On Fri, 08 Jan 2010 03:48:08 -0800, delboy wrote:


2) The point I am trying to make (at least in my last posting) is that
there is good evidence that the climate has been variable before, with
naturally cold and warm periods. The fact that measured global
temperatures have increased by a fraction of a degree over the last 100
years, and the ice caps are melting, doesn't necessarily mean that this
will be a continuing trend.

There are hints in fairly reputable circles, e.g. New Scientist, that
there could be two opposing effects operating:

On the warming side
the greenhouse effect forced by rising carbon dioxide levels from
burning foosil fuel and by rising methane levels from agriculture,
melting permafrost and (some say) sublimation of methane clathrates

On the cooling side
the extended quite sun effect. The sun has now been stuck in its
sunspot minimum for the last two years. A very long quiet sun
coincided with the Little Ice Age. The hypothesis is that:
- during a solar minimum the solar wind is also at a minimum
(known fact)
- if the solar wind is reduced, so is size of the sun's
magnetosphere (known fact)
- the magnetosphere deflects cosmic rays, which are high energy
charged particles from outside the solar system
- more cosmic rays cause more clouds as they disintegrate in
our atmosphere and ionise it.
- hence a prolonged solar minimum causes cloudier weather.
- increased cloudiness reflects more sunlight, cooling the earth
(known fact)

Hence a long solar minimum will start a cooling trend if it lasts
long enough to propagate outward far enough to affect the size of
the solar magnetosphere. The solar wind travels at 400-750 km/s,
the heliopause is around 150 AU in radius, so you'd expect to see
this cooling effect to start between 1 and 2 years after a long
solar minimum started.

NOTE: this cooling effect has nothing to do with variations in the sun's
energy output, which is pretty stable though it is thought to have
risen by about 25% since the earth formed. Just as well it *is* stable
life as we know it would be impossible near a variable star.

I'd just add that we've now had two rather poor, cloudy soaring seasons
and the solar minimum started 2 years ago....

Nobody knows, or seems to know, whether the cooling associated with a
solar minimum (assuming it is) is a bigger or a smaller effect than
current greenhouse warming.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |