Transcript The CLOUD Experiment at CERN

The CLOUD Experiment at CERN
Jasper Kirkby /CERN
Bulgarian teachers visit
16 October 2008
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Climate forcings
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0.7oC rise since 1900 (not uniform)
IPCC findings:
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Total anthropogenic 1.6 W/m2
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Negligible natural (solar)
contribution: 0.12 W/m2
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Clouds poorly understood
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Earth’s radiation energy budget
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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”) 3
NASA CERES satellite
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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 4
Why clouds areJohnimportant
for
climate
change
Constable, Cloud study,
1821
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Clouds cover
~65% of globe,
annual average
Net cooling of
30 W/m2
c.f. 1.6 W/m2
total
anthropogenic
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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
ship tracks
• Aerosol particles = condensation seeds
• Charged particles = condensation seeds
(at high supersaturations)
• Can cosmic rays
influence aerosols,
clouds and climate?
bubble chamber
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Little Ice Age and the sunspot record
The frozen Thames,
1677
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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)
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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
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Little Ice Age and
Medieval Warm Period
Global observations
high GCR flux
cool climate
low GCR flux
warm climate
Austrian 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
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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
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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
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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
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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
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“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
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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/
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