Environmental Engineering Reference
In-Depth Information
modeling studies extend beyond 2100, many show substantial changes
occurring by 2100 that indicate the potential for even greater changes in
the following centuries. Indeed, some major shifts such as the expansion of
shrublands in Arctic regions are already evident in recent decades (Sturm
et al., 2001; Tape et al., 2006), and this shift is consistent with results from
warming experiments in the region (Walker et al., 2006). One important
consequence of this expansion is that the resulting decrease in surface al-
bedo can amplify local summer warming in the future by a factor of two or
more (Chapin et al., 2005).
Major biome shifts also appear likely in some temperate and tropical
regions by 2100 (Scholze et al., 2006). The Eastern part of the Amazon rain-
forest, for example, may shift to a seasonally dry forest or even a savanna
due to likely rainfall decreases in the dry season by 2100 (Cox et al., 2004;
Malhi et al., 2009). Beyond 2100, these shifts become more likely. High
CO 2 levels will likely promote expansion of vegetation into currently bar-
ren tundra and desert ecosystems, because of higher water-use efficiencies,
which again would amplify local warming because of albedo effects (Bala
et al., 2006).
Most models used to simulate future vegetation changes rest on strong
empirical relationships between current climate and the distribution of major
biomes. Less is known about how transitions between equilibrium states
occur, and for instance whether deep roots of established trees limit their
sensitivity to climate shifts. Another source of uncertainty in projections of
vegetation change is potential interactions with local land use, which for
instance could accelerate regional climate change in tropical forests (Malhi
et al., 2008). Despite these uncertainties, higher emissions scenarios will
almost certainly result in climate shifts that are large enough to cause major
vegetation shifts by 2100 and beyond.
Some Climate Changes Beyond 2100
More is known about the very long term (millennia) and the present
century, but there is a gap in understanding and more limited knowledge
of climate system behavior over the next few centuries. Here we present
two examples of areas where information on the next few centuries is
available.
Circulation
About half of the AR4 climate models were used to project the future
climate beyond 2100 to 2200. These simulations were performed using the
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