Updating The Chilling Stars
Why star positions matter for climate physics
The Making of History’s Greatest Star Map is an excellent account of the European Space Agency’s Hipparcos mission by the project scientist, Michael Perryman. It brings back vivid recollections:
of dismay after the launch in 1989, when the satellite failed to go into the right orbit and frantic steps were needed to improvise a survivable orbit and re-configure the observing programme.
- of satisfaction when operations continued despite unplanned exposure to the Earth’s radiation belts, as well as some nasty solar flares, until the radiation damage became fatal in 1993.
- of the appetizer in 1994, when early results of the Hipparcos star mapping helped in accurate prediction of the impacts of the fragmented Comet Shoemaker-Levy 9 on the planet Jupiter.
- of joy on Isola di San Giorgo, Venice, in 1997 when the Hipparcos science team announced their first large-scale results, after a huge computational effort.
Astrometry took that great leap forward 30 years after Pierre Lacroute of the Strasbourg Observatory first proposed a space mission to measure the positions of stars, 20 years after Erik Høg of the Copenhagen Observatory refined the concept, and 17 years after ESA earmarked it as something to do. Ground-based astrometry had stalled, because of imprecisions due the turbulence of the atmosphere, and its remaining aficionados had little lobbying power. As a result, Hipparcos remained a distinctly European space project – the first in which there was no competition with the US or Soviet space science programmes.
Applications of the Hipparcos Catalogue of 100,000 plus stars and the Tycho 2 Catalogue with 2.5 million stars (to a lesser but still unprecedented accuracy) have ranged from detecting a bend in the Milky Way Galaxy to checking Einstein’s theory of gravity, General Relativity. But wanting to pursue here the relevance of Hipparcos to climate physics, I’m pleased to see that Michael Perryman points the way.
In The Making of History’s Greatest Star Map, pp. 236-243, Perryman notes the role of Hipparcos in refining observations the wobbles of the Earth’s axis, which are involved in the pacing of ice ages (the Milankovitch theory). Then he points to the link between solar activity and climate change, as evidenced by the Little Ice Age, the Medieval Warm Period and other variations. As to the mechanism for the solar connection, Perryman singles out the suggestion that cosmic rays, modulated by solar activity, influence cloud cover.
He continues the story with the Sun’s journey through the Galaxy and the icy intervals on Earth that correspond to exposure to intense cosmic rays when passing through spiral arms. That’s a major topic in The Chilling Stars and, as Perryman says, the Hipparcos data have improved our knowledge of motions in the Galaxy.
It’s reassuring when a professor of astronomy with no scientific or political axe to grind gives serious attention to the cosmic-ray/climate link (the Svensmark hypothesis). Let me reciprocate by reviewing what’s said about the climate-related significance of Hipparcos and its successor Gaia in The Chilling Stars and see if it needs updating or extending.
Do clouds disappear? 2
24/05/2010Added 12 June 2010: There is now a thoughtful reply from Eimear Dunne.
Climate Change – News and Comments, and an echo of a Falsification Test
Wake up! Models don’t trump observations
It tells of unremitting attempts to falsify the Svensmark hypothesis by claiming that there’s no important effect on global cloud cover when eruptions from the Sun briefly cut the influx of cosmic rays, in “Forbush decreases”. The centrepiece is a summary of results published last year by Svensmark, Bondo and Svensmark. They show very plainly, in observations of the real world, that Forbush decreases have big impacts both on aerosols (chemical specks that grow into cloud condensation nuclei) and on low-level clouds.
That earlier post continues with the efforts in 2009-10 by Wolfendale and Arnold and their collaborators, who try to deny the Svensmark group’s result, by using relatively weak Forbush decreases. Svensmark can explain exactly how the impacts in those cases are masked by quasi-random meteorological noise, like tigers hidden in a jungle’s undergrowth.
Real-world results by Svensmark, Bondo & Svensmark (2009) for the remarkable loss of fine aerosols from the atmosphere (black curve) following five strong Forbush decreases in cosmic rays (red curve). Each aerosol datum point is the daily mean from about 40 AERONET stations world-wide, using stations with more than 20 measurements a day.
New nonsense comes in an abstract posted on the CERN website. It’s for a paper by researchers at Leeds, to be presented at a meeting about aerosols in Helsinki in three months’ time.
At issue are the Svensmark team’s results on aerosols (see right). These show fine aerosols disappearing from the sky, because the shortage of cosmic rays lessens the chemical production of the clusters of sulphuric acid and water molecules that seed the aerosols.
According to the people in Leeds, that can’t be right because they have a computer model that contradicts it.
The GLOMAP model was developed by Ken Carslaw, and the unlucky person named as lead author is a graduate student, Eimear Dunne.
An open letter to the lead author
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