Chapter 2
Observational Requirements for
Modeling of Global and Regional
Climate Change
Anthony D. Del Genio
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY 10025
USA
2.1 Introduction
Predicting the rate and geographic distribution of future climate changes caused by anthropogenic perturbations such as increasing greenhouse gas and aerosol concentrations is perhaps
the most important single problem in the earth sciences today. General circulation models
(GCMs) are the tools of choice for making such projections. Simulating climate change with
GCMs has become a worldwide activity; 12 modeling groups thus far have performed equilibrium doubled CO2 calculations with atmosphere-only GCMs, and 8 are simulating transient
greenhouse gas increase scenarios with coupled ocean-atmosphere models for the 1995 IPCC
scientific assessment.
Unfortunately, the predictions of the various modeling groups differ widely: equilibrium warmings range from 1.7 to 5.3°C, and the rate and geographic distribution of warming depends
on the type of ocean representation used and the type of climate forcing assumed (e.g., whether
effects of tropospheric aerosols are included in addition to greenhouse gases). In fact, it has not
been proven that decadal climate change is predictable; in simple models of the coupled system,
multiple equilibria are easily produced with slightly different initial conditions (Marotzke and
Willebrand, 1991). This latter aspect of climate change requires a fundamental breakthrough
in our understanding of the coupled climate system, and it does not appear to be particularly
amenable to insight using observations of the current climate. But the issues of how to specify
accurate climate forcings and simulate realistic feedbacks as responses to these forcings can
definitely benefit from a thoughtfully designed observing strategy.
In this paper we address the question of how data sets and models can be used together to
ultimately produce more accurate predictions of climate change (within the constraints set by
the unknown predictability of the system). Section 2.2 describes the current status of climate
models and model-data comparisons as they pertain to climate change prediction. Section
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
Ii:> Springer-Verlag Berlin Heidelberg 1996
Observational Requirements for
Modeling of Global and Regional
Climate Change
Anthony D. Del Genio
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY 10025
USA
2.1 Introduction
Predicting the rate and geographic distribution of future climate changes caused by anthropogenic perturbations such as increasing greenhouse gas and aerosol concentrations is perhaps
the most important single problem in the earth sciences today. General circulation models
(GCMs) are the tools of choice for making such projections. Simulating climate change with
GCMs has become a worldwide activity; 12 modeling groups thus far have performed equilibrium doubled CO2 calculations with atmosphere-only GCMs, and 8 are simulating transient
greenhouse gas increase scenarios with coupled ocean-atmosphere models for the 1995 IPCC
scientific assessment.
Unfortunately, the predictions of the various modeling groups differ widely: equilibrium warmings range from 1.7 to 5.3°C, and the rate and geographic distribution of warming depends
on the type of ocean representation used and the type of climate forcing assumed (e.g., whether
effects of tropospheric aerosols are included in addition to greenhouse gases). In fact, it has not
been proven that decadal climate change is predictable; in simple models of the coupled system,
multiple equilibria are easily produced with slightly different initial conditions (Marotzke and
Willebrand, 1991). This latter aspect of climate change requires a fundamental breakthrough
in our understanding of the coupled climate system, and it does not appear to be particularly
amenable to insight using observations of the current climate. But the issues of how to specify
accurate climate forcings and simulate realistic feedbacks as responses to these forcings can
definitely benefit from a thoughtfully designed observing strategy.
In this paper we address the question of how data sets and models can be used together to
ultimately produce more accurate predictions of climate change (within the constraints set by
the unknown predictability of the system). Section 2.2 describes the current status of climate
models and model-data comparisons as they pertain to climate change prediction. Section
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
Ii:> Springer-Verlag Berlin Heidelberg 1996