The most cost effective mirrors to cover a large fraction of the Earth and reflect back the sun's heat are... the polar ice caps. Which we are melting because o

The most cost effective mirrors to cover a large fraction of the Earth and reflect back the sun's heat are... the polar ice caps. Which we are melting because of climate change. This is one of the main reasons people are so worried about it being "too late" to fix climate change. There are positive feedback loops like this where a little increased heat causes even more rise in temperature.