Jump to content

User:Niallrobinson/sandbox: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
Line 3: Line 3:
==Climate effects==
==Climate effects==


Atmospheric aerosols affect the climate of the earth by changing the amount of incoming [[solar radiation]], and outgoing terrestrial long wave radiation retained in the earth's system. This occurs through several distinct mechanisms which are split into "direct", "indirect"<ref name="Haywood2000">Haywood, James, and Olivier Boucher. 2000. “Estimates of the direct and indirect [[radiative forcing]] due to tropospheric aerosols: A review.” Reviews of Geophysics 38 (4): 513. doi:10.1029/1999RG000078. http://www.agu.org/pubs/crossref/2000/1999RG000078.shtml.</ref><ref>Twomey, S. 1977. “The influence of pollution on the shortwave albedo of clouds.” Journal of the Atmospheric Sciences 34 (7): 1149-1152. doi:10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2.</ref> and "semi-direct" aerosol effects. This is quantified in the ''Single Scattering Albedo'' (SSA), the ratio of scattering alone to scattering plus absorption (''extinction'') of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.
Atmospheric aerosols affect the climate of the earth by changing the amount of incoming [[solar radiation]], and outgoing terrestrial long wave radiation retained in the earth's system. This occurs through several distinct mechanisms which are split into "direct", "indirect"<ref name="Haywood2000">Haywood, James, and Olivier Boucher. 2000. “Estimates of the direct and indirect [[radiative forcing]] due to tropospheric aerosols: A review.” Reviews of Geophysics 38 (4): 513. doi:10.1029/1999RG000078. http://www.agu.org/pubs/crossref/2000/1999RG000078.shtml.</ref><ref>Twomey, S. 1977. “The influence of pollution on the shortwave albedo of clouds.” Journal of the Atmospheric Sciences 34 (7): 1149-1152. doi:10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2.</ref> and "semi-direct" aerosol effects. The interaction of an aerosol with radiation is quantified in the ''Single Scattering Albedo'' (SSA), the ratio of scattering alone to scattering plus absorption (''extinction'') of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.


The aerosol climate effects are the biggest source of uncertainty in future climate predictions.<ref name="Forster2007"/> The [[Intergovernmental Panel on Climate Change]], IPCC, says: ''While the radiative forcing due to [[greenhouse gas]]es may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time'' [http://www.grida.no/climate/ipcc_tar/wg1/237.htm#678]. A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available [http://www.grida.no/climate/ipcc_tar/vol4/english/wg1figspm-3.htm here].
The aerosol climate effects are the biggest source of uncertainty in future climate predictions.<ref name="Forster2007"/> The [[Intergovernmental Panel on Climate Change]], IPCC, says: ''While the radiative forcing due to [[greenhouse gas]]es may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time'' [http://www.grida.no/climate/ipcc_tar/wg1/237.htm#678]. A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available [http://www.grida.no/climate/ipcc_tar/vol4/english/wg1figspm-3.htm here].

Revision as of 15:40, 12 July 2012

Climate effects

Atmospheric aerosols affect the climate of the earth by changing the amount of incoming solar radiation, and outgoing terrestrial long wave radiation retained in the earth's system. This occurs through several distinct mechanisms which are split into "direct", "indirect"[1][2] and "semi-direct" aerosol effects. The interaction of an aerosol with radiation is quantified in the Single Scattering Albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction) of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.

The aerosol climate effects are the biggest source of uncertainty in future climate predictions.[3] The Intergovernmental Panel on Climate Change, IPCC, says: While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time [1]. A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available here.

Direct effect

The Direct aerosol effect consists of any direct interaction of radiation with atmospheric aerosol, such as absorption or scattering. It affects both short and longwave radiation to produce a net negative radiative forcing.[4] The magnitude of the resultant radiative forcing due to the direct effect of an aerosol is dependent on the albedo of the underlying surface, as this affects the net amount of radiation absorbed or scattered to space. e.g. if a highly scattering aerosol is above a surface of low albedo it has a greater radiative forcing than if it was above a surface of high albedo. The converse is true of absorbing aerosol, with the greatest radiative forcing arising from a highly absorbing aerosol over a surface of high albedo.[1] The Direct aerosol effect is a first order effect and is therefore classified as a radiative forcing by the IPCC.[3]

Indirect effect

The Indirect aerosol effect consists of any change to the earth's radiative budget due to the modification of clouds by atmospheric aerosols, and consists of several distinct effects. Cloud droplets form onto pre-existing aerosol particles, known as cloud condensation nuclei (CCN).

For any given meteorological conditions, an increase in CCN leads to an increase in the number of cloud droplets. This leads to more scattering of shortwave radiation i.e. an increase in the albedo of the cloud, known as the Cloud albedo effect, First indirect effect or Twomey effect.[5] Evidence supporting the cloud albedo effect has been observed from the effects of ship exhaust plumes [6] and biomass burning[7] on cloud albedo compared to ambient clouds. The Cloud albedo aerosol effect is a first order effect and is therefore is classified as a radiative forcing by the IPCC.[3]

An increase in cloud droplet number due to the introduction of aerosol acts to reduce the cloud droplet size, as the same amount of water is divided between more droplets. This is the effect of suppressing precipitation, increasing the cloud lifetime, known as the Cloud lifetime aerosol effect, Second Inderect effect or Albrecht effect.[3] This is been observed as the suppression of drizzle in ship exhaust plume compared to ambient clouds [8], and inhibited precipitation in biomass burning plumes [9]. This cloud lifetime effect is classified as a climate feedback (rather than a radiative forcing) by the IPCC due to the interdependence between it and the hydrological cycle [3]. However, it has previously been classified as a negative radiative forcing.[10]

Semi-direct effect

The Semi-direct effect concerns any radiative effect of caused by absorbing atmospheric aerosol such as soot, apart from direct scattering and absorption, which is classified as the direct effect. It encompasses many individual mechanisms, and in general is more poorly defined and understood than the direct and indirect aerosol effects. For instance, if absorbing aerosols are present in a layer aloft in the atmosphere, they can heat surrounding air which inhibits the condensation of water vapour, resulting in less cloud formation.[11] Additionally, heating a layer of the atmosphere relative to the surface results in a more stable atmosphere due to the inhibition of atmospheric convection. This inhibits the convective uplift of moisture [12], which in turn reduces cloud formation. The heating of the atmosphere aloft also leads to a cooling of the surface, resulting in less evaporation of surface water. The effects described here all lead to a reduction in cloud cover i.e. an increase in planetary albedo. The semi-direct effect classified as a climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle [3]. However, it has previously been classified as a negative radiative forcing.[10]

Instances of aerosol affecting climate

Solar radiation reduction due to volcanic eruptions

Volcanoes are a large natural source of aerosol, and have been linked to changes in the earth's climate, often with consequences for the human population. Eruptions linked to changes in climate include the 1600 eruption of Huaynaputina which was linked to the Russian famine of 1601 - 1603[13][14][15], leading to the deaths of two million, and the 1991 eruption of Mount Pinatubo which cause a global cooling of approximately 0.5°C lasting several years.[16][17]

Aerosols have are also though to affect weather and climate on a regional scale. The failure of the Indian Monsoon has been linked suppression of evaporation of water from the Indian Ocean due to the semi-direct effect of anthropogenic aerosol.[18] It is also thought that this suppression was associated with increased precipitation in the African Sahel.[18].

References

  1. ^ a b Haywood, James, and Olivier Boucher. 2000. “Estimates of the direct and indirect radiative forcing due to tropospheric aerosols: A review.” Reviews of Geophysics 38 (4): 513. doi:10.1029/1999RG000078. http://www.agu.org/pubs/crossref/2000/1999RG000078.shtml.
  2. ^ Twomey, S. 1977. “The influence of pollution on the shortwave albedo of clouds.” Journal of the Atmospheric Sciences 34 (7): 1149-1152. doi:10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2.
  3. ^ a b c d e f Forster, Piers, Venkatachalam Ramaswamy, Paulo Artaxo, Terje Berntsen, Richard Betts, David W Fahey, James Haywood, et al. 2007. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In Climate Change 2007: The Physical Science Basis, ed. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor, and H.L. Miller, 129-234. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, October. http://elib.dlr.de/51416/.
  4. ^ Charlson, R J, S E Schwartz, J M Hales, R D Cess, J A Coakley, J E Hansen, and D J Hofmann. 1992. “Climate forcing by anthropogenic aerosols.” Science (New York, N.Y.) 255 (5043) (January): 423-30. doi:10.1126/science.255.5043.423. http://www.ncbi.nlm.nih.gov/pubmed/17842894.
  5. ^ Twomey, S. 1977. “The influence of pollution on the shortwave albedo of clouds.” Journal of the Atmospheric Sciences 34 (7): 1149-1152. doi:10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2.
  6. ^ Ackerman, A S, O B Toon, J P Taylor, D W Johnson, P V Hobbs, and R J Ferek. 2000. “Effects of Aerosols on Cloud Albedo : Evaluation of Twomey’s Parameterization of Cloud Susceptibility Using Measurements of Ship Tracks.” Physics 57 (1995): 2684-2695. doi:10.1175/1520-0469(2000)057<2684:EOAOCA>2.0.CO;2.
  7. ^ Kaufman, Y. J., and Robert S. Fraser. 1997. “The Effect of Smoke Particles on Clouds and Climate Forcing.” Science 277 (5332) (September): 1636-1639. doi:10.1126/science.277.5332.1636. http://www.sciencemag.org/cgi/doi/10.1126/science.277.5332.1636.
  8. ^ Ferek, R J, Timothy Garrett, P V Hobbs, Scott Strader, Doug Johnson, J P Taylor, Kurt Nielsen, et al. 2000. “Drizzle Suppression in Ship Tracks.” Journal of the Atmospheric Sciences 57 (16): 2707-2728. doi:10.1175/1520-0469(2000)057<2707:DSIST>2.0.CO;2. http://journals.allenpress.com/jrnlserv/?request=get-abstract&issn=1520-0469&volume=57&page=2707.
  9. ^ Rosenfeld, D. 1999. “TRMM observed first direct evidence of smoke from forest fires inhibiting rainfall.” October 26 (20): 3105-3108. http://dx.doi.org/10.1029/1999GL006066.
  10. ^ a b Hansen, J., M. Sato, and R. Ruedy. 1997. “Radiative forcing and climate response.” Journal of Geophysical Research 102 (D6): 6831-6864. doi:10.1029/96JD03436. http://www.agu.org/pubs/crossref/1997/96JD03436.shtml.
  11. ^ Ackerman, A S, O B Toon, D E Stevens, A J Heymsfield, V Ramanathan, and E J Welton. 2000. “Reduction of tropical cloudiness by soot.” Science 288 (5468): 1042-1047. doi:10.1126/science.288.5468.1042. http://www.ncbi.nlm.nih.gov/pubmed/10807573.
  12. ^ Koren, Ilan, Yoram J Kaufman, Lorraine a Remer, and Jose V Martins. 2004. “Measurement of the effect of Amazon smoke on inhibition of cloud formation.” Science 303 (5662) (February): 1342-5. doi:10.1126/science.1089424. http://www.ncbi.nlm.nih.gov/pubmed/14988557.
  13. ^ "1600 Eruption Caused Global Disruption", Geology Times, 25 Apr 2008, accessed 13 Nov 2010
  14. ^ Andrea Thompson, "Volcano in 1600 caused global disruption", MSNBC.com, 5 May 2008, accessed 13 Nov 2010
  15. ^ "The 1600 eruption of Huaynaputina in Peru caused global disruption", Science Centric
  16. ^ McCormick, M P, L W Thomason, and C R Trepte. 1995. “Atmospheric effects of the Mt Pinatubo eruption.” Nature 373 (6513): 399-404. doi:10.1038/373399a0. http://jack.pixe.lth.se/kfgu/KOO090_FKF075/Artiklar/P05.pdf.,
  17. ^ Stowe, L. L., R. M. Carey, and P. P. Pellegrino. 1992. “Monitoring the Mt. Pinatubo aerosol layer with NOAA/11 AVHRR data.” Geophysical Research Letters 19 (2): 159. doi:10.1029/91GL02958. http://www.agu.org/pubs/crossref/1992/91GL02958.shtml.
  18. ^ a b Chung, C E, and V Ramanathan. 2006. “Weakening of North Indian SST Gradients and the Monsoon Rainfall in India and the Sahel.” Journal of Climate 19 (10): 2036-2045. doi:10.1175/JCLI3820.1. http://journals.ametsoc.org/doi/abs/10.1175/JCLI3820.1.
Retrieved from "https://en.wikipedia.org/w/index.php?title=User:Niallrobinson/sandbox&oldid=501898759"