Climate system

The Earth's climate system is a complex system made up of five important parts that work together: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (Earth's upper rocky layer), and the biosphere (living things). Climate is the average weather over many years, usually 30 years. It is shaped by many processes, like ocean currents and wind patterns. These currents and winds help move heat from warm tropical regions to cooler areas. Solar radiation is the main force that drives this movement.

The water cycle also plays a big role by moving energy through the climate system. Certain chemical elements, like carbon and nitrogen, are always moving between the different parts of the climate system. The climate can change because of natural reasons, such as changes in the Sun's intensity or volcanic eruptions, as well as human activities. One major change is caused by people burning fossil fuels. This increases greenhouse gases in the atmosphere and leads to climate change. While human activity also releases cooling aerosols, their effect is much smaller than that of greenhouse gases. These changes can be made even stronger by processes in the climate system.

Components

The Earth’s climate system has five main parts that work together. The atmosphere is the layer of air around our planet. It is made mostly of nitrogen, oxygen, and argon, with small amounts of gases like water vapor and carbon dioxide that help trap heat.

The hydrosphere includes all the water on Earth, mostly in oceans. These oceans hold a lot of heat and affect weather patterns. The cryosphere is where water is frozen, like in ice sheets, sea ice, and snow. The Earth’s crust—the land we live on—shapes wind and rain patterns. Finally, the biosphere includes all living things, which also play a role in the climate by trapping heat and water.

Flows of energy, water and elements

Energy and general circulation

The Earth gets energy from the Sun and a tiny bit from inside the planet and the Moon. The Earth sends energy back into space in two ways: by reflecting sunlight and by giving off a type of heat called infrared radiation. The balance between the energy coming in and going out decides if the Earth is warming or cooling.

More sunlight reaches areas near the equator than the poles. This difference in temperature makes air and water move around the world. Warm air rises, moves toward the poles, cools, and then sinks back down. The Earth's rotation pushes this moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This creates patterns in the wind and ocean currents.

Salt in ocean water makes it heavier, and this affects how the ocean moves. Currents in the ocean help carry heat from warm areas to cold areas. Wind also helps push ocean water. Salt in water changes when it freezes, and sometimes colder water from deep below comes up to the surface, cooling the air above.

Hydrological cycle

The water cycle shows how water moves between the Earth and the sky. Plants and sunlight turn water from oceans and lakes into vapor, leaving salt behind. This vapor falls back to Earth as rain. Some places get more rain than others. When water turns into vapor, it takes a lot of heat, and when it condenses into clouds and rain, it releases heat. This heat is an important source of energy for the atmosphere.

Biogeochemical cycles

Important elements for life keep moving through the Earth's systems. The carbon cycle is very important for climate because it affects gases in the air, like CO₂ and methane. Plants take in carbon dioxide from the air, and later, living things release it back. Volcanoes also release carbon dioxide from deep inside the Earth. Rain with carbon dioxide can slowly wear away rocks, and the minerals from these rocks end up in the sea, where they can become part of rocks again.

The nitrogen cycle shows how nitrogen moves. Nitrogen in the air is changed by tiny living things into a form that plants and animals can use. Human actions, like burning fossil fuels and using fertilizers, have changed how carbon and nitrogen move in nature.

Main article: Earth's energy budget
Main articles: Earth's Energy Imbalance, atmosphere, oceans, angular momentum, Monsoons, density, ocean circulation, thermohaline circulation, freezing point temperature, upwelling
Further information: latent heat
Main article: carbon cycle
Main articles: methane, photosynthesis, acidic, weathering, sedimentary rocks
Main article: nitrogen cycle
Further information: fixing nitrogen
Main articles: fossil fuels, fertilizers

Changes within the climate system

Main article: Climate change

Climate is always changing, from season to season and over longer times. These changes happen because parts of Earth's climate system, like the air, water, ice, land, and living things, affect each other. Sometimes, things outside the climate system, like changes in Earth's orbit, can also cause changes. When we talk about climate change, we usually mean changes that last for at least 30 years, like the current warming of the planet. These changes can cause effects, such as rising sea levels.

Parts of the climate system can change on their own. For example, pressure differences between places like the Azores and Iceland can shift weather patterns across the North Atlantic for many years. The ocean and atmosphere can work together to create patterns like El Niño, which can change weather worldwide for several years. Because the ocean is much bigger and can store more heat than the atmosphere, it can cause changes that last even longer.

External forces, like changes in the amount of energy from the Sun or human activities, can also change the climate. The Sun is the main source of energy for Earth's climate. Small changes in the Sun's energy can affect the climate over long periods. Greenhouse gases, such as carbon dioxide and methane, trap heat in the atmosphere. Human activities, like burning fossil fuels, have increased these gases, leading to more warming. Aerosols, tiny particles in the air, can either cool or warm the planet. Changes in how land is used, like cutting down forests, can also affect the climate.