Earths Climate

LIVING PLANET

Our planet is a small oasis of life in the vastness of space. There may be others in the universe, but this is the only one we know about. Earth is close enough to the Sun to stop the oceans from freezing solid. A force of attraction called gravity holds on to the planet's atmosphere, and this provides living things with vital gases. It also acts like an insulating blanket, keeping temperatures within the limits that allow life to survive.

Earth is a unique planet. It is the only one in the Solar System that has both an atmosphere and oceans of water, and these have created ideal conditions for life to evolve and flourish. Currents in the atmosphere and oceans carry heat and moisture around the globe, so life can exist almost everywhere. These currents also create the weather. This changes daily, but in predictable patterns. The pattern of weather in a particular place is its climate. Climates vary slowly over time, forcing life to adapt to new conditions, but recently the rate of climate change has sped up.

Tropics face Sun all year round

North Pole

South faces Sun in southern summer

TILTED EARTH

The Sun shines directly on the tropics around the Equator, with a concentrated energy that creates tropical climates. Sunlight strikes the poles at an angle, dispersing its energy and allowing ice sheets to form. The spinning Earth is tilted on its axis, so as it orbits the Sun, the Sun's rays heat the north more intensely during the northern summer, and the south more intensely during the northern winter. It takes a year for Earth to orbit the Sun, creating annual seasons.

North Pole

BARREN DESERT

Liquid water is vital to living things, so regions where any water is either permanently frozen or is dried up by the Sun are lifeless deserts. Plants may be able to grow in places where there are reserves of liquid water below the surface, but much of the landscape is bare rock and sand. In a hot desert like this one in Israel, a slight rise in average temperature could wipe out all traces of life.

TEEMING WITH LIFE

In regions where the climate is warm and wet, living things can grow and multiply to form rich ecosystems like this rainforest. A tangle of trees and other plants provide food for a huge variety of insects and other animals. Yet they have all evolved to flourish in the conditions created by a particular type of climate, and many may not be able to survive rapid climate change.

SWIRLING CURRENTS

Intense sunlight in the tropics generates warm air currents that flow toward the poles in a series of rising and sinking"cells/"transferring heat to areas where solar heating is less intense. This cools the tropics and warms the temperate and polar regions, giving the planet a more even climate. Winds and weather systems driven by high-level air currents also carry moisture from the oceans over the continents, where it falls as rain or snow. This provides the vital water that allows life to flourish on land, from the Equator to the fringes of the polar ice. Variations in temperature and rainfall create a variety of climate zones such as deserts and rainforests, which can be recognized by both their climates and their wildlife.

High-level jet streams blow east

Earth's spin makes temperate winds swerve east

Sinking dry air creates deserts

High-level jet streams blow east

Earth spins toward the east

Earth's spin makes temperate winds swerve east

Sinking dry air creates deserts

Atmospheric cell

Rising warm, moist air near the Equator causes rain over the tropics

Earth's spin makes tropical winds swerve west

CHANGING CLIMATES

For most of human history, the world's climates have been unusually stable, enabling civilizations to rise and prosper. But climates are changing. Polar ice is melting, temperate regions are suffering more heatwaves and severe storms, and the tropics seem to be getting drier. Climate scientists working at research stations like this one in Antarctica are certain that the world is getting warmer.

Earth spins toward the east

Moving weather systems transfer water from the oceans to the continents

Atmospheric cell

Rising warm, moist air near the Equator causes rain over the tropics

Earth's spin makes tropical winds swerve west

WARMING WORLD

Global average temperatures started rising in about 1900. They have risen and fallen many times since then, but the trend has crept upward—slowly at first, but more rapidly since the 1970s. The rise in temperature roughly matches the rise of modern industry, the growth of huge cities, and the increasing quantities of fuel such as coal and oil that we burn to provide energy for heating, electrical power, and transportation.

SVANTE ARRHENIUS

In the 1890s Swedish chemist Svante Arrhenius decided that past ice ages might have been caused by fewer volcanic eruptions pumping gases such as carbon dioxide into the atmosphere. These gases retain heat, so reducing them would make Earth cool down. He then wondered what would happen if intense industrial activity produced more of these gases by burning fuels such as coal. He realized that it would make the world warm up—and so discovered the factor that linked industrialization and fuel use with changing global temperatures. He was not to know that, within a century, this process would start to have a dramatic effect on world climate.

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