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Global effects of albedo change due to urbanization

Spångmyr, Mattias (2010) In Lunds universitets Naturgeografiska institution - Seminarieuppsatser
Dept of Physical Geography and Ecosystem Science
Abstract
Human population on Earth is increasing and is projected to continue increasing for many years to
come. Most of the increase will probably occur in cities and the extent of urban areas will increase
with it. As cities grow larger and new cities are built, the many and diverse climatic effects of
urbanization will become more evident.
A specific climatic effect of urbanization which has not received as much attention as it might
deserve is the change in the reflective properties of the surface. This report aims to investigate the
climatic effects of urbanization, especially albedo (the ratio of incoming to outgoing solar radiation
for a given surface), by reviewing relevant literature. Through this it aims to answer what the effects
... (More)
Human population on Earth is increasing and is projected to continue increasing for many years to
come. Most of the increase will probably occur in cities and the extent of urban areas will increase
with it. As cities grow larger and new cities are built, the many and diverse climatic effects of
urbanization will become more evident.
A specific climatic effect of urbanization which has not received as much attention as it might
deserve is the change in the reflective properties of the surface. This report aims to investigate the
climatic effects of urbanization, especially albedo (the ratio of incoming to outgoing solar radiation
for a given surface), by reviewing relevant literature. Through this it aims to answer what the effects
of albedo change due to urbanization are in a global perspective.
Urbanization has many effects on surface albedo. It reduces it through the introduction of dark
surfaces, through changing the surface geometry to better capture solar radiation, and through
reducing snow cover in winter. It can also increase it by increasing the cloud cover and by emitting
air pollutants and aerosols. Some effects, such as a modified surface moisture regime or climate
changes downwind of cities, can act to both reduce and increase it, with the net effect very
dependant on local factors.
Studies report that cities usually have lower albedo values than rural surfaces, commonly 2-5 %
lower than crop-lands at the same latitude for example. The radiative forcing of this albedo
reduction is very small. This is mainly because the fraction of Earth's land surface covered by urban
areas is only 0.44 % according to the best estimate. While the climatic effects of albedo change due
to urbanization are small on a global scale, they are quite distinct on regional to local scales. The
small extent of urban areas today is still more than twice as large as the estimate cited in the last
assessment report by the IPCC (AR4). With the projected increase in urban populations, the small
global effects will become progressively more important and will need to be taken into account in
future studies of climate and land use change. (Less)
Abstract (Swedish)
Hur många gånger har du tagit på dig en svart tröja och sedan upptäckt hur varmt det blir när solen
tittar fram? Med hjälp av den erfarenheten är det säkert tydligt att mörka material värms upp mer av
solens strålar än ljusa material. Man säger att mörka material ”tar till sig”, eller absorberar, en
större andel av den strålning som solen sänder ut i form av ljus. Det som inte absorberas kan istället
”studsa vidare”, eller reflekteras, och andelen strålning som reflekteras av den totala mängden
inkommande strålning kallas för albedo.
Precis som svarta tröjor har även andra mörka ytor ett lågt albedo. Asfalt, mörka tak och väggar
med mera är exempel på ytor som ofta hittas där människor bor och jobbar. I städer och
tätbebyggelse... (More)
Hur många gånger har du tagit på dig en svart tröja och sedan upptäckt hur varmt det blir när solen
tittar fram? Med hjälp av den erfarenheten är det säkert tydligt att mörka material värms upp mer av
solens strålar än ljusa material. Man säger att mörka material ”tar till sig”, eller absorberar, en
större andel av den strålning som solen sänder ut i form av ljus. Det som inte absorberas kan istället
”studsa vidare”, eller reflekteras, och andelen strålning som reflekteras av den totala mängden
inkommande strålning kallas för albedo.
Precis som svarta tröjor har även andra mörka ytor ett lågt albedo. Asfalt, mörka tak och väggar
med mera är exempel på ytor som ofta hittas där människor bor och jobbar. I städer och
tätbebyggelse utgör dessa ytor en stor del av markytan. Därför bidrar de till att sänka
tätbebyggelsens albedo och orsaka en uppvärmning. Den här rapporten syftar till att, genom att
granska relevant litteratur, undersöka hur städernas utbredning, eller urbaniseringen, påverkar det
globala klimatet med fokus på dess påverkan på markytans albedo.
Mörka ytor utgör bara en av tätbebyggelsens effekter på markytans albedo. Vissa effekter, såsom
ökat molntäcke och utsläpp av luftföroreningar, kan höja tätbebyggelsens albedo (sett från utanför
atmosfären) medan andra både kan öka och minska albedo. Mörka ytor, ett minskat snötäcke i
tätbebyggelse på vintern och att solens strålar kan reflekteras flera gånger mellan byggnader så att
mer absorberas, gör att tätbebyggelse oftast har ett lägre albedo än dess omgivning.
Effekten av tätbebyggelsens förändring av albedo blir mycket liten på global nivå, eftersom
tätbebyggelsen täcker så liten yta när man ser till hela jorden. Ungefär 0.44 % av den totala
landytan beräknas vara täckt av tätbebyggelse. Även om ytan är liten är den förmodligen minst
dubbelt så stor som t.ex. den internationella klimatpanelen IPCC citerade i sin senaste rapport och
även om effekterna är små ur ett globalt perspektiv påverkar urbaniseringen klimatet högst märkbart
på regional till lokal nivå. Då allt fler människor kommer att bo i städer och städerna kommer att
växa och bli fler, kommer städernas effekter på
klimatet att bli allt viktigare i framtiden. Därför
måste forskningen på området fortsätta och
urbaniseringen bör tas i beaktande i framtida
studier av klimat- och markyteförändringar. (Less)
Please use this url to cite or link to this publication:
author
Spångmyr, Mattias
supervisor
organization
alternative title
Kan städernas mörka sidor förvärra klimatuppvärmningen?
year
type
M2 - Bachelor Degree
subject
keywords
physical geography, albedo, urbanization, solar radiation, the energy balance, geography, land use, land cover
publication/series
Lunds universitets Naturgeografiska institution - Seminarieuppsatser
report number
180
language
English
id
1856904
date added to LUP
2011-03-17 11:33:17
date last changed
2011-12-20 11:38:28
@misc{1856904,
  abstract     = {Human population on Earth is increasing and is projected to continue increasing for many years to
come. Most of the increase will probably occur in cities and the extent of urban areas will increase
with it. As cities grow larger and new cities are built, the many and diverse climatic effects of
urbanization will become more evident.
A specific climatic effect of urbanization which has not received as much attention as it might
deserve is the change in the reflective properties of the surface. This report aims to investigate the
climatic effects of urbanization, especially albedo (the ratio of incoming to outgoing solar radiation
for a given surface), by reviewing relevant literature. Through this it aims to answer what the effects
of albedo change due to urbanization are in a global perspective.
Urbanization has many effects on surface albedo. It reduces it through the introduction of dark
surfaces, through changing the surface geometry to better capture solar radiation, and through
reducing snow cover in winter. It can also increase it by increasing the cloud cover and by emitting
air pollutants and aerosols. Some effects, such as a modified surface moisture regime or climate
changes downwind of cities, can act to both reduce and increase it, with the net effect very
dependant on local factors.
Studies report that cities usually have lower albedo values than rural surfaces, commonly 2-5 %
lower than crop-lands at the same latitude for example. The radiative forcing of this albedo
reduction is very small. This is mainly because the fraction of Earth's land surface covered by urban
areas is only 0.44 % according to the best estimate. While the climatic effects of albedo change due
to urbanization are small on a global scale, they are quite distinct on regional to local scales. The
small extent of urban areas today is still more than twice as large as the estimate cited in the last
assessment report by the IPCC (AR4). With the projected increase in urban populations, the small
global effects will become progressively more important and will need to be taken into account in
future studies of climate and land use change.},
  author       = {Spångmyr, Mattias},
  keyword      = {physical geography,albedo,urbanization,solar
radiation,the energy balance,geography,land use,land cover},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lunds universitets Naturgeografiska institution - Seminarieuppsatser},
  title        = {Global effects of albedo change due to urbanization},
  year         = {2010},
}