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.

• This scenario includes both natural factors and human emissions of greenhouse gases.

Scenario 2: Natural and Anthropogenic Factors

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 best-case analysis of climate change

• Some people feel that these reports are too conservative

Bell Curve of Possible Outcomes

IPCC

Biblical

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”

Time

Turkey’sConfidence

Surprise!

0

Models

IPCC

Discontinuous

Discontinuities are common throughout nature

• H2O

-4°C 0°C 4°C

Liquid

Solid

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 Yes Climate Change

We Act

We Do NOT Act

Waste MoneyInvent new technologyReduce reliance on oil

Spend MoneySave 1B LivesInvent new technologyReduce reliance on oil

Life goes on Billions dieLarge warsHorrible famine and droughtEnd of world as we know itTotal economic collapse

Concept from:Greg Craven

Why Don’t We Act?Failure of the “Risk Thermostat”

We respond strongest

to threats that are: Climate Change is:

Visible Invisible

With historical precedentUnprecedented

Immediate Drawn out

With simple causality With complex causality

Caused by another “tribe”Caused by all of us

Have direct personal impactsUnpredictable & 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/