(Guest Blogger- Richard)
For 100s of millions of years the Earth's temperature has fluctuated through a range of about five degrees Celsius. The fluctuations are a function of Sol's varying output, our planet's orbital and axial relationship to the sun, cosmic radiation (alters our cloud cover) and shifting ocean currents. At present the Earth is on the crest of one of these cycles.
In the past (early dinosaur era) the atmosphere has had CO2 levels exceeding 5%. CO2 has presently recently risen from 0.027% to almost 0.04%, which is nothing. 98% of the greenhouse gases (mainly water vapour) are not man-made, so environmentalists would have us all suffer economically and even die. (This is because cars are so light --to save gas and CO2 emissions-- that the occupants are more likely to die in accidents --over 20,000 deaths/yr and 200,000 more serious injuries/yr in the USA alone).
I believe more CO2 would cause a greening of our planet on a grand scale. Even at 0.04% CO2 most plants are struggling to get CO2 for photosynthesis. A doubling of CO2 is known to double fruit crop output, and would likely do similar wonders for most other plant species.
Plants would even survive better in dry regions because they could close their stomata (leaf pores) to conserve water and get enough CO2 to continue photosynthesizing.
As for humans the changes in environment would be so gradual that lifetimes would come and go, so no one will drown or dramatically lose property. In most cases, if someone finds the regional climate to be too hot or wet, they can do what people already do for all sorts of reasons: move a few hundred miles to a place they prefer.
In many ways Environmentalism is a religion (incl. the present anthropogenic global warming furor). It is a belief system that uses snippets of (scientific) fact but only if it suits Environmentalist beliefs*. It even has its goddess, "Gaia", that many believe in either implicitly (revering Nature, over Mankind) or explicitly.
*While Al Gore tells us about melting glaciers, neither he nor the media tell you that Antarctica's Ice Cap is the thickest it has ever been. The breaking off of the Ross Ice Shelf was more likely caused by increased flow of glacier ice off the continent, than by any melting.