Environmental Engineering Reference
In-Depth Information
Climate Change
The temperature of the earth has largely changed through time. Atmospheric
temperature records are available from the late 1880s and reconstructions of
the temperature regimes across the globe show that in the latter part of the
20th century the atmosphere of the earth has warmed considerably faster
than at any time during the previous millennium. A time series of global
mean temperatures show that during the 20th century we experienced
relatively cooler global temperatures up to the 1940s, followed by increasing
warming, particularly after the 1980s (Jones et al. 2001). There are large
uncertainties surrounding the prediction of changes in world's climate,
but there is considerable agreement that temperatures will continue to rise,
with average global surface temperature projected to increase by between
1.4 and 5.8°C above 1990 levels by 2100.
The net primary production of wetland plants is related to latitude
and temperature, with greater productivity occurring at lower and
warmer latitudes (Turner and Gosselink 1975). Warmer temperatures are
also expected to change the geographical distribution of salt marshes and
forested wetlands. For many species, specially mangroves, the limiting
factor for the geographic distribution is low temperature or freezing events
that exceed tolerance limits (Snedaker 1995), and the limits of tropical
and subtropical mangrove communities are expected to migrate to higher
latitudes. A warmer climate might also favor highly opportunistic exotic
species to take advantage over native species (Malcolm and Markham
1996), and salt marsh plant composition could also affect ecosystem
productivity.
There are large uncertainties regarding the impacts of a warmer climate
on coastal wetlands, and the reciprocal effects of wetlands response on
climate, potentially moderating or enhancing warming. The increase in
atmospheric CO
2
is a major driver of climate change and coastal wetlands
have shown a great potential as carbon sinks (Chmura et al. 2003). Increased
atmospheric CO
2
could increase net primary production and carbon
sequestration, if nutrients, precipitation, and other factors are not limiting
to plant growth. Increased CO
2
has shown to produce higher growth rates
and greater biomass in different salt marsh plants and mangrove seedlings
(Rozema et al. 1991). Related research on the effects of elevated atmospheric
CO
2
on different wetland systems suggests that growth enhancement is a
common consequence, but climate-related changes to the carbon cycle are
likely to alter the sequestration service provided by salt marshes, mangroves
and other coastal ecosystems in ways that are still unclear.
There are different types of photosynthetic pathways. Most plants use
C3 photosynthesis, in which the CO
2
is fi rst incorporated into a 3-carbon
compound, but the C
4
photosynthetic carbon cycle is an elaborated addition
