Title: Extraterrestrial Climate Forcing: Variations in Orbital and Solar Properties
1Extraterrestrial Climate Forcing Variations in
Orbital and Solar Properties
- In Defense of Milankovitch
- G. Roe
- Variations in Solar Luminosity and their Effect
on Earths Climate - P. Foukal, C. Frölich, H. Spruit, T.M.L. Wigley
2Overview
- Climate change back then
- What is Milankovitch theory?
- What are the problems with the theory?
- How is the theory defended?
- And climate change now
- What solar properties were studied by Foukal et
al.? - What are the impacts of these variations on
climate? - Are there other properties that need to be
studied that may impact climate? - Summary
3Climate change back then
4Milankovitch Theory
- Long term variations in earths orbit cause
interglacial cycles - Climate changes occur due to changes in total
solar insolation (TSI) - Orbital variations are quasi-periodic thus
glacial periods should be easily calculated and
correlate to changes in TSI
Roe 2006
5Orbital Parameters and Impacts on TSI
- Milankovitch theory has been applied to
- Eccentricity
- 100,000 and 400,000 years
- Obliquity
- 41,000 years
- Axial precession
- 19,000 and 23,000 years
- Orbital inclination
- 100,000 years
Zachos et al. 2001, Teunter 2000, Roe 2006
6Problems with Milankovitch Theory
- Not well defined theory has become muddled with
additional research - Roe 2006 Stick with Milankovitchs original
1941 theory - Orbitally induced variations in summertime
insolation in the northern high latitudes are in
antiphase with the time rate of change of ice
sheet volume. Roe 2006 - Milankovitchs original parameters eccentricity,
obliquity, and axial precession
Roe 2006
7Problems with Milankovitch Theory
- Roe 2006
- CO2 and tropical SSTs may produce dominant
climate forcing than changes in TSI - Difficult to separate these signals in
determining cause of ice age uncertainty in what
is forcing the glacial cycle - Debate of the timing of temperature changes and
global extent of glacial periods - Large lag observed between orbital forcing and
ice ages - TSI variations are not significant enough to
produce the changes observed in global ice volume - Effect is greater than causation
- Obliquity effects are stronger than eccentricity
effects this may not have always been true
Roe 2006, Zachos et al. 2001, Lea 2004, Wunsch
2004
8Defending Milankovitch
- Two ocean sediment core studies used
- SPECMAP (Imbrie et al. 1985)
- HW04 (Huybers and Wunsch 2004)
- Statistical method used to correlate ice volume
change with June 65N insolation changes - Correlation of -0.4 and -0.2, and lag of 6000 and
8000 years for SPECMAP and HW04 respectively - Important discovery Insolation changes better
correlate to ice volume rate of change - Correlation of -0.8 and -0.4, and no lag and lag
of 1000 years for SPECMAP and HW04 respectively
Roe 2006
9Defending Milankovitch
Ice Volume and Solar Insolation
Rate of Change of Ice Volume and Solar Insolation
Roe 2006
10Defending Milankovitch
Ice Volume and Solar Insolation
Rate of Change of Ice Volume and Solar Insolation
(best fit linear regression)
Roe 2006
11CO2 Effects and Other Problems
- CO2 Effects
- CO2 concentration variations found to lag behind
changes in ice melting - Shortwave TSI variations found to be 5 times
larger than the effects of radiation forcing from
CO2 - Still unexplained
- Milankovitch theory can not explain rapid
deglaciations at the end of some ice ages
Roe 2006
12Climate change now
13Solar Variations and Global Warming
- Solar luminosity data studied since 1978
- Has solar luminosity changed significantly to
affect TSI and global climate? - Sunspots and faculae
- Photospheric effective temperature
- Solar diameter
Foukal et al. 2006
14Sunspots and Faculae
- Sunspots and faculae
- Sunspots intense areas of magnetic convection
- Faculae bright (visible) areas around sunspots,
considered thermal leaks - 11 year cycle considered to small time frame to
have significant impacts on climate - Solar luminosity peaks with maxima of sunspots
amplitude variation of 0.05-0.07 - Other research shows that Maunder minimum led to
temperature changes of 0.2-0.8C
Foukal et al. 2006, Beer et al. 1999, Bard et al.
2000
15Photospheric Effective Temperature and Solar
Diameter
- Photospheric effective temperature
- Photospheric temperature (excluding sunspots) has
slowly increased since 1978 - 0.01 increase in TSI per decade
- TSI increase too small to impact global climate
- Solar diameter
- Improved measurement techniques show solar
diameter has not changed, with an error of a few
kilometers
Foukal et al. 2006
16Changes in TSI Since 1978
- TSI has not varied significantly since
observations began in 1978 - TSI variation needs to be 3 times greater have a
similar impact of Maunder minimum (0.2-0.8C
cooling)
Foukal et al. 2006
17Other Solar Variations
- Variations of amount of UV radiation from sun
(Foukal et al. 2006, Yu 2002) - Possibly impacting stratospheric temperatures
- Variations in cosmic ray flux and solar wind (Yu
2002, Shivav 2005) - Possibly affecting CCN in atmosphere, impacting
formation of clouds - Plasma variations and interactions with
ionosphere (Yu 2002, Foukal et al. 2006) - These properties, as well as their interactions
with global climate, is not completely understood
18Summary
- Variations in orbital parameters cause
interglacial periods - Improved correlation through change in ice volume
- Still problem of rapid deglaciations
- Total solar irradiance has only slightly
increased since measurements began - Change has negligible impacts on climate and is
not significant enough to cause global warming - Other solar parameters, such as UV radiation and
cosmic ray flux, need to be studied more
thoroughly