· 90% of damage caused by rising temperatures
· Conclusions based on reports going back to 1970
Global warming is disrupting wildlife and the environment on every continent, according to an unprecedented study that reveals the extent to which climate change is already affecting the world's ecosystems.
Scientists examined published reports dating back to 1970 and found that at least 90% of environmental damage and disruption around the world could be explained by rising temperatures driven by human activity.
Big falls in Antarctic penguin populations, fewer fish in African lakes, shifts in American river flows and earlier flowering and bird migrations in Europe are all likely to be driven by global warming, the study found.
The team of experts, including members of the UN's intergovernmental panel on climate change (IPCC) from America, Europe, Australia and China, is the first to formally link some of the most dramatic changes to the world's wildlife and habitats with human-induced climate change.
In the study, which appears in the journal Nature, researchers analysed reports highlighting changes in populations or behaviour of 28,800 animal and plant species. They examined a further 829 reports that focused on different environmental effects, including surging rivers, retreating glaciers and shifting forests, across the seven continents.
To work out how much - or if at all - global warming played a role, the scientists next checked historical records to see what impact natural variations in local climate, deforestation and changes in land use might have on the ecosystems and species that live there.
In 90% of cases the shifts in wildlife behaviour and populations could only be explained by global warming, while 95% of environmental changes, such as melting permafrost, retreating glaciers and changes in river flows were consistent with rising temperatures.
"When we look at all these impacts together, it is clear they are across continents and endemic. We're getting a sense that climate change is already changing the way the world works," said lead author Cynthia Rosenzweig, head of the climate impacts group at Nasa's Goddard Institute for Space Studies in New York.
Most of the reports examined by the team were published between 1970 and 2004, during which time global average temperatures rose by around 0.6C. The latest report from the IPCC suggests the world is likely to warm between 2C and 6C by the end of the century.
"When you look at a map of the world and see where these changes are already happening, and how many species and systems are already responding to climate change after only a 0.6C rise, it just heightens our concerns for the future," Rosenzweig said. "It's clear we have to adapt to climate change as well as try to mitigate it. It's real and it's happening now."
A large number of the studies included in the team's analysis reveal stark changes in water availability as the world gets warmer. In many regions snow and ice melts earlier in the year, driving up spring water levels in rivers and lakes, with droughts following in the summer. Understanding shifts in water availability will have a big impact on water management and be critical to securing supplies, the scientists say.
By collecting disparate reports on wildlife and ecosystems, it is possible to see how disruption to one part of the environment has knock-on effects elsewhere. In one study rising temperatures caused sea ice in Antarctica to vanish, prompting an 85% fall in the krill population. A separate study found that the population of Emperor penguins, which feed on krill in the same region, had also fallen by 50% during one warm winter.
A loss of krill, also a dietary staple for whales and seals, was cited as a factor in recent accounts of cannibalism among polar bears in the Arctic. In 2006 Steven Amstrup, a world expert in polar bears at the US Geological Society, investigated three cases of the animals preying on one another in the southern Beaufort sea. A lack of their usual prey may have prompted the bears to turn on each other.
Other reports show how the early arrival of spring in Europe has far-reaching effects down the food chain. The warmer weather causes trees to unfurl their leaves earlier, which causes a rise in leaf-eating grub numbers sooner in the year. Blue tits that feed on the grubs have largely adapted to the shift, by giving birth to their young two weeks earlier.
"It was a real challenge to separate the influence of human-caused temperature increases from natural climate variations or other confounding factors, such as land-use changes or pollution," said David Karoly, a co-author based at Melbourne University in Australia.