how would a new maunder minimum affect the...
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How would a new Maunder minimum affect the climate?
Georg Feulner
Potsdam Institute for Climate Impact Research, Germany
2010 SORCE Science Meeting, Keystone, Colorado, 19 May 2010
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Outline
• Introduction: Solar activity and Earth’s climate
• Climate effects of a new Maunder minimum
• Some comments on projections of future climate
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Outline
• Introduction: Solar activity and Earth’s climate
• Climate effects of a new Maunder minimum
• Some comments on projections of future climate
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Discovery of Sunspots
1610
Galileo Galilei
Johann FabriciusGalileo Galilei
Thomas Harriot
Christoph Scheiner
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Sun and Weather
1801: Herschel uses the prize of grain to investigate
possible connections between weather and periods without any observed sunspots
William Herschel (1738–1822)
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Sunspot Record
SIDC
Main feature: Regular cycle of about 11 years
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Search for Sun-Climate Connection
Lean & Rind (2008)
~ 0.1°C
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Search for Sun-Climate Connection
• Small modulating effect of solar activity on global temperatures well established
• General: Difficulty to extract small solar signal from climate records with natural variability of at least the same order of magnitude...
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Search for Sun-Climate Connection
~ 0.3°C
Global annual mean surface temperatures:
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Total Solar Irradiance
NASA
PMOD
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Solar Spectral Irradiance
Lean (2000)
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Flux of Galactic Cosmic Rays
Lockwood & Fröhlich (2007)
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Sun-Climate Interaction
• Certain: TSI variation is only 0.1% over one solar cycle, but small effect on climate
• Very likely: Ultraviolet radiation varies by a few percent and affects the upper atmosphere (but mechanism still unclear)
• Uncertain/speculative: Variations of solar wind and magnetic field and hence flux of cosmic rays with possible climate effects (e.g. through clouds)
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Sunspot RecordTwo “Grand Minima”; most pronounced:
late 17th-century “Maunder Minimum” (Eddy 1976)
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Solar Activity ProxiesCosmogenic isotopes (like 14C and 10Be) trace solar
activity over longer timescales:
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Maunder Minimum and Little Ice Age
• Timing: Correlation, but regionally different onset of cool periods...
• Forcing: Reduction in TSI (and changes in SSI), but strong volcanic eruptions during that time...
• Uncertainties in reconstructed TSI, other forcings (volcanoes!) and (regional/global) temperatures...
• But: Contribution (at least) of low solar activity to somewhat cooler climate certain
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Outline
• Introduction: Solar activity and Earth’s climate
• Climate effects of a new Maunder minimum
• Some comments on projections of future climate
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How likely is a new Grand Minimum?
• Various pieces of evidence that recent Grand Maximum will come to an end in the next decades
• But: Time of onset, level and extent of any new Grand Minimum uncertain
• Maybe most convincing: At least 4 Grand Minima occurred during the last millennium!
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Solar Activity Proxies
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The model
Earth-system model of intermediate complexity (EMIC) CLIMBER-3α (Montoya et al. 2006):
• Statistical-dynamical atmosphere model POTSDAM-2
• Ocean general circulation model MOM3
• Models for sea ice, ice-sheets, land surface and vegetation
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Atmosphere: POTSDAM-2
Ocean: MOM3
Sea ice
Land
VegetationIce
CLIMBER-3α
The model
Advantage: EMICs are much faster than GCMs, ideal for long timescales, ensembles, sensitivity studies...
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Millennium Simulations
IPCC (2007)
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Performance for past Grand Minima
Feulner & Rahmstorf (2010), GRL
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Future forcings
Feulner & Rahmstorf (2010), GRL
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Projected temperatures
Feulner & Rahmstorf (2010), GRL
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Summary
Feulner & Rahmstorf (2010), GRL
• Global temperature reduction in 2100 relative to 1961-1990 with currently favored Maunder-Minimum TSI (-0.08%): 0.1°C
• With stronger TSI forcing (-0.25%): 0.3°C
• For comparison: Global warming under IPCC A1B and A2 scenarios: 3.7°C and 4.5°C, respectively
• Caveats: Uncertainties in reconstructions, forcings, only TSI variation modeled
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Outline
• Introduction: Solar activity and Earth’s climate
• Climate effects of a new Maunder minimum
• Some comments on projections of future climate
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Empirical methods
Lean & Rind (2009)
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Global cooling?
Keenlyside et al. (2008)
Modeling with repeated forcing by observed sea-surface temperatures to improve forecasts for the
North Atlantic region and globally
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Criticism• IPCC scenario actually performs better
• Forecast too cold for 1994-2004 - and almost certainly too cold for 2000-2010
• Unclear how well sea-surface temperatures trace ocean circulation
• Model artifact (“coupling shock”) when switching from observed sea-surface temperatures to modeled ones (Rahmstorf 1995)
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The Realclimate bet
“If the average temperature 2000-2010 (their first forecast) really turns out to be lower or equal to the average temperature 1994-2004, we will pay them €
2500. If it turns out to be warmer, they pay us € 2500. This bet will be decided by the end of 2010. We offer the same for their second forecast: If 2005-2015 turns out to be colder or equal compared to 1994-2004, we
will pay them € 2500 – if it turns out to be warmer, they pay us the same.”
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Thanks for your attention!