Global climate changes and rising
tropospheric ozone levels may exacerbate urban air pollution problems.
Projections based on some SRES scenarios show increases in tropospheric
ozone of more than 40 ppb over most of the Northern Hemisphere mid-latitudes.
Such increases would approximately double the baseline levels of ozone
entering many metropolitan regions, substantially degrading air quality.
Climate change would affect the meteorological conditions (regional temperature,
cloud cover, and surface wind) that influence photochemistry, and the
occurrence of major pollution episodes. While warmer temperatures would
generally contribute to more urban ozone, the change in frequency and
intensity of pollution episodes has not been evaluated. Adverse health
effects attributable to urban air quality would be exacerbated by increases
in heat waves that would accompany anthropogenic climate change.
|WGI TAR Sections 4.4.4 & 4.5-6, & WGII TAR Sections 188.8.131.52 & 9.6|
Deposition and Climate Change
The sulfate aerosols formed from sulfur emissions
from the burning of fossil fuels lead to both acid deposition and a cooling
of the climate system. Acid deposition has adverse impacts on both
terrestrial and aquatic ecosystems and causes damage to human health and
many materials. Some of these impacts could be exacerbated by climate
change (e.g., through increase in humidity and temperature). Actions to
reduce sulfur emissions have been taken in many countries, and declines
in sulfate deposition have been observed in some regions in recent years
(see Table 8-3). In the SRES scenarios, this
situation has led to projections of future sulfate aerosol abundances
that are lower than those in the SAR. This has led, in turn, to less negative
projections for the radiative forcing by aerosols, hence less of a cooling
effect to offset the greenhouse gas-induced warming.
|WGI TAR Sections 184.108.40.206, 5.5.3, 6.7, & 6.15, WGII TAR Sections 5.6, 5.7.3, & 220.127.116.11, & SRES Section 3.6.4|
Stratospheric Ozone Depletion and Climate
|8.10|| Depletion of the stratospheric ozone
layer leads to an increased penetration of UV-B radiation and to a cooling
of the climate system. Ozone depletion has allowed for increased
penetration of UV-B radiation, with harmful effects on human and animal
health, plants, etc. During the last 2 decades, the observed losses of stratospheric
ozone have decreased the downward infrared emissions to the troposphere
from the (now colder) lower stratosphere. Stratospheric ozone depletion
has also altered tropospheric ozone concentrations, and, by allowing more
ultraviolet sunlight into the troposphere, it has led to more rapid photochemical
destruction of CH4 thereby reducing its radiative forcing. These
effects lead also to a cooling of the climate system.
||WGI TAR Sections 4.2.2 & 6.4|
|8.11||Many of the halocarbons that cause depletion
of the ozone layer are also important greenhouse gases. Chlorofluorocarbons,
for example, add a notable fraction to the total positive radiative forcing
since the pre-industrial era. The negative radiative forcing from the associated
stratospheric ozone depletion (noted above) reduces this by about half.
The Montreal Protocol will eventually eliminate both of these radiative-forcing contributions. However, one class of substitutes for the now-banned chlorofluorocarbons is hydrofluorocarbons, which are among the greenhouse gases listed under the Kyoto Protocol. This overlap can give rise to a potential conflict beween the goals of the two Protocols.
|WGI TAR Sections 4.2.2 & 6.3.3|
|8.12||Climate change will alter the temperature
and wind patterns of the stratosphere, possibly enhancing chlorofluorocarbon
depletion of stratospheric ozone over the next 50 years. Increases
in greenhouse gases lead in general to a colder stratosphere, which alters
stratospheric chemistry. Some studies predict that current rates of climate
change will result in significant increases in the depletion of the Arctic
stratospheric ozone layer over the next decade before chlorofluorocarbon
concentrations have declined substantially. Although many climate/ozone-layer
feedbacks have been identified, no quantitative consensus is reached in
||WGI TAR Sections 4.5, 6.4, & 18.104.22.168|
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