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Projections of future Climate Change
Lead Authors: Boer, G.J, Stouffer R.J, Dix M, Noda A, Senior C.A,
Raper S, Yap K.S
Presenter: Rudzani Makhado
Module: Climate Change
Lecturer: Dr Richard Knight
Assignment task: Article Review
University of Western Cape
Due date: 09 Sep 2005
Table of Contents
1. Introduction
2. Climate Change
3. Projections of Climate Change
4. Conclusion
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Note: Click on the underlined hyperlinked words for further information
Introduction
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The purpose of this review is to assess and quantify
projections of possible future climate change, from the
hierarchy of models to provide indicators of global as well as
regional patterns of climate change.
One type of the configuration in this climate model hierarchy is
an Atmospheric General Circulation Model (AGCM), with
equations describing the time evolution of temperature, winds,
precipitation, water vapour and pressure.
It was until the late 1980s, where a more comprehensive
Atmosphere-Ocean Global Climate Models or AtmosphereOcean General Circulation Model or simply AOGCMs begun to
run with slowly increasing CO2, and preliminary results of these
models appeared in the 1990 IPCC Assessment (IPCC, 1990).
Introduction Cont…
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Since 1995, sequence of experiments continued, including
additional forcings, experimenting other greenhouse gases
such as Chlorofluorocarbon (CFCs).
Climate Change
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Climatic changes may occurs, both naturally (eruption of
volcano) and as a consequence of human activity (burning of
fossil fuel).
Climate models are used to quantify this changes, based on
the physical processes governing the climate system.
The simulated climate change depends, therefore, on projected
changes in emissions, the changes in atmospheric
greenhouse gases and particulate (aerosols) concentrations
that result, and the manner in which the models respond to
these changes.
Climate Change Cont…
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The response of the climate system to a given change in
forcing is broadly characterised by its “climate sensitivity”.
Since these requires many years to come into equilibrium with
a change in forcing, remains a “commitment” to further climate
change even if the forcing itself ceases to change.
The availability of multiple simulations from a given model with
the same forcing, and of simulations from many model with
similar forcing, allows ensemble change and the agreement or
disagreement (a measure of reliability) of models results.
Projections of Climate Change
-Projections of future climate change can be stimulated from Global
Mean Response, Patterns of Future Climate Change, Range of
Temperature Response to SRES Emission scenarios, Factors that
Contribute to the Response, Changes in Variability and Changes
of Extreme Events.
1. Global Mean Response
There are number of new AOGCM climate simulations with various
forcings that can provide estimates of possible future climate
change. Each model’s simulation of a future climate state is
treated as a possible outcome for future climate. These
simulations falls under three categories:
Projections of Climate Change Cont…
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The first are integrations with idealised forcing, namely, 1%/yr
compound increase of Carbon dioxide (CO2), which also
represents other greenhouse gases like methane. These runs
extend at least to the time of effective CO2 doubling at year 70,
and are useful for direct model intercomparison since they use
exactly the same forcing and thus are valuable to calibrate model
response.
A second category of AOGCM climate model simulations uses
specified time-evolving future forcing where the simulations start
sometime in the 19th century to the 20th century. The state is
subsequently used to begun simulations of future climate with
estimated forcings of greenhouse gases.
A third category are AOGCM simulations using as an initial state
the end of the 20th century integrations, and then following the A2
and B2 scenarios. These simulations are assessed to quantify
possible future climate change and its consistency at the end of
the 21st century.
Projections of Climate Change Cont..
2. Patterns of Future Climate Change
For the change in annual mean surface air temperature in the various
cases, the model experiments show the familiar pattern
documented in the Second Assessment Report of the IPCC, with
a maximum warming in the high latitudes of the Northern
Hemisphere and a minimum in the Southern Ocean (due to ocean
heat uptake), evident in the zonal mean for the CMIP2 model and
the geographical patterns for all categories of models (Figure 1).
Projections of Climate Change Cont..
Figure 1: Multi-model ensemble of annual mean temperature change.
However, difference in models also occurs especially in the regional
moderating of warming mainly over industrialised areas.
Projections of Climate Change Cont..
3. Range of Temperature Response to SRES Emission Scenarios
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This section investigates the range of future global mean
temperature changes resulting from the thirty-five final SRES
emissions scenario with complete greenhouse gas emissions.
To investigate this, implications of the full range of the final SRES
scenarios, a simple climate model is used as a tool to simulate the
AOGCM results (Wigley and Raper, 1992).
Atmospheric concentrations of greenhouse gases are calculated
from the emissions using gas cycle model (Widley 1993).
Although, the strength of the climate feedbacks on the carbon
cycle are uncertain, the models show that they are in the direction
of greater temperature change, giving greater atmospheric CO2
concentrations.
Projections of Climate Change Cont..
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The estimated total historical anthropogenic radiative forcing
from 1765 to 1990 followed by forcing resulting from the six
illustrated SRES scenarios are both shown in (figure 2: Simple
model results)
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Based on the comparison using the simple climate model, the
final scenarios for the three markers A1B, A2 and B2 give
temperature changes that are slightly smaller than the draft
scenarios (Smith et al., 2001).
Projections of Climate Change Cont..
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The change in the scenarios is 1 to 2%. However, in the longterm, the level of emissions of long-lived greenhouse gases such
as carbon dioxide and nitrous oxide become the dominant
determinant of the resulting global mean temperature changes.
Projections of Climate Change Cont..
4. Factors that Contribute to the Response
Factors that contribute to the climatic models response includes the
followings:
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Climate sensitivity- a basic measure of the response of the climate
system to a change in forcing.
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The role of climate sensitivity and ocean heat uptake.
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Thermohaline circulation changes, and
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Time-scale of response.
Projections of Climate Change Cont..
5. Changes in Variability
The capacity of the models to stimulate the large-scale variability of
climate (e.g. El Niňo-Southern Oscillation, ENSO) has improved in
recent years through the development of ocean-atmosphere
models. These changes in variability occurs on different timescale as outlined below:
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Intra-seasonal variability (daily precipitation variability, Circulation
patterns),
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Interannual variability-year-to-year variability in climate features
(e.g. ENSO, MONSOON) and
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Decadal and Longer time-scale variability.
Projections of Climate Change Cont..
6. Changes of Extreme Events
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Possible future changes in extreme weather and climate event
are assessed from global models. These models stimulate
changes in temperature, precipitation and convection, Extratropical storms, Tropical cyclones and Commentary on changes
in extremes of weather and climate to predict climatic changes.
Although, these models have improved over-time, still some
limitations that affect the stimulations of extreme events in term
of special resolution and simulation errors due exists.
Conclusion
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Climatic models are the viable tools to predict future climatic
changes.
However, there is a need to improve our understanding of
climate changes so as correct some of the errors encountered in
climate change models.
References
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IPCC (1990) Climate Change: The IPCC Scientific Assessment.
Contribution of Working Group I to the First Assessment Report
of the Intergovernmental Panel on Climate Change. In: Houghton J.T,
Jenkins G.J and Ephraums J.J (eds). Cambridge University
Press,
Cambridge, UK and New York. 365pp
Smith S. J, Wigley T.M.L, Nakic´enovic´ N and Raper S.C.B (2001) Climate
implications of greenhouse gas emission scenarios. Technological
Forecasting and Social Change, 65, 195-204.
Wigley T.M.L and Raper S.C.B (1992) Implications for Climate and Sea level
of revised IPCC emission scenarios. Nature, 330, 127131
Widley T.M.L (1993) Balancing the Carbon Budget. Implications for
Projections of Future Carbon dioxide concentration changes. Tellus,
45B, 409-425
Additional Readings
For more information on this subject, visit the
following sites.
Climate Change Prediction
Future Projection on Climate Change
Global Climate Change
Intergovernmental Panel on Climate Change (IPCC)
Projections of Climate Change