Climate System Components

All parts of the Earth system are important for the climate in a certain area. Therefore, no single place is independent of all others on our globe. The best example of the component interactions are the joint glacials and interglacials of both hemispheres, although the triggering comes from the northern hemisphere with its major landmasses. If the northern hemisphere is closest to the Sun in boreal winter, the declination of the Sun is high (it can vary from 21.8 to 24.5°) and the eccentricity of the Earth's orbit is larger than on average the probability for an inception of a glacial is high. As observations of atmospheric composition, reconstructed from air bubbles in Antarctic ice, confirm, the main long-lived greenhouse gases in the atmosphere, namely carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), then start declining and also the southern hemisphere with higher solar radiation flux density will "descend" into a glacial as well. Although the processes leading to this joint glacials are not yet fully understood, it is clear that ocean, atmosphere, biosphere and cryosphere have interacted strongly to create global mean surface temperatures 5°C lower than in interglacials.

Box 2.1: Climate System Components and their Typical Timescales

Climate must change continuously as the components of the climate system interact non-linearly at very different time scales from minutes to billion years (see also table 2.1). And because the radiation flux density of the Sun also varies on time scales from minutes to billions of years. In addition, the Earth's orbit around the Sun varies quasi-periodically through changed positions of the neighbouring major planets (Venus, Jupiter, Saturn). Understanding the Earth system, of which climate is an important part, is therefore a very complex endeavour and far from being in a very mature stage.

Table 2.1: Climate system components and their typical time scales, together with some climate phenomena

Component

Typical Time-scales

Some Climatically Relevant Phenomena

Atmosphere

Minutes to Millennia

Planetary Boundary Layer Height, Greenhouse Gas Composition, Annual Cycles of Temperature and Precipitation, Storm Tracks

Ocean

Seasons to about 100,000 years

Boundary Currents (e.g. Gulf Stream), Global Conveyor Belt, Single and Multi-year Sea Ice

Biosphere

Days to Millennia

Blooming, Biomass Production, Biome Distribution, Vegetation Cover, High Biodiversity in the Tropics, Vegetation Period, Anthropogenic Monocultures, Algae Blooms, Food Webs in Ocean and on Land

Cryosphere

Days to Millions of Years

Snow Cover, Ice Sheets, Ice Caps, Mountain Glaciers, Permafrost, Frozen Ground, Lake and River Ice, Sea Ice

Lithosphere

Years to Many Million Years

Continental Drift, Subduction of Oceanic Crusts, Formation of Mountain Ranges, Earthquakes, Volcanoes, Fossil Fuel Formation

Pedosphere (Soils)

Decades to Many Millennia

Weathering of Rocks, Humus Formation, Cycling of Elements through Microbiological Processes, Changed Atmospheric Composition by Emissions from Soils

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