Plant trees & plants to absorb more CO2, reduce tropical deforestation.
Convert waste vegetation - leaves, straw, etc. - into charcoal & bury.
Burn biomass for fuel. Capture the resulting CO2 & bury it.
Separate out industrial CO2 & bury it undergroud in old oil wells.
Paint it White
Paint roofs, roads, & pavements bright white to reflect lots of sunlight.
Use giant towers & artificial trees to scrub pure CO2 from the air.
Enhanced Land Weathering
Accelerate natural CO2 absorption by rocks by adding minerals to soil.
Enhanced Ocean Weathering
Stir megatonnes of limestone into oceans so more CO2 is absorbed by less acidic waters.
Air-spray particles of sea salt to make clouds whiter & reflect more sunlight.
Add iron filings to surface water & boost growth of CO2 - absorbing algae.
Scatter sulphate particles high in the atmosphere to reflect sunlight & lower heat.
Launch thousands of orbiting mirrors to divert sunlight away from the surface.
Cover vast areas of unused land with foil. No, seriously.
All-Out Nuclear War
Fill the atmosphere with terratonnes of soot, dropping temperatures.