1. NATS 101 Lecture 32 Climate Change (cont’d)

2. Outline IPCC summary from Kevin Trenberth Current energy flow and balance How changing the GHG concentrations causes climate to change –Stephen Boltzmann law (reminder) Feedbacks and subsequent changes

3. Role of the IPCC: The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio- economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. Review by experts and governments is an essential part of the IPCC process. Role of the IPCC: The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio- economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. Review by experts and governments is an essential part of the IPCC process.

4. 1988 - The establishment of the IPCC WMO, UNEP 1990 - First IPCC Assessment Report 1992 - IPCC Supplementary Reports 1994 - IPCC Special Report 1995 - Second IPCC Assessment Report 1996 - COP-2, 1997 - COP-3 2001 - Third IPCC Assessment Report 2002 - COP-8, 2003 - COP-9 2007 - Fourth IPCC Assessment Report 1992- Adoption of the UNFCCC 1994- Entry into force of the UNFCCC Ratified by 189 countries 1997- Adoption of Kyoto Protocol at COP-3 2005 Feb 16- Kyoto Protocol ratified by 164 countries (But not by USA or Australia)

5. Scenarios of future emissions of greenhouse gases, aerosols Scenarios of future concentrations of greenhouse gases and aerosols Projections of future climate: The response, global, regional Assessment of observations, processes and models Impacts Adaptation Mitigation Policy options

6. The role of the IPCC is to provide policy relevant scientific advice to policy makers and the general public. IPCC scientists from different countries with different value systems & backgrounds, gather together to produce the best consensus science possible, and with statements about confidence and uncertainty. The role of the IPCC is to provide policy relevant scientific advice to policy makers and the general public. IPCC scientists from different countries with different value systems & backgrounds, gather together to produce the best consensus science possible, and with statements about confidence and uncertainty.

7. A major strength of the IPCC process has been the intergovernmental process, through reviews and then approval of the Summary for Policy Makers on a word-by-word basis. A major strength of the IPCC process has been the intergovernmental process, through reviews and then approval of the Summary for Policy Makers on a word-by-word basis. But it has also been subject to criticism as it is much more political. In principle, this process is designed to provide a report in which the content is determined by the science while how it is stated is determined jointly with the governments. Hence it aids communication between scientists and politicians.

8.  The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.  Moreover, most of the observed changes are now simulated by climate models over the past 50 years adding confidence to future projections.  IPCC report online IPCC report online  The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.  Moreover, most of the observed changes are now simulated by climate models over the past 50 years adding confidence to future projections.  IPCC report online IPCC report online IPCC 2007 Report on Climate

9. 2007: The Nobel Peace Prize goes to the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change". 2007: The Nobel Peace Prize goes to the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change". Nobel Peace Prize

10. GLOBAL Energy Flow Thru Atmosphere

11. Global Atmo Energy Balance Ahrens, Fig. 2.14 Solar in IR Out In a stable climate, Solar Energy IN = IR Energy OUT

12. WaterVapor60% CarbonDioxide26% O 3 8% CH 4 N 2 0 6% 6% Clouds also have a greenhouse effect Kiehl and Trenberth 1997 The Natural Greenhouse Effect: clear sky

13. Changing CO 2 concentrations CO 2 concentrations have varied naturally by a factor of 2 over the past few hundred thousand years Fossil fuel burning since the industrial revolution has created a sharp increase in CO 2 concentrations CO 2 concentrations are now higher than at any time in past few hundred thousand years And concentrations are increasing faster with time Last 4 Ice Age cycles: 400,000 years See http://epa.gov/climatechange/science/recentac.html Man made You are here

14. Global Atmo Energy Imbalance Ahrens, Fig. 2.14 Solar in Atmosphere IR Out is reduced Increasing GHG concentrations decrease Energy out So Energy IN > Energy OUT and the Earth warms

15. Radiative Forcing (RF) Components {Global-average estimates and ranges; typical geographical extent and assessed level of scientific understanding}

16. Stefan-Boltzmann’s Law (review from Lecture 5) The hotter the object, the more radiation emitted. When the temperature is doubled, the emitted energy increases by a factor of 16! Stefan-Boltzmann’s Law E= (5.67x10 -8 Wm -2 K -4 )xT 4 E=2x2x2x2=16 4 times (T is temperature in Kelvin) Sun Temp: 6000K Earth Temp: 300K Aguado, Fig. 2-7

17. Change in IR Emission to Space Notice that because of Earth’s greenhouse gases, 91% (=64/70) [195/235 = 83%] of the IR emitted to space comes from the atmosphere and only 9% (=6/70) [40/235 = 17%] comes from the surface When GHG’s are added to the atmosphere, the altitude of IR emission to space rises In the troposphere, air temperature decreases with altitude So the temperature of the emission to space decreases So the energy emission to space decreases because the emission energy decreases with decreasing temperature

18. Change in IR Emission to Space BEFORE GHG increase IN=OUTAFTER GHG increase IN>OUT NH SH Ahrens, Fig. 2.21 Altitude Temperature 1. Altitude of IR emission to space rises Altitude of IR emission to space Temperature of IR emission to space 2. Temperature of IR emission to space decreases 3. IR emission to space decreases because of colder emission temperature IR emission to space tropopause

19. Change in IR Emission to Space ( cont’d) AFTER GHG increase IN>OUT Eventual solution IN=OUT SH Ahrens, Fig. 2.21 Temperature 4. Atmosphere warms until… 5. Temperature of IR emission to space increase to original temperature 6. IR emission to space increases until it matches the original IR emission before GHG increases SH Ahrens, Fig. 2.21 Temperature 1. Altitude of IR emission to space rises 2. Temperature of IR emission to space decreases 3. IR emission to space decreases because of colder emission temperature

20. Anthropogenically-Caused Warming Initially after increasing GHG concentrations, the IR radiation to space decreases, such that Solar in > IR out –Causing the Earth to start warming IF GHG concentrations level off at some point, then eventually the Earth warms enough that Solar in = IR out –“Eventually” depends on how fast the oceans warm The warmer Earth represents a new climate regime –With bad and good consequences that we partially understand

21. Complexity of Climate System The climate system involves numerous, interrelated components.

22. Closer Look at Climate System

23. Climate Feedback Mechanisms

24. Positive and Negative Feedbacks Assume that the Earth is warming. Warming leads to more melting of ice Less ice reduces Earth’s albedo Earth absorbs more sunlight Earth becomes warmer melting more ice Works in the other direction as well: Cooling makes more ice which reflects sunlight which makes Earth colder which makes more ice =>’Positive’ Feedback Mechanism

25. Positive and Negative Feedbacks Assume that the Earth is warming. Warming leads to more evaporation from oceans, which increases water vapor in atmosphere. More water vapor increases absorption of IR, which strengthens the greenhouse effect. This raises temperatures further, which leads to more evaporation, more water vapor, warming… “Runaway Greenhouse Effect” =>’Positive’ Feedback Mechanism

26. Positive and Negative Feedbacks Again assume that the Earth is warming. Suppose as the atmosphere warms and moistens, more low clouds form. More low clouds reflect more solar radiation, which decreases solar heating at the surface. This slows the warming, which would counteract a runaway greenhouse effect on Earth. ‘Negative’ Feedback Mechanism

27. Positive and Negative Feedbacks Atmosphere has a numerous checks and balances, some that counteract climate changes and some that enhance changes All feedback mechanisms operate simultaneously. The dominant effect is difficult to predict with complete certainty. Cause and effect is very challenging to prove.

28. Complexities of GHG caused Warming So, as the Earth starts warming, other things start to change… The atmosphere can hold more water vapor –Water vapor is a GHG => more warming (‘positive’ feedback) –More intense precipitation events and severe weather Land heats up faster than the oceans (remember sea breeze) –Less snowpack => earlier and smaller run-off => drier summers –Relative humidity over land will likely drop in general –Continental interiors will generally get drier? Clouds will change????? –Having more clouds increases albedo, cooling the Earth –More clouds increase Greenhouse effect warming the Earth Wind patterns start changing –Storm tracks and precipitation patterns change. –Winter storm tracks may move more poleward Ice starts melting –Reducing the albedo => more warming –Continental ice melt causes sea level to rise

29. SVP and Temperature (from Lecture 9) Claussius Clapeyron equation defines water vapor saturation vapor pressure (SVP) versus temperature SVP defines water holding capacity of air SVP nearly doubles with a 10 o C warming Ahrens Fig. 4.5

30. Total water vapor Observations show that water vapor in LOWER troposphere is indeed increasing. Surface temperature increase: 0.6  C since 1970 over global OCEANS and 4% more water vapor. Water holding capacity of atmosphere increases about 7% per o C (4% per  F) increase in temperature. From Trenberth/IPCC Since late 1970’s, ocean surface has been warming at ~0.14  C/decade => ~1% WV increase/decade. Observed WV trend since 1988 is ~1.2% per decade Water vapor increase at higher temperatures

31. WaterVapor60% CarbonDioxide26% O 3 8% CH 4 N 2 0 6% 6% Clouds also have a greenhouse effect Kiehl and Trenberth 1997 The Natural Greenhouse Effect: clear sky

32. Upper Tropospheric Water Vapor Trends Far less water vapor as in lower troposphere because temperatures are much colder (SVP much less) Fractional changes in UT WV are almost as important as in LT WV because temperatures are much colder so IR emitted from upper troposphere is small reducing outgoing IR to space Climate models generally predict UT WV should increase as climate warms Very challenging to measure UT WV At least indirect inferences that UT WV is increasing Some doubt about the robustness of this result and its generality

33. Observational Evidence of Water Vapor Feedback Increasing water vapor concentrations shift the altitude of water IR emission upward which DECREASES its emission (because of colder temperatures) Atmospheric temperatures have also been increasing over time (at least in theory) which should INCREASE the IR emission from water vapor To isolate the water vapor concentration change, Subtract the IR measured from water (=‘T12’ from HIRS) from emission measured from O 2 (whose concentrations have not changed) (=‘T2’ from MSU) If IR from water is becoming less than emission from O 2, the atmospheric water concentrations have increased => THIS IS WHAT IS OBSERVED Soden et al. 2005

34. Annual anomalies of global average SST and land surface air temperature Land increased 0.4 o C vs ocean suggesting 3% decrease in RH over land SST Land Trenberth/IPCC Land surface temperatures are rising faster than SSTs

35. Evidence for reality of climate change Glaciers melting 1900 2003 Alpine glacier, Austria 1909 Toboggan Glacier Alaska 2000 Muir Glacier, Alaska

36. Snow cover and Arctic sea ice are decreasing Spring snow cover shows 5% stepwise drop during 1980s Arctic sea ice area decreased by 2.7% per decade (Summer: -7.4%/decade) 2007: 22% (10 6 km 2 ) lower than 2005 Trenberth/IPCC

37. Arctic sea ice disappears in summer by 2050 Already 2007 lowest on record by 22% Abrupt Transitions in Summer Sea Ice Gradual forcing results in abrupt Sept ice decrease Extent decreases from 80 to 20% coverage in 10 years. Relevant factors: Ice thinning Arctic heat transport Albedo feedback Trenberth from Holland et al., GRL, 2006 2007 x

38. from ocean expansion and melting glaciers Since 1993 Global sea level has risen 43 mm (1.7 inches) 60% from expansion as ocean temperatures rise, 40% from melting glaciers Since 1993 Global sea level has risen 43 mm (1.7 inches) 60% from expansion as ocean temperatures rise, 40% from melting glaciers from Steve Nerem via Trenberth Sea level is rising:

39. Today 125,000 years ago Research indicates that less than 8°F of Arctic warming caused Greenland to lose enough water to raise sea level by up to 12 feet during the Last Interglacial Period Image from Bette Otto-Bliesner, National Center for Atmospheric Research

40. www.gfdl.noaa.gov 1 meter 4 meters 2 meters 8 meters

41. Increasing melt zones. Melt descending into a moulin: a vertical shaft carrying water to the base of the ice sheet. NSIDC (above) Braithwaite: Univ. Manchester Surface melt on Greenland

42. Greenland ice mass budget Researchers Mass Change Method Time Span (GT/year) Krabill et al. 2000 -47 Aircraft Surveys 1994-1999 Velicogna et al. 2006 -200 to -260 GRACE 2002-2006 Luthcke et al. 2007* -145 to -175 GRACE 2003-2006 Zwally et al. 2007* -80 to -100 ICESat 2003-2005 GRACE is a gravity recovery mission ICESat is a lidar topographymission NASA website on Greenland ice sheet A great deal of effort is going into estimating how the Greenland ice sheet is changing 100 GT/yr ~ 0.3 mm/yr sea level rise

43. Key Points: Climate Change Increasing GHG concentrations warms the Earth Proxy data are used to infer the past climate. Data show that the Earth’s Climate Has changed in the past Is changing now And will continue to change Key question is determining whether recent changes are due to natural causes or man.

44. Key Points: Climate Change The climate system is very complex. Contains hundreds of feedback mechanisms All feedbacks are not totally understood. Three general climate change mechanisms: Astronomical Atmospheric composition Earth’s surface

45. Assignment for Next Lectures Topic - Anthropogenic Climate Change Reading - Ahrens, Ch 14: 373-400 (383- 412) Problems - 14.5, 14.8, 14.10, 14.12, 14.13, 14.15, 14.16, 14.19