patterns of evaporation and precipitation. Observations from 1950 to 2008 show that very saline
waters have become even more saline and lowsaline waters have freshened, increasing the contrast between low and high salinity areas. It is
likely that this contrast is due to changes in freshwater transport between ocean waters and the
atmosphere caused by warming of the lower
atmosphere [30] (hydrological cycle, see below).
Ocean currents have an enormous impact on
climate as well. Currents are generated by forces
affecting the water such as wind, gradients in temperature and salinity, breaking of waves, and
mixing of waters of different densities. Ocean currents form the great conveyor belt, also called
thermohaline circulation. The thermohaline circulation is driven by horizontal mixing of water
caused by density differences. Thermohaline circulation transports warm, saline surface waters
northward and colder, denser waters southward.
The warm, saline water is cooled when it reaches
the high latitudes of the Northern Hemisphere and
then sinks. From there waters are transported back
southward [31]. Perturbations of ocean salinity will
affect deep ocean water circulation and will affect
transport of heat from ocean to land as well [32].
Atmospheric CO 2 is in equilibrium with CO 2
dissolved in the surface ocean [5]; its uptake is
limited by mixing of surface and deep water. By
introducing more CO 2 to the atmosphere, a greater
amount of CO 2 will be dissolved in ocean waters.
This will lead to a reduction of ocean pH, a process called “ocean acidification.” Over the last
250 years, oceans have absorbed about
1.55 Â 10
14 kg of anthropogenic carbon [33],
which has caused average pH of ocean surface
waters to drop from 8.2 to 8.1 [34]. Ocean acidification is problematic because it is detrimental to
marine ecosystems, as acidic conditions negatively affect formation of corals and both chitinous and calcareous shells of arthropods and
molluscs, respectively [30]. In addition, less CO 2
dissolves in acidic solutions, and the solubility of
CO 2 decreases as temperature increases [5].
Polar Amplification
It has been observed that the polar regions and
especially the Arctic region of the Northern
Hemisphere are warming faster than the rest of
the planet, primarily because of the albedo feedback [186, 187]. The albedo feedback comes from
the warming of the ocean and atmosphere that
leads to sea ice melting, which in turn leads to
lower albedo over the polar cap and further
absorption of the sunlight and further warming
(white sea ice that reflects sunlight changes to
relatively much darker open water).
As the melting of land and sea ice in polar
regions accelerates (along with hydrological cycle
changes, see below), more freshwater flows into the
ocean. Due to its low salinity, this water is less
dense, and its introduction disrupts the normal thermohaline circulation that drives ocean flow, for
example, mixing surface and deep waters. There is
evidence that this meltwater has weakened the
Atlantic overturning circulation [188]. Europe
receives about a third of a sun’s worth of energy
from the Gulf Stream [5], and changes in the Atlantic Meridional Overturning Current (AMOC) will
impact European weather as climate warms.
Hydrological Cycle
A simplified global hydrological cycle depicts
ocean and land surfaces heated by the sun’s radiation, resulting in evaporation of water that moves
with winds in the atmosphere, condenses to form
clouds, and falls back to the Earth’s surface as rain
or snow, flowing back to oceans via rivers
[5]. However, human-induced climate change
has a direct influence on precipitation and the
hydrological cycle, especially for extreme events.
Increased heating leads to greater evaporation and
thus surface drying, increasing the intensity and
duration of droughts. The water-holding capacity
of air increases by about 7% per
C warming [35]
leading to an increase in water vapor in the atmosphere; water vapor is also a powerful greenhouse
gas. On balance, the relative humidity of the atmosphere has not been seen to increase with temperature as much as the holding capacity; globally the
increase is only about 2% per
C warming, due to
reduced moisture over land and moisture transport. The increased moisture capacity of the atmosphere at higher temperatures has multiple effects
[189]. Storms (tropical and extratropical cyclones,
thunderstorms) supplied with increased moisture
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications
291
waters have become even more saline and lowsaline waters have freshened, increasing the contrast between low and high salinity areas. It is
likely that this contrast is due to changes in freshwater transport between ocean waters and the
atmosphere caused by warming of the lower
atmosphere [30] (hydrological cycle, see below).
Ocean currents have an enormous impact on
climate as well. Currents are generated by forces
affecting the water such as wind, gradients in temperature and salinity, breaking of waves, and
mixing of waters of different densities. Ocean currents form the great conveyor belt, also called
thermohaline circulation. The thermohaline circulation is driven by horizontal mixing of water
caused by density differences. Thermohaline circulation transports warm, saline surface waters
northward and colder, denser waters southward.
The warm, saline water is cooled when it reaches
the high latitudes of the Northern Hemisphere and
then sinks. From there waters are transported back
southward [31]. Perturbations of ocean salinity will
affect deep ocean water circulation and will affect
transport of heat from ocean to land as well [32].
Atmospheric CO 2 is in equilibrium with CO 2
dissolved in the surface ocean [5]; its uptake is
limited by mixing of surface and deep water. By
introducing more CO 2 to the atmosphere, a greater
amount of CO 2 will be dissolved in ocean waters.
This will lead to a reduction of ocean pH, a process called “ocean acidification.” Over the last
250 years, oceans have absorbed about
1.55 Â 10
14 kg of anthropogenic carbon [33],
which has caused average pH of ocean surface
waters to drop from 8.2 to 8.1 [34]. Ocean acidification is problematic because it is detrimental to
marine ecosystems, as acidic conditions negatively affect formation of corals and both chitinous and calcareous shells of arthropods and
molluscs, respectively [30]. In addition, less CO 2
dissolves in acidic solutions, and the solubility of
CO 2 decreases as temperature increases [5].
Polar Amplification
It has been observed that the polar regions and
especially the Arctic region of the Northern
Hemisphere are warming faster than the rest of
the planet, primarily because of the albedo feedback [186, 187]. The albedo feedback comes from
the warming of the ocean and atmosphere that
leads to sea ice melting, which in turn leads to
lower albedo over the polar cap and further
absorption of the sunlight and further warming
(white sea ice that reflects sunlight changes to
relatively much darker open water).
As the melting of land and sea ice in polar
regions accelerates (along with hydrological cycle
changes, see below), more freshwater flows into the
ocean. Due to its low salinity, this water is less
dense, and its introduction disrupts the normal thermohaline circulation that drives ocean flow, for
example, mixing surface and deep waters. There is
evidence that this meltwater has weakened the
Atlantic overturning circulation [188]. Europe
receives about a third of a sun’s worth of energy
from the Gulf Stream [5], and changes in the Atlantic Meridional Overturning Current (AMOC) will
impact European weather as climate warms.
Hydrological Cycle
A simplified global hydrological cycle depicts
ocean and land surfaces heated by the sun’s radiation, resulting in evaporation of water that moves
with winds in the atmosphere, condenses to form
clouds, and falls back to the Earth’s surface as rain
or snow, flowing back to oceans via rivers
[5]. However, human-induced climate change
has a direct influence on precipitation and the
hydrological cycle, especially for extreme events.
Increased heating leads to greater evaporation and
thus surface drying, increasing the intensity and
duration of droughts. The water-holding capacity
of air increases by about 7% per
C warming [35]
leading to an increase in water vapor in the atmosphere; water vapor is also a powerful greenhouse
gas. On balance, the relative humidity of the atmosphere has not been seen to increase with temperature as much as the holding capacity; globally the
increase is only about 2% per
C warming, due to
reduced moisture over land and moisture transport. The increased moisture capacity of the atmosphere at higher temperatures has multiple effects
[189]. Storms (tropical and extratropical cyclones,
thunderstorms) supplied with increased moisture
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications
291