Geoscience Reference
In-Depth Information
24
Future climate change and
arid zone geomorphology
Richard Washington and David S. G. Thomas
24.1
Introduction
major climate modelling groups in the world. As a re-
sult of this effort, monthly (and in many cases daily) data
from more than 20 GCMs are available up to the year
2100 at a spatial resolution of approximately 2.5
Climate change and its impact on arid zones, particularly
during the Late Quaternary, has served as an important
source of knowledge of both processes and rates of change
in arid zone geomorphology, highlighting the dynamism
and sensitivity of arid regions. Future climates will also
change as a result of a variety of mechanisms and are pre-
dicted to do so at an unprecedented rate in forthcoming
decades. What is different about the twenty-first century,
however, is that for the first time in the Earth's history we
have predictive tools that quantify the nature and extent
of future climate change. Driven largely by greenhouse
gas emissions, initially emitted from fossil fuel burning
and then supplemented by feedbacks in the Earth System
towards the end of the century, this change can be simu-
lated in global climate model s (GCMs), thereby allowing
at least some of the changes to be anticipated.
This chapter provides an overview of the basis for un-
certainties in, and nature of, climate change projections
in arid zones from global climate models. This is nec-
essary before discussing the potential geomorphological
impacts of these changes, on dunes, dust and hydrological
changes.
×
2.5
degrees or roughly 250 km
250 km, with finer resolu-
tion for higher latitudes). These models are forced with
changing gaseous atmospheric composition, which results
from emissions from fossil fuel consumption. Increasing
greenhouse gas concentration is therefore the basis for pre-
dicting climates of future decades. Since these emissions
cannot be known from first principles, several possible
agreed concentrations of emissions have been established
and these are referred to as the Special Report on Emission
Scenarios (SRES). An often used subset of these scenar-
ios, together with the corresponding global temperature
increase, is as follows:
×
SRESA2 - a high future emissions scenario that results
in a best estimate temperature change of
Cby
3.4
2100.
SRESA1B - a more middle-of-the-road future emissions
scenario of
2.8 C by 2100.
1.8 C
SRESB1 - a low future emissions scenario of
by 2100.
24.2 Climate change projections: basis
and uncertainties
These emission scenarios are often referred to as A2,
A1B and B1 or high, middle and low, respectively.
There are numerous uncertainties involved in mak-
ing climate change projections even before the impacts
of climate change are considered. Climate models are
the only approach available for making projections, but,
The Intergovermental Panel on Climate Change Fourth
Assessment Report (IPCC AR4) featured a coordi-
nated global climate modelling exercise involving all the
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