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.
Sun still sulks
20/06/2010Pick of the pics and Climate Change: News and Comments
The Sun still sulks
Two magnetograms from the ESA-NASA SOHO spacecraft contrast the Sun’s liveliness of exactly 10 years ago (20 June 2000) on the left with its feeble performance today (20 June 2010) on the right. In these images made with Stanford’s Michelson Doppler Interferometer, north magnetic polarity is white, south magnetic polarity is black.
Solstice sunrise over Stonehenge 2005. Credit: User: Solipsist.
In the current issue of the Royal Astronomical Society’s magazine Astronomy and Geophysics, Nigel Weiss of Cambridge considers the long-term variability of the Sun and alternative theories about it, especially concerning “grand maxima” in activity like that in the 20th Century, and “grand minima” like the Maunder Minimum of 300 years ago associated with the Little Ice Age. Weiss’s conclusion is that there’s a 40 % chance the current grand maximum will be followed by a grand minimum.
As for the climatic implications, Weiss and I agreed to differ some years ago. Although we both say that the Intergovernmental Panel on Climate Change underestimates the influence of the Sun, Weiss thinks it can’t compete with man-made global warming. His article ends:
Even if the Sun does enter a new Maunder-like grand minimum, any cooling effect will be small compared with the warming produced by anthropogenic greenhouse gases.
Contrast that with Henrik Svensmark’s conclusion in an article for the Danish newspaper Jyllands-Posten.
That the Sun might now fall asleep in a deep minimum was suggested by solar scientists at a meeting in Kiruna in Sweden two years ago. So when Nigel Calder and I updated our book The Chilling Stars, we wrote a little provocatively that “we are advising our friends to enjoy global warming while it lasts.”
In fact global warming has stopped and a cooling is beginning. Mojib Latif from the University of Kiel argued at the recent UN World Climate Conference in Geneva that the cooling may continue through the next 10 to 20 years. His explanation was a natural change in the North Atlantic circulation, not in solar activity. But no matter how you interpret them, natural variations in climate are making a comeback.
The outcome may be that the Sun itself will demonstrate its importance for climate and so challenge the theories of global warming. No climate model has predicted a cooling of the Earth – quite the contrary. And this means that the projections of future climate are unreliable. A forecast saying it may be either warmer or colder for 50 years is not very useful, and science is not yet able to predict solar activity.
So in many ways we stand at a crossroads. The near future will be extremely interesting. I think it is important to accept that Nature pays no heed to what we humans think about it. Will the greenhouse theory survive a significant cooling of the Earth? Not in its current dominant form. Unfortunately, tomorrow’s climate challenges will be quite different from the greenhouse theory’s predictions. Perhaps it will become fashionable again to investigate the Sun’s impact on our climate.
References
N. Weiss, “Modulation of the Sunspot Cycle”, Astronomy and Geophysics, Vol. 51, pp. 3.9-3.15, 2010
H. Svensmark: “While the Sun sleeps” (in Danish), Jyllands-Posten, 9 September, 2009
For a related post on this blog see https://calderup.wordpress.com/2010/05/12/puzzling-sun/
Postscript on the Song of the Sun
I see that Sheffield solar physicists now generate music from observations of the magnetic coronal loops. Read about it (and hear it): http://www.telegraph.co.uk/science/space/7840201/Music-of-the-sun-recorded-by-scientists.html
For an earlier Song of the Sun, using its internal vibrations seen by SOHO’s MDI, click on the second item here (but beware – it’s about 18 MB with visuals) http://www.esa.int/esaSC/SEMLAJWO4HD_index_0.html