude of species had risen on average by 29 metres per decade during the past century.
An analysis of 34,500 dated Norwegian herbarium records for 1940–2006 revealed an average delay in fruiting of 12.9 days since 1980.
Studies of sites such as Monterey Bay, where communities overlap, have found that cold-adapted species are always in decline while warm-adapted organisms are always on the increase. Such shifts have been seen in 294 species, right across the globe, in animals as diverse as ocean fish, tropical birds and European butterflies.Lead image:
Andy Reago and Chrissy McClarren/Flickr CC BY
- Biological impacts of climate change (2005) [PDF]
- National Wildlife Federation: The Gardener’s Guide to Global Warming [PDF]
- Climate-related change in an intertidal community over short and long time scales (1999) [PDF]
- A significant upward shift in plant species optimum elevation during the 20th century (2008)
- Danish Climate Centre: How to calibrate bio-indicators and assess changes in climate and in biodiversity [PDF]