Climate Modelling
Demonstrating and Predicting
Climate Change
How Do We Know Today’s Changes
Aren’t Natural?
• Today, scientists are more than 90 % certain that
current changes in climate are due to human
emissions of greenhouse gases.
• How do scientists know that today’s changes are
human-caused, and not natural?
1. They develop complex computer models of the
climate system to test the effects of different factors
on the climate system.
2. They compare current changes to changes that have
happened in the past.
Scenario 1: Natural Changes Only
• This scenario models an Earth with only
natural factors affecting climate.
• The scenario includes natural changes in the
Sun’s energy, volcanic eruptions, and natural
emissions of greenhouse gases.
Scenario 2: Natural and Anthropogenic Factors
• This scenario includes both natural factors and
human emissions of greenhouse gases.
Which scenario fits observed data?
More models, same conclusion
What is the conclusion?
• Scenario #2, including human emissions of
greenhouse gases, matches real-life observations
very closely. This shows that human emissions of
greenhouse gases are affecting the global
climate.
• Are today’s changes greater than natural changes
in the past?
• Greenhouse gas levels in the atmosphere are
higher today than they have been for the last 800
000 years.
Hasn’t it been hot in the past?
• Although Earth’s temperature is not yet higher
than it has been in the past 800 000 years,
scientists are concerned that the high levels of
greenhouse gases will cause Earth to warm up
very quickly over the next 100 years.
• Temperatures 1°C – 2°C warmer may have
been suitable for past ecosystems, but
humans have evolved and adapted to current
climate conditions
What about the future?
• A climate projection is a scientific estimate of
future climate conditions
• Also called GCMs (general circulation models,
or global climate models) they are based on
many variables such as:
– Nutrient cycles (especially carbon and water)
– Concentrations of GHGs and how they will change
– Positive and negative feedback loops
– Ocean currents, and wind currents
GCMs
• Represent the physical processes in the
atmosphere, ocean, cryosphere and land
surface
• GCMs depict the climate using a three
dimensional grid over the globe
Uncertainty in GCMs
• some physical processes, such as those related to
clouds have to be averaged over large areas
• various feedback mechanisms have to be
simulated, for example, water vapour and
warming, ocean circulation and ice/snow albedo
• Most of the uncertainty comes from not knowing
what choices humans will make in the future
– Will we continue to use fossil fuels?
– Will we switch to clean energy sources?
United Nations IPCC
• Policy makers and the public rely on information from
the United Nations Intergovernmental Panel on Climate
Change
• The latest (2007) IPCC reports show that climate change
will cause dire impacts on humanity
• But because of time constraints, political influence, and
consensus requirements, the IPCC reports reflect a bestcase analysis of climate change
• Some people feel that these reports are too
conservative
Bell Curve of Possible Outcomes
Biblical
IPCC
Game Over
“Black Swan”
• Rare event beyond the realm of normal
expectations
• Usually hard to predict
• Large impact – changes everything
• Usually “predicted” in hindsight
• Examples: Transistor, 9-11,
Internet, Global Warming
“Black Swan”
Turkey’s
Confidence
0
Surprise!
Time
Models
Discontinuous
IPCC
Discontinuities are common throughout
nature
• H2O
Liquid
Solid
-4°C
0°C
4°C
Actual Arctic Melt vs IPCC Models
IPCC Climate Model
MIT Temperature Study
• Danger
2009 MIT Study:
95% chance that
“Business-as-usual”
temperature increase
will exceed 3.5ºC (6.3ºF)
in 2095
MIT Temperature Study
• Danger
and a 50% chance that
temperature will exceed
5ºC (9ºF)!
MIT Temperature Study
Temperature Impact Analogy
+2°C
20 mph
Temperature Impact Analogy
+4°C
40 mph
Temperature Impact Analogy
+6°C
60 mph
Choices
To Act or Not to Act:
4 Outcomes
No Climate Change
We Act
Waste Money
Invent new technology
Reduce reliance on oil
Life goes on
We Do NOT Act
Concept from:Greg Craven
Yes Climate Change
Spend Money
Save 1B Lives
Invent new technology
Reduce reliance on oil
Billions die
Large wars
Horrible famine and drought
End of world as we know it
Total economic collapse
Why Don’t We Act?
Failure of the “Risk Thermostat”
We respond strongest
to threats that are:
Visible
With historical precedent
Immediate
With simple causality
Caused by another “tribe”
Have direct personal impacts
Climate Change is:
Invisible
Unprecedented
Drawn out
With complex causality
Caused by all of us
Unpredictable & indirect impacts
Denial Strategies
Displaced commitment “I protect the environment in other ways”
Condemn the accuser “You have no right to challenge me”
Denial of responsibility “I am not the main cause of this problem”
Rejection of blame “I have done nothing wrong”
Ignorance “I didn’t know”
Powerlessness “I can’t make any difference”
Fabricated constraints “There are too many impediments”
After the flood “Society is corrupt”
Comfort
“It’s too hard for me to change my
behavior”
Climate Simulation
• http://forio.com/simulation/climate-development/