Michael Mcneil wrote:
"Col" wrote in message



However the downside of all this is that the climatic bands will all
shift northwards, leading to enormous disruption to farming, not to
mention the stress on the ecosystem.



How so?

If the planet as a whole gets warmer, one would generally expect
temepratures to rise everywhere. So the crops which grow best now in
the middle west would need to be moved further northward for the same
temperature conditions. But climate change may also affect rainfall, so
areas with adequate precipitation might become arid.

It should also be noted that not all crops do better with increased CO_2
concentration. This situation is really quite complicated. It is an
oversimplification to suggest that in a warmer world that crops will be
easier to grow. Indeed, it might even make matters worse.

Also, one wonders about the motives of those who on the one hand
question predictions of global climate change from increased greenhouse
gas concentrations and then go ahead and predict that if it does happen,
we have have a boon in agriculture. That prediction is even less
certain that the predictions of global warming.