Lecture 8: Anthropogenic Climate Change. Instructor: Prof. Johnny Luo. Acknowledge: IPCC

Transcription

1 Lecture 8: Anthropogenic Climate Change Instructor: Prof. Johnny Luo Acknowledge: IPCC

2 Energy Budget Fluid (atmosphere/ ocean) motions to redistribute energy Energy imbalance (forcing) and climate change (response)

3 Outlines 1. Anthropogenic forcing #1: Greenhouse gases (GHGs) 2. Anthropogenic forcing #2: Aerosols 3. Other anthropogenic forcings: land surface uses, aviation contrails, etc. 4. GCM - the primary tool for understanding climate change 5. Aspects of future climate changes (responses)

4 A few points to keep in mind: 1. Majority ( > 99.9%) of the atmospheric gases do NOT participate in the greenhouse effect (GHE). 2. Water vapor is several times more important than CO 2 in terms of GHE, but it s treated separately because change in water vapor constitutes a climate feedback mechanism.

5 IPCC 2007 Ice core + instrumental data If we put the Mauna Loa record in perspective (10,000 years), we will see that this change is: 1) unprecedented, especially the speed with which CO 2 has been increasing. 2) It closely follows the pace of our industrialization.

6 160,000 year climate history inferred from ice core of Vostok, Antarctica Atmospheric CO 2 and temperature come hand in hand

7 CO 2 & Climate for three neighboring planets Venus Earth Mars Distance to the Sun Planetary albedo Effectitve temperature 0.7 AU 1 AU 1.5 AU K 255 K 211 K T s : 735 K 288 K 227 K Composition CO 2 : 97% N 2 :78%,O 2 :21% CO 2: 96% 93 bar 1 bar bar Strong CO 2 greenhouse effect Weak CO 2 greenhouse effect (due to thin atmosphere)

8 Carbon Cycle The global carbon cycle: pre-industrial natural (before 1750) fluxes in black and anthropogenic ( ) in red (IPCC report 2007). Unit: Gt C yr -1 (1Gt = 10 9 ton = kg) for fluxes and Gt C for reservoirs. Total atmospheric mass ~ 5,000,000 Gt.

9 CO 2 N 2 O IPCC 2007 CH 4 Translate into radiative forcing (W m -2 ) ( )

10 Outlines 1. Forcing #1: Greenhouse gases (GHGs) 2. Forcing #2: Aerosols 3. Other forcings: land surface uses, aviation contrails, etc. 4. GCM - the primary tool for understanding climate change 5. Aspects of future climate changes

11 MODIS visible image of Sahara desert: aerosol reflects sunlight (cooling) but also traps IR radiation (warming). The net effect is cooling.

12 Ship tracks in visible image. Aerosols change clouds

13 Anthropogenic forcing of aerosols ( ) IPCC 2007

14 Outlines 1. Forcing #1: Greenhouse gases (GHGs) 2. Forcing #2: Aerosols 3. Other forcings: land surface uses, aviation contrails, etc. 4. GCM - the primary tool for understanding climate change 5. Aspects of future climate changes

15 IPCC to 2005

16 Putting everything together 1. GHGs: positive 2. Aerosols: negative 3. Land use: negative

17 Outlines 1. Forcing #1: Greenhouse gases (GHGs) 2. Forcing #2: Aerosols 3. Other forcings: land surface uses, aviation contrails, etc. 4. GCM - the primary tool for understanding climate change 5. Aspects of future climate changes

18 GCM originates from computer model designed to predict weather - numerical weather prediction (NWP). NWP was one of the major purposes for the first electronic computer developed by von Neumann at IAS, Princeton. Developing a GCM is to create a computerbased (numerical), virtual world.

19 interfaces Three key components of a GCM: atmosphere, ocean and land

20 Primitive Equations of the atmospheric component (fluid mechanics + thermodynamics + radiation + cloud microphysics) du dt dv dt dw dt = tanφ uv R tanφ = u R ( u = 2 + v R dρ = ρ V dt dt dp C p = α + Q dt dt dq = s( q) + D dt p = ρrt ( q) 2 2 ) uw R + vw R f u ' + fv f fu 1 p ρ z ' w 1 ρr ρr p + F φ g + F 1 p cosφ λ z φ + F λ Equations of Motion (3 components: u, v, w) Continuity Equation (density) Thermodynamics (temperature) Water Vapor Equation Equation of State (density, temperature & pressure)

21 Outlines 1. Forcing #1: Greenhouse gases (GHGs) 2. Forcing #2: Aerosols 3. Other forcings: land surface uses, aviation contrails, etc. 4. GCM - the primary tool for understanding climate change 5. Aspects of future climate changes

22 Forcing (predicted for the future) GCM response Before we show details of climate prediction, it helps to first investigate a simpler scenario: Double CO 2. Double CO 2 is a benchmark experiment in climate change science. which produces similar climate forcing as double CO 2 : 4 W m -2. R TOA = S 0 4 (1 α) OLR = S 0 4 (1 α) σt 4 e = 04 w m -2 2% increase in solar constant Double CO 2

23 Surface temperature (T s ) changes as a function of lat & mon Atmospheric temperature changes as a function of lat & height

24 ~ 4 w m -2 Climate Sensitivity: climate response (T s ) Vs. climate forcing (Q). λ dt s dq Without any feedback, λ ~ 0.26 K/ (w m -2 ). 4 w m -2 forcing translates into ~1.0 K. Hansen et al Water vapor contribution comes from three parts: increase in total water vapor, change in vertical distribution and lapse rate change. With water vapor feedback, λ ~ 0.5 K/(w m -2 ). 4 w m -2 forcing translates into ~2.0 K. With albedo and cloud feedback added in, λ ~ 1.0 K/(w m -2 ). So 4 w m -2 forcing translates into ~4.0 K.

25 IPCC 2007

26 IPCC 2007