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63-472: The primary goal is to understand the influence of galactic cosmic rays (GCRs) on aerosols and clouds, and their implications for climate. Although its design is optimised to address the possibility of cosmic rays nucleating cloud particles, (as posed by, for example, Henrik Svensmark and colleagues) CLOUD allows as well to measure aerosol nucleation and growth under controlled laboratory conditions. Atmospheric aerosols and their effect on clouds are recognised by

126-949: A Master of Science in Engineering (Cand. Polyt) in 1985 and a Ph.D. in 1987 from the Physics Laboratory I at the Technical University of Denmark . Henrik Svensmark is director of the Center for Sun-Climate Research at the Danish Space Research Institute (DSRI), a part of the Danish National Space Center . He previously headed the sun-climate group at DSRI. He held postdoctoral positions in physics at three other organizations: University of California, Berkeley , Nordic Institute for Theoretical Physics , and

189-538: A Reply to Lockwood and Fröhlich which concludes that surface air temperature records used by Lockwood and Fröhlich apparently are a poor guide to Sun-driven physical processes, but tropospheric air temperature records do show an impressive negative correlation between cosmic-ray flux and air temperatures up to 2006 if a warming trend, oceanic oscillations and volcanism are removed from the temperature data. They also point out that Lockwood and Fröhlich present their data by using running means of around 10 years, which creates

252-574: A 15-hour delay. Long-term changes in cloud cover (> 3 months) and GCR gave correlations of p=0.06. More recently, Laken et al. (2012) found that new high quality satellite data show that the El Niño Southern Oscillation is responsible for most changes in cloud cover at the global and regional levels. They also found that galactic cosmic rays, and total solar irradiance did not have any statistically significant influence on changes in cloud cover. Lockwood (2012) conducted

315-498: A growing crystal, thus increasing the number of crystals in the system. So both primary and secondary nucleation increase the number of crystals in the system but their mechanisms are very different, and secondary nucleation relies on crystals already being present. It is typically difficult to experimentally study the nucleation of crystals. The nucleus is microscopic, and thus too small to be directly observed. In large liquid volumes there are typically multiple nucleation events, and it

378-474: A laboratory study by Svensmark, Pepke and Pedersen published in Physics Letters A showed that there is in fact a correlation between cosmic rays and the formation of aerosols of the type that seed clouds. Extrapolating from the laboratory to the actual atmosphere, the authors asserted that solar activity is responsible for approximately 50 percent of temperature variation. In a detailed 2013 post on

441-554: A larger role. Svensmark detailed his theory of cosmoclimatology in a paper published in 2007. The Center for Sun-Climate Research at the Danish National Space Institute "investigates the connection between solar activity and climatic changes on Earth". Its homepage lists several publications earlier works related to cosmoclimatology. Svensmark and Nigel Calder published a book The Chilling Stars: A New Theory of Climate Change (2007) describing

504-457: A nucleus that may be only of order ten molecules across it is not always clear that we can treat something so small as a volume plus a surface. Also nucleation is an inherently out of thermodynamic equilibrium phenomenon so it is not always obvious that its rate can be estimated using equilibrium properties. However, modern computers are powerful enough to calculate essentially exact nucleation rates for simple models. These have been compared with

567-430: A photochemically and biologically driven seasonal cycle of particle concentrations and cloud formation in good agreement with observations. CLOUD insofar allows to explain a large fraction of cloud seeds in the lower atmosphere involving sulphuric acid and biogenic aerosols. CLOUD researchers note that cosmic rays have little influence on the formation of sulphuric acid–amine particle formation: "The ion-induced contribution

630-409: A range of complex chemical reactions with sulfuric acid , ammonia and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans ( plankton ). Although they observe that a fraction of cloud nuclei is effectively produced by ionisation due to the interaction of cosmic rays with the constituents of Earth atmosphere, this process is insufficient to attribute

693-415: A range of complex chemical reactions with sulfuric acid , ammonia and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans ( plankton ). Although they observe that a fraction of cloud nuclei is effectively produced by ionisation due to the interaction of cosmic rays with the constituents of Earth atmosphere, this process is insufficient to attribute all of

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756-455: A small correlation every 22 years, less than 14 percent of global warming since the 1950s could be attributed to cosmic ray rate. The study concluded that the cosmic ray rate did not match the changes in temperature, indicating that it was not a causal relationship. Another 2013 study found, contrary to Svensmark's claims, "no statistically significant correlations between cosmic rays and global albedo or globally averaged cloud height." In 2013,

819-499: A substance or mixture . Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self-organized structure appears. For example, if a volume of water is cooled (at atmospheric pressure ) significantly below 0   °C, it will tend to freeze into ice , but volumes of water cooled only a few degrees below 0   °C often stay completely free of ice for long periods ( supercooling ). At these conditions, nucleation of ice

882-459: A thorough review of the scientific literature on the "solar influence" on climate. It was found that when this influence is included appropriately into climate models causal climate change claims such as those made by Svensmark are shown to have been exaggerated. Lockwood's review also highlighted the strength of evidence in favor of the solar influence on regional climates. Sloan and Wolfendale (2013) demonstrated that while temperature models showed

945-408: Is "considerable evidence" for solar influence on Earth's pre-industrial climate and to some degree also for climate changes in the first half of the 20th century. Svensmark's coauthor Calder responded to the study in an interview with LondonBookReview.com, where he put forth the counterclaim that global temperature has not risen since 1999. Later in 2007, Svensmark and Friis-Christensen brought out

1008-547: Is at the limit of current technology, and CERN know-how has been crucial for CLOUD being the first experiment to achieve this performance." CERN posted a 2009 progress report on the CLOUD project. J. Kirkby (2009) reviews developments in the CERN CLOUD project and planned tests. He describes cloud nucleation mechanisms which appear energetically favourable and depend on GCRs. On 24 August 2011, preliminary research published in

1071-514: Is delayed until the system enters the unstable region where a small perturbation in composition leads to a decrease in energy and, thus, spontaneous growth of the perturbation. This region of a phase diagram is known as the spinodal region and the phase separation process is known as spinodal decomposition and may be governed by the Cahn–Hilliard equation . In many cases, liquids and solutions can be cooled down or concentrated up to conditions where

1134-418: Is difficult to disentangle the effects of nucleation from those of growth of the nucleated phase. These problems can be overcome by working with small droplets. As nucleation is stochastic , many droplets are needed so that statistics for the nucleation events can be obtained. To the right is shown an example set of nucleation data. It is for the nucleation at constant temperature and hence supersaturation of

1197-441: Is either slow or does not occur at all. However, at lower temperatures nucleation is fast, and ice crystals appear after little or no delay. Nucleation is a common mechanism which generates first-order phase transitions , and it is the start of the process of forming a new thermodynamic phase. In contrast, new phases at continuous phase transitions start to form immediately. Nucleation is often very sensitive to impurities in

1260-459: Is generally small, reflecting the high stability of sulphuric acid–dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates." This result does not support the hypothesis that cosmic rays significantly affect climate, although a CERN press release states that neither does it "rule out a role for cosmic radiation" in climate. Dunne et al. (2016) have presented

1323-415: Is illustrated in the animation to the right. This shows nucleation of a new phase (shown in red) in an existing phase (white). In the existing phase microscopic fluctuations of the red phase appear and decay continuously, until an unusually large fluctuation of the new red phase is so large it is more favourable for it to grow than to shrink back to nothing. This nucleus of the red phase then grows and converts

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1386-441: Is the very first nucleus of that phase to form, or because the nucleus forms far from any pre-existing piece of the new phase. Particularly in the study of crystallisation, secondary nucleation can be important. This is the formation of nuclei of a new crystal directly caused by pre-existing crystals. For example, if the crystals are in a solution and the system is subject to shearing forces, small crystal nuclei could be sheared off

1449-691: The Cosmoclimatology theory that cosmic rays "have more effect on the climate than manmade CO 2 ": A documentary film on Svensmark's theory, The Cloud Mystery , was produced by Lars Oxfeldt Mortensen and premiered in January 2008 on Danish TV 2. In April 2012, Svensmark published an expansion of his theory in the Monthly Notices of the Royal Astronomical Society In the new work he claims that

1512-505: The Niels Bohr Institute . In 1997, Svensmark and Eigil Friis-Christensen popularised a theory that linked galactic cosmic rays and global climate change mediated primarily by variations in the intensity of the solar wind , which they have termed cosmoclimatology . This theory had earlier been reviewed by Dickinson. One of the small-scale processes related to this link was studied in a laboratory experiment performed at

1575-607: The Danish National Space Center (paper published in the Proceedings of the Royal Society A , February 8, 2007). Svensmark's conclusions from his research downplay the significance of the effects of man-made increases in atmospheric CO 2 on recent and historical global warming , with him arguing that while the climate change role of greenhouse gases is considerable, solar variations play

1638-725: The Danish National Space Institute. To investigate the role of cosmic rays in cloud formation low in the Earth's atmosphere, the SKY experiment used natural muons (heavy electrons) that can penetrate even to the basement of the National Space Institute in Copenhagen. The hypothesis, verified by the experiment, is that electrons released in the air by the passing muons promote the formation of molecular clusters that are building blocks for cloud condensation nuclei. Critics of

1701-514: The Danish findings. CERN started a multi-phase project in 2006, including rerunning the Danish experiment. CERN plans to use an accelerator rather than rely on natural cosmic rays. CERN's multinational project will give scientists a permanent facility where they can study the effects of both cosmic rays and charged particles in the Earth's atmosphere. CERN's project is named CLOUD (Cosmics Leaving OUtdoor Droplets). Dunne et al. (2016) have presented

1764-751: The Earth's history. The connection to evolution is a culmination of this work." Preliminary experimental tests have been conducted in the SKY Experiment at the Danish National Space Science Center. CERN , the European Organization for Nuclear Research in Geneva, is preparing comprehensive verification in the CLOUD Project. Svensmark conducted proof of concept experiments in the SKY Experiment at

1827-661: The IPCC as the main source of uncertainty in present radiative forcing and climate models, since an increase in cloud cover reduces global warming. The core of the experiment is a stainless steel chamber of 26 m volume filled with synthetic air made from liquid nitrogen and liquid oxygen. The chamber atmosphere and pressure is being measured and regulated by various instrumentations. The aerosol chamber can be exposed to an adjustable particle beam simulating GCRs at various altitude or latitude. UV illumination allows photolytic reaction. The chamber contains an electric field cage to control

1890-653: The character of my papers are misleading, or where my work does not live up to scientific standards" Mike Lockwood of the UK's Rutherford Appleton Laboratory and Claus Froehlich of the World Radiation Center in Switzerland published a paper in 2007 which concluded that the increase in mean global temperature observed since 1985 correlates so poorly with solar variability that no type of causal mechanism may be ascribed to it, although they accept that there

1953-617: The classical theory, for example for the case of nucleation of the crystal phase in the model of hard spheres. This is a model of perfectly hard spheres in thermal motion, and is a simple model of some colloids . For the crystallization of hard spheres the classical theory is a very reasonable approximate theory. So for the simple models we can study, classical nucleation theory works quite well, but we do not know if it works equally well for (say) complex molecules crystallising out of solution. Phase-transition processes can also be explained in terms of spinodal decomposition , where phase separation

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2016-414: The concentration of dissolved chemicals in the water increases. Thus small droplets of water, as found in clouds, may remain liquid far below 0   °C. An example of experimental data on the freezing of small water droplets is shown at the right. The plot shows the fraction of a large set of water droplets, that are still liquid water, i.e., have not yet frozen, as a function of temperature. Note that

2079-489: The crystal phase in small droplets of supercooled liquid tin; this is the work of Pound and La Mer. Nucleation occurs in different droplets at different times, hence the fraction is not a simple step function that drops sharply from one to zero at one particular time. The red curve is a fit of a Gompertz function to the data. This is a simplified version of the model Pound and La Mer used to model their data. The model assumes that nucleation occurs due to impurity particles in

2142-515: The data period of his study. A (2003) critique by physicist Peter Laut of Svensmark's theory reanalyzed Svensmark's data and suggested that it does not support a correlation between cosmic rays and global temperature changes; it also disputes some of the theoretical bases for the theory. Svensmark replied to the paper, stating that "...nowhere in Peter Laut’s (PL) paper has he been able to explain, where physical data have been handled incorrectly, how

2205-569: The diversity of life on Earth over the last 500 million years might be explained by tectonics affecting the sea-level together with variations in the local supernova rate, and virtually nothing else. This suggests that the progress of evolution is affected by climate variation depending on the galactic cosmic ray flux. The director of DTU Space, Prof. Eigil Friis-Christensen, commented: "When this enquiry into effects of cosmic rays from supernova remnants began 16 years ago, we never imagined that it would lead us so deep into time, or into so many aspects of

2268-407: The drift of small ions and charged aerosols. The ionisation produced by cosmic rays can be removed with a strong electric field. Besides, humidity and temperature inside the chamber can be regulated, allowing for fast adiabatic expansion for artificial clouds (compare cloud chamber ) or experiments on ice microphysics. According to Kirkby "the level of cleanliness and control in a laboratory experiment

2331-528: The effect of cosmic rays in the UK. He states: "Although the statistically significant non-linear cosmic ray effect is small, it will have a considerably larger aggregate effect on longer timescale (e.g. century) climate variations when day-to-day variability averages out". Brian H. Brown (2008) of Sheffield University further found a statistically significant (p<0.05) short term 3% association between Galactic Cosmic Rays (GCR) and low level clouds over 22 years with

2394-444: The energy barrier for nucleation. The time until the appearance of the first crystal is also called primary nucleation time, to distinguish it from secondary nucleation times. Primary here refers to the first nucleus to form, while secondary nuclei are crystal nuclei produced from a preexisting crystal. Primary nucleation describes the transition to a new phase that does not rely on the new phase already being present, either because it

2457-443: The existing theories including the classical nucleation theory explain well the steady nucleation state when the crystal nucleation rate is not time dependent, the initial non-steady state transient nucleation, and even more mysterious incubation period, require more attention of the scientific community. Chemical ordering of the undercooling liquid prior to crystal nucleation was suggested to be responsible for that feature by reducing

2520-615: The hypothesis claimed that particle clusters produced measured just a few nanometres across, whereas aerosols typically need to have a diameter of at least 50 nm in order to serve as so-called cloud condensation nuclei. Further experiments by Svensmark and collaborators published in 2013 showed that aerosols with diameter larger than 50 nm are produced by ultraviolet light (from trace amounts of ozone , sulfur dioxide , and water vapor), large enough to serve as cloud condensation nuclei. Scientists are preparing detailed atmospheric physics experiments to test Svensmark's thesis, building on

2583-541: The illusion of a continued temperature rise, whereas all unsmoothed data point to a flattening of the temperature, coincident with the present maxing out of the magnetic activity of the Sun, and which the continued rapid increase in CO 2 concentrations seemingly has been unable to overrule. In April 2008, Professor Terry Sloan of Lancaster University published a paper in the journal Environmental Research Letters titled "Testing

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2646-486: The journal Nature showed there was a connection between Cosmic Rays and aerosol nucleation. Kirkby went on to say in the definitive CERN press Release "Ion-enhancement is particularly pronounced in the cool temperatures of the mid-troposphere and above, where CLOUD has found that sulphuric acid and water vapour can nucleate without the need for additional vapours. The first CLOUD experiments showed that sulphuric acid (derived from sulphur dioxide, for which fossil fuels are

2709-554: The liquid or solution is significantly less thermodynamically stable than the crystal, but where no crystals will form for minutes, hours, weeks or longer; this process is called supercooling . Nucleation of the crystal is then being prevented by a substantial barrier. This has consequences, for example cold high altitude clouds may contain large numbers of small liquid water droplets that are far below 0   °C. In small volumes, such as in small droplets, only one nucleation event may be needed for crystallisation. In these small volumes,

2772-400: The liquid tin droplets, and it makes the simplifying assumption that all impurity particles produce nucleation at the same rate. It also assumes that these particles are Poisson distributed among the liquid tin droplets. The fit values are that the nucleation rate due to a single impurity particle is 0.02/s, and the average number of impurity particles per droplet is 1.2. Note that about 30% of

2835-424: The main outcomes of 10 years of results obtained at the CLOUD experiment performed at CERN. They have studied in detail the physico-chemical mechanisms and the kinetics of aerosols formation. The nucleation process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve ions formation due to cosmic rays but also

2898-424: The main outcomes of 10 years of results obtained at the CLOUD experiment performed at CERN. They have studied in detail the physico-chemical mechanisms and the kinetics of aerosols formation. The nucleation process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve ions formation due to cosmic rays but also

2961-555: The northern hemisphere summer. Besides biogenic vapours produced by plants, another class of trace vapours, amines have been shown by CLOUD to cluster with sulphuric acid to produce new aerosol particles in the atmosphere. These are found close to their primary sources, e.g. animal husbandry , while alpha-pinene is generally found over landmasses. The experiments show that sulfuric acid and oxidized organic vapors at low concentrations reproduce suitable particle nucleation rates. The nucleation mechanism used on global aerosol models yields

3024-415: The nucleation of crystals in that there is clear evidence for heterogeneous nucleation, and that nucleation is clearly stochastic. The freezing of small water droplets to ice is an important process, particularly in the formation and dynamics of clouds. Water (at atmospheric pressure) does not freeze at 0   °C, but rather at temperatures that tend to decrease as the volume of the water decreases and as

3087-418: The nucleus at a surface, is much more common than homogeneous nucleation. For example, in the nucleation of ice from supercooled water droplets, purifying the water to remove all or almost all impurities results in water droplets that freeze below around −35   °C, whereas water that contains impurities may freeze at −5   °C or warmer. This observation that heterogeneous nucleation can occur when

3150-612: The predominant source) as such has a much smaller effect than had been assumed. In 2014, CLOUD researchers presented newer experimental results showing an interaction between oxidised biogenic vapours (e.g., alpha-pinene emitted by trees) and sulphuric acid. Ions produced in the atmosphere by galactic cosmic rays enhance the formation rate of these particles significantly, provided the concentrations of sulphuric acid and oxidised organic vapours are quite low. This new process may account for seasonal variations in atmospheric aerosol particles, which are being related to higher global tree emissions in

3213-716: The present climate modifications to the fluctuations of the cosmic rays intensity modulated by changes in the solar activity and Earth magnetosphere. Henrik Svensmark Henrik Svensmark (born 1958) is a physicist and professor in the Division of Solar System Physics at the Danish National Space Institute (DTU Space) in Copenhagen . He is known for his work on the hypothesis that fewer cosmic rays are an indirect cause of global warming via cloud formation. Henrik Svensmark obtained

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3276-401: The present climate modifications to the fluctuations of the cosmic rays intensity modulated by changes in the solar activity and Earth magnetosphere. Oceanographer Paul Farrar (2000) argued that, based on the spatial distribution of the cloud variation during Svensmark's study period, the variation was due to an El Niño which was synchronized with the cosmic ray signal used by Svensmark during

3339-459: The proposed causal link between cosmic rays and cloud cover", which found no significant link between cloud cover and cosmic ray intensity in the last 20 years. Svensmark responded by saying "Terry Sloan has simply failed to understand how cosmic rays work on clouds". Dr. Giles Harrison of Reading University , describes the work as important "as it provides an upper limit on the cosmic ray-cloud effect in global satellite cloud data". Harrison studied

3402-405: The rate of homogeneous nucleation is essentially zero, is often understood using classical nucleation theory . This predicts that the nucleation slows exponentially with the height of a free energy barrier ΔG*. This barrier comes from the free energy penalty of forming the surface of the growing nucleus. For homogeneous nucleation the nucleus is approximated by a sphere, but as we can see in

3465-456: The schematic of macroscopic droplets to the right, droplets on surfaces are not complete spheres and so the area of the interface between the droplet and the surrounding fluid is less than a sphere's 4 π r 2 {\displaystyle 4\pi r^{2}} . This reduction in surface area of the nucleus reduces the height of the barrier to nucleation and so speeds nucleation up exponentially. Nucleation can also start at

3528-482: The scientists' blog RealClimate , Rasmus E. Benestad presented arguments for considering Svensmark's claims to be "wildly exaggerated". ( Time magazine has characterized the main purpose of this blog as a "straightforward presentation of the physical evidence for global warming". ) Nucleation In thermodynamics , nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within

3591-426: The surface of a liquid. For example, computer simulations of gold nanoparticles show that the crystal phase sometimes nucleates at the liquid-gold surface. Classical nucleation theory makes a number of assumptions, for example it treats a microscopic nucleus as if it is a macroscopic droplet with a well-defined surface whose free energy is estimated using an equilibrium property: the interfacial tension σ. For

3654-489: The system is not evolving with time and nucleation occurs in one step, then the probability that nucleation has not occurred should undergo exponential decay . This is seen for example in the nucleation of ice in supercooled small water droplets. The decay rate of the exponential gives the nucleation rate. Classical nucleation theory is a widely used approximate theory for estimating these rates, and how they vary with variables such as temperature. It correctly predicts that

3717-479: The system to this phase. The standard theory that describes this behaviour for the nucleation of a new thermodynamic phase is called classical nucleation theory . However, the CNT fails in describing experimental results of vapour to liquid nucleation even for model substances like argon by several orders of magnitude. For nucleation of a new thermodynamic phase, such as the formation of ice in water below 0   °C, if

3780-523: The system. These impurities may be too small to be seen by the naked eye, but still can control the rate of nucleation. Because of this, it is often important to distinguish between heterogeneous nucleation and homogeneous nucleation. Heterogeneous nucleation occurs at nucleation sites on surfaces in the system. Homogeneous nucleation occurs away from a surface. Nucleation is usually a stochastic (random) process, so even in two identical systems nucleation will occur at different times. A common mechanism

3843-470: The time until the first crystal appears is usually defined to be the nucleation time. Calcium carbonate crystal nucleation depends not only on degree of supersaturation but also the ratio of calcium to carbonate ions in aqueous solutions. In larger volumes many nucleation events will occur. A simple model for crystallisation in that case, that combines nucleation and growth is the KJMA or Avrami model . Although

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3906-495: The time you have to wait for nucleation decreases extremely rapidly when supersaturated . It is not just new phases such as liquids and crystals that form via nucleation followed by growth. The self-assembly process that forms objects like the amyloid aggregates associated with Alzheimer's disease also starts with nucleation. Energy consuming self-organising systems such as the microtubules in cells also show nucleation and growth. Heterogeneous nucleation, nucleation with

3969-535: The tin droplets never freeze; the data plateaus at a fraction of about 0.3. Within the model this is assumed to be because, by chance, these droplets do not have even one impurity particle and so there is no heterogeneous nucleation. Homogeneous nucleation is assumed to be negligible on the timescale of this experiment. The remaining droplets freeze in a stochastic way, at rates 0.02/s if they have one impurity particle, 0.04/s if they have two, and so on. These data are just one example, but they illustrate common features of

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