Climate Connections
Making Sense of Seasonal Observations

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Many birds on this continent are migrating an average of 9 days earlier and breeding sooner than they did 30 years ago! (Photo: Fran Ludwig)
How Can a Changing Climate Affect Plants and Animals?

In the distant past, most climate changes occurred slowly, over many thousands of years. Plant and animal species adapted to new environments or moved elsewhere. But as Earth's climate changes more quickly, some species may not be able to react quickly enough to thrive or survive.

Some animals — and even plants — can shift their ranges as temperatures continue to warm. They may move further north or into higher elevations where it’s cooler. Some can also tolerate a wider range of conditions (e.g., temperatures) than others. Those that can't are at greater risk.

But there's a catch. First, a species may not find another suitable habitat to move to. Why? Competition for resources, new predators, and physical barriers (e.g., roads) are just a few of the problems they could face. Also, all components of an ecosystem don’t respond in the same way to a warming climate. Because living things are interdependent with one another and their environment, a changing climate can have a ripple effect. (See box, below.)

Next: What Do Scientists Know About Climate Change? >>

The Challenge of Change for Living Things

Imagine these scenarios, which are based on actual scientific research.

  • A species of butterfly is adapted to emerge from its chrysalis just as the wildflower it depends on for nectar blooms. But as the climate warms, the flower may bloom long before the adult emerges.

  • Wintering monarch butterflies need dry wings in order to withstand cold temperatures. But the rainfall and storms in the region where they overwinter are predicted to increase as the climate continues to change. This, combined with other risks related to a warming climate, could affect the survival of the entire Eastern Monarch population.

  • The climate warms in some low-elevation regions where robins winter. Come spring, the robins start arriving in their mountainous breeding grounds an average of two weeks earlier than in the past. But there they find loads of snow remaining, and so they risk starvation.

  • Some birds migrate short distances each year as temperatures warm and food sources are abundant. As the climate warms, those species arrive on breeding grounds even earlier. But other birds use day length as a trigger to migrate. They fly long-distances to breeding grounds only to encounter heavy competition for food and nesting sites from the "early birds."

  • Many insect-eating songbirds migrate north from the neotropics in the spring. Their cue to migrate is day length. Their migration coincides with the leafing out of trees. Why? The migrating birds rely on caterpillars that eat the trees' young leaves. But trees leaf out in response to warm temperatures, so if they leaf out early, songbirds could arrive too late to feast on a main food source.

  • Gray whales are staying longer in the Arctic feeding grounds. The expanding ice cover is their cue to migrate, but with less ice and more open water, they stay to feed. As a result, many pregnant females do not reach the safe, warm birthing lagoons of Mexico before their babies are born. Gray whale babies born in the open sea have difficulty surviving and the gray whale population, once endangered, suffers a decline.

  • Caterpillars of a type of moth feed mainly on leaves from one tree species. With warmer springs, the caterpillars now hatch 2 to 3 weeks before the leaves emerge. The caterpillars can't survive more than a few days without food. What's more, a bird species that depends on the caterpillars to feed its young also loses its food source . . . and so on, up the food chain.


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