The dawning realization among climate scientists and their supporters of the dire consequences we can expect if nothing is done about our continuing to pour carbon dioxide into the atmosphere has moved them to deal with the people who have refused to accept that conclusion. The refusers have called themselves "skeptics" but a movement has begun to insist that they instead be called "deniers". Why is this distinction important and what does it mean?
The essential issue here is whether science is "settled" or not. It is possible to argue that science is never settled, and that is the approach of some global warming deniers. But science can be settled yet get modified in future investigation. For example, gravity. Aristotle's ideas were overthrown by Newton's theory. And later Newton was superseded by Einstein's theory of gravity, which even today people don't realize. And Einstein's theory may too be superseded. But with Newton the science was settled even though it has been superseded. This is because after Newton, the science, even though imperfect, was enough to use. With Aristotle we wouldn't be building rockets and sending satellites into space. But with Newton we can, even without Einstein. It turns out that we do need Einstein for GPS, but in all other ways, Newton's Laws of Motion are all we need to do a lot of things.
That's what settled science is, it's declaring that there's enough there for practical use. And that is the case for the effects of carbon dioxide in our atmosphere. There isn't anything to argue about anymore. Certainly climate is complex and there is a lot to investigate and to understand, but not about CO2 and its consequences for the planet if left to increase.
Those who deny the impact of anthropogenic CO2 are truly deniers and not skeptics because the impact of CO2 is settled science. We know that without any CO2 in the atmosphere earth would be a ball of ice, and with what we've had for eon's has permitted civilization to prosper. But it doesn't take a high intellect to realize that doubling the amount of CO2 in the atmosphere is certain to have consequences. People who ignore that are ignoring science, and that makes them deniers not skeptics.