t
oucans screech. Howler monkeys howl.
Insects hum. One sound is missing from this cloud forest in Costa Rica, though. T ere’s no chorus of croaking frogs. T at’s weird. Harlequin frogs have lived here
for thousands of years. Now, they’ve vanished. T e frogs’ disappearance is a warning. It’s a
sign that Earth’s climate is changing. Weather patterns are shiſt ing. Climate change changes environments. It can make places warmer or colder than they were in the past. It also can make them wetter or drier. T ese changes are usually slow. T ey
take place over a long period of time. Oſt en, the change is barely noticeable. Take what’s happening now, for example. Temperatures have risen 0.8°C in the past century. Earth is slightly warmer than it was 100 years ago. T at doesn’t seem like much of a warm-up.
Yet it’s enough to change habitats across the planet. And when habitats change, animals must, too. Some animals can’t survive the changes. So they move to find new habitats or even go extinct. Others thrive with the changes. T eir populations grow and spread out.
Predicting the Future Scientists are watching what’s happening to many of these animals. T ey call them predictor species. T at’s because they’re like an early warning system. T ey’re telling us that something in the environment is changing, even if we can’t feel it or see it yet. T ey’re warning us that other organisms could be aff ected soon, too. Scientists have already learned one thing.
Even a little warm-up can have a big impact. To see how, let’s take a closer look at some predictor species. See how the changing climate is changing them.
4 NATIONAL GEOGRAPHIC EXTREME EXPLORER
Fragile Frogs Our first stop is that cloud forest in Costa Rica. It’s not as wet as it used to be. Some streams have dried up. T at’s a problem for harlequin frogs. Like all amphibians, the frogs drink
and breathe through their skin. T ey need to keep their skin damp to be healthy. T ey need water to live. To survive, these frogs had
to find new, wet habitats. T ey hopped to other streams. T ey crowded together on wet rocks. Unfortunately, a killer lived in
some streams. It’s a deadly fungus. T is fungus attacks the frogs’ skin. It kills the frogs. Crowding made the fungus problem worse. It helped the fungus easily spread from frog to frog. Climate change set off this tragic chain of
events in the rain forest. It changed the frogs’ environment. T e frogs couldn’t change fast enough to survive.
Corals in Trouble T ings are changing in the ocean, too. Visit the Great Barrier Reef to see how. It’s famous for its colorful corals. Purple sea fans sway in water. Yellow and pink corals cover the seafloor. In some spots, though, the reef looks odd. T e corals are white. T ey’ve lost their color. T ese corals are dead or dying. T e color change is a warning. It tells
biologists that something has changed in the ocean. T e water has warmed as much as 1°C. It’s getting too hot for some corals to survive. T e water warm-up could soon aff ect other species, scientists predict. T at’s because many fish and other sea creatures live in reefs. If the corals die, they could lose their habitat.
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