On 19/10/2012 09:37, Graham Easterling wrote:
On Thursday, October 18, 2012 10:39:34 PM UTC+1, Stephen Davenport wrote:
On Thursday, October 18, 2012 8:32:16 PM UTC+1, Steve Jackson wrote:

Stephen, I hope my A level students will rationalise that warming in
Scandinavia might just be more than a localised event, mirrored
perhaps in the UK, so certainly of continental proportions, long
before fossil fuel burning became an issue.
===========

Well, I hope they're smart enough to notice a faulty syllogism that concludes the *certainty* of a continent-wide phenomenon based on flimsy premises of "might just be" and "mirrored perhaps". And "continental proportions" still ain't global.

Stephen.

I am bemused by people (not just Steve) using past variations in the climate to justify sceticism over global warming.

I would hope everyone on USW would accept:-
1. The earth has warmed over the last 100 years
2. CO2 is a greenhouse gas and mankind has been pumping it into the atmosphere.

The only real arguments should be over the relative importance of other factors influencing the Earths climate and positive/negative feedback mechanisms. As these are poorly understood then it seems commonsense that attempts should be made to minimise mankinds affect on the atmosphere.

Saying the Earth's been warmer/colder in the past is irrelevant, of course it has!

They are using a common fallacy that sets up the strawman that
everything is due to CO2, then show that some changes are natural and
then deny that any of it is due to CO2. Works for Daily Wail readers.

If you look back over the past 150 years where we have pretty good
records (even sceptics sponsored research like BEST which goes back
further) shows additional warming from GHG forcing after 1970's.

Roughly speaking the natural rise in global temperature due to solar
flux over 150 years and the rise in the 3 decades from 1970 to 2000 due
to GHG forcing appear to be about equal in magnitude. Although I happen
to thing that some of that latter rise was the upside of a periodic
luni-solar term of 58y (2x Inex) also seen to peak in 1940, 1880(weak)
and 1824.

We should be on the downside of a periodic term at the moment but global
temperature rise has merely slowed. If my hunch is right it will pick up
again with a vengeance about 2018.

It is known that the sun is a weak variable star with 0.1% TSI
variability over the solar cycle (more at some wavelengths) and from
astrophysics that on geological timescales it will get brighter.

From an experimentalists point of view it would be handy if the sun
would give us one solar cycle with 1% TSI variation so that we could
more accurately characterise the Earth's actual impulse response.

As it is we are stuck with the deniers chanting "it is only a theory" as
they do about evolution, big bang cosmology and relativity.

--
Regards,
Martin Brown