Not much. Scientists are calling for a 90 percent cut in global warming emissions. US uses about 15 percent of global total, 15 percent for EU, thirty percent for China, five percent for India. Basic arithmetic says this number will not be achieve when China and India are growing instead of cutting. And the rest of the world is growing as well.
Plus reducing by one third instead of ninety percent does not mean you achieve a one third reduction in global warming, according to the models, but a smaller negligible reduction.
To answer your question:
Individuals- develop a CO2 free energy source that is so cheap that countries will want to use it instead of fossil fuel energy like coal.
Governments- same as above, or start massive wars that destroy industry and energy use, and perhaps throw up reflecting pollution into the atmosphere.
Unfortunately, most of the solutions provided center on trying to make fossil fuel energy more expensive, which does not work as other countries will refuse to do so.
Other solutions proposed are more religious environmentalism and have nothing to do with global warming, for example recycling.