The Medway Handyman wrote:

BTW. I do believe in climate change, its been going on for
thousands of years. I don't believe its man made.

Do you mean that you don't believe human activity has increased
the proportion of carbon dioxide in the atmosphere?

Not necessarily no.

There is overwhelming evidence that CO2 levels have been increasing
over the last 100 years
(see eg http://www.carbonify.com/carbon-dioxide-levels.htm)
The level has been increasing steadily at a little over 2ppm for 50 years
from February 2004 to February 2009 it increased from 376 to 386ppm:
http://climateprogress.org/2009/02/13/
noaa-global-carbon-dioxide-co2-levels-2008/.

In my view there is no plausible explanation for this except human activity.
If the activity were periodic then the period must be much shorter
than any other plausible terrestrial or solar-system cause.

I think the climate is changing because it does so every now & then and
always has. The Thames used to freeze over regularly for example & we
didn't have 20+ million cars on the roads.

Not really relevant, but I don't think the Thames used to freeze regularly
within historical records.
Pepys records it freezing over, but it seems pretty clear from his diary
that this was a very unusual event.

Having said that, there is obviously a periodic variation in temperature.
There are ice-ages roughly every 100,000 years,
with warm periods of about 10,000 years in between.
(See eg http://www.edge.org/documents/archive/edge219.html#dysonf
for a very interesting article by Freeman Dyson,
who is a well-known sceptic on the global warming issue,
but who accepts that human activity has made a big difference.
He points out incidentally that we are on the point of a new ice age.
His view - roughly - is that the effects of global warming are not as bad
as the pessimists say.)





--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College Dublin