Climate change and the role of the Sun

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Climate change and the role of the Sun
Joanna D. Haigh Department of Physics Imperial
College London
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Outline

• Why be concerned with this topic?
• Why has this subject historically been viewed
  with scepticism?
• How much does solar output vary?
• What are the observed impacts of solar
  variability on tropospheric climate?
• What is the impact of solar variability on the
  stratosphere?
• Can we explain the observed impacts?

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Intergovernmental Panel on Climate Change (2001)
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Admiral Robert Fitzroy (1805-1865)

• Captain of HMS Beagle.
• 1854 head of new Met. Dept. of Board of Trade.
• 1861 established first formal weather stations
  and storm warnings.

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Richard Morrison, a.k.a. Zadkiel, (Punch, 1863)
Astro-meteorologists
Patrick Murphy (satirical engraving 1838)
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Titanic
Lawrence, Weather, 2000
The Sun-Climate Connection(Did Sunspots Sink the
Titanic?) NOAA website, 2001
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Solar cycle length and N. H. temperature
solar cycle length
temperature
above Friis-Christensen and Lassen (1991)
top right Lassen and Friis-Christensen (2000)
right Laut and Gundermann (2000)
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Sunspot cycle
17 June 1997 20 March 2000
15 October 2004
(Images courtesy University of Hawaii)
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Sunspot cycle
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Solar corona
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All existing space-based measurements of the
solar constantFröhlich et al
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Total solar irradiance (TSI) composite
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Reconstructed solar irradiance
sunspot no.
TSI estimates
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N.Atlantic ice flow-deposited sedimentBond et
al, Science, 2002
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Temperature in NW Europe
Eddy (1976)
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Low cloud and galactic cosmic rays
updated
Marsh Svensmark 2000
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Upper troposphere temperatures(NH summer)
30 hPa geopotential height(annual mean, Hawaii)
750-200hPa thickness July August 3-year running
average
solar 10.7cm flux
Labitzke and van Loon (1995)
van Loon and Shea (2000)
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Solar signal in vertical velocity from NCEP data
(Gleisner and Thejll, 2003)
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Temperature signals
Haigh (Phil.Trans., 2003)
mean
solar trend
volcanic ENSO
solar
(95 sig) NAO
volcanic (95 sig)
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NCEP zonal mean zonal wind
Haigh et al (J. Clim., 2004)
mean
solar trend
volcanic ENSO
components(35N,200hPa) N
AO
components (30S,200hPa).
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Sun in visible, UV and X-ray
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Solar spectrum
Lean (1991) adapted by Lockwood
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Min/max activity in UV
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Altitude of unit optical depth
(Andrews, 2000)
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Ozone (observations)
(Tourpali, 2003)
1979
2001
Hood and Soukharev (2003)
Lee and Smith (2003)
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Ozone (models)
UKMO
Lee and Smith (2003)
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How might solar activity influence tropospheric
climate?

• Total solar irradiance (TSI)
• orbital variations
• variable emission
• Solar UV irradiance
• Energetic particles
• solar protons
• cosmic rays

Energy input to Earth radiative
forcing Heating the stratosphere dynamical
coupling with troposphere Atmospheric
ionisation chemistry and microphysics
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Earth energy budget
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Earths orbital parameters Milankovitch
climate cycles
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Earth orbital parameters - temporal variation
eccentricity precession obliquity
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Geographical distribution of solar irradiance
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TSI and radiative forcing
sunspot no.
TSI estimates
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Why is radiative forcing a useful concept?

• Because GCMs, limited observational studies,
  suggest that the perturbation to global average,
  equilibrium surface temperature, Tg, is related
  to radiative forcing, RF, by
•  
• where ?, the climate sensitivity parameter, is
  independent of the nature of the forcing.
• 0.6 K (W m-2)-1 0.3 lt ? lt 1.0
  
• so ?TSI of 2.2 W m-2 since 1900 implies ?Tg of

 
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Reconstructed solar irradiance NH land temp.
sunspot no.
total solar irradiance estimates
instrumental record
NH land surface temperature reconstruction
(Mann et al)
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Energy balance model calculations
(Crowley, Science, 2000)
Radiative forcing
Temperature response
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GCM global mean surface temperature simulations
IPCC 2001
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Spectral irradiance
solar min
max-min
Haigh (Nature, 1994)
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Stratosphere-troposphere coupling

• GCM simulations of solar UV impact
• GCM studies using generic heating of lower
  stratosphere
• Simplified GCM studies to assess
  processes/mechanisms

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UGCM zonal wind
January
solarmax-solarmin
(no ?O3)
(2D model ?O3)
Haigh (Science1996 QJRMS 1999)
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UM zonal wind
January solarmax-solarmin
Larkin et al (2000)
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Zonal mean zonal wind
Observations Model mean max-min
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UGCM mean meridional circulation
January change (solar max solar min) in
MMC at 682hPa
Haigh (1999)
strat-trop/GCM
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UM mean meridional circulation
mean max-min

Larkin (2000)
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Potential mechanisms

• Increased static stability weakens tropical
  upwelling and Hadley cells
• Changes in u affect growth/propagation of
  planetary waves
• Baroclinic lifecycles modified

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Simplified (dynamical core) GCM experiments
(courtesy Mike Blackburn, Univ. Reading)

• Full dynamics.
• No orography.
• Highly simplified physics (e.g. radiation).
• Experiments involved heating the lower
  stratosphere by
• 5K at all latitudes
• 5K at equator, cos2(lat) variation

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Uniform heating expt
u mmc T

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cos2(lat) heating expt.
u mmc T

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Baroclinic lifecycle experiments
cos2(lat) heating expt. uniform
heating expt.
Standard BLC day 0
day 10 day 20
day 30
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Conclusions 1/2

• The study of solar-climate links is important in
  the context of climate change detection/attributio
  n.
• There are detectable signals of climate response
  to solar activity on decadal, centennial and
  millennial timescales.
• Historical scepticism due to belief in solar
  constant, association with astrology and poor
  science/statistics.
• The response is not spatially uniform. The
  troposphere shows vertical bands of warming in
  mid-latitudes and a weakened and broadened Hadley
  circulation.
• The vertical structure of the apparent ozone
  response is not well understood.

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Conclusions 2/2

• (Any) thermal perturbation to the lower
  stratosphere exerts a dynamical influence on the
  circulation of the lower atmosphere.
• Solar influence on climate provides an
  interesting test-bed for theories of
  stratosphere-troposphere coupling
• The geographical pattern of the solar influence
  can only be understood via dynamical feedbacks.
• Baroclinic waves may play a key role.

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Hershel, Phil.Trans.Roy.Soc. 1801
more or less light and heat from the sun may
be liable to produce a great variety in the
severity or mildness of the seasons Before we
can generalize the influence of a certain cause,
we ought to confine our experiment to one
permanent situation, where local circumstances
may be supposed to act nearly alike at all times,
which will remove a number of difficulties.
when many things which are already known to
affect the temperature of different countries
come to be properly combined with the results we
propose to draw from solar observations, we may
possibly find this subject less intricate than we
might apprehend
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Thank you