Climate models are computer programs that simulate weather patterns over time. There are three main types of global climate models: Earth balance models, Earth models of intermediate complexity, and general circulation models. The first climate model was developed in the late 1960s and combined atmospheric and oceanic processes. Climate models help scientists make climate predictions and test theories to better understand the climate system.

1. Chapter 4. Climate change model
Dr. Raja Kathiravan

2. What is Physical models
– Have you ever played with a toy airplane as a child? Maybe you've seen
a model volcano in a museum exhibit that showed how they work or a
classroom demonstration with a jar on how a cloud is produced. These
different types of models are physical representations that simulate
how a real-world situation would behave.
Mathematical or computer simulation models
– A model uses ideas that are tested through some kind of mechanism.
– The ideas are then compared to real-world phenomena to see if they
are valid.
– Earth system models simulate the physical processes that affect climate
and energy—including atmosphere, land, ice, and ocean interactions, as
well as human activities like energy use and agriculture.
– Often they are mathematically constructed using computer programs,
which can be complex.
– These types of models are called mathematical (computer) models.
– When computer models are used to predict the climate they are called
global climate models.

3. How Construct a climate model?
• To build a good model, it must be start with good past data.
• The Ministry of Environment and Forest & Climate Change supports long-
term field experiments involving the world’s most climate-sensitive
ecosystems.
• Building and running a climate model is complex process of
– identifying and quantifying Earth system processes,
– representing them with mathematical equations,
– setting variables to represent initial conditions and
– subsequent changes in climate forcing, and
– repeatedly solving the equations using powerful supercomputers.
Climate Drift: Model drift refers to bad long-term changes in general
circulation models that are unrelated to either changes in external forcing
or internal low-frequency variability.
• Drift can be caused by a number of factors.
• simulation’s initial state may not be in dynamical balance, ‘coupling
shock’’ may occur during the coupling of model components

4. • numerical errors may exist in the model that mean that heat or moisture is
not fully conserved
Conclusion due to Drift
• Drift shows little systematic directional bias either from region to region or
from model to model. As a result, drift generally becomes less important
(compared to any forced trend) for larger regions or when considering
averages across multiple models.
• Drift affects the full ocean, while forced changes, at least over the
historical period, are usually confined to the upper few hundred meters
(except in high-latitude regions),
• drift generally dominates any forced signal below 1–2 km. As such, any
examination of subsurface changes or depth-integrated changes (e.g.,
Space between sea level) must pay particular attention to drift and the
method used for the correction of drift.
• The adjustment time scale of the atmosphere is fast, as the ocean is
coupled to the atmosphere, if surface ocean properties drift then
atmospheric properties will also drift.

5. THE EVOLUTION OF CLIMATE MODELLING
• Climate models lay at the heart of our understanding of the changing
climate.
• Crucially, scientists use models to project how these changes might
continue to play out in the decades ahead.
• But today's cutting-edge models are very different to the first ones
sketched out on paper almost a century ago.
• More than 50 key moments in the development of climate models.
• in 1895, the Swedish physical chemist Svante Arrhenius had described an
energy budget model that considered the radiative effects of carbon
dioxide in a paper presented to the Royal Swedish Academic of Sciences.
• The story of climate modeling using numerical methods begins with Lewis
Fry Richardson, an English mathematician and meteorologist, when he
publishes a book, entitled "Weather Prediction by Numerical Process“

6. • The book describes his idea for a new way to forecast the weather using
differential equations and viewing the atmosphere as a network of
gridded cells.
• when he applies his own method, it takes him six weeks doing calculations
by hand just to produce an eight-hour forecast.
• The Norwegian meteorologist, Vilhelm Bjerknes, who had argued at the
turn of the 20th century that atmospheric changes could be calculated
from a set of seven “primitive equations”.
• Guy Callendar uses a 1D radiative transfer model to show that rising CO2
levels are warming the atmosphere. He did all the calculations by hand,
without the aid of a computer and it is appreciated by the climate scientist
Ed Hawkins.
• John von Neumann, a Princeton mathematician who worked on the
Manhattan Project during the second world war, proposes that new
computers, such as the ENIAC at the University of Pennsylvania, be used to
forecast weather.

7. • A group was formed at Princeton by von Neumann is headed by Jule G
Charney, who later becomes a key figure in climate science.
• In 1950, Using ENIAC computer a 2D model divides the atmosphere into
grid cells in the way Richardson had proposed.
• But it still takes about 24 hours of computing to produce a 24-hour
forecast – with mixed accuracy.
• As Charney’s results begin to improve, the US Weather Bureau and
military decide to create the Joint Numerical Weather Prediction Unit
(JNWPU).
• By May of 1955, the unit is producing real-time forecasts in advance of the
weather using an IBM 701 computer, but the accuracy is inconsistent.
• By 1958, with advances in computing speeds, the unit is producing
forecasts looking out several days.
• A Swedish-Norwegian collaboration beats the JNWPU team by a few
months to deliver the world’s first real-time numerical weather forecast
using BESK ("Binary Electronic Sequence Calculator").

8. • Joseph Smagorinsky, who has worked under both von Neumann and
Charney research unit based in Maryland. The goal is to create a 3D
general circulation model (GCM) of the global atmosphere based on
“primitive equations”.
• It is the first with a permanent programme developing GCMs, is later
renamed the General Circulation Research Laboratory in 1959 and then
renamed again as the Geophysical Fluid Dynamics Laboratory (GFDL) in
1963.
• A Russian climatologist called Mikhail Budyko, publishes a book called (in
English), “The Heat Balance of the Earth’s Surface” . He calculates the
Earth’s average global temperature by balancing incoming solar energy
with outgoing thermal energy.
• Smagorinsky (Russia) and Syukuro Manabe (Japan) work together to
gradually add complexity to the model GCMs, such as the evaporation of
rainfall and the exchange of heat across ocean, land and ice
• Norman Phillips, working under John von Neumann, publishes a paper
entitled, “The general circulation of the atmosphere: A numerical
experiment. His numerical experiment, which realistically depicts seasonal
patterns in the troposphere, is later hailed as the first “general circulation
model” (GCM) of the atmosphere.

9. • Fritz Möller, a University of Munich publishes a paper entitled, "On the
Influence of Changes in the CO2 Concentration in Air on the Radiation
Balance of the Earth's Surface and on the Climate”. Möller concludes that
the “theory that climatic variations are affected by variations in the CO2
content becomes very questionable”.
• Arakawa and Mintz developed “Mintz-Arakawa Model” with the first
iteration running by 1963 and published “Computational Design for Long-
Term Numerical Integration of the Equations of Fluid Motion”.
• The Kasahara-Washington model offers finer resolution, but its main
legacy is that it establishes National Centre for Atmospheric Research
(NCAR) as a leading climate modeling centre from the 1960s onwards.
• The Committee on Atmospheric Sciences at the National Academy of
Science (NAS) publishes a report called Weather and Climate Modification:
Problems and Prospects.
• Kirk Bryan, Michael Cox and Manabe – Bryan is model a 3D circulation of
the ocean through “A numerical investigation of the oceanic general
circulation”.

10. • “A Global Climatic Model Based on the Energy Balance of the Earth-
Atmosphere System”, is published by WILLIAM D SELLERS AND IT SHOWS “The
major conclusions of the analysis are that removing the Arctic ice cap would
increase annual average polar temperatures by no more than 7oC, that a
decrease of the solar constant by 2–5% might be sufficient to initiate another
ice age, and that man's increasing industrial activities may eventually lead to a
global climate much warmer than today.”
• NASA's Nimbus III satellite is launched 1969 carries with it infrared
spectrometers and radiometers to measure atmospheric temperatures and
radiation profiles. But, It failed three months later.
• Manabe and Wetherald using a 3D GCM to investigate for the first time the
effects of doubling atmospheric CO2 levels in 1975.
• Manabe with Kirk Bryan, presents the results from the first coupled
atmosphere-ocean GCM (AOGCM), It takes 50 days of computing to simulate
three centuries of atmospheric and oceanic interactions.
• Various climate modeling groups, including those at UCLA, NCAR and the UK
Met Office, submit papers setting out how their current models work.
particularly the UCLA paper by Akio Arakawa and Vivian Lamb – form the
backbone of most climate models’ “computational domain” for years
afterwards.

11. • In 1980 “WORLD CLIMATE RESEARCH PROGRAMME” were started at
Geneva, to organise observational and modeling projects at an
international scale. Also it is working for understanding and prediction of
El Niño and its associated impact on the global climate.
• In 1983, The Community Climate Model (CCM) is created NCAR in
Colorado, aims to work freely available global atmosphere model for use
by the wider climate research community .
• James Hansen was worked to simulate the global climate effects of time-
dependent variations of atmospheric trace gases and aerosols on 1988.
• To understand the processes influencing climate change and to develop
climate models a Centre for Climate Prediction and Research is opened in
UK in the year 1990

12. What is climate models explain?
Climate models are computer programs that simulate weather patterns
over time. By running these simulations, climate models can estimate the
Earth's average weather patterns of the climate under different conditions

13. Types of Global Climate Models
• In order to make climate predictions such as the Earth's future
temperature, scientists use three types of global climate
models:
• Earth Balance Models (EBMs),
• Earth Models of Intermediate Complexity (EMICs), and
• General Climate Models (GCMs).
Components of climate models
– Atmosphere
– Ocean
– Sea ice
– Land surface
– Marine biogeochemistry
– Ice sheets
– Coupling between the components

14. When was the first climate model?
• In the late 1960s, NOAA's Geophysical Fluid Dynamics Laboratory in
Princeton, New Jersey, developed the first-of-its-kind general circulation
climate model that combined both oceanic and atmospheric processes.
Atmosphere-Ocean General Circulation Models (AOGCMs).
• There is considerable confidence that Atmosphere-Ocean General
Circulation Models (AOGCMs) provide credible quantitative estimates of
future climate change, particularly at continental and larger scales
(adapted from IPCC, 2007).
• The use of AOGCMs is limited in projecting climate change at the regional
and sub-regional level, because significant differences in climate occur at a
scale below the resolution of the AOGCMs.
• The limitations and uncertainties associated with modeling, global
circulation models and regional climate models can be applied usefully to
identify a range of uncertainties allowing strategic policy-making for
adaptation.

15. • Models help us to work through complicated problems and understand
complex systems. They also allow us to test theories and solutions.

16. Earth Balance Models
• The oldest and simplest type of climate model.
They consider a balance of energy entering and
leaving a system (i.e. the Earth).
• Balance energy equations are then used to
calculate the surface temperature using known
variables such as zonal surface temperature and
every latitude zone.
• These models are one-dimensional in the direction of only the latitude of
the Earth. Thus, they are not global models but are zonal or latitudinal
models.
• This means that the flow of energy is considered from one latitude to the
next and not at other smaller locations across the globe.
• This is a disadvantage because each calculation of surface temperature only
considers variables such as surface albedo (the proportion of the incident
light or radiation that is reflected by a surface, typically that of a planet or
moon.), or its surface reflection of solar radiation that is constant for the
whole latitudinal zone.
• The advantage of these models is that they can calculate the energy of the
Earth in detail. They are also simple enough to be used in the classroom as
teaching tools.

17. The global mean temperature T can be modeled by the energy balance equation
(EBM)
The first term on the right is incoming heat absorbed by the Earth and its
atmosphere system. The second term is heat radiating out as if the Earth
were a blackbody with all of the outgoing long wave radiation (OLR)
escaping to space
•T (K, kelvins) is the average temperature in the Earth’s
photosphere(upper atmosphere, where the energy balance occurs in
this model) (1 kelvin = 1C);
• t (years) is time; • R (W-yr/m2K) is the averaged heat capacity of the
Earth/atmosphere system (heat capacity is the amount of heat
required to raise the temperature of an object or substance 1 kelvin (=
1 C));
• Q (W/m2) is the annual global mean incoming solar radiation (or
insolation) per square meter of the Earth’s surface;
• σ (dimensionless) is planetary albedo (reflectivity), and
(W/m2K4) is a constant of proportionality, the Stefan-Boltzmann
constant.

18. • Note that (1) is an autonomous ordinary differential equation (ODE),
meaning that the expression for the derivative does not explicitly involve
the independent variable t. Values for the parameters are:
• R = 2.912 W-yr/m2K) [Ichii et al. 2003, Table 1]; Q = 342 W/m2 [Kaper
and Engler 2013, 17], α = 0.30 [Kaper and Engler 2013, 17], and σ = 5.67
X 108 W/m2 K4.
Earth Models of Intermediate Complexity (EMICs) :
• an important class of climate models, primarily used to investigate the
earth's systems on long timescales or at reduced computational cost.
• are of medium complexity compared to the other two models.
• They are three-dimensional in that they represent physical processes in
three dimensions, including the atmosphere, oceans, land, and the
cryosphere, or sea ice and glaciers on land.
• Compared to the other types, these models can predict climate over
longer time scales of several 10,000 years or glacial years. The
disadvantage is that they only consider the natural Earth system and not
the interaction between humans and nature. They also have coarse
resolution.

19. Figure : Schematic illustration of the structure of the climate model of intermediate
complexity MOBIDIC that includes a zonally averaged atmosphere, a 3-basin zonal
oceanic model (corresponding to the Atlantic, the Pacific and the Indian Oceans) and
simplified ice sheets. More details about this model are available at the
address: http://www.climate.be/index.php?page=MoBidiC%40Description.
Intermediate-complexity
models are models which
describe the dynamics of
the atmosphere and/or
ocean in less detail than
conventional General
Circulation Models (GCMs).

20. Advantages over EBM
• Like EBMs, EMICs involve some simplifications, but they always include a
representation of the Earth’s geography, i.e. they provide more than
averages over the whole Earth or large boxes.
• Secondly, they include many more degrees of freedom than EBMs. As a
consequence, the parameters of EMICs cannot easily be adjusted to
reproduce the observed characteristics of the climate system, as can be
done with some simpler models.
• The level of approximation involved in the development of this model
varies widely between different EMICs.
• Some models use a very simple representation of the geography, with
a zonal averaged representation of the atmosphere and ocean.
• A distinction is always made between the Atlantic, Pacific and Indian
basins (Fig.) because of the strong differences between them in the
circulation. As the atmospheric and oceanic circulations are fundamentally
three-dimensional, some parameterizations of the meridional transport
are required.
• Those developed for EMICs are generally more complex and physically
based than the ones employed in 1-D one-dimensional EBMs.

21. • On the other hand, some EMICs include components that are very similar to
those developed for GCMs, although a coarser numerical grid is used so that
the computations proceed fast enough to allow a large number of relatively
long simulations to be run.
• Some other components are simplified, usually including the atmosphere
because this is the component that is most depending on computer time in
coupled climate models.
General circulation models (GCM)
• General circulation models provide the most precise and complex
description of the climate system.
• Currently, their grid resolution is typically of the order of 100 to 200 km.
As a consequence, compared to EMICs (which have a grid resolution
between 300 km and thousands of kilometres), they provide much more
detailed information on a regional scale.
• A few years ago, GCMs only included a representation of the atmosphere,
the land surface, sometimes the ocean circulation, and a very simplified
version of the sea ice.
• Nowadays, GCMs take more and more components into account, and
many new models now also include sophisticated models of the sea ice,
the carbon cycle, ice sheet dynamics and even atmospheric chemistry
(Fig. ).

22. A simplified representation of part of the domain of a general circulation model, illustrating
some important components and processes. For clarity, the curvature of the Earth has been
amplified, the horizontal and vertical coordinates are not to scale and the number of grid points
has been reduced compared to state-of-the-art models.
Because of the large
number of processes
included and their relatively
high resolution, GCM
simulations require a large
amount of computer time.
For instance, an experiment
covering one century
typically takes several weeks
to run on the fastest
computers. As computing
power increases, longer
simulations with a higher
resolution become
affordable, providing more
regional details than the
previous generation of
models.

23. • But the United Nations' Intergovernmental Panel on Climate Change
simply averages up the 29 major climate models to come up with the
forecast for warming in the 21st century, a practice rarely done in
operational weather forecasting.
• A global climate model (GCM) is a complex mathematical representation
of the major climate system components such as atmosphere, land
surface, ocean, and sea ice, Marine biogeochemistry, Ice sheets,
Coupling between the components - Earth system models and their
interactions.
• Earth's energy balance between these seven components is the key to
long-term climate prediction.

24. Global average response to warming
• What is the response to global warming?
Responding to climate change involves two possible approaches:
• reducing and stabilizing the levels of heat-trapping greenhouse gases in
the atmosphere (“mitigation”) and
• adapting to the climate change already in the pipeline (“adaptation”).
• three responses to global warming are resistance, resilience, and
transition
• According to NOAA's 2021 Annual Climate Report
• the combined land and ocean temperature has increased at an average
rate of 0.14 degrees Fahrenheit ( 0.08 degrees Celsius) per decade since
1880; however, the average rate of increase since 1981 has been more
than twice as fast: 0.32 °F (0.18 °C) per decade.
• Over the last century, the average surface temperature of the Earth has
increased by about 1.0o F (=0.56oC). In 2050 it may increase 2.7oF (1.5oC).

25. Climate change observed to date are
– a reduction in the mass of global ice caps and glaciers, r
– icing sea levels,
– acidification of our oceans, and
– increased frequency and intensity of extreme weather events.
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