>Do you believe (and does science support) the claim that humans are making any kind of measure-able, threatening impact on the earth's climate as to warrant legislation?
Yes and yes. Although I don't think that climate change in its present form will act quickly enough to cause a true threat to human civilization as a whole, I do think there is enough evidence to conclude that at least a good portion of climate change is due to human activity. Besides, burning fossil fuels does more than just change the greenhouse effect. It also pumps carcinogenic chemicals into the atmosphere that make up a threat to overall human health, and of course it also uses up fossil fuels, which are a rapidly diminishing resource that isn't going to last forever...or even for more than a few decades at this rate.
>I'm all in favor of protecting the environment and endangered species and I do see the potential harm that could possibly result if we don't. But I also don't think that heavy handed legislation is the answer.
I think that if anything, the legislation is just being put in the wrong place. Rather than setting arbitrary limits on how much of specific gases a company can produce, or selling 'pollution credits', we should just put down one single imperative on the basis of economic rent. That is to say, for all the pollution that a company releases into the general environment, they have to pay the government the equivalent cost of the harm that pollution will cause (either by its effect on the public or by the cost of cleaning it up, whichever is more reasonable). And if a company wants to run its factories in other countries and then sell their products here, then they still have to pay the government the equivalent cost of cleaning up whatever of their pollution's harmful effects will enter the environment of this country. That way, the public is compensated for all the pollution pumped into their environment, and there is no loss of competition to foreign corporations.
Unfortunately, like so much else, this requires a government that ISN'T corrupt to the core to start with...
