As scientific evidence has accumulated that the planet is warming and that humans are behind it, many previous skeptics have been won over. There remains a vocal cadre of critics, however, at least some of whose arguments have shifted over the last several years from outright denial that the earth is warming to insisting it's unrelated to human activity — and even if it is, likely nothing much to worry about.
Some of the most vocal skeptics have done relatively little recent peer-reviewed scientific research on the topic, and some have had their voices amplified via financial support from industries opposed to any government regulation or taxation of greenhouse gas emissions. Others do have training and experience, at least in some aspects of the wide-ranging issue, and are not bankrolled by industry. But overall, their number represents a distinctly minority position in the ongoing and normal colloquy among scientists about the evidence of climate change and its likely impacts.
Climate-change modeling is less certain in forecasting impacts on a regional scale, and in assessing warming's role in extreme weather like hurricanes. But the regional resolution of the models is improving, and the 2007 IPCC report offered more detail than previous ones. Researchers also are busily assessing regional vulnerabilities to possible climate-change scenarios. So while there remain more robust debates in these areas, new research is constantly adding new layers of understanding. One needs to try to stay current on the latest published studies, on who's doing them and who's funding them.
There are a number of climate-change skeptics, less-often quoted perhaps than some more vocal ones discussed later,  who have more substantial climate science research publications and who have accepted little or no fossil industry and advocacy group money. These typically include:
- John R. Christy at Univ. of Alabama, who pointed out that satellite temperature observations did not match those from the network of surface instruments (after years of high-level scientific discussions, the differences were eventually reconciled, mostly as a satellite calibration error). Background.  Rolodex entry. 
- Richard Lindzen at MIT, who publishes extensive research on atmospheric dynamics and circulation. Bio, publications, contact info.  Wikipedia. 
- Bill Gray,  at Colorado State University's Tropical Meteorology Project.  One of the acknowledged gurus of short-term hurricane forecasting, Gray has weighed in not only on the question of whether climate change is causing more and bigger hurricanes (he says no) but also on whether human emissions are causing global warming — a question beyond his immediate research field. Profile (paid archive ).