Cosmic Rays Affect Global Temperatures, New Study Confirms

  • Date: 10/03/15
  • Reporting Climate Science

Cosmic rays do affect the Earth’s climate but are not responsible for global warming, according to scientists.

A link between the strength of solar activity, the amount of cosmic radiation entering the atmosphere and year-to-year changes in global temperatures, is reported in a paper describing this study.

Periods of weak solar activity result in more cosmic rays entering the atmosphere, more cloud cover in the lower atmosphere and a cooling in global temperatures, the researchers hypothesise in their paper published in the Proceedings of the National Academy of Sciences (PNAS). While periods of strong solar activity result in a reduction in the amount of cosmic radiation entering the atmosphere, fewer lower level clouds and a warming in temperatures.

The researchers, led by Anastasios Tsonis of the University of Wisconsin–Milwaukee, report a “weak to moderate coupling” between cosmic radiation and year-to-year changes in global temperatures in their paper, entitled Dynamical evidence for causality between galactic cosmic rays and interannual variation in global temperature. They report “a significant, although modest, causal effect” of cosmic radiation on short-term, year-to-year variability in global temperatures. 

The researchers suggest that cosmic rays affect temperature by triggering cloud formation as a result of ionisation and that the flux of cosmic rays entering the Earth’s atmosphere is mediated by the the Sun. Strong solar activity has the affect of “swiping away” cosmic rays that arrive at the top of the Earth’s atmosphere while periods of weak solar activity are linked with an increase in the amount of cosmic radiation entering the atmosphere.

More clouds in the upper troposphere trap outgoing long-wave radiation and so warm the Earth while more clouds in the lower troposphere reflect incoming solar radiation and cool the planet. Similarly fewer clouds in the upper atmosphere trap less outgoing radiation and so cool the planet while fewer clouds in the lower atmosphere allow more solar radiation through and therefore this acts to warm the planet.

Data suggests that increased cosmic radiation results in more low-level clouds but has no effect on middle-level or high-level clouds. Therefore increases in cosmic radiation linked to weak solar activity can cool the planet while decreases in cosmic radiation linked with weaker solar activity can cool the planet. 

Cosmic rays constitute a “nontraditional forcing in the climate system”, the authors state in their paper. But they are careful to point out that they found “no measurable evidence of a causal effect” linking cosmic rays with the long term rise in temperatures seen during the 20th century.

The paper conclude as follows: “Our results suggest weak to moderate coupling between CR and year-to-year changes of GT. They resonate with the physical and chemical evidence emerging from laboratory studies suggesting a theoretical dynamic link between galactic CR and GT. However, we find that the realized effect is modest at best, and only recoverable when the secular trend in GT is removed (by first-differencing). Thus, it is important to stress that they do not suggest that CR influences can explain global warming and should not be misinterpreted as being in conflict with the IPCC. Indeed, the opposite is true: we show specifically that CR cannot explain secular warming, a trend that the consensus attributes to anthropogenic forcing. Nonetheless, the results verify the presence of a nontraditional forcing in the climate system, an effect that represents another interesting piece of the puzzle in our understanding of factors influencing climate variability.”

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