GCMs

1. General Circulation Models (GCMs)

2. General Circulation Models (GCMs)
 Definition:
 General Circulation Models, or GCMs,
are complex computer programs that
scientists use to simulate and study the
Earth’s climate system.
 They help us understand how the
climate works now, how it worked in
the past, and how it might change in
the future.

3. General Circulation Models
(GCMs)
 GCMs are like a digital Earth, divided
into small pieces, where every part
interacts with the others — the
atmosphere, oceans, land, and ice.
 Think of it like a giant weather
simulator that not only predicts
tomorrow’s weather but also shows
how the climate could change in the
next 50–100 years.

4. 1. Components of GCMs
 GCMs simulate the Earth by dividing it into
four main components:
 Atmospheric Component:
 This part simulates (To act like the real thing
for practice or understanding)the air
around us — the atmosphere . It considers
temperature, wind patterns, pressure,
clouds, and humidity.
 Example: It helps predict how a heatwave
might spread across continents.

5. Ocean Component:
 This part simulates oceans, including
currents, temperature, salinity
(saltiness), and how oceans interact
with the atmosphere.
 Example: It can show how El Niño
(warming of Pacific Ocean) affects
rainfall in different parts of the world.

6. Land Surface Component:
 Simulates land processes such as
 Vegetation
 soil moisture
 snow cover
 and heat exchange.
 Example: Helps predict how a drought
could affect crops in a region.

7. Ice Component:
 Simulates polar ice sheets and sea ice
and their effect on climate.
 Example: Shows how melting ice in
Greenland could increase sea levels
globally.

8. 2. Grid System
 The Earth is divided into a three-dimensional
grid (like tiny cubes or blocks).
 Each grid cell represents a specific area on Earth,
 and the model calculates climate variables for
that cell.
 Example: Imagine covering a globe with tiny
boxes;
 each box has its own temperature, wind speed,
and rainfall data.
 This makes it easier to understand regional
climate variations.

9. 3. Physical Laws
 GCMs follow basic laws of physics such as:
 Conservation of energy (energy cannot
disappear)
 Conservation of mass (matter cannot
disappear)
 Conservation of momentum (movement
rules)
 These laws explain how energy moves
between the sun, atmosphere, oceans, and
land.

10. 3. Physical Laws
 Example: If sunlight heats the ocean,
GCM calculates how that energy
transfers to the air and affects wind
patterns.

11. 4. Climate Projections
 GCMs are used to predict future climate based
on greenhouse gas (GHG) scenarios.They
simulate:
 Temperature changes (will it get hotter?)
 Precipitation patterns (more rain, less rain, or
droughts?)
 Other climate variables like wind patterns or
ocean circulation.
 Example: A GCM might predict that South Asia
will experience more intense monsoon rains by
2050 under high emissions.

12. 6. Use in Climate Research
 GCMs are extremely important in climate
science because they:
 Help policymakers plan for climate change.
 Aid in disaster preparedness, like predicting
floods or heatwaves.
 Help researchers study long-term climate
trends, such as global warming and sea-level
rise.
 Example: Using GCMs, the UN’s IPCC reports
estimate that global temperatures could rise
1.5°C to 4°C by 2100 depending on emissions.

13. 5. Validation and Calibration
 Validation: Scientists compare GCM
results with historical climate data to
check if the model is accurate.
 Calibration: Adjusting the model to
correct errors and improve predictions.
 Example: If a model predicts rainfall
higher than reality, scientists adjust
parameters to match historical
observations.

14. Easy Analogy:
 Think of the Earth as a huge, complex
engine. GCMs are like a super advanced
simulator that shows how every part of
the engine (air, water, land, ice) affects
the others.
 By testing different “fuel scenarios”
(greenhouse gas emissions), scientists
can see what happens in the future and
prepare for it.

15. Thank you