NATS 101 Lecture 32 Climate Change (cont’d)

1. NATS 101Lecture 32Climate 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. IPCC Role of the IPCC: The role of the IPCC is toassesson 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 IPCC 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. WGIII Mitigation Policy options Adaptation WGII Impacts IPCC Scenarios of future emissions of greenhouse gases, aerosols WGI Scenarios of future concentrations of greenhouse gases and aerosols Feedbacks Assessment of observations, processes and models WGI Projections of future climate: The response, global, regional

6. IPCC A major strength of the IPCC process has been theintergovernmentalprocess, through reviews and then approval of theSummary for PolicyMakerson 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 isdetermined by the sciencewhilehow it is statedis determined jointly with the governments. Hence it aids communication between scientists and politicians.

7. IPCC 2007 Report on Climate • 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

8. Nobel Peace Prize IPCC 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".

9. GLOBAL Energy Flow Thru Atmosphere

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

11. The Natural Greenhouse Effect: clear sky CH4 N20 6% O3 8% Water Vapor 60% Carbon Dioxide 26% Clouds also have a greenhouse effect Kiehl and Trenberth 1997

12. ChangingCO2 concentrations • CO2 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 CO2 concentrations • CO2 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 Man made You are here See http://epa.gov/climatechange/science/recentac.html

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

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

15. 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 of16! • Stefan-Boltzmann’s Law E= (5.67x10-8 Wm-2K-4 )xT4 E=2x2x2x2=16 4 times (T is temperature in Kelvin) Sun Temp: 6000K Earth Temp: 300K Aguado, Fig. 2-7

16. 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

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

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

19. 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

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

21. Closer Look at Climate System

22. Climate Feedback Mechanisms

23. 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

24. 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

25. 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.

26. 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

27. 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 10oC warming Ahrens Fig. 4.5

28. Water vapor increase at higher temperatures Water holding capacity of atmosphere increases about 7% per oC (4% per F) increase in temperature. 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. Total water vapor 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 From Trenberth/IPCC

29. The Natural Greenhouse Effect: clear sky CH4 N20 6% O3 8% Water Vapor 60% Carbon Dioxide 26% Clouds also have a greenhouse effect Kiehl and Trenberth 1997

30. 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 WVare 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

31. 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 O2 (whose concentrations have not changed) (=‘T2’ from MSU) • If IR from water is becoming less than emission from O2, the atmospheric water concentrations have increased => THIS IS WHAT IS OBSERVED Soden et al. 2005

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

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

34. Snow cover and Arctic sea ice are decreasing Arctic sea ice area decreased by 2.7% per decade (Summer: -7.4%/decade) 2007: 22% (106 km2) lower than 2005 Spring snow cover shows 5% stepwise drop during 1980s Trenberth/IPCC

35. 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 2007 x Trenberth from Holland et al., GRL, 2006

36. Sea level is rising: 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 from Steve Nerem via Trenberth

37. Research indicates that less than8°F of Arctic warmingcaused Greenland to lose enough water toraise sea level by up to 12 feet during the Last Interglacial Period Today 125,000 years ago Image from Bette Otto-Bliesner, National Center for Atmospheric Research

38. 1 meter 2 meters www.gfdl.noaa.gov 4 meters 8 meters

39. Surface melt on Greenland 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

40. Greenland ice mass budget A great deal of effort is going into estimating how the Greenland ice sheet is changing Researchers Mass ChangeMethodTime Span (GT/year) Krabill et al. 2000 -47Aircraft Surveys1994-1999 Velicogna et al. 2006 -200 to -260GRACE2002-2006 Luthcke et al. 2007* -145 to -175GRACE2003-2006 Zwally et al. 2007* -80 to -100ICESat2003-2005 GRACE is a gravity recovery mission ICESat is a lidar topographymission NASA website on Greenland ice sheet 100 GT/yr ~ 0.3 mm/yr sea level rise

41. 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.

42. 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

43. 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