Your generosity is reflected in what you do with your own money, not in what you do with other people's money. If I give a lot of money to charity, then I am generous. If you give a smaller fraction of your money to charity, then you are less generous. But if you want to tax me in order to give my money to charity, that does not make you generous.
I am worried about climate change. In one respect, I may be more worried than other people. I am worried because I have very little confidence that we know what is causing it....One of my fears is that we could reduce carbon emissions by some drastic amount, only to discover that-oops-it turns out that climate change is being caused by something else.