Thought I'd chip my two penneth worth in here as I've been working on climate change effects on plants for the last ten years and although not a climatologist have obviously read a fair bit around the subject.
Firstly, if you don't think that climate change is a reality and is going to have a major impact on both the natural environment and our own civilisation then you are either deluding yourself or haven't read the evidence (probably both). It truly is over-whelming, the vast majority of scientists involved (I'm talking thousands here) agree on the general thrust, those that don't are very few and are generally in the pay of special interest groups (e.g. the oil industry - though I have to say that in my experience the oil industry are starting to accept what's going on and beginning to look to the future, moreso than most climate change sceptics).
Secondly, to the question in hand. I think that predicting what the impact of climate change on man and the natural environment is one hell of a lot harder than proving it is occurring. This is where I do think there are some alarmists and some wild extrapolations, though we don't know that they won't come to pass! Personally, and taking a longer term view, we aren't able to wipe out life on earth (not without physically breaking up the planet and I don't think we have enough nuclear weapons to do that), and it is very unlikely that man made climate change will cause species extinctions on a scale with the great extinctions of the past where over 95% of all species on earth have been wiped out. Also, whilst I think we should be looking to preserve biodiversity and our natural environment I think we should be honest and say that this is for our own benefit and not some mystical 'mother nature'. So given that, I think the most important impact of climate change is on mankind and in that respect Alex's question is an important one (if difficult to answer). As mentioned already increased flooding does result in large numbers of deaths in Bangladesh, heat waves do finish off the old and frail, not to mention crop failures lead to starvation. Though it is impossible to say that any one event is due to climate change.
If you go to
http://www.ipcc.ch/ipccreports/assessments-reports.htm you will have access to the IPCC 4th Assessment Report. This is the condensed knowledge that mankind has on climate change and it's likely effects, put together by an international group of scientists numbering in their thousands under the auspices of the UN. The working group one report details the science involved and the predictions that that science makes, the working group two report details the likely impacts of those changes on the world (and man). There is a synthesis report of the whole thing, there are technical summaries of each report and there are executive summaries for the really hard of understanding (e.g. politicians).