What this shows
In this illustrative comparison, U.S. net-zero lowers projected 2100 warming from about 2.65°C to 2.51°C in the medium case and from about 3.45°C to 3.28°C in the high case.
Getting the entire United States to net-zero would be a huge, heroic, and extraordinarily difficult undertaking. Yet even if the United States somehow accomplished that enormous task, while the rest of the world stayed on roughly the same path, the effect on the future path of global climate change would still be very small — only about 0.1°C to 0.2°C by 2100 in this illustration.
The United States may have contributed a great deal to past climate change. But in this U.S.-only counterfactual, it has very little leverage over the path of future global temperature unless the rest of the world changes course too.