Lets be clear about a few things:
1. Projection is not the same thing as Prediction. Coupled global climate models used in the IPCC AR4 are used for projections. They start from a climatological state of the "current" climate. They do not initialize the model with the current state of the ocean.
2. From ice core data, CO2 concentrations have varied 100 ppm (from sub 200 to sub 300) over the last 400,000 years! By 2050, in a business as usual scenario the projection is for CO2 to climb to 450, and by 2100 achieve 950 ppm.
3. Temperature responds largely to solar increase in first 800 years and combination of solar/GHG the remaining thousands of years.
4. The anthropogenic forcing change is 1-2 W/m2 and is roughly equal in magnitude to the solar forcing change (solar variability is roughly 1.6 W/m2).
5. If the sun (increase in shortwave forcing) were largely responsible for the recent observed warming, the whole atmosphere should be warming. Tropospheric temperatures aloft have been in decline for the last 35 years while surface temperatures have been warming.
6. GCMs project that GHG forcing is more significant in the currnt climate than solar variability.
7. Even in a warming scenario, it is still possible to have a neutral or negative temperature trend during a decade.
So, let us assume that warming happens. What is the big deal?
A. It is likely that food production area's will shift due to changing temperature and precipitation. This is possible over the Great Plains even if the warming isn't extreme. China could also be potentially vulnerable to this changing climate. We already know that Africa has experienced some changes like this leading to long droughts, shortfalls of food, and revolution.
B. Some other changes could be earlier snow melt combined with either less or more snowfall over the Cascade or Rocky mountains. The snowfall in the west in winter provides water during the summer when it melts. Changing this time of snowmelt may leave these vulnerable areas without water later in the summer.
So, it is for these reasons, these local reasons that scientists communicate the impacts early. It takes time to adapt to these types of changes and mitigation can only help in the short term. Longer term its all about adaptation largely based on economics.
We all have to separate the science and opinion from this issue. There are scientific facts. They are not subject to opinion without evidence via the scientific method. Although it is in the theory stage, Idon't hear much politicized discussion questioning the speed of light
