You need to distinguish between skepticism and denialism. Skepticism is the lifeblood of science. That's why we have the peer review process and that's why time and again we have had to revise or abandon previous beliefs because they didn't hold up to careful examination or new knowledge or were based on experiments that couldn't be replicated, etc.
Legitimate scientists understand the need for skeptical inquiry. That's why the recent research by Richard Muller and his Berkeley team is so important. Muller is a first-class scientist and very hard-nosed empiricist. He approached the climate change issue as a skeptic and assumed that a careful analysis of all the relevant data would show that the earth isn't really getting significantly warmer. So he was genuinely surprised to find that the data really do demonstrate significant and continuing warming. Muller carefully examined the favorite alternative explanations like urban "heat islands" etc and after controlling for all of them, still found clear evidence of warming at just about the rate of the IPCC consensus.
Denialism is another kettle of fish. Denialists cherry-pick the data, sorting for any bits and pieces that will support the conclusion they have already embraced. They ignore data--the Muller's BEST study--that doesn't. They pounce on short-term downward movements in temperature and ignore steady long-term upward movements. Etc. etc.
And let's be clear, many of the most well-known deniers, like Lord Moncton, for instance, are not even scientists, much less geophysicists or climatologists. But their non-scientific views are accepted without criticism and republished on denialist websites while the real work of real scientists gets mocked.
The tragedy is that while we cannot reverse the warming trend, we can prepare for and adapt to a warmer world. But the denialist attitude leads to apathy in the face of danger and that will lead to avoidable or mitigatable catastrophes.