I raggi cosmici, veri responsabili dell'effetto serra

Esperti del Max Planck Institute di Heidelberg hanno scoperto che l’effetto serra potrebbe dipendere esclusivamente dall’attività solare, in particolare dall’azione dei raggi cosmici. Se così fosse l’uomo verrebbe scagionato dall’accusa di favorire il surriscaldamento globale. A bordo di un aereo attrezzato con uno spettrometro a ioni gli scienziati hanno analizzato gli strati più alti della troposfera, verificando una abbondante presenza di ioni positivi caratterizzati da una massa notevole. Questi ultimi interferirebbero con il normale processo di formazione delle nubi e in particolare con il cosiddetto “albedo”, corrispondente alla capacità delle formazioni nuvolose di riflettere la luce. La presenza di questi gruppi di particelle elettriche agevolerebbe la formazione dei nuclei di condensazione - minutissime particelle il cui diametro può variare da 0,001 unimicron a circa 10 unimicron – incrementando il numero di nubi e amplificando l’effetto serra. I raggi cosmici sono il risultato del cosiddetto vento solare, sciame di particelle prodotto dalla nostra stella, che influenza non solo la formazione delle nubi, ma addirittura la salute dell’uomo. A conclusioni simili sono giunti anche studiosi che hanno recentemente pubblicato un articolo sulla rivista Journal of Geophysical Research-Space Physics. In questo caso, i ricercatori, basandosi sul fatto che esiste un innalzamento delle temperature in prossimità della superficie terrestre, ma non nella parte medio-bassa dell’atmosfera, si sono resi conto che il vento solare, effettivamente, influisce direttamente sul surriscaldamento globale. In particolare Fangqun Yu, scienziato all’università di New York-Albany negli Stati Uniti, ha evidenziato che l’effetto dei raggi cosmici non è uguale in ogni punto dell’atmosfera, ma varia, facilitando nella maggior parte dei casi lo sviluppo di sistemi nuvolosi: questi ultimi imprigionano i raggi ultravioletti riflessi dalla superficie terrestre e provocano un’impennata delle temperature. Secondo gli esperti entro il 2100 l’effetto serra determinerà un rialzo termico compreso fra 1,8 e 5,4 gradi centigradi.

E l'opinione di Henrik Svensmark...

The impact of cosmic rays on the climate could be greater than scientists suspect after experiments showed they may have a pivotal role in cloud formation. Researchers have managed to replicate the effect of cosmic rays on the aerosols in the atmosphere that help to create clouds. Henrik Svensmark, a weather scientist in Denmark, said the experiments suggested that man’s influence on global warming might be rather less than was supposed by the bulk of scientific opinion. Cosmic rays — radiation, or particles of energy, from stars, which bombard the Earth — can create electrically charged ions in the atmosphere that act as a magnet for water vapour, causing clouds to form. Dr Svensmark suggests that the Sun, at a historically high level of activity, is deflecting many of the cosmic rays away from Earth and thus reducing the cloud cover. Clouds reflect the Sun’s rays back into space and are considered to have an important cooling effect. However, if during periods of high activity the Sun’s magnetic field pushes a greater proportion of cosmic rays away from the Earth, fewer clouds will form. The research, published in the journal Proceedings of the Royal Society, concentrates on how ions are created and behave in the atmosphere when cosmic rays from stars hit it. Cosmic rays were replicated by the use of ultraviolet light that were turned on and off in both short bursts and long exposures to create ions. The researchers found that the presence of ions encouraged the formation of clusters of molecules. In the atmosphere these clusters of ozone, sulphur dioxide and water are understood to act as aerosols in attracting water vapour, culminating in the formation of clouds. The number of clusters, according to the report, is proportionate to the number of ions present, which in turn depends on the frequency of cosmic rays reaching the Earth. “The experiment indicates that ions play a role in nucleating new particles in the atmosphere and that the rate of production is sensitive to the rate of ion density,” the report concluded. “One might expect to find a relationship between ioni-sation and cloud properties. This feature seems to be consistent with the present work”. The report added that the ions were likely to generate a reservoir of clusters of aerosol molecules in the atmosphere that “are important for nuclea-tion processes in the atmosphere and ultimately cloud formation”. The findings are unlikely to change radically the views of mainstream climatologists. Nevertheless, a team of scientists will shortly begin a larger experiment at a particle accelerator in Europe in the hope of learning more about the effects of cosmic rays on cloud cover. According to the Intergovern-mental Panel for Climate Change, by far the biggest influence on climate change is the level of greenhouse gases released by mankind, largely through the use of fossil fuels. Peter Stott, of the Met Office’s Hadley Centre and one of Britain’s leading climate scientists, said that Dr Svensmark’s theory should be taken “with a cellar of salt”. Small, localised effects on cloud formation might be possible but he dismissed the suggestion of cosmic rays being responsible for global warming.