There are essentially four bad things that could result from climate change as far as typical Americans are concerned:
(1) Ice caps could melt causing sea levels to rise and causing storms in coastal areas to become more worrisome. Anybody with a topographic map can see who the winners and losers are in a rising sea level scenario, although far more elaborate reports show the same thing. Suffice it to say that South Florida, coastal property owners, people who abut salt water wetlands and estuaries (e.g. many people in Louisiana), and people on low lying islands are screwed if the sea level rises too much.
(2) Droughts could be more intense and longer, turning arid places to deserts, expanding existing major deserts, and turning places that get sufficient moisture now into arid environments. This is a really troubling possibility as it could lead to massive crop failure, famine, and large scale migration of people from arid areas that could provoke wars.
(3) Increased temperatures could allow previously tropical flora and fauna to move to higher latitudes than their conventional range, including disease carrying bugs to which local humans, flora and fauna lack resistance. This would require significant adaptations in the affected regions.
(4) Snow capped alpine areas could get less snow, destroying ski resort based economies where they currently exist. Bad news for Vail, but it probably won't utterly destroy life as we know it. The more serious piece of this development, however, would be that snow packs are a principal source of fresh water for people in the river basins that the snowpacks feed.
Note that any one of these possibilities, by itself, is a real problem, regardless of its precise cause or the mechanism of that cause, and that shrinking ice caps, retreating alpine deserts, expanding deserts, and the migration of tropical flora and fauna to higher latitudes have all independently been observed over the last few centuries and particularly intensely in the last dozen or so decades.
Even if sea levels stop rising or ski areas stay white, if a couple of the other observed trends continue, the world has a problem. Conservely, even if the predicted droughts and tropical zoology range expansions don't happen, rising sea levels or shrinking alpine snow cover present their own worries.
Maybe there are other effects as well. But, it doesn't matter much if there are or there aren't. Ice caps, sea levels, glaciers, desert area, droughts and tropical zoology ranges aren't just canaries in the mine, they are the harm causing symptoms of climate change themselves. These observed phenomena are the principal reasons that we care if climate changes. And, to the extent that man made air pollutants are linked to these particular symptoms, it really doesn't matter if every single prediction of global warming models pans out. Maybe there will be global cooling elsewhere, for example. Who cares? The results are robust enough to act upon. The data that climate change is really happening is overwhelming.
Also, there are two kinds of policy responses to climate change. One is to stop making the situation worse by controlling air pollution. The other is to prepare to respond to the symptoms of climate change whatever the reasons for it may be. Even if there is a lack of political will to address the former, because of doubts (even if never very well grounded scientifically) about the cause of climate change, that shouldn't matter when it comes to policy responses to address the latter.
Natural climate change will flood beach front properties, drown the Everglades, shrink the land area of Louisiana dramatically, devistate the Colorado ski industry, cause crop failures and civil war spawning mass migrations, and welcome tropical bugs into more Northern climes just as well as man made climate change. These traumas aren't going to get any easier to deal with if we wait for them to happen.
The point of this post is that one only needs a quite weak set of assumptions about climate change to justify some kinds of policy actions, and an even weaker set of assumptions about climate change to justify other particular sets of policy actions. So, even if one is skeptical about some versions of global climate change models or the mechanism involved in formulating them, this doesn't necessarily mean that the skepticism is about anything that really matters from a policymaker's perspective on particular issues that really matter.
In the same way, skepticism about the Higgs boson's existence doesn't imply that one should be skeptical about the accuracy of Kepler's laws in the solar system or the rules for determining the voltage at a particular point in an electrical circuit. Climate change data, like non-fundamental laws of physics, are robust enough that they can speak for themselves and be relied upon even in the absence of a perfect theory to explain them.