It doesn't matter if plants, and ocean ecologies are CO2 sinks or not. They are clearly not soaking up as much CO2 as we are producing. I defy you to find a single climatologist that thinks otherwise. What matters is to what extent CO2 is responsible for warming, and to what extent reductions in CO2 can lead to cooling vs. other more economical methods.
I don't know much about climatology, but I'm disheartened by how politicized the science is on both sides. The public perception of science and scientists as relatively unbiased, and unprejudiced is taking a beating. I don't think that is a good thing however global warming plays out. To think that policy should always be dictated by political bent and not by objective solutions robs us of all facts and reduces us to a set of knee jerk opinions.
That is the rational thing to do. There is no proof that warming is caused by human activity. There does seem to be evidence of warming. The right thing to do is plan for a warmer future, not destroy the economy in a futile effort to "stop" global warming. Leftists see this as an opportunity to attack and destroy the U.S. economy.