IPCC

1. 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 warming 2007: 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).

2. 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 not considered. Missing, inaccurate or non-representative data, inappropriate spatial or temporal resolution, poorly known or changing model parameters. Images from IPCC report

3. 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.

4. 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. Image from Thinkquest

5. So, what causes radiative forcing? Solar input - relatively constant, but can be slightly higher or lower than usual

6. 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. Image from nasa.gov Sunspots Author: Hans Bernhard

7. 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

9. Components of a fully coupled general circulation model Removed image due to copywright. It can be found at the Australian Department of Meteorology. 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.

10. Development of climate models over time IPCC, adopted by Australian Department of Climate Change and Energy Efficiancy

11. 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.

12. All models are wrong; some models are useful. -G.E. Box (UW Professor) Models (con’t) 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.

13. 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

14. 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).

15. Image from IPCC

16. 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)?

17. 1981 We can test our GCM! Image from USGS Image source: New York Times 1963 Mount Agung (Indonesia) volcanic eruption (ok, really, this is a picture of the 1991 Mount Pinatubo eruption) Jim Hansen

18. 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

19. Attribution The 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.

20. Is CO2 the only greenhouse gas that is important?

21. It turns out (unfortunately), no. 1) Methane (CH4) - From rice paddies and cows. 2) N2O - from agriculture, including fertilizer 3) Ozone (O3) - not anthropogenic and… 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,……

22. Image from NOAA

23. Image from NASA 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…..

24. 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

25. The Ozone hole CFC’s in the stratosphere = Ozone hole. CFC’s in the troposphere = global warming Source: NASA

26. The Ozone hole This ozone debate plays out like this: Scientists report that CFCs are causing problems with ozone layer. Industry denies that this is a problem. Scientists confirm this problem. Industry maintains that it is too expensive to switch to other propellants in spray bottles. Under international pressure, CFCs are outlawed* in the 1997 Montreal accords. 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). Source: NASA *CFCs are still being produced in some third world countries.

27. IPCC

28. Prediction Specification, in advance, of events or changes in a system. Again, the IPCC includes many predictions, based on the outcomes of the GCMs.

29. 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. Source: Wikipedia National Center for Atmospheric Research laboratory in Boulder, Colorado

30. IPCC 2007

31. Image from NASA

32. Image from NASA

33. Image by Robert A. Rohde for Global Warming Art

34. 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: Empirical-theoretical Reductionistic-holistic Source: Robert A. Rohde

35. An analogy (Image of doctor and patient) 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. Holistic science (Image of scientists studying a town) 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.

36. 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

37. Systems with multiple variables Sensitivities Positive feedbacks Negative feedbacks Thresholds (“Tipping points”) Complexity (non-linear feedbacks)

38. Thresholds Source: Wikimedia Commons, Bart de Goeij Source: Wikimedia Commons, Gertjan R. Side view Back view

39. Feedback Loops & Tipping Points http://www.youtube.com/watch?v=5T_3WJPYY9g First 6:45 of video

40. Tipping points http://www.youtube.com/watch?v=XJNH3HTDpuk Interview with Jim Hansen

41. 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