Some people need to scrape together cash to buy enough gas to get to work. Poor people spend a disproportionate amount of their income on necessities like fuel for an aging inefficient vehicle, electricity or natural gas to heat a cheaply-constructed home, and factory-farmed food created with cheap nitrogen fertilizer.

All of those necessities get more expensive with a carbon tax, so we need a way to cushion the impact on those who struggle to pay for the basics.

While the impact of global warming does impact the global poor quite heavily (think of places like Bangladesh) it doesn't really hurt the poor in developed places much more than the rich in developed places. I was a lot less worried about El Niño when I rented an apartment, for example.