I guess I should have said 'severely depleted', like around 95% since the year 1000. I think that's the figure they were using from the Oceans convention last year.

Well I doubt if we'll actually have any accurate figures from the year 1000 anyway, but whether it's 80% or 95%, it's still pretty close to a mass extinction due to overfishing alone - and I use the former term very loosely.

Certainly some species are down to a tiny proportion of their original populations. I'm thinking about North Sea Cod and herring as examples.

That's funny Mozz....
Because I always think of Al Gore and the 'Mass Polar Bear' extinction..(you know, the FOUR bears that drowned in a storm) whenever I hear people talking about how bad AGW is, and how it's too late to stop it....

People generally lose interest in anything that does not provide validation for preconceived notions, unfortunately.

Usually we are led kicking and screaming towards accepting reality, as it is rarely as we expect or hope it to be.

I still hold out a very, very, very, slim hope, that the problems of climate change may have been overstated, but to move forward on the probability of that incredibly unlikely proposition being correct, is too foolhardy to be contemplated, by any prudent person.

Even the most intransigent skeptics now try and question the rate of change, and the possible negative scenarios, instead of just pretending that nothing significant is even occurring.

mozzaok wrote on Sep 5^th, 2010 at 1:10pm:



OK, well that's a good place to start off. We've talked through the physical basis for warming by carbon dioxide, but if that was all we had to worry about, the warming for a doubling of CO2 would be slightly less than 1 degree C.

What you've brought up is the question of climate sensitivity - in other words, that other greenhouse gas, water vapour and the additional effect of increasing average concentrations of water vapour in reponse to the greenhouse effect warming due to CO2.

When you say that skeptics question the rate of change, that's correct - but there is uncertainty over the precise climate sensitivity even among established climate scientists.

Climate sensitivity is a measure of how responsive the temperature of the climate system is to a change in the radiative forcing due to carbon dioxide, methane, nitrous oxide etc.  It is usually expressed as the temperature change associated with a doubling of the concentration of carbon dioxide in the Earth's atmosphere.

You'll also come across the term climate feedback.

The mean value of climate sensitivity is usually expressed as 3 degrees C plus or minus 1.5 for a doubling of CO2.

A few points there, but do some maths for me. What was the CO2 concentration in 1850? What is the concentration today? Is that a doubling?

By the way, nowhere have I mentioned extrapolation.

gizmo_2655 wrote on Sep 5^th, 2010 at 5:26pm:



Of course we can say what the atmospheric CO2 level was in 1850. It was around 288ppm (+/- 5). Where have you been in the last 20 years? Double 290ppm and you get 580ppm.

Quote:


Horsefeathers.

We're not  there yet. We haven't had a doubling yet - just about 1/3 of a doubling, and the amount of warming fits in pretty close to the predicted climate sensitivity.

Do I have to explain to you where we get the 1850 figure from?