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The CLOUD Experiment at CERN

Jasper Kirkby /CERNBulgarian teachers visit

16 October 2008

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Climate forcings

• 0.7oC rise since 1900 (not uniform)

• IPCC findings:

‣ Total anthropogenic 1.6 W/m2

‣ Negligible natural (solar) contribution: 0.12 W/m2

‣ Clouds poorly understood

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Earth’s radiation energy budget

• Atmosphere contains “greenhouse gases” which absorb longwave (infrared) radiation

• Most important greenhouse gases are H2O (95% of greenhouse effect) and CO2 (4%)• Most (2/3) of energy reaching Earth’s surface is radiation back from atmosphere

(“greenhouse effect”)

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NASA CERES satellite

• Data from CERES satellite (Clouds and Earth’s Radiant Energy System)

• Climate models aim to simulate Earth’s climate on computers

• Clouds are poorly simulated

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Why clouds are important for climate change

• Clouds cover ~65% of globe, annual average

• Net cooling of 30 W/m2

• c.f. 1.6 W/m2 total anthropogenic

John Constable, Cloud study, 1821

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• All cloud droplets form on aerosol “seeds” known as cloud condensation nuclei - CCN

• Cloud properties are sensitive to number of droplets

• More aerosols/CCN => brighter clouds, with longer lifetimes

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Seeds for cloud formation

contrails

bubble chamber

ship tracks

• Aerosol particles = condensation seeds• Charged particles = condensation seeds (at high supersaturations)

• Can cosmic rays influence aerosols, clouds and climate?

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Little Ice Age and the sunspot record

The frozen Thames, 1677

• Inactive sun (low sunspots) ⇒ cold climate• Active sun (high sunspots) ⇒ warm

climate

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Possible physical mechanism

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Galactic Cosmic Rays (GCRs)

• Generated by supernovae

• Enter our solar system and are partially deflected by solar wind

• Mostly high energy protons

• Tiny energy input (= starlight)

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Sun (photosphere) seen in visible (677nm) at solar max (2001)

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Sun (corona) seen with extreme UV eyes (20nm)

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GCR-climate - 2000yr

• Little Ice Age and Medieval Warm Period

• Global observations

high GCR flux

cool climate

low GCR fluxwarm

climateAustrian speleothem:

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GCR-climate - 10 kyr (Holocene)Bond et al, Science 294,

2001

• LIA is merely the most recent of around 10 such events in Holocene

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GCRs and Indian Ocean monsoon

•Solar/GCR forcing of Indian Ocean monsoons (ITCZ migration) on centennial—even decadel—timescales

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CLOUD EXPERIMENT

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CLOUD Collaboration

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CLOUD concept

• Study cosmic ray - aerosol - cloud microphysical interactions in the laboratory:‣ Recreate atmosphere in aerosol chamber‣ Attach analysing instruments to measure aerosols

+ cloud droplets‣ Use CERN particle beam as adjustable source of

“cosmic rays”

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CLOUD facility at CERN PS (2009 →)

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CLOUD 3m aerosol chamber

• Stainless steel chamber, 3m diameter, 3.8m height

• Ports for sampling probes, optical readout & instrumentation

• Thermal housing and precision temperature control

• Operation range: 1.0 → 1.1 bar absolute-90oC → 100oC

• CERN UHV standard for inner surfaces

• Air supply from cryogenic liquids

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CLOUD experimental goals

• Influence of cosmic rays on: ‣ Aerosol nucleation and growth:

Ion induced nucleation of aerosols from trace gases

Aerosol growth to cloud condensation nuclei (CCN)

Activation of CCN into cloud droplets‣ Cloud microphysics (global electrical circuit):

Ice particle formation Collision efficiencies of aerosols and droplets Freezing mechanism of polar stratospheric clouds

• Evaluate climatic significance of laboratory measurements by cloud modeling and field studies

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Conclusions• Climate has continually varied in the past, and

the causes are not well understood - especially on the 100 year timescale relevant for today’s climate change

• Strong evidence for solar-climate variability, but mechanism is not understood. A cosmic ray influence on clouds is a leading candidate

• CLOUD at CERN aims to study the cosmic ray-cloud mechanisms in a controlled laboratory experiment

• The question of whether - and to what extent - the climate is influenced by solar/cosmic ray variability remains central to our understanding of anthropogenic climate change

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Messages to take back to your classroom• Always be sceptical of what you read or hear in

science (including what you heard in my talk!):

‣ Especially in the popular media, which is often sensationalist and wrong when it comes to science

• This doesn’t mean you doubt everything you hear; it means you decide for yourself if it makes sense, and you always think about alternative explanations:

‣ To help you, there is an enormous amount very good (and bad) information available on the web

• Science is never “settled” - it always has uncertainties, and this is its strength: the current orthodoxy can always be thrown out by new experimental results

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Two quotations for your students• “In questions of science, the

authority of a thousand is not worth the humble reasoning of a single individual”, Galileo Galilei, 1632

• "The first principle of science is that you must not fool yourself, and you are the easiest person to fool", Richard Feynman, 1964

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Some (good) scientific climate blogs & debates

• Anthropogenic global warming viewpoint:‣ RealClimate: http://www.realclimate.org/

• Sceptical viewpoint:‣ Climate Science (Roger Pielke Sr.):

http://climatesci.org/‣ Climate Audit (Steve McIntyre):

http://www.climateaudit.org/

• Lots of interactive climate plots:‣ Climate4You (Ole Humlum):

http://www.climate4you.com/‣ WoodforTrees (Paul Clark):

http://www.woodfortrees.org/