I do believe firmly that there is a greenhouse effect. That's simple heat balances of the kind any student in mechanical, chemical or physical engineering can set up for him/herself and calculate the answer to.
What I'm a whole lot less certain about is the impact humans have. Despite feverish research, we are beginning to realise the problem isn't as easy as it looks. People make solid arguments for changes in the heat flux from the Sun, slight oribital wobbles as the Earth travels around the Sun, the still-not-well-understood effect of aerosols and clouds, the impact of various thermohaline cycles in oceans, and many, many more. Heck, it was recently discovered that the so-called lungs of the Earth---rainforests---release substantial amounts of methane into the atmosphere. And really recently people have begun to worry that it isn't CO2 which will be the killer greenhouse gas, but NOx, because it is largely unregulated and thus unmonitored. We just don't know. There is a lot of honest science in that field, but I'm also sure that many people will concede that there is still a heck of a lot of valuable data and computing power missing.
However, since large shifts in the climate will do nobody good, it makes sense to excercise caution. Unfortunately, to many with power to vote, it isn't a worthwhile effort. They are used to solving problems when they show up because then all noses are aligned in one direction.
So here's to the new wines England and the Netherlands are able to grow in a century if the worst comes to the worst; it will be most interesting what people think of them.