If it were as simple
as you claim, and as critical, why wasn't a carbon tax passed in 2009 when Republicans could not have stopped it? Was it even attempted?
Probably a similar reason why that carbon tax you mention wasn't passed. (Why do it if others aren't, and lose competitiveness economically?)
The Democrats could barely get a health care bill through in 2009, a health care bill that was based on a Republican plan. Ballooning health care costs were an issue throughout all the 2000s, which nearly everybody agreed needed to be addressed in some manner. The concept of Democrats also being able to also push through a carbon tax at that time is absolutely ludicrous. Try convincing the average Republican that climate change is 1) happening, 2) caused by humans, 3) addressable without destroying the economy. We can't even get broad consensus that there is a problem, much less on a solution.
In this world many people assume that the truth lies somewhere in the middle between two sides, and one side is a mixture of those who accept climate science, and those who continually demonize the science and lie about economic consequences. Suppose the Democrats were 100% in agreement on the climate science and how the problem should be addressed, which obviously they're not. Then in that political world, moderates would assume that the truth lies somewhere between the climate science (in this hypothetical world the Democratic stance) and the official Republican party stance. Meaning that the moderates in the country would think that the Democrats would probably be extreme in their views, just because the Republicans have gone so far in the extreme the other way.
And in reality, Democrats are not a monolithic body, they have a variety of views in how to address the problem, and there are even a handful of Democrats from areas with heavy fossil-fuel industry that pay attention to their campaign contributors rather than the science, which makes this supposed Democratic control.
I'll ask you this: why would not even a handful of Republicans support addressing climate change, enough to make this even a slightly bipartisan issue? Why does it fall entirely on a single political party to come to a solution? Shouldn't this be a non-partisan issue where we come up with a solution that people of multiple political views can support?