IPCC

1992: Still trying to sort out effects of natural variation and human impacts

1996: “The balance of evidence suggests a discernible human influence on global climate”

2001: Humans are “likely” to cause global warming2007: Humans are “very likely” to cause global warming.

Two notes: 1) In scientific talk, it does not get much more certain than “very likely”; and 2) The IPCC is inherently conservative and often supports minimum possible climate change (rather than maximum possible change).

Projections of human behaviour not easily amenable to prediction (e.g. evolution of political systems).Chaotic components of complex systems.

Inadequate models, incomplete or competing conceptual frameworks, lack of agreement on model structure, ambiguous system boundaries or definitions, significant processes or relationships wrongly specified or notconsidered.

Missing, inaccurate or non-representative data, inappropriate spatial or temporal resolution,poorly known or changing model parameters.

Images from IPCC report

Radiative Forcing

To compare different variables, you need a common unit (to compare apples with apples, as

the saying goes).

Radiative forcing is the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system.

A positive forcing (more incoming energy) tends to warm the system, while a negative

forcing (more outgoing energy) tends to cool it.3

A Watt (as in James)

A unit of power = Work / time(Your standard household bulb uses 60 Watts)

Because we care about the Earth’s surface, we use Watts/meters2

I like steam engines. A lot.

4

Image from Thinkquest

So, what causes radiative forcing?

Solar input - relatively constant, but can be slightly higher or lower than usual

Sunspots

Chinese records of sunspots go back to Book of Changes (800 B.C.E.): "A dou is seen in the Sun" and "A mei is seen in the Sun". ”Dou" and "mei" are taken to mean darkening or obscuration.

Author: Hans Bernhard

Image from nasa.gov

So, what causes radiative forcing?

Solar input - relatively constant, but can be slightly higher or lower than usual

CO2 (& other greenhouse gases) - increases radiative forcing

Aerosols - decreases radiative forcing

Year AD

1800 1850 1900 1950 2000

W/m

2

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

CO2

Temperature

Solar

Aerosols

Components of a fully coupled general circulation model

GCMs contain our best current understanding for how the physical processes interact (for instance, how evaporation depends on the wind and surface temperature, or how clouds depend on the humidity and vertical motion) while conserving basic quantities like energy, mass and momentum. These estimates are based on physical theories and empirical observations made around the world.

Removed image due to copywright. It can be found at the Australian Department of Meteorology.

Development of climate models over time

IPCC, adopted by Australian Department of Climate Change and Energy Efficiancy

Models

We cannot predict how one variable will inherently influence another. Therefore, we have to make models. Models lead to “emergent” properties, which is large scale behavior that is not a priori predictable from the small scale interactions that make up the system.

Models are inherently theoretical. As such, they are often very quantitative.

Models (con’t)All models are wrong; some models are useful.

-G.E. Box (UW Professor)

These models are all simplifications of the actual phenomena. But these models can still be valuable.

The problem with models (or any theoretical approach) lie in the assumptions.

IPCC: Critical aspects

Validation - assessment of the accuracy of the model

Attribution - the ability to assign causes to effects (distinguish causation from

correlation)

Prediction - specification, in advance, of events or changes in a system

Validation

Validation reflects an assessment of the accuracy (not precision) of the model.

This is done by attempting to duplicate current climate data, or “backcasting” (as

opposed to forecasting) past climates when the Earth was very different (such as 18,000 years ago, during the maximum extent of the

ice age).

Image from IPCC

Science is the investigation of the natural world, based on

the rules of reason and logic. Science is testable and/or

predictable.

How do you test a model, particularly of a GCM (Global

Climate Model)?

1963 Mount Agung (Indonesia) volcanic eruption(ok, really, this is a picture of the 1991 Mount Pinatubo eruption)

1981

Jim Hansen

We can test our GCM!

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They found that the changes calculated by their simple model corresponded in all essential respects — including timing and approximate magnitude — to the observed global temperature changes. The GCM worked!

But, more importantly, the the results also showed that volcanic aerosols could significantly cool the surface.

Hot dog! It works!

Image source: New York Times

AttributionThe ability to assign causes to

effects.

This is a problem inherent in systems with multiple variables.

The simplest approach is “sensitivity analysis”, in which each variable is tested for its

possible effect. The IPCC report is all about attribution.

Is CO2 the only greenhouse gas that is important?

It turns out (unfortunately), no.

1) Methane (CH4) - From rice paddies and cows.2) N2O - from agriculture, including fertilizer3) Ozone (O3) - not anthropogenicand…4) CFCs (Chloroflorocarbons) - From refrigeration

and spray (and fire retardant)

The big problem is that these gases could be much more potent than CO2. But, an even bigger problem was,……

Image from NOAA

Despite the fact that these gases are much less abundant, they are much more potent than CO2. But, for the case of CFCs, there was an even bigger problem…..

Image from NASA

The Ozone hole

In addition to being greenhouse gases, CFCs destroy ozone (O3). Consequently, they cause an ozone hole over the South Pole.

Note that the ozone hole has no effect on global warming (except that the presence of CFCs both destroys the ozone AND causes global warming).

Source: NASA

The Ozone hole

CFC’s in the stratosphere = Ozone hole.

CFC’s in the troposphere = global warming

Source: NASA

The Ozone hole

This ozone debate plays out like this:

1. Scientists report that CFCs are causing problems with ozone layer.

2. Industry denies that this is a problem.

3. Scientists confirm this problem.

4. Industry maintains that it is too expensive to switch to other propellants in spray bottles.

5. Under international pressure, CFCs are outlawed* in the 1997 Montreal accords.

6. Industry finds new propellants (there is no major loss in the spray industry and some indications that there is some economic gain by switching away from CFCs).

*CFCs are still being produced in some third world countries.

Source: NASA

IPCC

Prediction

Specification, in advance, of events or changes in a system.

Again, the IPCC includes many predictions, based on the outcomes of the GCMs.

IPCC & GCMs

The IPCC reports are based on the composite

results of a variety of different GCMs.

It is important to realize that the GCMs just act to quantifiy (“put numbers on”) the effects that are

already occurring.

National Center for Atmospheric Research laboratory in Boulder, Colorado

Source: Wikipedia

IPCC 2007

Image from NASA

Image from NASA

Image by Robert A. Rohde for Global Warming Art

GCMs are a different approach to science:

Although we can separate the variables and treat each individually, they interact with each other.

This type of interaction requires that you do science in a different way than has been done in the past: Integrated and with a systems approach. This is sometimes known as holistic. This approach must be done IN ADDITION to the reductionist approach.

This is the second of the major divisions in science:

1) Empirical-theoretical2) Reductionistic-holistic

Source: Robert A. Rohde

Holistic scienceAn analogy

The doctor can help a patient who has cancer. But, this solves a symptom, not the cause. Society is usually willing to solve a symptom.

But, if you want to really solve the problem, you have to study the system. This requires a systematic approach, looking at environmental, genetic predisposition, and individual facts (the field of epidemiology) as well as basic understanding of cell processes (molecular biology).

The medical community has been extremely successful at getting both funded. This is less true for the scientific community.

(Image of doctor and patient)

(Image of scientists studying a town)

Holistic science & Science of the future

Problem based

Interdisciplinary

Problems of society, not problems of science (such as, How do we maintain a habitable Earth?)

Emphasis on predictive power of science

Systems with multiple variables

1) Sensitivities

2) Positive feedbacks

3) Negative feedbacks

4) Thresholds (“Tipping points”)

5) Complexity (non-linear feedbacks)

Thresholds

Side view Back view

Source: Wikimedia Commons, Bart de Goeij Source: Wikimedia Commons, Gertjan R.

Feedback Loops & Tipping Points

http://www.youtube.com/watch?v=5T_3WJPYY9g

First 6:45 of video

Tipping points

http://www.youtube.com/watch?v=XJNH3HTDpuk

Interview with Jim Hansen

After 1975, it is all about Global Climate Models

• 1956 – first GCM (Phillips)• 1975 – model of 2xCO2 predicts several

degree warming (Manabe)• 1981 – models show sulfate aerosols =

cooling (Hansen)• 1991-1995 – model predicts cooling via

Pinnatubo. Verified in 1995. (Hansen)• 1998 – models can recreate ice-age

climates