Climate

Climate is the usual pattern of weather in a place over a long time. Weather is what is happening outside today. Climate is what the weather is usually like across many years. Scientists figure out a region's climate by studying the weather there for at least 30 years. A single rainy day does not change a desert's climate. A single hot week does not change the climate of Alaska.

Climate depends on a few main things. The first is how close a place is to the equator. Places near the equator get sunlight that hits the ground almost straight on, so they stay warm all year. Places near the poles get sunlight at a low angle, so the same amount of sunlight is spread over more ground. That is why the Arctic is cold and the Amazon is hot.

Height above sea level matters too. The higher you go, the colder the air gets. Mountains can have snow on top even when the valleys below are warm. Mount Kilimanjaro sits almost on the equator, but its peak stays icy because it is more than 19,000 feet tall, about three and a half miles up.

Oceans shape climate as well. Water heats up and cools down slowly, so places near the coast usually have milder weather than places far inland. Ocean currents carry warm or cold water around the planet. The Gulf Stream brings warm water from the Caribbean across the Atlantic, which is why parts of Britain stay greener in winter than parts of Canada at the same latitude.

Scientists group climates into a few big types. Tropical climates near the equator are hot and wet. Dry climates, like the Sahara, get very little rain. Temperate climates have four clear seasons. Polar climates stay cold all year, with ice and short summers. Each climate type supports different plants and animals. Camels live in dry climates. Polar bears live in polar climates. Rainforests grow in tropical ones.

Climate is not fixed forever. Earth has gone through warm periods and ice ages over millions of years. During the last ice age, about 20,000 years ago, sheets of ice covered much of North America. Today, Earth's climate is changing again, this time because humans are adding gases to the air that trap heat. Scientists agree the planet is warming. They are still working out exactly how much each region will change, and how fast.