Cosmic Rays Help Resolve Global Warming Puzzle
ALBANY, New York, July 31, 2002 (ENS) - For the first time, researchers have evidence that interstellar cosmic rays could be the missing link that would explain why increases in Earth surface temperatures observed over the past 20 years, known as global warming, exist simultaneously with unchanging temperatures of the low atmosphere.
Because of this discrepancy, some have argued that global warming is unproven. They suggest that true global warming should show uniformly elevated temperatures from Earth's surface up through the atmospheric layers.
In the past, researchers have theorized that changes in cloud cover could help explain the phenomenon, but had not come up with an observation that could account for the difference in temperature profiles.
High clouds generally reflect sunlight while lower clouds tend to retain surface energy. Both effects are well known to science and both have significant effects on global temperatures.
A cosmic ray is a high speed particle - either an atomic nucleus or an electron - that travels throughout the Milky Way Galaxy, including the solar system. Some of these particles originate from the Sun, but most come from sources outside the solar system and are known as galactic cosmic rays.
Previous research has proposed a link between cosmic rays and cloud cover, but had not suggested the altitude dependence of the current study.
Yu's National Science Foundation supported study, published in the July 2002 issue of the American Geophysical Union's "Journal of Geophysical Research-Space Physics," proposes that cosmic rays are responsible for the varying heat profiles.
"A systematic change in global cloud cover will change the atmospheric heating profile," Yu said. "In other words, the cosmic ray induced global cloud changes could be the long sought mechanism connecting solar and climate variability."
Yu's hypothesis, if confirmed, could illuminate the Sun's role in global warming. The amount of cosmic rays reaching Earth depends on solar winds, which vary in strength by space weather conditions.
Yu points out that indications of Earth's warming have coincided with decreased cosmic ray intensity during the 20th century.
Yu proposes that the amount and charge of ions generated by cosmic rays can contribute to the formation of dense clouds by stimulating the production rate of low atmosphere particles that make the clouds more opaque.
Human contributions to climate change are not ruled out by explanations for the natural causes of global warming, but humans may not be solely responsible for the observed temperature increases.
Natural and human made differences in atmospheric chemistry, like greenhouse gas concentrations, can also affect the cosmic rays' influence on clouds, Yu says.
Such height dependent atmospheric differences can increase the quantity of ambient particles in the lower troposphere and decrease the particles in the upper air, says Yu, affecting the type of cloud cover over the Earth.
NASA links about cosmic rays: http://lheawww.gsfc.nasa.gov/users/jacob/cosmic.asp
Cosmic Rays Tutorial: http://ast.leeds.ac.uk/haverah/aims.shtml
Learn more about the solar wind at: http://science.msfc.nasa.gov/ssl/pad/solar/sun_wind.htm