1 The CLOUD Experiment at CERN Jasper Kirkby /CERN Bulgarian teachers visit 16 October 2008

2 Climate forcings 0.7 o C rise since 1900 (not uniform) IPCC findings: ‣ Total anthropogenic 1.6 W/m 2 ‣ Negligible natural (solar) contribution: 0.12 W/m 2 ‣ Clouds poorly understood

3 Earth’s radiation energy budget Atmosphere contains “greenhouse gases” which absorb longwave (infrared) radiation Most important greenhouse gases are H 2 O (95% of greenhouse effect) and CO 2 (4%) Most (2/3) of energy reaching Earth’s surface is radiation back from atmosphere (“greenhouse effect”)

4 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

5 Why clouds are important for climate change Clouds cover ~65% of globe, annual average Net cooling of 30 W/m 2 c.f. 1.6 W/m 2 total anthropogenic John Constable, Cloud study, 1821

6 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

7 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?

8 Little Ice Age and the sunspot record The frozen Thames, 1677 Inactive sun (low sunspots) ⇒ cold climate Active sun (high sunspots) ⇒ warm climate

9 Possible physical mechanism

10 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)

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

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

13 GCR-climate yr Little Ice Age and Medieval Warm Period Global observations high GCR fluxcool climate low GCR fluxwarm climate Austrian speleothem:

14 GCR-climate - 10 kyr (Holocene) Bond et al, Science 294, 2001 LIA is merely the most recent of around 10 such events in Holocene

15 GCRs and Indian Ocean monsoon Solar/GCR forcing of Indian Ocean monsoons (ITCZ migration) on centennial— even decadel—timescales

16 CLOUD EXPERIMENT

17 CLOUD Collaboration

18 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”

19 CLOUD facility at CERN PS (2009 →)

20 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 -90 o C → 100 o C CERN UHV standard for inner surfaces Air supply from cryogenic liquids

21 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

22 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

23 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

24 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

25 Some (good) scientific climate blogs & debates Anthropogenic global warming viewpoint: ‣ RealClimate: Sceptical viewpoint: ‣ Climate Science (Roger Pielke Sr.): ‣ Climate Audit (Steve McIntyre): Lots of interactive climate plots: ‣ Climate4You (Ole Humlum): ‣ WoodforTrees (Paul Clark):