Because most of them recognize, on at least some level, that greenhouse gasses cause global warming, and warming is likely to be a bad thing.

Some sources for more information:

http://www.skepticalscience.com/

http://aip.org/history/climate/summary.h...

http://www.epa.gov/climatechange/

http://news.nationalgeographic.com/news/...

http://www.realclimate.org/

http://www.newscientist.com/article/dn11...

http://answers.yahoo.com/question/index;... (I posted a question asking people to give links to information at varying levels of experience)

That is a good question.

We now know that climate models cannot predict the future. We know that the simplistic view that increased CO2 keeps making the atmosphere warmer is also not true. That is how CO2 levels are increasing quickly and the temperature is not.

Some warmists are getting very confused. They say that CO2 warms the atmosphere. When you present evidence of the pause they say the heat has gone into the oceans. So which is it: Does it warm the atmosphere or the oceans? Whichever you choose you need to change the rest of your model to fit. If the energy is in the oceans it is not affecting the atmosphere for the crops.

Lincoln will be turning in his grave: "... government of the people, by the people, for the people, shall not perish from the earth." You now have to replace the word "people" with the words "lobby groups". Financial institutions have vested interest in carbon trading because they can see commissions at every stage. Insurance companies can see the benefit in keeping people scared because it sells insurance. Green organisations gain power and influence and so wealth.

Governments like to keep the populace concerned as well. It gives them a reason for existence. Some organisations see it as a way to get themselves permanently funded. We can currently cancel funding to the UN because governments vote on it. If they were to receive a world tax of some sort they could be self-sustaining. A bureaucrat's dream.

If you notice, all governments that are strong on carbon tax collecting are all pretty weak on climate actions they are going to take with the money collected. In fact, many have said it is about wealth distribution not climate. So we are being misled.

Chem F has it right. If you read some of the denier responses you will clearly see some at least are telling deliberate bare faced lies. Why? Because they have a personal ideology to defend. Truth gets in the way.

No one, NO ONE is concerned with CO2 you exhale or any other living thing exhales. That is all part of the natural carbon cycle and has zero impact on anything. They know this but keep pretending otherwise. The Carbon dioxide in the atmosphere regulates the planets temperature. Without it we would freeze. With too much it would get uncomfortably warm.

Over the last century and a bit we have added 40% more CO2 to the atmosphere. Every year we collectively add more again than we did the year before. We are on an accelerating drive to change our planets atmosphere. The main source of this additional CO2 is the burning of fossil fuels.

The best evidence available as collected for decades says this additional CO2 is altering the climate by retaining more of the sun's energy.

Since the location of cities choice of crops to grow etc is related to climate and sea levels, then to alter the climate and raise sea levels is not a wise move.

So in the interests of future generations and indeed current ones governments are taking the advice of scientists in the field to try to moderate the rate of green house gas emissions to stall climate Change.

Like anything that can be measured, it must be taxed. Governments don't want to reduce it! They like the revenue. However, taxing something does, in effect, discourage its production.

They don't. They just want to tax you for releasing CO2 and you do that every time you exhale.

Top climate scientists say there is no man-made Global Warming.

The Great Global Warming Swindle