"There is more to climate than temperatures. Also, relatively small temperature increases can have large effects."

Can you explain how small increase in temperature has large effect. Seasonally there are huge swings in terms of temperature, and regional climate patterns such El Nino can can produce significant affects. And there are other cyclical regional climate changes. Drought patterns, severe storm patterns, etc.

"It might benefit some life forms, but it would harm far more. Good for mountain pine beetles, bad for mountain pine trees."
It's unlikely that global warming is causing this- going up and down mountains will have more temperature affect than 1 C- and regional affects can be mostly the cause- plus disease itself is a random affect. For instance disease such as bird flu couldn't reasonably be tied to global warming. And you have situations where a disease vector runs across drought situation thereby increasing it's affect, just like drought and disease may also increase the chance major forest fires which might wipe out the bettle, or could simply provide more weakened trees.

"The US midwest could well become a desert, though the Canadian north could open up for agriculture - plus Canada would have an even greater percentage of North America's fresh water. That plus the longest undefended border in the world shared with the world's most powerful military makes me nervous."

You going have changing weather and climate- and this has nothing to do with GW. In general GW is thought to cause more rain- but even this is not very significant in comparison cyclic regional changes which have yearly, decadal or century cycles.

"I remember when car companies whined that increasing fuel economy would devastate them - Toyota and Honda seem to be doing OK these days. I think reducing CO2 emissions in an imaginative way could actually benefit the economy directly. Guess who wants us to keep burning oil, coal and natural gas??"

Well, if you worried about CO2, coal is much more significant source of CO2 emission. So nuclear powerplants will make a bigger difference than can be got by improving MPG of cars or even taking all cars completely off the road.
Though there are also a small amount of coal burning powerplant that capture the CO2- and pump into oil field to improve oil yield from old oil fields.

"All the ice doesn't have to melt for there to be a significant problem. If 10 percent were to melt, ocean levels would rise about 10 meters."

If 10% of Antarctic were to melt then you get this 10 meters, but Antarctic isn't going to melt- this is fantasy.

"Even without ice cap melting and subsequent sea level rise, global warming will have catastrophic effects. "

Such as?