Climate change is already affecting birds in diverse ways

The Earth is undergoing profound changes to its climate. There is little doubt that this results from human activities, mainly the burning of fossil fuels (). Climate change is expected to have far-reaching effects on the Earth’s natural systems. At the species level, climate change may affect distribution, abundance, behaviour and other factors, with different species affected in different ways (, , , , , , , ). Climate change is expected to act in combination with other threats, often making their impacts considerably worse. Furthermore, inappropriate or inadequately planned mitigation measures may also have detrimental impacts on biodiversity. For example, clearance of natural habitats to cultivate biofuels (as alternatives to fossil fuels) increasingly threatens birds and other biodiversity.

• The world's climate has changed significantly over recent decades, and larger changes are predicted
• There is strong evidence that climate change is impacting a wide range of organisms
• Climate change is already affecting birds in diverse ways
• Climate change is already documented as having impacted many bird species
• Climate change is driving poleward shifts in the distributions of species
• Seabirds are key indicators of the impact of climate change on the world’s oceans
• In Hawaii, climate change will increase the impact of disease
• Climate change is impacting the distribution, abundance and migration of Australian birds
• Tracking the impacts of climate change on European birds

Many species will suffer from range shifts and losses, and some will become extinct

While some species may benefit from climate change, much larger numbers are predicted to suffer. Modelling studies indicate that the ranges currently occupied by many species may become unsuitable for them as climate changes, with the climate space suitable for particular species likely to shift in latitude or altitude (, ), contract (, ), or even disappear. Species whose climate space disappears or both contracts and shifts substantially will be of particular concern (). Studies suggest that many species will not be able to keep up with their changing climate space. Both local and global extinctions are likely, even of species currently considered safe. The most susceptible species will be those with restricted ranges, bounded distributions (for example on mountain-tops, small islands or along coasts: ), specialised habitat requirements or poor dispersal abilities (). While bird species differ greatly in dispersal abilities, most are relatively mobile compared to other organisms—which will be impacted even more severely.

• Climate change may make habitats become unsuitable in large parts of the range of Worthen's Sparrow
• Climate change may force European species northwards
• In the Arctic tundra, climate change will cause dramatic losses in waterbird breeding habitat
• In southern Africa, the range of Cape Longclaw is predicted to retreat to upland areas
• In Europe, species with ranges that both contract and shift are likely to be most at risk
• Sea level rise poses a major threat to coastal ecosystems and the biota they support
• The biological traits of some bird species render them particularly vulnerable to climate change

The extent of warming will be critical

The size of the extinction crisis caused by climate change will be directly related to the degree of global warming (). A global average temperature rise of 2°C in the next century will almost certainly lead to numerous extinctions, but leave open some practical management options for the conservation of biodiversity. Temperature rises beyond this level are predicted to lead to catastrophic extinction rates, with few management options and a bleak future for both biodiversity and people.

• The number of montane endemic birds that go extinct in Australia depends on the degree of warming