Climate change alone is expected to threaten with extinction approximately one quarter or more of all species on land by the year 2050, surpassing even habitat loss as the biggest threat to life on land. Species in the oceans and in fresh water are also at great risk from climate change, especially those that live in ecosystems like coral reefs that are highly sensitive to warming temperatures, but the full extent of that risk has not yet been calculated.

Climate change is a threat because species have evolved to live within certain temperature ranges, and when these are exceeded and a species cannot adapt to the new temperatures, or when the other species it depends on to live cannot adapt, for example its food supply, its survival is threatened.

The IPCC has predicted that by 2100, assuming that current trends in burning fossil fuels continue, the surface of the Earth will warm on average by as much as 6 degrees Celsius (around 11 degrees Fahrenheit) or more. It is not possible to predict how most species, including our own, and how most ecosystems, will respond to such extreme warming, but the effects are likely to be catastrophic.

“Climate change is already having an impact on biodiversity, and is projected to become a progressively more significant threat in the coming decades. Loss of Arctic sea ice threatens biodiversity across an entire biome and beyond. The related pressure of ocean acidification, resulting from higher concentrations of carbon dioxide in the atmosphere, is also already being observed.
Ecosystems are already showing negative impacts under current levels of climate change … which is modest compared to future projected changes…. In addition to warming temperatures, more frequent extreme weather events and changing patterns of rainfall and drought can be expected to have significant impacts on biodiversity.”

Greenhouse gases, such as carbon dioxide, absorb heat from sunlight, preventing it from escaping back into space. As the level of greenhouse gases rises, so will temperatures. The Intergovernmental Panel on Climate Change predicts that by 2100, temperatures may rise as much as 6 degrees Celsius (11 degrees Fahrenheit). Though changes in climate have happened in the past, the rapid severity of this change will directly affect ecosystems and biodiversity.

The polar regions are already affected by rising temperatures. Diminishing ice packs have reduced the habitats of polar bears, penguins, puffins and other Arctic creatures. As the ice melts, it will cause a rise in sea level, which will affect and perhaps destroy ecosystems on coast lines. Changes in temperatures will also cause shifts in mating cycles, especially for migratory animals that rely on changing seasons to indicate their migration and reproductive timing.

Rising sea levels will also cause changes to sea temperature and perhaps even currents. Such changes would have a strong impact on zooplankton, an essential part of the food chain in the ocean. Shifts in where plankton are found and how big their populations are could upset the biodiversity in the ocean. Whales especially could be affected as many species require mass amounts of plankton to survive. In addition, increased carbon dioxide causes acidification of the ocean, affecting creatures and plants that are sensitive to pH imbalances.

As biodiversity decreases, there will be far-reaching effects. Disruptions in the food chain may greatly affect not only ecosystems but also humanity’s ability to feed an ever-growing population. For example, losing diverse insect species will decrease plant pollination. There is also a risk of decreased ability to produce medicine as key plants are lost to extinction. Biodiversity also protects against natural disasters, such as grasses that have evolved specifically to resist the spread of wildfires.