I repeat: Live thrived under much harsher conditions in the past. It will not suddenly die out. I find your pessimism unfounded. I'm sure humankind will exist for at least another millennium.
Ocean acidification will not kill all algae. They existed for much longer than most other forms of live. They survived the +14 °C 300 million years ago, guess how acid the oceans were back then. Also about 300 million years ago oxygen levels in the atmosphere peaked at about 35 % indicating a very strong production by plants. The algae species from back then are still alive today!
That's no problem.The protests that brought down East Germany weren't that much organized at first. People went to the street every monday and that was it. Internet and instant messenger didn't exist back then. Most didn't even had a telephone at home and TV was censored by the state.Children were pretty successful too. The whole worldwide protest grew from a single child.
The USA is big, yes, but the population live in the cities not in between them.
Now you know what to do:Pick a day and go protest every week on that day in your city. Politics eventually will feel the pressure.