Look to the sun
An experiment by Danish scientists offers convincing evidence linking global warming to an increase in cosmic radiation
Ian Douglas Clark
Thursday, October 12, 2006
Since Newton's inadvertent experiment with gravity beneath the apple tree, scientists have constrained their theories of how nature operates with the need for experimental evidence -- replicable measurements and quantifiable data -- as proof. While the evidence may sometimes prove the obvious, it may also completely change the accepted view of fundamental processes. Ptolemy's theory of the Earth-centred solar system involved impossibly intricate gyrations of the sun, moon and planets. Copernicus' celestial measurements and Galileo's telescope provided experimental observations of moons orbiting Jupiter and reversals in planetary motion to prove we have a sun-centred solar system.
The science of global climate change is no different, where a heated debate exists between two theories -- climate warming forced by CO2 from human activities (anthropogenic global warming or AGW) and natural warming by changes in the Sun's activity.
Last week, the Danish National Space Center released the results of an experiment that demonstrates how cosmic rays could influence natural warming. In so doing, it ruptured a bedrock of some in the AWG camp. As put by Eigil Friis-Christensen, director of the Danish National Space Center, "Some said there was no conceivable way in which cosmic rays could influence cloud cover. [Our] experiment now shows how they do so, and should help to put the cosmic-ray connection firmly onto the agenda of international climate research."
For decades now, the 20th-century increase in global temperature has been largely blamed on the rise in CO2 from human activities. And why not, given that CO2 is a greenhouse gas that can trap infrared radiation and warm the atmosphere? The problem is that the rise in CO2 is not enough to account for this temperature rise. To compensate, the AGW theory assumes an amplification by water vapour of two to three times.
Water vapour is the major greenhouse gas in the atmosphere and accounts for as much as 95% of the natural greenhouse warming that keeps the Earth habitable. According to this theory, a minor amount of warming by CO2 triggers a larger increase in water vapour. Computer models incorporate this amplified forcing and extrapolate over the next 100 years to predict temperature increase of 1.5 degrees to 4.5 degreesC. Further extrapolation of climate feedbacks has produced the wild speculations of an overheated planet that have led to the catastrophic predictions of The Day After Tomorrow and An Inconvenient Truth.
Supporting the other side of the debate, there are remarkably strong correlations between measures of past solar activity and global temperature. For example, the coldest periods of the Little Ice Age, some 300 years ago, occurred when no sunspots were observed on the face of the sun. Moreover, the rise in temperature over the past 100 years occurred when the sun increased its output to its highest levels in the past 1,000 years.
The problem in this theory is that radiant heat from the more active sun is not enough to explain the rise in 20th-century temperatures. However, a change in solar activity affects more than the light the sun emits. It also changes the sun's magnetosphere that sweeps out past the Earth and partly shields us from the harmful high-energy cosmic radiation originating from supernovae deep in the Milky Way. The theory is that these cosmic rays affect our climate by ionizing particles and gases in our atmosphere. These ionized molecules act as nucleation points for water droplets and lead to the formation of clouds. Clouds reflect sunlight back into space and have by far the greatest impact on the Earth's energy balance and climate. Changes in solar activity, then, have a second and more potent impact on our climate through changes in the cosmic ray flux and thus on cloudiness.
This brings us to the burden of scientific evidence in the climate debate. Until now, the evidence for both sides has relied essentially upon wiggle-matching -- how well the ups and downs in temperature over time match with the ups and downs of solar activity, or of CO2 in the atmosphere. Until now, both theories lacked experimental evidence.
The Danish discovery has changed this. Researchers led by the Space Centre's Henrik Svensmark published experimental evidence in the proceedings of the prestigious British Royal Society showing that high-energy cosmic rays do have the ability to ionize molecules in our atmosphere and nucleate clouds. Mr. Svensmark's team managed to reproduce the gases and chemistry of the lower atmosphere inside a chamber of seven cubic metres. Into this simulated atmosphere, they fired a beam of charged particles like the high-energy cosmic radiation that manages to penetrate the Earth's magnetic shielding. Their measurements of the charged particles they created and the rates of nucleation match with those required to have a measurable impact on climate. They provide experimental evidence to support the theory.
The Danes are not the only team to have sought experimental evidence for cosmic ray forcing of the climate. University of Ottawa researcher Jan Veizer and colleague Nir Shaviv use geology and meteorites to show a cosmic ray connection with climate over the past 600-million years. The research team at CERN, the EU's foremost centre for high-energy physics, announced last month that their new CLOUD experiments would test the theory of cloud formation by cosmic rays. NASA is also taking the solar connection more seriously. This past spring, two new satellites were launched to collect data on the link between cloud formation and climate. All this activity signals a recognition that the solar-cosmic ray-cloudiness connection must be taken seriously in climate research.
While these Danish experiments provide new evidence to support the theory of solar-forcing of climate change, the CO2 warming theory remains untested and unverified. Beyond wiggle-matching, no experimental evidence has been produced to show that an increase in CO2 can accelerate the water cycle and increase greenhouse warming with water vapour. In fact, ice core evidence from the past shows that it doesn't.
In the natural sciences, if you can't measure it, you can't prove it.
© National Post 2006