Determining causes of warming: Climate models & the smoking gun

Transcription

1 Determining causes of warming: Climate models & the smoking gun

2 Announcements TONIGHT: HW #6 (paper outlines) due in lecture! bring up at Break HW #7 (presentation outlines) due in section next week your TA, if you did not get assignments

3 Tonight: three night series : 1) An Inconvenient truth 2) Impacts: Observed Warming and Projected Sea Level Changes 3) How do we know? (A smoking gun?) and The Climate Hoax and discussion

4 Outline 1) How do we know warming is anthropogenic? (is there a smoking gun?) Introduction to GCM s Factoring out the forcings 2) The Great Global Warming Swindle

5 Key tasks: 1) Determine if the earth is warming? By how much? (last time) 2) detail history of climate main forcings 3) Test our understanding of forcingswhich can be causing current warming?

6 Recall: Warming of ~ 1 degree since 1950 (average planetary temperature) Recall: Warming has occurred in both Hemispheresbut mostly NORTH

7 And Rate of Warming has increased

8 Key forcings? What about other Key forcings?

9 The main variable forcings: 1)Solar intensity 2)Volcanic activities 3) Greenhouse gasses 4) anthropogenic aerosols

10 Radiation: Sunspot intensity ~ 11 year fairly predictable cycle Larger cycles seem to be superimposed *have excellent data since 1970 s- so recent changes well known

11 Volcanic eruptions Episodic & non-predictable (but very well known) Notice radiative forcing is always DOWN

12 Greenhouse gasses- increasing rapidly since 1950s

13 Human-generated aerosols (particle pollution) Pretty Well known Only a factor since industrial revolution *Notice radiative forcing is always DOWN * Acts in opposition to GHG forcing.

14 Note sunspot forcing was up ~ yr but has actually gone back down more recently. All main (known) forcings

15 But how to understand net effect? Key tool: GCM s global circulation models

16 Fig

17 Running a Model Apply forcing Calculate how Earth System changes Run model so that global circulation looks like reality

18 A test of models: can Hindcast Hindcast Past Climate Change Apply NATURAL forcings sunspot cycles & volcanic eruptions Calculate how Earth System changes Hindcast = run backwards, Do changes match observed temperature records?

19 Fig a Climate change if only related to sun spot cycles and volcanoes

20 Fig a Note: using only natural forcings, predictions are correct going BACKWARD in time, but not forward Notice drop in temp after 1940 is well modeled by natural forcings Climate change if only related to sun spot cycles and volcanoes

21 Applying anthropogenic forcing Apply ANTHROPOGENIC forcings 1) Changes in greenhouse gases 2) Changes in aerosols Calculate how Earth System changes

22 Fig b Climate change if only related to human emissions of GHGs and aerosols

23 Fig a Using only human forcings, predictions are pretty good recently, but are off early in century Climate change if only related to anthropogenic forcing

24 All Known forcings Apply NATURAL & ANTHROPOGENIC forcings Sunspot cycles and Volcanic Eruptions Changes in greenhouse gases Changes in aerosols Calculate how Earth System changes

25 Fig c Climate change if related to sun spot cycles, volcanoes, GHGs, and aerosols

26 From the IPCC 2007 report Bottom line: 1) Models seem to work well (you can run backward and get right answer) you can only explain recent warming due to anthropogenic forcings (for which GHG are main ones..)

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29 What about the future? It depends..

30 What will happen in the FUTURE? Depends on: - sociopolitcal and economic factors - physical climate response to anthropogenic emissions Each column is a different possible emissions scenario based on possible sociopolitical and economic factors

31 A1. Very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes is convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. Three options: - A1F1: fossil fuel intensive - A1T: non-fossil energy sources - A1B: balanced diverse energy sources A2. Very heterogeneous world. Major underlying theme is self reliance and preservation of local identities. Continuously increasing population. Economic development is regionally oriented and per capita economic growth and technological change more fragmented and slower than other scenarios. B1. A convergent world with the same global population, that peaks in mid-century and declines thereafter, and rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. Major underlying theme is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives. B2. Very heterogeneous world. Major underying theme is local solutions to economic, social and environmental sustainability. Continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.

32 Each column is a different emissions scenario Emissions Resulting Concentrations Resulting Radiative Forcing Calculated Future Global Temperature

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34 All models predict global warming, however the amount of warming is not precisely known because: Feedbacks aren t exactly the same in all models Many processes are parameterized (fudged until we know more)

35 Sea Ice Extent will decline in all seasons and both hemispheres

36 Sea ice in the Arctic will be seasonal rather than permanent

37 Greenland Ice Sheet Melting: Model Predictions

38 Predicted Changes in Sea Level due to Thermal Expansion of the Oceans

39 Sea Level Predictions for

40 Greenland ice sheet contains water equivalent to 7.2 m of sea level rise.

41 Total Greenland ice sheet contains water equivalent to 7.2 m of sea level rise.

42 What Will Happen in Future? Predictions of Future depend on: 1. Future GHG emissions sociopolitical, economic forces? 2. Future Aerosol emissions (pollution) sociopolitical, economic forces? 3. Climate sensitivity (which model is used) depending on how processes are parameterized, models predict C for doubling CO2 4. Ice sheet models and amount of Ocean heating predictions are for cm of sea level rise over next ~100 years End up with RANGE OF POSSIBILITIES (ALL possibilities include: significant global warming, increase in precip. globally, but drying of deserts, and sea level rise)

43 What Will Happen in Future? End up with RANGE OF POSSIBILITIES But, ALL possibilities include: significant global warming, increase in precip. globally, but drying of deserts sea level rise Very significant unknowns

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46 Break

47 The Swindle..