1 Climate Change 101March 12, 2007 Thomas C. Peterson NOAA’s National Climatic Data Center Asheville, North Carolina Climate Change 101: An Introduction to Climate Change Science Climate Change 101: An Introduction to Climate Change Science

2 Climate Change 101March 12, 2007 Outline of the talk: The nature of science The greenhouse effect The physics of climate change Global climate models Climate change detection and attribution Common questions Concluding comments

3 Climate Change 101March 12, 2007 The nature of science... science, which I define as a set of methods designed to describe and interpret observed or inferred phenomena, past or present, and aimed at building a testable body of knowledge open to rejection or confirmation. In other words, science is a specific way of analyzing information with the goal of testing claims. –Michael Shermer, director of Skeptics Society, 1997

4 Climate Change 101March 12, 2007 Science is never 100% certain Science does not deal in certainty, so “fact” can only mean a proposition affirmed to such a high degree that it would be perverse to withhold one’s provisional assent. –Stephen Jay Gould, geologist, 1999

5 Climate Change 101March 12, 2007 Science is self-correcting In practice, contemporary scientists usually submit their research findings to the scrutiny of their peers, which includes disclosing the methods and data which they use, so that their results can be checked through replication by other scientists. –IPCC 4 th Assessment Report, 2007

6 Climate Change 101March 12, 2007 Competing claims, information, and even misinformation can be assessed Testability –Can it be proved false? Fruitfulness –Does it yield observable surprising predictions? Scope –How many different phenomena does it explain? Simplicity –How many assumptions does it make? Conservatism –Is it consistent with our well founded beliefs? Theodore Schick, Jr. & Lewis Vaughn, philosophers, 2001

7 Climate Change 101March 12, 2007

8 Climate Change 101March 12, 2007 We need the greenhouse effect The Earth’s surface temperature is ~60ºF Without the greenhouse effect it would be ~5ºF But humans are changing the radiative properties of the atmosphere and thereby the greenhouse effect

9 Climate Change 101March 12, 2007 Climate Forcing Summary From Ravishankara (2006) Warming versus cooling effects are like the tortoise versus the hare.

10 Climate Change 101March 12, 2007 Do you believe in global warming? I believe in quantum physics.

11 Climate Change 101March 12, 2007 Quantum physics tells us that Infrared (IR) energy can only be absorbed and radiated in very small particle-like packets of energy called quanta

12 Climate Change 101March 12, 2007 Quantum physics tells us that Infrared (IR) energy can only be absorbed and radiated in very small particle-like packets of energy called quanta Each molecule can absorb and radiate quanta at different wavelengths

13 Climate Change 101March 12, 2007 Quantum physics tells us that Infrared (IR) energy can only be absorbed and radiated in very small particle-like packets of energy called quanta Each molecule can absorb and radiate quanta at different wavelengths Two atom molecules can absorb very little IR energy –E.g., Nitrogen (N 2 ) and Oxygen (O 2 ) 98% of the atmosphere

14 Climate Change 101March 12, 2007 Quantum physics tells us that Infrared (IR) energy can only be absorbed and radiated in very small particle-like packets of energy called quanta Each molecule can absorb and radiate quanta at different wavelengths Two atom molecules can absorb very little IR energy –E.g., Nitrogen (N 2 ) and Oxygen (O 2 ) 98% of the atmosphere Three or more atom molecules do absorb and radiate in the IR –E.g., Carbon Dioxide (CO 2 ), water vapor (H 2 O), methane (CH 4 ) 2% of the atmosphere CO 2 only 0.04% of the atmosphere

15 Climate Change 101March 12, 2007 Global climate models Computer generated numerical simulations of the climate system

16 Climate Change 101March 12, 2007 Climate change detection and attribution Often linked together but are two separate processes Very mathematically intensive –Involves the temporal and spatial patterns of climate change –So this description is quite simplified

17 Climate Change 101March 12, 2007 Climate change detection Examine the instrumental temperature record for the last 100 years Examine the paleoclimate record for the past 1000 or 2000 years Examine climate model control runs –No changes in forcing –Run for 10,000s of years Is the recent observed climate change outside the bounds of natural climate variability?

18 Climate Change 101March 12, 2007 Yes, the recent observed climate change is beyond the bounds of natural variability

19 Climate Change 101March 12, 2007 Attribution: What is the cause of the detected climate change? Attribution is primarily model based analysis What mix of forcings is required to create the detected climate change?

20 Climate Change 101March 12, 2007 Attribution example: Most of the warming over the past 50 years is likely due to greenhouse gas increases IPCC TAR

21 Climate Change 101March 12, 2007 Are CO 2 and other greenhouse gasses really responsible for changing the global temperature? Quantum physics says we should expect them to be

22 Climate Change 101March 12, 2007 Climate models say they are Are CO 2 and other greenhouse gasses really responsible for changing the global temperature?

23 Climate Change 101March 12, 2007 Are CO 2 and other greenhouse gasses really responsible for changing the global temperature? Historical observations indicate they are related

24 Climate Change 101March 12, 2007 Are CO 2 and other greenhouse gasses really responsible for changing the global temperature? Ice cores can give us the long view

25 Climate Change 101March 12, 2007 Are CO 2 and other greenhouse gasses really responsible for changing the global temperature? The long view says they are definitely related

26 Climate Change 101March 12, 2007 Common questions

27 Climate Change 101March 12, 2007 You can’t predict the weather 10 days in advance, how can you predict the climate 100 years from now? Weather forecasting and climate projections are very different –Weather forecasting is primarily based movements and interactions of weather parameters Predicting a storm 1 day late is an error –Climate projections are primarily based on the physics of long-term changes in solar energy and infrared radiation The same climate physics that allow us to 100% accurately predict that next summer will be warmer than next winter After Kiehl and Trenberth (1997)

28 Climate Change 101March 12, 2007 Don’t urban heat islands – hot local temperatures caused by buildings and concrete- make U.S. and global temperatures unreliable? No The urban effect is minor with land data Ocean data has no urban effect and shows warming Increasing temperatures supported by: –plant bloom dates –Lake/river freeze/thaw dates –Glaciers melting –Etc. Peterson and Owen (2005)

29 Climate Change 101March 12, 2007 Additional supporting evidence: the shrinking Arctic sea-ice

30 Climate Change 101March 12, 2007 Don’t satellites show no warming? One satellite data set did several years ago As another group tried to reproduce it, an error in the data processing was discovered Both satellite and surface data currently show warming

31 Climate Change 101March 12, 2007 What are the climate projections for my area? Models aren’t accurate at city level But can use projections for a large region such as the Eastern US Projections are not from the Intergovernmental Panel on Climate Change (IPCC) But based on all the models that were run to contribute to the IPCC –Over 25 models –Three emission scenarios

32 Climate Change 101March 12, 2007 Precipitation

33 Climate Change 101March 12, 2007 Total precipitation: From Peterson et al., 2007b 1σ = ~68% 2σ = ~95%

34 Climate Change 101March 12, 2007 Precipitation projections: Total precipitation very uncertain However, models project heavy precipitation will increase Created for a report due to be released in late 2007.

35 Climate Change 101March 12, 2007 Temperature

36 Climate Change 101March 12, 2007 Low CO 2 scenario From Peterson et al., 2007b

37 Climate Change 101March 12, 2007 Mid-range CO 2 increases From Peterson et al., 2007b

38 Climate Change 101March 12, 2007 Business as usual CO 2 From Peterson et al., 2007b

39 Climate Change 101March 12, 2007 Temperature projections Projections show more change in the future than recently observed Even if we stopped emitting CO 2 now there would still be warming for the next few decades How warm it will be 100 years from now is dependent on future emissions of greenhouse gases

40 Climate Change 101March 12, 2007 Does anthropogenic global warming pass the rating criteria? Testability –Can it be proved false? Yes, the last decade could have been cold, laboratory tests on CO 2 could have proven theory wrong Fruitfulness –Does it yield observable surprising predictions? Yes, predicts increase in heavy precipitation which has been observed Scope –How many different phenomena does it explain? Changes in temperature, precipitation, atmospheric circulation, storms, mountain glacier melting, arctic sea-ice melting, etc. Simplicity –How many assumptions does it make? None, based on quantum physics Conservatism –Is it consistent with our well founded beliefs? Yes, no previously unknown phenomena are required to explain it

41 Climate Change 101March 12, 2007 Ockham’s razor 14 th Century English Franciscan friar and philosopher William of Ockham developed this principle: –All things being equal, the simplest solution tends to be the best one. Greenhouse gases warming the planet is simple Alternate climate change explanations are not –Require ignoring CO 2 ’s radiative effect –Paying attention to unproven explanations »It is just part of a natural cycle (that doesn’t show up in the paleoclimate record) »It is all due to changes in solar geomagnetism »It is all due to urban contamination of data sets »A negative feedback like the cloud-iris effect will save us »It is all due to cosmic rays »Etc.

42 Climate Change 101March 12, 2007 Final comment Stepping out into record hot weather, a friend who is an expert on climate change detection and attribution was asked if the high temperatures they were experiencing were due to global warming He responded: –You can’t attribute any one day’s temperature to global warming –But unusually warm weather like that does give us the privilege of experiencing the weather we are bequeathing our children and grandchildren

43 Climate Change 101March 12, 2007 Selected References Kiehl, J., and K. Trenberth, 1997: Earth’s annual global mean energy budget. Bull. Amer. Meteor. Soc., 78, Peterson, Thomas C. and Timothy W. Owen, 2005: Urban Heat Island Assessment: Metadata are Important. Journal of Climate, 18, Peterson, Thomas C., Xuebin Zhang, Manola Brunet India, Jorge Luis Vázquez Aguirre, 2007a: Changes in North American extremes derived from daily weather data. Proceedings of the National Academy of Science, in preparation. Peterson, Thomas C., Marjorie McGuirk, Tamara G. Houston, Andrew H. Horvitz and Michael F. Wehner, 2007b: Climate Variability and Change with Implications for Transportation, National Research Council, in press.

44 Climate Change 101March 12, 2007