In article ,
Alex Stephens Jr writes:

"John Hall" wrote in message
.. .


If you look at 2050 in isolation, then you are effectively turning the
climate forecast into a weather forecast, and it is likely to be worse -
less accurate and much less detailed - than an attempt to forecast the
next season in 2010. But if you regard it as a climate forecast for the
period 2045-2055, then the picture should be different. It won't tell
you about individual years, but it will tell you about the
characteristics of the period. Forty years is a far way away, but it
should be possible to say something like 95% confidence that mean
temperature for 2045-55 will be between 1 and 2 degrees (say) higher
than it is now.

Thanks again for an excellent reply John.
95% certainty on a figure ±0.5ºC at a range of 40 years ± years.
And presumably precipitation estimations must be equally as accurate.
I have to say that is utterly phenomenal. I had no idea the climate was so
easily modelled.

I hope that in saying that you're going by something more than my "Forty
years is a far way away, but it should be possible to say something like
95% confidence that mean temperature for 2045-55 will be between 1 and 2
degrees (say) higher than it is now." The "say" was supposed to indicate
that the "between 1 and 2 degrees" was being used purely to illustrate
the point I was making, rather than to suggest that is what the models
are actually saying (though I would think that it would be in the right
ball park). I have a tendency to pontificate, but I'm certainly not an
expert in the field of either GW or computer modelling, and I wouldn't
want to have mistakenly given you that impression.

It is indeed easier than a 2 day weather forecast apparently.

Wow.... Nope, I can't get my head around it. It doesn't fit. Not the actual
figure, but the confidence percentile, it's way too high with too little a
margin for error on such a timescale. And you don't need a PhD in statistics
to work that one out. :-)

Eeee, who's guilty of this crime? Name and shame.


See above. Nobody may be saying exactly that, as my "it should be
possible to say something like" was meant to indicate. But averaging
over a 10 year period such as 2045-55, it seems to me quite plausible to
forecast the mean temperature for the period pretty accurately with a
high degree of confidence.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)