Monitoring Climate Change from Space Richard Allan Department of Meteorology, University of Reading

Why Monitor Earths Climate from Space? Global Spectrum Current Detection Understanding Prediction

The problem... IPCC:

Absorbed Solar or Shortwave Radiation (S/4)(1-α) Thermal/Infra-red or Outgoing Longwave Radiation (OLR)=σT e 4 πr2πr2 S Earths Radiation balance in space 4πr24πr2 There is a balance between the absorbed sunlight and the thermal/longwave cooling of the planet: (S/4)(1-α) σT e 4 How does it balance? Why is the Earths average temperature about 15 o C? e.g. Lacis et al. (2010) Science

Earths global annual average energy balance 240 Wm Wm -2 Surface Temperature = +15 o C SolarThermal Efficiency ~61.5% Radiating Efficiency, or the inverse of the Greenhouse Effect, is strongly determined by water vapour absorption across the electromagnetic spectrum

Now double CO 2 or reduce suns output: a radiative forcing 240 Wm Wm Wm -2 Surface Temperature = +15 o C SolarThermal: less cooling to space Efficiency ~60.5% Radiative cooling to space through longwave emission drops by about 4 Wm -2 resulting in a radiative imbalance

The climate system responds by warming 240 Wm Wm Wm -2 Surface Temperature = +15 o C Solar >Thermal Efficiency ~60.5% Heating

240 Wm Wm -2 Surface Temperature = +16 o C Solar =Thermal Efficiency ~60.5% The 2xCO 2 increased temperature by about 1 o C in this simple example. So whats to worry about? The climate system responds by warming

But its not that simple… IPCC (2007)

Climate forcing and feedback : a natural experiment

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Clouds affect radiation fluxes Radiation fluxes affect clouds

Temperature Additional surface heating Reduced reflection of suns rays Melting ice and snow CO 2 Feedback loops or vicious circles amplify or diminish initial heating or cooling tendencies e.g. Ice albedo Feedback

One of the strongest positive amplifying feedbacks involves gaseous water vapour CO 2 Greenhouse effect Net Heating Temperature Water vapour

Cloud Feedback: a complex problem Clouds cool the present climate Will clouds amplify or reduce future warming?

Monitoring Climate From Space

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IRIS/IMG spectra: Harries et al. 2001, Nature CO 2 O3O3 CH 4 Satellite measurements (1970, 1997) confirm the effect of increasing greenhouse gases 1/wavelength Stronger greenhouse effect

Monitoring Natural forcings: The Sun See also: Implied changes in global temperature ACRIM/VIRGO Lean (2000) Y.Wang (2005) IPCC WG (p )

Monitoring Sea level Coastal tide gaugesRecontructed (proxy) Satellite altimetry IPCC 2007 Fig (p. 410)

Current rises in global sea level Research by Rahmstorf et al. (2007) Science, 4 May Is sea level rising faster than projections made by numerical climate simulations?

Monitoring sea surface temperature

Monitoring Land Ice From Space Right: NASA's ICE-Sat satellite - Ice, Cloud and land Elevation Satellite Above: results from Gravity Recovery And Climate Experiment (GRACE) mission

NSIDC : Arctic sea ice: recovery from 2007 minimum but robust downward trends in extent since 1979 measured by SSM/I satellite instruments

Remote sensing clouds and aerosol from space: Cloudsat and CALIPSO Cloudsat radar CALIPSO lidar Target classification Insects Aerosol Rain Supercooled liquid cloud Warm liquid cloud Ice and supercooled liquid Ice Clear No ice/rain but possibly liquid Ground Work by Dr. Julien Delanoë and Prof. Robin Hogan, University of Reading Radar: ~D 6, detects large particles (e.g. ice) Lidar: ~D 2, more sensitive to thin cirrus, low-level liquid clouds and aerosol pollutants but signal is attenuated

How will the water cycle change? Work by Dr. Ed Hawkins and Prof. Rowan Sutton, University of Reading

Trenberth et al., work published in the Bulletin of the American Meteorological Society (2009) and Intergovernmental Panel on Climate Change (2007)

Physical basis: water vapour Physics: Clausius-Clapeyron Low-level water vapour concentrations increase with atmospheric warming at about 7%/K –Wentz and Shabel (2000) Nature; Raval and Ramanathan (1989) Nature

Extreme Precipitation Large-scale rainfall events fuelled by moisture convergence –e.g. Trenberth et al. (2003) BAMS Intensification of rainfall (~7%/K?)

Allen and Ingram (2002) Nature Global Precipitation is constrained by energy balance

Changing character of rainfall events Precipitation Heavy rain follows moisture (~7%/K) Mean Precipitation linked to radiation balance (~3%/K) Light Precipitation (-?%/K) Temperature See discussion in Trenberth et al. (2003) Bulletin of the American Meteorological Society

Increased Precipitation More Intense Rainfall More droughts Wet regions get wetter, dry regions get drier? Regional projections?? Precipitation Change (%) Climate model projections (see IPCC 2007) Precipitation Intensity Dry Days

Precip. (%) Allan and Soden (2008) Science Using microwave measurements from satellite to monitor the water cycle

The rich get richer… Allan et al. (2010) Environmental Research Letters Dry Wet Precipitation change (%) Observations Models

Conclusions Earths radiative energy balance drives climate change It also provides a rich spectrum of information Monitoring and detecting climate change Understanding physical processes Enabling and evaluating prediction Challenges... Clouds & Aerosol Precipitation Regional impacts

Earths global average energy balance: no atmosphere 240 Wm -2 Surface Temperature = -18 o C SolarThermal Efficiency = 100%

240 Wm -2 Temperatures rise Solar >Thermal Heating Earths global average energy balance: add atmosphere

Earths global average energy balance: present day 240 Wm Wm -2 Surface Temperature = +15 o C SolarThermal Efficiency ~60% The greenhouse effect helps to explain why our planet isnt frozen. How does it work?