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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Climate system | 2/3 | https://en.wikipedia.org/wiki/Climate_system | reference | science, encyclopedia | 2026-05-05T14:48:37.926807+00:00 | kb-cron |
=== Energy and general circulation === The climate system receives energy from the Sun, and to a far lesser extent from the Earth's core, as well as tidal energy from the Moon. The Earth gives off energy to outer space in two forms: it directly reflects a part of the radiation of the Sun and it emits infra-red radiation as black-body radiation. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the total of incoming energy is greater than the outgoing energy, Earth's Energy Imbalance is positive and the climate system is warming. If more energy goes out, the energy imbalance is negative and Earth experiences cooling. More energy reaches the tropics than the polar regions and the subsequent temperature difference drives the global circulation of the atmosphere and oceans. Air rises when it warms, flows polewards and sinks again when it cools, returning to the equator. Due to the conservation of angular momentum, the Earth's rotation diverts the air to the right in the Northern Hemisphere and to the left in the Southern hemisphere, thus forming distinct atmospheric cells. Monsoons, seasonal changes in wind and precipitation that occur mostly in the tropics, form due to the fact that land masses heat up more easily than the ocean. The temperature difference induces a pressure difference between land and ocean, driving a steady wind. Ocean water that has more salt has a higher density and differences in density play an important role in ocean circulation. The thermohaline circulation transports heat from the tropics to the polar regions. Ocean circulation is further driven by the interaction with wind. The salt component also influences the freezing point temperature. Vertical movements can bring up colder water to the surface in a process called upwelling, which cools down the air above.
=== Hydrological cycle === The hydrological cycle or water cycle describes how it is constantly moved between the surface of the Earth and the atmosphere. Plants evapotranspirate and sunlight evaporates water from oceans and other water bodies, leaving behind salt and other minerals. The evaporated freshwater later rains back onto the surface. Precipitation and evaporation are not evenly distributed across the globe, with some regions such as the tropics having more rainfall than evaporation, and others having more evaporation than rainfall. The evaporation of water requires substantial quantities of energy, whereas a lot of heat is released during condensation. This latent heat is the primary source of energy in the atmosphere.
=== Biogeochemical cycles ===
Chemical elements, vital for life, are constantly cycled through the different components of the climate system. The carbon cycle is directly important for climate as it determines the concentrations of two important greenhouse gases in the atmosphere: CO2 and methane. In the fast part of the carbon cycle, plants take up carbon dioxide from the atmosphere using photosynthesis; this is later re-emitted by the breathing of living creatures. As part of the slow carbon cycle, volcanoes release CO2 by degassing, releasing carbon dioxide from the Earth's crust and mantle. As CO2 in the atmosphere makes rain a bit acidic, this rain can slowly dissolve some rocks, a process known as weathering. The minerals that are released in this way, transported to the sea, are used by living creatures whose remains can form sedimentary rocks, bringing the carbon back to the lithosphere. The nitrogen cycle describes the flow of active nitrogen. As atmospheric nitrogen is inert, micro-organisms first have to convert this to an active nitrogen compound in a process called fixing nitrogen, before it can be used as a building block in the biosphere. Human activities play an important role in both carbon and nitrogen cycles: the burning of fossil fuels has displaced carbon from the lithosphere to the atmosphere, and the use of fertilizers has vastly increased the amount of available fixed nitrogen.
== Changes within the climate system ==
Climate is constantly varying, on timescales that range from seasons to the lifetime of the Earth. Changes caused by the system's own components and dynamics are called internal climate variability. The system can also experience external forcing from phenomena outside of the system (e.g. a change in Earth's orbit). Longer changes, usually defined as changes that persist for at least 30 years, are referred to as climate changes, although this phrase usually refers to the current global climate change. When the climate changes, the effects may build on each other, cascading through the other parts of the system in a series of climate feedbacks (e.g. albedo changes), producing many different effects (e.g. sea level rise).
=== Internal variability ===