Monitoring Climate Change from Space

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Monitoring Climate Change from Space
Richard Allan Department of Meteorology,
University of Reading
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Why Monitor Earths Climate from Space?

• Global
• Spectrum
• Current
• Detection
• Understanding
• Prediction

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The problem...
IPCC www.ipcc.ch/ipccreports/ar4-wg1.htm
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Earths Radiation balance in space
4pr2
Thermal/Infra-red or Outgoing Longwave Radiation
(OLR)sTe4
pr2
S
Absorbed Solar or Shortwave Radiation (S/4)(1-a)

• There is a balance between the absorbed sunlight
  and the thermal/longwave cooling of the planet
  (S/4)(1-a) sTe4
• How does it balance? Why is the Earths average
  temperature about 15oC? e.g. Lacis et al. (2010)
  Science

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Earths global annual average energy balance
Solar
Thermal
240 Wm-2
240 Wm-2
Efficiency 61.5
390 Wm-2
Surface Temperature 15oC
Radiating Efficiency, or the inverse of the
Greenhouse Effect, is strongly determined by
water vapour absorption across the
electromagnetic spectrum
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Now double CO2 or reduce suns output a
radiative forcing
Solar
Thermal less cooling to space
240 Wm-2
236 Wm-2
Efficiency 60.5
390 Wm-2
Surface Temperature 15oC
Radiative cooling to space through longwave
emission drops by about 4 Wm-2 resulting in a
radiative imbalance
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The climate system responds by warming
Solar gt
Thermal
240 Wm-2
236 Wm-2
Efficiency 60.5
Heating
390 Wm-2
Surface Temperature 15oC
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The climate system responds by warming
Solar
Thermal
240 Wm-2
240 Wm-2
Efficiency 60.5
397 Wm-2
Surface Temperature 16oC
The 2xCO2 increased temperature by about 1oC in
this simple example. So whats to worry about?
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But its not that simple
IPCC (2007)
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Climate forcing and feedback a natural
experiment
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• Clouds affect radiation fluxes
• Radiation fluxes affect clouds

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Feedback loops or vicious circles amplify or
diminish initial heating or cooling tendencies
e.g. Ice albedo Feedback
Melting ice and snow
? CO2
?Temperature
Reduced reflection of suns rays
Additional surface heating
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One of the strongest positive amplifying
feedbacks involves gaseous water vapour
? CO2
? Water vapour
?Temperature
? Greenhouse effect
? Net Heating
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Cloud Feedback a complex problem

• Clouds cool the present climate
• Will clouds amplify or reduce future warming?

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Monitoring Climate From Space
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Satellite measurements (1970, 1997) confirm the
effect of increasing greenhouse gases
IRIS/IMG spectra Harries et al. 2001, Nature
CH4
?Stronger greenhouse effect
CO2
O3
1/wavelength
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Monitoring Natural forcings The Sun
ACRIM/VIRGO
IPCC WG1 2.7.1 (p.188-193)
0.2
Implied changes in global temperature
0.1
0.0
Lean (2000) Y.Wang (2005)
See also http//www.pmodwrc.ch/pmod.php?topictsi
/composite/SolarConstant
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Monitoring Sea level
IPCC 2007 Fig. 5.13 (p. 410)
Satellite altimetry
Coastal tide gauges
Recontructed (proxy)
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Current rises in global sea level
Is sea level rising faster than projections made
by numerical climate simulations?
Research by Rahmstorf et al. (2007) Science, 4 May
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Monitoring sea surface temperature
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Monitoring Land Ice From Space
Above results from Gravity Recovery And Climate
Experiment (GRACE) mission
Right NASA's ICE-Sat satellite - Ice, Cloud and
land Elevation Satellite
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Arctic sea ice recovery from 2007 minimum but
robust downward trends in extent since 1979
measured by SSM/I satellite instruments
NSIDC http//nsidc.org/news
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Remote sensing clouds and aerosol from space
Cloudsat and CALIPSO

• Radar D6, detects large particles (e.g. ice)
• Lidar D2, more sensitive to thin cirrus,
  low-level liquid clouds and aerosol pollutants
  but signal is attenuated

Cloudsat radar
CALIPSO lidar
Insects Aerosol Rain Supercooled liquid
cloud Warm liquid cloud Ice and supercooled
liquid Ice Clear No ice/rain but possibly
liquid Ground
Target classification
Work by Dr. Julien Delanoë and Prof. Robin Hogan,
University of Reading
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How will the water cycle change?
Work by Dr. Ed Hawkins and Prof. Rowan Sutton,
University of Reading
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Trenberth et al., work published in the Bulletin
of the American Meteorological Society (2009) and
Intergovernmental Panel on Climate Change (2007)
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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

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Extreme Precipitation

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

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Global Precipitation is constrained by energy
balance
Precipitation 2-3/K
Water vapour 7/K
Allen and Ingram (2002) Nature
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Changing character of rainfall events
Heavy rain follows moisture (7/K)
Mean Precipitation linked to radiation balance
(3/K)
Precipitation ?
Light Precipitation (-?/K)
Temperature ?
See discussion in Trenberth et al. (2003)
Bulletin of the American Meteorological Society
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Climate model projections (see IPCC 2007)

• Increased Precipitation
• More Intense Rainfall
• More droughts
• Wet regions get wetter, dry regions get drier?
• Regional projections??

Precipitation Intensity
Dry Days
Precipitation Change ()
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Using microwave measurements from satellite to
monitor the water cycle
Precip. ()
Allan and Soden (2008) Science
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The rich get richer
Wet
Precipitation change ()
Observations
Dry
Models
Allan et al. (2010) Environmental Research Letters
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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

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Earths global average energy balance no
atmosphere
Solar
Thermal
240 Wm-2
240 Wm-2
Efficiency 100
240 Wm-2
Surface Temperature -18oC
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Earths global average energy balance add
atmosphere
Solar gt
Thermal
240 Wm-2
Heating
240 Wm-2
Temperatures rise
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Earths global average energy balance present
day
Solar
Thermal
240 Wm-2
240 Wm-2
Efficiency 60
390 Wm-2
Surface Temperature 15oC
The greenhouse effect helps to explain why our
planet isnt frozen. How does it work?
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