ATS 421/521. Climate Modeling. Spring Lecture 3 HW1 due. Radiative Forcing Feedbacks Climate Sensitivity. Monday, April 8, 13

Transcription

1 ATS 421/521 Climate Modeling Spring 2013 Lecture 3 HW1 due Radiative Forcing Feedbacks Climate Sensitivity

2 Special lecture at the LaSells Stewart Center: Title: Air Bubbles in Ice, Salt in the Sea Speakers: Lynne Talley and Jeff Severinghaus Time: 7 pm Date: Tuesday, April 9 Place: LaSells Stewart Center, Oregon State University

3 Radiative Forcing Feedbacks Climate Sensitivity

4 Concepts of radiative forcing and feedbacks are attempt to separate different processes that control the response of the climate system to a specific change makes it easier to disentangle complex interactions

5 Radiative Forcing Instantaneous change of the radiative energy balance at the top of the troposphere (after adjustment of the stratosphere) due to a change in something (e.g. greenhouse gas concentrations, incoming solar radiation, surface albedo, aerosols) with everything else (e.g. temperature, water vapor) fixed. Useful to compare effects of different causes of climate change. Sign convention: positive forcing leads to warming negative forcing leads to cooling.

6 Radiative Forcing for CO2: ΔQ [W/m 2 ] natural logarithm ΔQ = 5.35 W/m 2 ln(c/c0) final CO2 concentration initial CO2 concentration C/C0 e.g. doubling of CO2: ΔQ2xC = 5.35*ln(2) = 3.7 W/m 2 calculated using detailed radiative transfer models (e.g. MOTRAN docs/projects/modtran.html)

7 Earth s Energy Budget Trenberth et al. BAMS 2009

8 Earth s Energy Budget Instantaneous effects of increased CO2 Trenberth et al. BAMS 2009

9 Earth s Energy Budget Instantaneous effects of increased CO2 Trenberth et al. BAMS 2009

10 Earth s Energy Budget Instantaneous effects of increased CO2 Trenberth et al. BAMS 2009

11 Earth s Energy Budget Instantaneous effects of increased CO2 Trenberth et al. BAMS 2009

12 Earth s Energy Budget Instantaneous effects of increased CO2 - Trenberth et al. BAMS 2009

13 Earth s Energy Budget Radiative Forcing : ΔQCO2 = 1.7 W/m 2 Instantaneous effects of increased CO2 - Trenberth et al. BAMS 2009

14 IPCC 2007

15 Methane CH4 Produced in wetlands various human activities e.g. energy industry, rice paddies, cows Removed by chemical reaction with OH Lifetime ~ 12 years

16 Methane CH4 Produced in wetlands various human activities e.g. energy industry, rice paddies, cows Removed by chemical reaction with OH Lifetime ~ 12 years Radiative Forcing : ΔQCH4 = 0.5 W/m 2

17 Aerosols (Particles)

18 Aerosols (Particles)

19 Aerosols (Particles) Small particles in the atmosphere from volcanic eruptions or human emissions can lead to increased reflection of sunlight, (direct effect)

20 Aerosols (Particles) Small particles in the atmosphere from volcanic eruptions or human emissions can lead to increased reflection of sunlight, (direct effect) more clouds and/or smaller droplets and increased cloud reflectivity (indirect effect)

21 Aerosols (Particles) - Small particles in the atmosphere from volcanic eruptions or human emissions can lead to increased reflection of sunlight, (direct effect) more clouds and/or smaller droplets and increased cloud reflectivity (indirect effect)

22 Aerosols (Particles) - Small particles in the atmosphere from volcanic eruptions or human emissions can lead to increased reflection of sunlight, (direct effect) more clouds and/or smaller droplets and increased cloud reflectivity (indirect effect) surface cooling

23 Pinatubo plume three days before climactic eruption. Pinatubo stratospheric ash layer seen from space shuttle

24 Solar Radiation

25 Solar Radiation Increases in the sun s energy output lead to increased solar radiation incident at the top of the atmosphere

26 Solar Radiation Increases in the sun s energy output lead to increased solar radiation incident at the top of the atmosphere surface warming

27 Solar Variability 1 W m -2 Q = 0.25 W m -2 Satellite measurements of solar radiation on surface perpendicular to sun s rays for average on Earth s surface divide by 4 (ratio area sphere over disc)

28 Long Term Solar Reconstruction (based on sunspot observations) 1 W m -2 Q = 0.25 W m -2 Lean et al. (2005) Astrophys. J. Kopp & Lean (2011) Geophys. Res. Lett.

29 Global, mean radiative forcings of important atmospheric agents over the period Source: IPCC, AR4, 2007

30 16

31 Feedbacks Changes in climate (as a response to the initial radiative forcing), which amplify (positive feedback) or reduce (negative feedback) the initial forcing.

32 Initial change in temperature due to radiative forcing ΔQ Tropopause Altitude ΔT Assume positive radiative forcing ΔQ (e.g. increased CO2). This leads to a surface warming. Assume warming is uniform (troposphere is well mixed). This leads to increased outgoing longwave radiation. (Planck feedback) Surface Te ΔT TeΔT Ts TsΔT Temperature

33 Planck Feedback T - Positive forcing leads to warming, which leads to increased outgoing longwave radiation F LW this cools the climate => negative feedback Planck feedback is nega3ve

34 Planck Feedback T - Positive forcing leads to warming, which leads to increased outgoing longwave radiation F LW this cools the climate => negative feedback Planck feedback is nega3ve

35 Water Vapor Feedback positive forcing leads to surface warming warmer air contains more water vapor (Clausius-Clapeyron equation) increased water vapor in atmosphere leads to additional warming because water vapor is a greenhouse gas => positive feedback Water Vapor T g water vapor per kg moist air - F LW water vapor feedback is positive

36 Water Vapor Feedback positive forcing leads to surface warming warmer air contains more water vapor (Clausius-Clapeyron equation) increased water vapor in atmosphere leads to additional warming because water vapor is a greenhouse gas => positive feedback Water Vapor T g water vapor per kg moist air - F LW water vapor feedback is positive

37 Tropopause ΔT ΔTwv Altitude Surface Te ΔT TeΔT Ts Temperature ΔTwv TsΔTΔTwv

38 Lapse-Rate Feedback lapse-rate is the temperature change with height positive forcing leads to surface warming and increased evaporation this cools the surface more water vapor is transported vertically release of latent heat during condensation (cloud formation) at higher altitudes leads to more warming there and more longwave radiation to space => negative feedback

39 Tropopause ΔT ΔTwv ΔTlr release of lated heat during condensation of water vapor leads to warming aloft Altitude Surface Te TeΔT Ts Temperature ΔT ΔTlr TsΔTΔTwv-ΔTlr increased evaporation cools the surface

40 Lapse Rate Feedback

41 Lapse Rate Feedback

42 Lapse Rate Feedback

43 Lapse Rate Feedback 5ºC

44 Lapse Rate Feedback 5ºC

45 Lapse Rate Feedback 5ºC

46 Lapse Rate Feedback 15ºC 5ºC

47 Ice-Albedo Feedback positive forcing leads to surface warming surface warming leads to melting of snow and ice this leads to a lower albedo and more absorbed sunlight at the surface which leads to more warming => positive feedback - ice and snow T - albedo ice-albedo feedback is positive

48 Ice-Albedo Feedback positive forcing leads to surface warming surface warming leads to melting of snow and ice this leads to a lower albedo and more absorbed sunlight at the surface which leads to more warming => positive feedback - ice and snow T - albedo ice-albedo feedback is positive

49 Cloud Feedbacks how clouds change if the climate warms is currently not well understood we ll talk more about this later in the course

50 Climate Sensitivity Usual definition: Global mean temperature increase due to a doubling of CO2: ΔT2xC. Radiative forcing due to CO2: For 2xCO2: More general: global mean temperature change radiative forcing := change in energy balance at the tropopause with everything else (T, q,...) constant

51 Our EBM in equilibrium: Climate Sensitivity or ΔT2xC = 1 K GCMs have ΔT2xC = K What s wrong?

52 3.4Wm 2 K 1,T 0 = 288K 1.7Wm 2 K 1,T 0 = 227K surface tropopause Determine B empirically from obs: 10 deg latitudinal averages of ERBE satellite (F) and NCEP reanalysis (T) data Implicitly includes feedbacks.

53 T 0, y 0 T 0, y 0 Feedback parameter Planck water vapor lapse rate cloud sfc albedo

54 Soden & Held (2006) J. Climate

55 Close to B eq. (2.16) with T0=288 K Soden & Held (2006) J. Climate