Mediterranean Ecosystems Worldwide: Climate Adaptation - Recent Advances and Issues in Environmental Science - page 38

DISCUSSION
This analysis provides the most comprehensive assessment to date of how climate
change is projected to impact mediterranean climates in all five mediterranean regions
across the globe and the implication of the climate change for adaptation potential of
the native biota. By analyzing the full suite of multiple simulations of 23 AOGCMs
under multiple emissions scenarios, we are able to present quantitative estimates of the
level of agreement in the projected contractions in the MCE. Previous studies focus
on one or several “bookend” AOGCM runs that attempt to encompass the range of
variability in the future projections. If one model projects a wetter future and the other
a drier future, the recommendations for conservation action could be vastly different
with no method for determining which future is more likely. This study quantifies
the level of agreement between a full suite of projected climatic futures, providing a
more robust and conservative estimate of impact and thus more confidence to support
conservation action.
One of the fi rst challenges to projecting the impacts of climate change on mediter-
ranean ecosystems worldwide is defi ning the MCE. The extent of the mediterranean
biome is typically mapped based on a combination of climate characteristics and plant
assemblages that vary from region to region [2]. Projecting how plant assemblages
will shift in response to climate change is subject to signifi cant uncertainty because it
requires compounding the uncertainty with projecting climate change with the uncer-
tainty inherent in projecting future distributions of individual species [24, 25]. In this
analysis, we minimize the uncertainty and focus on mediterranean climate shifts in the
future. As such, we utilize a conservative defi nition of mediterranean climate [17] that
is consistent across all mediterranean regions and minimizes “false-positives” (areas
that are not considered part of the mediterranean biome). Some areas that are tradition-
ally considered part of the mediterranean biome are not within our current or future
MCE, including the south coast of France, western Italy, northeastern Spain, portions
of central Chile, and the southern coast of South Africa. Most of these areas receive
less than 65% of their rain in the winter, and thus do not meet the fi rst Aschmann
condition (Figure 5). Despite the conservative nature of this defi nition, we do include
some false-positives, including parts of Argentina and the Middle East. These com-
missions could be the result of a lack of climate station data in these more remote and
mountainous areas. We performed a sensitivity analysis with the Köppen defi nition of
mediterranean climate, which is less conservative. This defi nition identifi es more of
the traditional areas, but also includes large areas of false-positives. However, when
focusing in on the fi ve mediterranean regions, the results of the projected fate of the
MCE are very similar using both defi nitions.
While there are some signifi cant discrepancies between our map of the current
MCE and commonly used maps of the mediterranean biome, such as the one mapped
by Olson et al. [2], preliminary analysis indicates signifi cant overlap between the
current MCE and the mapped hotspots of plant richness and endemism within the
mediterranean biome. Our current MCE corresponds well with the biogegraphical sec-
tors with high incidences of plant endemism in the Mediterranean Basin [7], areas of
high modeled endemic Banksia species richness in Western Australia [11], and areas