There is a large amount of uncertainty in terms of what climatic impacts will occur and when. Partially, this is because we don’t know how humanity will act. It is rather unclear whether we will curtail emissions, or whether we will continue our march towards destruction. But this uncertainty also derives from the fact that our climate and ecosystems are dynamic, non-linear systems. It is therefore hard to predict precisely what effects will happen at specific points in time as the Earth’s climate changes. This is why scientific projections about future warming always include multiple scenarios and ranges. Scientists don’t have a test case from which to derive predictions. We are the test case.
So, how should we as citizens react to this uncertainty? Should we make "Scientists don't know everything! They aren't sure!" our anthem and take this uncertainty as license to continue business as usual?
That would be like saying, "Well we don't know when or how the Axis powers will invade and occupy the United States, so let's not worry about it!"
Rather, the uncertainty must drive us to greater preventative action. We know that carbon and greenhouse gases will cause catastrophic impacts for humanity, but we don't precisely know how and when they will unfold. We must act decisively and immediately to avoid catastrophe.