Relationships Between the
Sun and Climate:
Time Scales of Decades to Centuries
Judith Lean
Naval Research Laboratory, Washington DC
Observed Sun-Climate Relationships
.. Holocene, past millennium, past century
How Much Does Solar Energy Output Vary?
What are the Mechanisms for Sun-Climate
Relationships?
.. direct, indirect, resonnances
Summary
Earth and
Sun
Variations
in the
Holocene
EARTH
~5oC
)F=0.6 Wm-2 ?
SUN
solar-related
surface
temperature
changes of
order #0.5oC
are evident in
the past 1,000
years
Stuiver et al., 1997
North Atlantic Climate
Bond et al., Science, 2001
drift ice and cooler surface water
in the Nordic and Labrador seas
repeatedly advected southward
and eastward to warmer
sub-polar regions
• surface winds and surface ocean hydrography are
apparently influenced by solar variability
• 1500-year cycle may involve solar variability
• North Atlantic Deep Water may amplify solar signals
InterTropical Convergence Zone
Neff et al., Nature, 2001
ITCZ:
- surface level circulation
of Northern and Southern
Hadley cells converge
- controls tropical rainfall,
Indian Ocean monsoon
δ18O in stalagmites in
Oman track ? 14 C for
3,000 years in
mid-Holocene
(when summer monsoon
was stronger than present)
high solar activity
low ? 14C
low δ18O
high rainfall
Earth and Sun Variations in the
Past Millennium
EARTH
Little Ice Age ∆T~0.8 oC
Glacial Ice Age ∆T~5oC
SUN
• C20th warming
exceeds variations in
prior centuries.
• Significant
variability exists prior
to the industrial
epoch.
Long-Term Solar Variability and
Climate Change: 1600-2000
dominant
solar
forcing
dominant
volcanic
forcing
Tamboora Coseguina
anthropogenic
plus
solar forcing
Krakatoa
Lean, Beer & Bradley, GRL, 22, 3195, 1995
Lean, Annu. Rev. Astron. Astrophys., 35, 33, 1997
Solar Centennial Cycles,
Drought and Culture
• semi-arid regions are particularly
vulnerable to hydrological changes
• severity of past droughts exceeds
contemporary events
Equatorial East
Africa
Verschuren et al.,
Nature, 2000
Maya Lowlands
Hodell et al.,
Science, 2001
high solar activity → low ∆ 14C → high δ18O
→ increased drought → cultural collapse
206-208 yr components of ∆ 14C and δ18O vary in phase
Earth and Sun Variations
in the Past Century
- instrumental record
Surface temperature changes are
nonuniform.. globally and temporally
0.6
1900-1950
Global annual mean
surface temperature
anomalies
1960-2000
0.4
Sunspot numbers
http://giss/nasa/gov
Solar Variability Detected in MSU Data
Michaels and Knappenberger, 2000
El Chichon
Pinatubo
MSU global temperature
residuals – with effects of
ENSO and volcanoes removed
-- track the solar cycle
El Nino
La Nina
Amplitude ~ 0.1oC
Data: Sato et al., 1993, Jap. Met.
Agency, Christy et al., 1998
North and Wu (2001) detected
solar cycles in C20th instrumental
surface temperatures
… 2X larger than expected from
EBM simulation with sensitivity
2oC for 2CO2
Solar Cycles and
Global Sea Surface Temperatures
SEA SURFACE
SOLAR
TEMPS
IRRADIANCE
White et al., 1997, 1998
30hP Pressure Surface near 24 km
varies ~ 0.1 km during Solar Cycle
Changes in
a constant
pressure
level reflect
changes in
integrated
temperature
below.
K. Labitzke & H. van Loon
Solar Decadal “Cycles” in Climate
3-5
Global surface temperature
10
27
Mann and Park 1994
Central England temperature
3.1
5.2 7.5
14.5
23
76
Mason 1976
4.5
US east coast temperature
9
20
22
Global marine air temperature
Newell et al. 1989
22
US drought
SOURCE
Mitchell et al. 1979
9.9
Beijing rainfall
18.7
56
84 126
Hamseed et al. 1983
11
US rainfall
18.6
Curie and O'Brien 1988
18.4
Nile floods
22
77
Hameed 1984
South American rainfall
African rainfall
3.8
3.5
7
20
10-12
18
Seleshi et al. 1994
North Atlantic pressure
3.4
5
11
PERIOD (years)
Karl and Riebsame 1984
Kelly 1977
Southern oscillation
3 3.8
North American forest fires
6
10-12
11
22 34
Auclaire 1992
8 9.3 11.3 14.8
Atlantic tropical cyclones
22
51.3
133
Cohen and Sweester 1975
Tropical corals
3.3
4.6 6 8 11
17
Dunbar et al. 1994
some periods other than the 2.2 year QBO present in climate records
Burroughs 1992; Lean & Rind, 1998
Solar Variability and Recent US Drought
DROUGHT AREA INDEX POWER SPECTRUM
Cook et al., 1997
• Drought Area
Index reconstructed
from tree-rings
since 1700
DROUGHT AREA INDEX BANDPASS FILTERING
•Solar and lunar
effects interact to
modulate DIA
• Ocean-atmosphere
interactions in the
North Pacific may
be responsible
How Much Does Solar Energy
Output Vary?
Source
Energy
(Wm-2)
Solar Cycle
Change (Wm-2)
Deposition
Altitude
Solar Radiation
• total
• UV 200-300 nm
• VUV 0-200 nm
1366
15.4
0.15
1.2
0.17
0.15
Particles
• electron aurora III
• solar protons
• galactic cosmic rays
0.06
0.002
0.0000007
Joule Heating of Thermosphere
• E=100 mVm-1
0.14
Solar Wind
0.0003
surface
10-80 km
50-500 km
90-120 km
30-90 km
0-90 km
100-500 km
above 500 km
Long-Term Solar
Irradiance Variations
are Speculated
Are Long-Term Solar Irradiance
Variations Occurring?
NO: Sunspot Numbers
reconstructed total irradiance
cycles track sunspot numbers
YES: Geomagnetic Activity
reconstructed total irradiance
cycles plus varying background
track aa index
YES: Cosmogenic Isotopes
reconstructed total irradiance
cycles plus varying background
track ? 10Be
Are Long-Term Solar Irradiance
Variations Occurring?
YES: Ca HK Flux in
Sun-like Stars
• observed Ca HK
brightness in 13 Sunlike stars exhibits a
greater range of
variation than is seen
in the present-day Sun
(Baliunas & Jastrow, 1990)
• reconstructed solar
irradiance with varying
background matches
the stellar distribution
better than with activity
cycles, alone
(Lean et al., 2001)
Terrestrial Solar Activity Proxies Vary
with Sun’s Open Flux
* closed flux
modulates
irradiance
Open
Flux
Radial
Interplanetary
Magnetic Field
Geomagnetic
Activity
Cosmic Ray Fluxes at Earth
Wang et al., 2000
How do Open and Closed Flux Vary with
Solar Activity over Many Cycles?
24 June 2002
open
flux in
coronal
holes
• Magnetic sources are deposited as bipolar
regions, with monotonically increasing strength
EIT284
closed
flux in
active
regions
• Flux transport model simulates evolution of
the surface magnetic field – transport by
meridional flow, diffusion, rotation
• Current-free extrapolation of simulated surface
magnetic fields estimates the magnetic
configuration of the corona
EIT304
NSO
Simulations with NRL’s
Photospheric Flux Transport and
Potential Field Extrapolation Models
surface
magnetic
fields of
opposite
polarity
• Open flux is estimated from fields that are
radial at 2.5RSun
Sheeley et al., Solar Phys., 1986; Wang and Sheeley
Sheeley,, ApJ
ApJ,, 1991, 1992
Secular Changes in Open Flux Occur
Without Corresponding Changes in
Closed Flux
Lean & Wang, SPD, 2002
Sun-Climate Mechanisms?
solar energy output
near UV
VIS
IR
radiation
Xrays
EUV
radiation
galactic cosmic
rays
solar
wind
energetic particles
heliosphere
& IMF
UV
radiation
thermosphere
ionosphere
mesosphere & lower thermosphere
stratosphere & ozone
climate
magnetosphere
energetic
particles
Climate Response to
Direct Solar Forcing
)T = κ ) F
= κ (S-S0)×0.7÷4
)T = surface temperature change (oC)
)F = climate forcing (Wm-2)
κ = climate sensitivity (oC per Wm-2)
GISS GCM SIMULATION OF TIME-DEPENDENT CLIMATE
RESPONSE TO SOLAR FORCING SINCE 1600
•
•
•
•
•
8oH10o horizontal resolution with 9 vertical layers
variable mixed layer depth with 250 meter max depth
specified "Q" flux for ocean heat transport
heat diffusion through bottom of mixed layer
0.8-1oC per Wm-2 sensitivity
Rind, Lean and Healy, JGR, 104, 1973, 1998
GISS GCM Simulation of Solar-Induced
Surface Temperature Changes since 1600
model
ocean
heat flow
dampens
decadal
response
C20th temperature changes of ~0.2 o in response to adopted
total solar irradiance variations: 0.45 oC since 1700
Climate Feedbacks Account for 65% of Response
to Solar Forcing in GISS GCM Simulation
water vapor: 35%
sea-ice/
snow cover: 10%
cloud cover: 20%
Latitude
Rind and Overpeck, 1994
Regional Climate Impacts of Solar
Total Irradiance Variability
Longitude
Solar UV Radiation Influences Ozone
Stratosphere
O3 has 2% solar
cycle variation
Troposphere
Surface
6%
Solar UV-Induced Ozone Changes
may Influence Climate
Dynamical Coupling via
Wind-Wave Interactions
Lower
Middle
Atmosphere Atmosphere
Radiative Forcing Sensitivity
Radioactive Coupling via
Absorption and Emission
Change Ozone &
Temperature
Change Winds &
Planetary Waves
Change
Temperature
Advection &
Temperature
Change Winds &
Planetary Waves
Change Climate
SOURCE: NASA Solar Influences on
Climate Workshop, Tucson 2000
Regional Impacts of Solar Cycle
UV-Induced Ozone Changes
GISS stratospheric GCM
simulation reproduces solar
cycle variation in geopotential
height near 24 km (30-mbar)
Shindell, Rind et al,
Science, 1999; JGR, 2000
GISS GCM simulated solar cycle
ozone changes influence NH high
latitude winter climate
Solar Variability is one of
Many Causes of Climate Change
Anthropogenic Forcings
• atmospheric GH gases - CO2, CH4, CFCs, O3, N2O
• tropospheric aerosols - direct and indirect effects of
sulfate, soot, carbon, biomass burning, soil dust, clouds
Natural Forcings
• solar variability - direct and indirect effects
• volcanic eruptions - stratospheric aerosols
Land Cover Changes
Internal Oscillations
• Climate Change Science,
An Analysis of Some Key
Questions, NRC, 2001
• IPCC, 1992, 1995, 2001
• atmosphere-ocean couplings
- ENSO (2-7 yrs), Arctic Oscillation (decadal)... Pacific Decadal
Oscillation (PDO), North Atlantic Oscillation (NAO)
Climate Forcings
2.4
2
1
CO2
0.35
halocarbons
N2O
CH4
tropospheric
ozone
0.25
fossil
fuel
burning
0
-1
-2
-3
stratospheric
ozone
0.2
sulphate
0.4
0.05
0.3
mineral aviation
dust
contrails
& cirrus
biomass
burning
0.1 0.25
solar
landuse
(albedo)
indirect
aerosol
0.23
warming
3
2.4 Wm -2 in next 50 years
cooling
Radiative Forcing (Wm-2)
IPCC 2001: 1750-2000
Future Anthropogenic
Forcing Scenario IS92a
Global Warming in the Twenty-first Century:
An Alternative Scenario
(Hansen et al., PNAS, 2000)
•
•
•
•
rapid warming in recent decades driven by non-CO2 GHGs
future forcing by non-CO2 GHGs reduced to zero
future aerosol forcings cancel
net forcing in next 50 years reduced to 1 Wm-2
EBM Simulations of Past Climate
Change with Multiple Forcings
forcings
Crowley, 2000
simulation: κ ~ 2oC for 2CO2
• simulated temperatures match Mann et al. reconstruction
• solar & volcanic forcings account for pre-industrial variations ~0.2oC
• 20th century mismatch
GISS GCM Simulations of Past Climate
Change with Multiple Forcings
forcings
Robinson et al., 2001
simulation: κ ~ 4oC for 2CO2
• simulated temps track borehole record
• omitting solar forcing →
.. higher sensitivity to GHGs
.. poorer tracking of centennial variations
Solar and Anthropogenic Atmospheric
Influences Differ with Height
O3 production
Mesosphere
Stratosphere
Hartley
bands
SR bands
Ly α
window
O3destruction
Troposphere
315
Stratosphere & Ozone
solar increase → warming
CO2 increase → cooling
volcanoes → warming
Surface & Climate
solar increase → warming
CO2 increase → warming
volcanoes → cooling
Climate System Oscillations
EL-NINO SOUTHERN OSCILLATION
http://www.pmel.noaa.gov, http://topex-www.jpl.nasa.gov
El Nino
La Nina
• warm equatorial
Pacific temps
•Easterly trade winds
subside
• increased rain in
South US & Peru
• West Pacific droughts
• cold equatorial
Pacific temps
• large E-W pressure
difference
• strong trade winds
• winters are warmer in
SE USA, colder in NW
NORTH ATLANTIC OSCILLATION
Positive NAO
• strong subtropical high,
deep Icelandic low
• stronger, northerly
Atlantic storm tracks
• warm, wet European
winters
• mild, wet, US winters
http://www.ldeo.columbia.edu/NAO
Negative NAO
• weak subtropical high
& Icelandic low
• weaker, east-west
storm paths bring cold
air to N.Europe
• US east coast snowy
winters
Solar Variability May Influence
Climate Oscillation Modes
Dettinger and White, JGR, submitted, 2001
ENSO:
solar total
irradiance
cycle
http://coaac.ucsd.edu/PERSONNEL/WHITE/
excites delayedaction oscillator
of the tropical
Pacific air-sea
climate
NAO/AO:
solar activity
(decadalcentennial)
volcanoes
GHGs
O3 depletion
polar
stratosphere
cooling/heating
simulated tropical
SST and zonal-wind
variations larger
than expected from
simple direct forcing
(by 2 to 3 X)
decadal ENSOlike variations
with comparable
climatic impacts
Science, 294, 7 Dec 2001:
Haigh, Bond et al., Shindell et al.
stratospheric
polar vortex
strong/weak
tropospheric
circulation
NAO/AO pos/neg
SUMMARY:
Long-Term Sun-Climate Relationships
There are numerous empirical Earth-Sun connections
on time scales of decades to millennia
- the result of solar forcing, internal oscillations or ...?
Climate models simulate paleo-temperature trends in
response to plausible solar forcing
- are long-term solar irradiance trends occurring?
- GCM’s don’t simulate 11-year temperature cycles because
feedback time responses are too long ..realistic?
- do decadal solar variations amplify climate oscillations?
Climate response to solar forcing is regionally specific
and concurrent with responses to other forcings
- fingerprint of climate change is complex
- different responses in pre- and post industrial epochs?
Determining climate response to solar variability has
been attempted for over a century .. problem is
difficult, unsolved…. and a unique opportunity.
Solar Forcing of
Ice Ages?
Ice volume has a pronounced
100,000 cycle associated with the
eccentricity of Earth’s orbit
(Hayes, Imbrie & Shackleton, 1976)
100,000
Variations in 10Be production by
solar magnetic activity may also
occur on 100,000-year time
scales (Sharma, 2002)
Future Solar Forcing of Climate
Lean, GRL, 2001
•11-year cycles
based on
Schatten et al., 1996
Hathaway et al., 1999
Thompson, 1993
• background is
±0.04Wm -2/year
Anthropogenic
Scenarios
• IS92a
IPCC, 1995
• Alternative
Hansen et al, 2000
Sun’s role in future climate change depends on irradiance
cycles and trends relative to anthropogenic scenarios