3 May 2007 GIST May Professor John Harries, Professor John Harries, Space and Atmospheric Physics group, Blackett Laboratory, Imperial College, London,UK A natural experiment: The Mt. Pinatubo eruption; net flux; time constants; and the ERB

3 May 2007 GIST May o o Work reported in Harries and Futyan GRL, 33, L23814, 2006 o o Acknowledge provision of data by Prof. Brian Soden, U.Miami, USA]

3 May 2007 GIST May Some Background Climate may be described in terms of ‘Forcing’ and ‘feedback’ processes. Forcing processes ( External processes which impose a change of climate balance): greenhouse gas changes; solar variations; volcanic eruptions. Feedback processes ( Internal processes which respond to a forced change): water vapour feedback; cloud feedback; land surface feedback; ice feedback; ocean feedback.

3 May 2007 GIST May Terrestrial Energy Budget (per unit surface area) and greenhouse forcing Input SW Power P in = I TS (1 – A) / 4 = S (1 – A) Output LW Power P out =  T E 4 =  (1 – g)T S 4 Power deposited/lost =  p G = greenhouse radiative forcing (in Wm-2) =  (T S 4 - T E 4) g = normalised greenhouse effect, g = G / (  T S 4 )  G / 390  0.40 A = planetary albedo  0.31  = Stefan-Boltzmann constant =  Wm -2 K -4 T E = effective temperature of Earth / atmosphere  254K T S = mean surface temperature of Earth  288K P in = P out +  p  1 Wm -2 (Hansen et al., Science, 2005)  235 Wm -2 ( I TS  1366 Wm -2 ) How big is  p =  F N = P in – P out ? Does it vary with time? Can volcanic eruption help? P in - P out =  p = F N

3 May 2007 GIST May Terrestrial Energy Budget: feedbacks and volcanic forcing S (1 – A) =  (1 – g) T S 4 +  p 1 +  p 2 + … hydrological cycle, circulation patterns, cloud cover & type greenhouse forcing delayed responses Delay due to feedback processes: eg. deep ocean warming SW LW Volcanic eruption forces a direct effect on A, and a response in g on scale of days to years In this experiment, we use Pinatubo to “ping” the system, and we watch how the system responds Direct decrease in A (and smaller increase in g) due to volcano

3 May 2007 GIST May Pinatubo: A natural perturbation to the system Pinatubo (Phillipines, June ) was powerful (20 Mt), and directed vertically: so, a large mass of injecta quickly reached the stratosphere. Tropospheric material was quickly washed out. Stratospheric zonal circulation is strong, and particles quickly circulated equatorial zone, spreading N and S more slowly. Decay from stratosphere slow.

3 May 2007 GIST May Pinatubo: A natural perturbation to the system Pinatubo (Phillipines, June ) was powerful (20 Mt), and directed vertically: so, a large mass of injecta quickly reached the stratosphere. Tropospheric material was quickly washed out. Stratospheric zonal circulation is strong, and particles quickly circulated equatorial zone, spreading N and S more slowly. Decay from stratosphere slow.

3 May 2007 GIST May Some Context: Recent work in USA has attempted to make measurements of stability of TOA radiation balance, and of evidence for “stored energy”,  p, by measuring net flux anomaly at TOA…..  p =  F N 20N -20S: Wielicki et al, (2001): revision in press Mt. Pinatubo, June 1991 Net Flux, F N

3 May 2007 GIST May Combination of ERBE and CERES data (Wong et al 2005; Loeb et al, 2006)

3 May 2007 GIST May …and to model it (Hansen, 2005) Pinatubo FNFN (stored energy) (lost energy)

3 May 2007 GIST May Following work on Pinatubo by Soden et al. [2002], we have used the perturbation caused by Pinatubo to study some of the process time constants in the system; We have analysed the time series of the parameters shown in next Figure, and measured the (assumed exponential) rise and decay of the perturbation in each parameter; Results produce characteristic time constants for certain processes, which ought to be captured by models.

3 May 2007 GIST May Figure 1. The time series of the anomalies of the following parameters [adapted from Soden et al., 2002]: (top to bottom) observed longwave and shortwave TOA fluxes for latitudes 60N–60S and for 1991–1996 ** ; Observed net flux formed from the difference between absorbed SW and emitted LW fluxes; Observed total column water vapour and lower tropospheric temperature for 90N–90S; (NVAP project; Randel et al., 1996). Observed 6.7 mm brightness temperature for 90N–90S (TOVS Radiances Pathfinder project: Bates et al., 1996). SW and LW flux anomalies Net flux anomalies (“stored energy”) T 6.7 Water vapour column and T

3 May 2007 GIST May

3 May 2007 GIST May Concluding remarks: Pinatubo offers a natural perturbation to the climate system;  F N –ve for volcanic eruption: +ve for stored energy; Processes which can respond immediately to the “instantaneous” insertion of aerosol from the volcano show very short time constants (few months), driven by the time taken for aerosols to become distributed; Processes which involve slower dynamical processes, eg moving water vapour around, take much longer (1-2 years); Rise and decay process time constants differ; Models ought to reproduce these relaxation times as validation.

3 May 2007 GIST May End

3 May 2007 GIST May Some of the evidence for climate change, and the uncertainties

3 May 2007 GIST May The temperature signal at the surface and the coincident changes in CO 2, CH 4, sulphates, etc…

3 May 2007 GIST May CERES (polar orbiter) monthly averages : LW SW

3 May 2007 GIST May Do we have evidence of “climate forcing” by increasing greenhouse gases? Harries et al., Nature, March Yes!

3 May 2007 GIST May There are, of course, uncertainties in many forcing processes….. IPCC

3 May 2007 GIST May But the major uncertainties are in feedbacks, not the forcings: Should we believe that we understand “climate change” well enough to predict our future? No! The feedback processes, especially clouds, water vapour, oceans, cause large uncertainty Climate change runs by different models for same conditions

3 May 2007 GIST May Terrestrial Energy Budget ShortwaveLongwave Albedo  1/3

3 May 2007 GIST May Variability and complexity in climate

3 May 2007 GIST May Studies of the Physics of the Earth’s Climate Balance, and the new Geostationary Earth Radiation Budget experiment (GERB) Professor John Harries Head, Space and Atmospheric Physics Climate is highly variable: + Many processes are non-linear; + Some processes are chaotic; + Natural variability in climate components; + Feedback processes cause variability. Climate is very complex: + Many greenhouse absorbers (CO2, CH4, H2O, FCC, O3, clouds..); + Many SW scatterers (clouds, aerosols, dust); + Both Forcing and Feedback processes; + Wide range of time and space scales are significant; Variability is in spectral, spatial and temporal space.