On Fri, 17 Jun 2011 16:26:40 +0100, Martin Brown wrote:

On 17/06/2011 14:32, Tudor Hughes wrote:

It depends what you're sceptical about. If you are saying the
earth has not got warmer then you are the equivalent of a flat-earther
and can be dismissed instantly. If, on the other hand, you are saying
that man's contribution to this warming is less significant than the
current consensus you should provide strong evidence for your view.

That seems quite reasonable to me. The scientific consensus including
the true sceptics (as opposed to deniers for hire) is that about half of
the warming since 1850 is due to changes in insolation and the rest is
due to GHG forcing which only really became significant from ~1970.

Could you point me to some references? My impression was that the
consensus was that changes in insolation were fairly small and had had
little effect on temperature. Also, I don't see how insolation can have
warmed the tropopshere yet cooled the higher atmosphere. That cooling was
only predicted by CO2 theory as far as I know.

Solar activity was high during the post-war period when slight cooling of
the troposphere occurred and during the early part of the rise from 1970
to around '85 but has been falling slowly since then. I find it hard to
see much correlation between solar activity and temperature changes.


I am inclined to the view that some of the very steep rise seen in the
last three decades of the twentieth century was at least partly due to a
periodic component with a period of about 60 years (hence the small
peaks at 1940 and 1880 in HADCRUT). However we are now on the downside
of that periodic term and temperatures are still holding up.

I took an interest in climate cycles around forty years ago but don't
recall a 60-yr cycle. A large study of cycles published in 1975 had a 100-
yr cycle peaking near 1940 but nothing shorter. Other research I heard of
in the late 60s also found 100-yr cycles, both globally and locally. From
these, we were supposed to cool globally until 1990 and the UK was
supposed to experience cold springs from 1970 to 2020. In my experience,
cycles are relatively easy to see in past data but are really unreliable
when extrapolated into the future.



So despite the fact that I do think AGW is both real and a potential
long term threat to civilisation I also believe that extrapolating from
the very steep rise in the 1970-2000 period exaggerates the problem.

I haven't extrapolated that temperature rise. However, I have used a 1980
prediction of the likely effect of doubling CO2 in the atmosphere. The
graph of the predicted rise is a reasonable match to that which has
occurred. It's certainly better than the prediction from climate
cycles. ;-)

See http://tinyurl.com/66jsa5k




--
Graham Davis, Bracknell
Whilst it's true that money can't buy you happiness, at least you can
be miserable in comfort.