Species Extinction

CHANGING CLIMATES INCREASE the uncertainties of life for all organisms. A long-term warming trend would alter the distribution of life on the planet as colder habitats shrink and warmer ones expand. Some species would become more common, and others would become rarer. We cannot predict with any precision which species will become extinct—or when. Plants and animals that are highly adapted to already extreme (hot, cold, or dry) climates are most likely to be the first and most drastically affected.

We consider a species to be extinct once all known individuals of that type have died. Many interacting factors affect the survival of individual organisms, and therefore the persistence of their species. In general, extinction results when a species' requirements and abilities no longer match the resources and hazards in its environment. For animals, these factors include food, water, and shelter from predators and weather extremes. For plants, they include water and nutrients and the action of herbivores and pollinators. Sometimes a factor is critically important, like rainfall in a desert. It determines whether enough individuals will survive that a species can persist. If that “limiting factor” changes in some way, survival rates may rise or fall. If they fall far enough, extinction results. Climate is a major limiting factor for life on Earth. When it changes, life on Earth also changes. A continuing trend of global warming, cooling, or drying will lead to extinctions that might otherwise not occur as soon. We still know little about the precise climate limits or thresholds of most species. Because it is also difficult to predict precisely what the climatic conditions will be like in any given place at any given time in the future, it is even harder to predict which species will become extinct as a direct result of climate change, and when it will happen. In addition, because species interact and rely on each other in many ways, climate change produces many sometimes indirect or complex effects among them. This adds further layers of uncertainty to predictions about extinctions. For the most part, we can make only very general predictions about climate change and extinctions. This uncertainty leads many climate scientists and ecologists to conclude that humans would be wise to avoid or resist contributing to the uncertain risks of climate change whenever it lies within our power to do so.