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Climate system

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The five components of the climate system and their interactions.

Earth's climate arises from the complex interactions of five major climate system components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's crust and upper mantle) and the biosphere (living things).[1] Energy, water and different chemical elements are constantly flowing between the different components of the system. The climate, defined as the average and variability of weather, is determined by a combination of processes in the climate system.[2]

The climate system changes due to internal variability and external forcings. These external forcings are constituted of natural forcings, such as variations in solar intensity and volcanic eruptions. Humans are currently responsible for global warming by emitting heat-trapping greenhouse gases and cooling aerosols.[1]

Components of the climate system

The atmosphere envelops the earth and stretches out hundreds of kilometers from the surface. It consists mostly of inert nitrogen (78%) and oxygen (21%) and argon (1%).[3] The trace gases in the atmosphere, water vapour and carbon dioxide are the gases most important for the workings of the climate system as they are greenhouse gases, which allow visible light from the sun to penetrate to the surface, but block some of the infrared radiation the Earth surface emits to balance the Sun's radiation. This causes surface temperatures to rise.[4] The hydrological cycle is the movement of water through the atmosphere. Not only does the hydrological cycle determine patterns of precipitation, it also has an influence on the movement of energy throughout the climate system.[5]

The ocean covers 71% of Earth's surface and has an average depth of nearly 4 kilometres (2.5 miles).[6] It can hold substantially more heat than the atmosphere.[7] The ocean has a salt content of about 3.5% on average, but this varies spatially.[8] Ocean water that has more salt also has a higher density and differences in density play an important role in ocean circulation. Ocean circulation is further driven by the interaction with wind. The salt component also influences the freezing point temperature.[9] Vertical movements can bring up colder water to the surface in a process called upwelling, which cools down the air above.[10] The thermohaline circulation transports heat from the tropics to the polar regions.[11]

The cryosphere contains all parts of the climate system where water is solid. This includes sea ice, ice sheets, permafrost and snow cover. Because there is more land in the Northern Hemisphere compared to the Southern Hemisphere, a larger part of this hemisphere is covered in snow.[12] Both hemispheres have about the same amount of sea ice. Most frozen water is contained in the ice sheets on Greenland and Antarctica, which average about 2 kilometres (1.2 miles) in height. These ice sheets slowly flow towards their margins.[13]

The Earth's crust mountains and valleys shape global wind patterns: vast mountain ranges form a barrier to winds and impact where and how much it rains.[14] Land closer to ocean has a more moderate climate than land further from the ocean.[citation needed] For the purpose of modelling the climate, the land is often considered static as it changes very slowly compared to the other elements that make up the climate system.[15]

Lastly, the biosphere interacts with the rest of the climate system as well. Vegetation is often darker or lighter than the soil beneath, so that more or less of the Sun's heat gets trapped in areas with vegetation.[16] Vegetation is good at trapping water, which is then later taken up by its roots. Without vegetation, this water would have run off to the closest rivers or other water bodies. Water taken up by plants instead evaporates.[17] Precipitation and temperatures impact the distribution of different vegetation zones.[18]

Flows of energy, water and elements

Carbon is constantly transported between the different elements of the climate system: fixed by living creatures and transported through the ocean and atmosphere.

The climate system receives energy from the Sun, and to a far lesser extent from Earth's core, as well as tidal energy from the moon. Earth gives off energy to outer space in two forms: it directly reflects a part of the radiation of the sun and it emits radiation as a black body. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.[19] More energy reaches the tropics than the polar regions and the subsequent temperature difference drives the global circulation of the atmosphere and oceans.[20]

Water is stored in all components of the climate system, with the oceans and ice containing the most. Its movement is driven by evaporation from oceans and other water bodies as a consequence of direct and indirect sunlight from the evapotranspiration of water from plants. Precipitation and evaporation are not evenly distributed across the globe, with some regions having more rainfall than evaporation, such as the tropics, and others having more evaporation than rainfall.[21]

Chemical elements, vital for life, are constantly also cycled through the different components of the climate system. In the carbon cycle, plants take up carbon dioxide from the atmosphere using photosynthesis, and this is re-emitted by the breathing of living creatures.[22] Volcanoes are also part of the extended carbon cycle. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological carbon dioxide sinks.

The nitrogen cycle describes the flows 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.[23] Human activities play an important role in both cycles: the burning of fossil fuels has displaced carbon from the lithosphere to the atmosphere, and the use of fertilizers has increased the amount of available nitrogen manifold.[24]

Internal variability

The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for periods of years to decades at a time.[25] Examples of this type of variability include the El Niño–Southern Oscillation, the Pacific decadal oscillation, and the Atlantic Multidecadal Oscillation. These variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere[26] and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the earth.[27]

The oceanic aspects of these circulations can generate variability on centennial timescales due to the ocean having hundreds of times more mass than the atmosphere, and thus very high thermal inertia. For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans. Understanding of internal variability helps scientists to attribute the recent climate change to greenhouse gases.[28]

Climate forcing and responses

Incoming sunlight

Further information: Milankovitch cycles and Solar Variation
Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes.

Slight variations in Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged, annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of kinematic change are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods.[29]

The Sun is the predominant source of energy input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate. Solar output varies on shorter time scales, including the 11-year solar cycle[30] and longer-term modulations.[31]

Volcanism

In atmospheric temperature from 1979 to 2010, determined by MSU NASA satellites, effects appear from aerosols released by major volcanic eruptions (El Chichón and Pinatubo). El Niño is a separate event, from ocean variability.

Although volcanoes are technically part of the lithosphere, which itself is part of the climate system, volcanism is defined as an external forcing agent.[32]

The eruptions considered to be large enough to affect the Earth's climate on a scale of more than a year are the ones that inject over 100,000 tons of SO2 into the stratosphere.[33] This is due to the optical properties of sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of sulfuric acid haze.[34] On average, such eruptions occur several times per century, and for a period of several years cause cooling by partially blocking the transmission of solar radiation to the Earth's surface. Small eruptions affect the atmosphere only subtly, as temperature changes are comparable with natural variability. However, because smaller eruptions occur at a much higher frequency, in total they too significantly affect Earth's atmosphere.[33][35]

Plate tectonics

Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography. This can affect both global and local patterns of climate and atmosphere-ocean circulation.[36] The position of the continents determines the geometry of the oceans and therefore influences patterns of ocean circulation. The locations of the seas are important in controlling the transfer of heat and moisture across the globe, and therefore, in determining global climate.[37]

Greenhouse gases

Greenhouse gases trap heat in the lower part of the atmosphere. In the Earth's past, many processes contributed to variations in greenhouse gas concentrations. Currently, emissions by humans are the cause of increasing concentrations of greenhouse gases.

Responses

The different elements of the climate system respond to external forcing in different ways. One important difference between the components is the speed at which they react to a forcing. The atmosphere typically responds within a couple of hours to weeks, while the deep ocean and ice sheets take centuries to millennia to reach a new equilibrium.[38] The initial response of a component to an external forcing can be damped by negative feedbacks and enhanced by positive feedbacks. For example, an decrease of solar intensity would immediate lead to a temperature decrease on Earth, and then allow ice and snow cover to expand. The extra snow and ice reflects more sunlight back into space, causing the Earth to cool down further.[39]

Notes and Sources

Notes

  1. ^ a b Planton 2013, p. 1451
  2. ^ "Climate systems". climatechange.environment.nsw.gov.au. Archived from the original on 2019-05-06. Retrieved 2019-05-06. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  3. ^ Barry & Hall-McKim 2014, p. 22
  4. ^ Gettelman & Rood 2016, pp. 14–15
  5. ^ Gettelman & Rood 2016, p. 16
  6. ^ Goosse 2015, p. 11
  7. ^ Gettelman & Rood 2016, p. 17
  8. ^ Goosse 2015, p. 11
  9. ^ Goosse 2015, p. 12
  10. ^ Goosse 2015, p. 13
  11. ^ Goosse 2015, p. 18
  12. ^ Goosse 2015, p. 20
  13. ^ Goosse 2015, p. 22
  14. ^ Goosse 2015, p. 25; Houze 2012
  15. ^ Gettelman & Rood 2016, pp. 18–19
  16. ^ Gettelman & Rood 2016, p. 19
  17. ^ Goosse 2015, p. 26
  18. ^ Goosse 2015, p. 28
  19. ^ Barry & Hall-McKim 2014, pp. 15–23
  20. ^ Bridgman & Oliver 2014, p. 131
  21. ^ Peixoto 1993, p. 5
  22. ^ Möller 2010, pp. 123–125
  23. ^ Möller 2010, pp. 128–129
  24. ^ Möller 2010, pp. 129, 197
  25. ^ Brown et al. 2015; Hasselmann 1976
  26. ^ Meehl et al. 2013; England et al. 2014
  27. ^ Brown et al. 2014; Palmer & McNeall 2014
  28. ^ Wallace et al. 2013
  29. ^ "Milankovitch Cycles and Glaciation". University of Montana. Archived from the original on 2011-07-16. Retrieved 2 April 2009.
  30. ^ Willson & Hudson 1991
  31. ^ Willson 2003
  32. ^ Man, Zhou & Jungclaus 2014
  33. ^ a b Miles, Grainger & Highwood 2004
  34. ^ "Volcanic Gases and Climate Change Overview". usgs.gov. USGS. Archived from the original on 29 July 2014. Retrieved 31 July 2014. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  35. ^ Graf, Feichter & Langmann 1997
  36. ^ Forest et al. 1999
  37. ^ Haug & Keigwin 2004
  38. ^ Ruddiman 2001, pp. 10–12
  39. ^ Ruddiman 2001, pp. 16–17

Sources

  • Barry, Roger G.; Hall-McKim, Eileen A. (2014). Essentials of the Earth's Climate System. Cambridge University Press. ISBN 978-1-107-03725-0. {{cite book}}: Invalid |ref=harv (help)
  • Bridgman, Howard A.; Oliver, John. E. (2014). The Global Climate System: Patterns, Processes, and Teleconnections. Cambridge University Press. ISBN 9781107668379. {{cite book}}: Invalid |ref=harv (help)
  • Brown, Patrick T.; Li, Wenhong; Cordero, Eugene C.; Mauget, Steven A. (2015). "Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise". Scientific Reports. 5. doi:10.1038/srep09957. ISSN 2045-2322. {{cite journal}}: Invalid |ref=harv (help)
  • Graf, H.-F.; Feichter, J.; Langmann, B. (1997). "Volcanic sulphur emissions: Estimates of source strength and its contribution to the global sulphate distribution". Journal of Geophysical Research: Atmospheres. 102 (D9): 10727–38. Bibcode:1997JGR...10210727G. doi:10.1029/96JD03265. {{cite journal}}: Invalid |ref=harv (help)
  • Meehl, Gerald A.; Hu, Aixue; Arblaster, Julie M.; Fasullo, John; Trenberth, Kevin E. (2013). "Externally Forced and Internally Generated Decadal Climate Variability Associated with the Interdecadal Pacific Oscillation". Journal of Climate. 26 (18). doi:10.1175/JCLI-D-12-00548.1. ISSN 0894-8755. {{cite journal}}: Cite has empty unknown parameter: |1= (help); Invalid |ref=harv (help)
  • Miles, M.G.; Grainger, R.G.; Highwood, E.J. (2004). "The significance of volcanic eruption strength and frequency for climate". Quarterly Journal of the Royal Meteorological Society. 130 (602): 2361–76. doi:10.1256/qj.30.60 (inactive 2019-06-07). {{cite journal}}: Invalid |ref=harv (help)CS1 maint: DOI inactive as of June 2019 (link)
  • Planton, S. (2013). "Annex III: Glossary" (PDF). In Stocker, T.F.; Qin, D.; Plattner, G.-K.; Tignor, M.; Allen, S.K.; Boschung, J.; Nauels, A.; Xia, Y.; Bex, V.; Midgley, P.M. (eds.). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. {{cite book}}: Invalid |ref=harv (help)
  • Peixoto, José P. (1993). "Atmospheric energetics and the water cycle". In Raschke, Ehrhard; Jacob, Jacob (eds.). Energy and Water Cycles in the Climate System. Springer-Verlag Berlin Heidelberg. ISBN 978-3-642-76957-3. {{cite book}}: Invalid |ref=harv (help)
  • Ruddiman, William F. (2001). Earth's Climate: Past and Future. W. H. Freeman and Company. ISBN 0-7167-3741-8. {{cite book}}: Invalid |ref=harv (help)
  • Willson, Richard C.; Hudson, Hugh S. (1991). "The Sun's luminosity over a complete solar cycle". Nature. 351 (6321): 42–44. doi:10.1038/351042a0. {{cite journal}}: Invalid |ref=harv (help)
  • Willson, Richard C. (2003). "Secular total solar irradiance trend during solar cycles 21–23". Geophysical Research Letters. 30 (5). doi:10.1029/2002GL016038. {{cite journal}}: Invalid |ref=harv (help)


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