In article ,
Alex Stephens Jr writes:
"John Hall" wrote in message
.. .
In article ,
Alex Stephens Jr writes:
"John Hall" wrote in message
...

Forecasting weather and forecasting climate are two very different
things. It may be well be easier to forecast the climate for the next
few decades than it is to forecast the weather for the next three
months.

A very interesting point John, though I'm not sure your statement is
correct.
How successful have previous climate forecasts been in the past?

I don't think that scientists have been making them for more than a
couple of decades - at least not using sophisticated computer models. So
I think it is probably still too early to say.

And at what stage does a weather forecast become a climate forecast?
Alex.



I think the distinction lies in what degree of temporal resolution the
forecast attempts. So if it tries to forecast day by day - or even month
by month - changes, it's a weather forecast. But if it says something
along the lines of "in N years time we expect summers (or winters or
whatever) to be 2C warmer on average than they are now and rainfall to
be 10% less", then it's a climate forecast. A climate forecast says
nothing about any individual day or month or season or year, but only
about what the new average is likely to be like when compared with the
current average. (And possibly also what the new extremes are likely to
be like in relation to current ones; eg 10% of summers are expected to
have an average temperature of more than such and such a figure, when
currently 10% are warmer than some other value.)

I think the Met office forecast for the three monthly period wasn't too
dissimilar to how you describe a climate forecast except in shorter period
and limiting geography.

Very different, because it was for a /particular/ three month period.
They said something along the lines of: "we expect this coming winter to
have a 70% chance of being warmer than the 1971-2000 average". That
makes it a weather forecast. If they had said "we expect 70% of winters
in the next decade to be warmer than the 1971-2000 average" then in
would have been a climate forecast.

Their error recently was to throw in a strange departure from average, why
they did this I have no idea.
Intrinsically it is easier to forecast short term - whether weather or
climate than it is to forecast longer term.

Yes, but forecasting climate in the long-term can be easier than
forecasting weather in the shorter term. Take those two example
forecasts above. With the first, if the winter wasn't warmer than
average most people would view it as having been wrong. It certainly
wouldn't have provided them with useful guidance. But the second
forecast would have provided useful guidance by the end of the decade if
most winters were warmer than average, even if the number was not
precisely 7 out of 10 but 6 or 8 (or arguably even if it was 9 or 10).


Likewise, I have little doubt that climate forecasts that throw in beyond
average scenario's will fail in time also. I don't see many GW forecasts
that allow a 30% chance of a fall in Global temperatures in x years time.
Perhaps there are though?
Alex


That's because, averaged over the whole globe, there seems very little
possibility of that happening unless the understanding embodied in the
models is fatally flawed. I suppose that a sudden unpredicted - and
possibly unpredictable - increase in volcanic activity or a reduction in
solar activity could lead to a reduction, though, at least temporarily
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)