When considering global warming’s impacts on species, it is essential to look at how entire ecosystems are affected as species interact and climate change interacts with other human-induced stresses. It is clear that a changing climate will have, and is already having, profound effects on the natural world. On every continent, plant and animal populations are changing in ways that reverberate through entire ecosystems and impact humanity in various ways.
Healthy ecosystems provide humanity with many valuable resources and services, ranging from food (such as fish) to coastal protection (sea ice provides a barrier that limits coastal erosion). Climate change has the potential to severely degrade or even completely eliminate certain types of arctic, alpine, and coastal ecosystems.
For example, as warming reduces sea ice extent, the amount of algae that grows on the underside of the sea ice is also reduced. These algae are the main food source for krill and other tiny marine creatures that are the base of the marine food chain. Reductions in their populations in turn affect fish, seals, whales, penguins (in Antarctica), and polar bears (in the Arctic).
In any ecosystem, some species can adapt more quickly than others. For example, many bird species have recently shifted their ranges towards the poles, so the kinds of birds we see in our garden have changed. However, the plants these birds depend upon for food and habitat cannot move as quickly as the birds, and ecosystems are thus torn apart, bringing about an increased risk of population declines and species extinctions.