http://en.wikipedia.org/wiki/Global_warming_controversy
Although there is a strong scientific consensus that global surface temperatures have increased in recent decades and that trend is caused mainly by human-induced greenhouse gas emissions, there are a minority of scientists who prefer to be non-committal on the subject.
Popular Media
The popular media continues to understate the scientific consensus about climate change as it focuses on being fair and unbiased and providing balanced coverage of conflict. Instead of putting a light on difficult scientific arguments, the popular media covers the human-interest controversies. As a result, the mainstream scientific consensus is “balanced” against a few extremists. Numerous studies on climate change and the media is listed at http://en.wikipedia.org/wiki/Media_coverage_of_climate_change
Other Scientific Arguments
One of the arguments against blaming greenhouse gases for climate changes is that Earth has never had a stable climate; its only constant is change and, at times, quite rapidly. Many times in the past, temperatures were far higher than today, and occasionally, temperatures were colder. As recently as 6,000 years ago, it was about 12.7 degrees F warmer than now. Ten thousand years ago, while the world was coming out of the thousand-year-long "Younger Dryas" cold episode, evidence suggests temperatures rose as much as 14 degrees F in a decade -- 100 times faster than the past century's 1.4 degrees F warming.
Solar variation is another influence climate change. The theory for climate change today is that the present level of solar activity is historically high as measured by sunspot activity and other factors. Solar activity could affect climate either by variation in the sun's output or by an indirect effect on the amount of cloud formation. Research has determined that solar variation has had little effect on current climate change.
Economic Influences
Because the formation of greenhouse gases is so closely related to our way of life, it’s difficult for people to accept that climate change can be impacted. Those that say stopping climate change through reducing greenhouse gases is an expensive, futile effort have an appealing message to do nothing, which results in an uphill battle for those who advocate for reduction of greenhouse gases.
Adaptation is the key, say others. Continue with life as usual until it is necessary to adapt. Adaptation will protect present and future generations from climate-change risks more than efforts to restrict CO2 emissions. However, the groundwork for our ability to adapt must be ongoing or adaptation will an option for only those who can afford it.
Political Wordsmithing
The political massaging that goes into talk about climate change also creates confusion. The ability to fund work, make policy, or realize progress on other issues is contingent upon how or whether climate change is referenced. Is climate change “catastrophic” and calling for “immediate and drastic reductions” environmental drama? Or is it “beneficial” for some areas and we need to “simply accommodate” to the coming changes?
One thing for sure, the amount of human-generated greenhouse gas emissions present in our atmosphere is uncharted territory.