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

Outline

• Introduction: Solar activity and Earth’s climate

• Climate effects of a new Maunder minimum

• Some comments on projections of future climate

Outline

• Introduction: Solar activity and Earth’s climate

• Climate effects of a new Maunder minimum

• Some comments on projections of future climate

Discovery of Sunspots

1610

Galileo Galilei

Johann FabriciusGalileo Galilei

Thomas Harriot

Christoph Scheiner

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)

Sunspot Record

SIDC

Main feature: Regular cycle of about 11 years

Search for Sun-Climate Connection

Lean & Rind (2008)

~ 0.1°C

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...

Search for Sun-Climate Connection

~ 0.3°C

Global annual mean surface temperatures:

Total Solar Irradiance

NASA

PMOD

Solar Spectral Irradiance

Lean (2000)

Flux of Galactic Cosmic Rays

Lockwood & Fröhlich (2007)

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)

Sunspot RecordTwo “Grand Minima”; most pronounced:

late 17th-century “Maunder Minimum” (Eddy 1976)

Solar Activity ProxiesCosmogenic isotopes (like 14C and 10Be) trace solar

activity over longer timescales:

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

Outline

• Introduction: Solar activity and Earth’s climate

• Climate effects of a new Maunder minimum

• Some comments on projections of future climate

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!

Solar Activity Proxies

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

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...

Millennium Simulations

IPCC (2007)

Performance for past Grand Minima

Feulner & Rahmstorf (2010), GRL

Future forcings

Feulner & Rahmstorf (2010), GRL

Projected temperatures

Feulner & Rahmstorf (2010), GRL

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

Outline

• Introduction: Solar activity and Earth’s climate

• Climate effects of a new Maunder minimum

• Some comments on projections of future climate

Empirical methods

Lean & Rind (2009)

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

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)

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.”

Thanks for your attention!