In fact, every individual thing created by humans is a microparticle of a drop with respect to climate change, so by your argument, no one ever has to do anything.

And why don't we take that argument to littering? One plastic bag is just a microparticle of a drop, so you might as well just throw it on the street, because it makes no difference, based on your argument.

Overall, the idea that there are so many humans in the world that you can do whatever you want with no moral consequences should be an obvious non-starter.

And in fact this obviously bad argument was discussed and systematically refuted in the eighteenth century by Kant:

https://en.wikipedia.org/wiki/Categorical_imperative

In my experience, the reason people advance such arguments is because they are pathologically wasteful of the world's resources in their own lives, and they tell themselves this story in order to justify their enthusiastic participation in the rape and murder of the biosphere. Would this be you?