[Brian Bailey]

Brian Bailey asked the Naked Scientists:

I wondered if it was possible to put a large umbrella type object in
geostationary orbit causing a large shadow on the Arctic and Antarctic thereby making it cooler in the summer in those places making more ice and snow to remain in those areas?

What do you think?

[lyner]

This would have to have the form of a cylinder all round the Earth or it would only obscure the Sun for a short while. (If it were just a big umbrella, it would be orbiting the Earth once a day and would only do its job when overhead at midday.)

You'd have to question the viability of any space borne system because of the vast amount of energy involved in getting it up there.
Reflecting the sun away with silver or white paint on all available terrestrial surfaces gets my vote. The sums suggest that it would be a workable solution to the problem. Take out shares in Dulux, quickly.

[RD]

US answer to global warming: smoke and giant space mirrors
Washington urges scientists to develop ways to reflect sunlight as 'insurance'
David Adam, environment correspondent The Guardian, Saturday January 27 2007

The US government wants the world's scientists to develop technology to block sunlight as a last-ditch way to halt global warming, the Guardian has learned. It says research into techniques such as giant mirrors in space or reflective dust pumped into the atmosphere would be "important insurance" against rising emissions, and has lobbied for such a strategy to be recommended by a major UN report on climate change

http://www.guardian.co.uk/environment/2007/jan/27/usnews.frontpagenews

Blocking Sun Not Feasible Warming Solution, Says Study
Jessica Marshall, Discovery News July 7, 2008 --

A proposal to reverse climate change by placing mirrors in the sky to reflect sunlight away from Earth won't give us back the same climate we had before we started emitting so much carbon dioxide, says a new study.

http://dsc.discovery.com/news/2008/07/07/sunshade-warming.html

[syhprum]

The only feasible 'sunshade' is the sulfur dioxide pumped out by volcanoes, it has been noticed that after large eruptions there follows cool summers and cold winters for a year or two but I do not see how we could influence how often this happens.

[Make it Lady]

Aren't we supposed to be having a super erruption from a super volcano soon. It think it might possibly wipe us all out but yes it would combat global warming at the same time.

The umberella in space always sounds a bit like something MR Burns would do on the Simpsons.

[LeeE]

MiL - I suspect you're thinking about the Yellowstone Volcanic system re being 'due' a super-eruption.

There have been three VEI8 (Volcanic Explosivity Index [level] eruptions at Yellowstone, the first being 2,100,000 years ago, the second being 1,300,000 years ago and the most recent being 640,000 years ago.  While the average interval between them works out to be about 730,000 years this is only taken from two samples, of intervals of 800,000 years and 660,000 years - hardly a good basis for making an accurate estimate.

That the Yellowstone system is still very much active is beyond doubt, and it is entirely possible that another VEI8 eruption might occur there, but as to when, if ever, it will occur is completely open to debate.  For example if, instead of comparing the average interval with the most recent recent interval, we go by the interval between the first and second eruptions, then far from being overdue another VEI8 eruption we've still got another 70,000 years to wait.

What is much more likely, and even probable, is that a minor eruption will occur 'soon' - perhaps even sometime in the next few thousand years.  Such an event would be entirely in keeping with the known behaviour of the Yellowstone system, which has had many more smaller eruptions than the large VEI8 ones, the most recent being about 70,000 years ago.

Either way, it's very unlikely that any eruption will occur in the timescale relevant to the current global climate change and even if it did, the effects and consequences of climate change wouldn't be countered by simply cooling the Earth.  For example, one of the most serious effects of climate change is that upon insects, upon whom we rely, via pollination, for a huge proportion of our food.  Once those insects have either died out, migrated or evolved to cope with the changing conditions, cooling the Earth won't change them back - the whole ecological system, of which they are a part, is too complex for such a simple and single-tracked solution.

<gratuitous Dad's Army private Fraser quote>We're all dooooomed, doooomed I tell ye'</gratuitous Dad's Army private Fraser quote>