Voluntary Income Tax, Voluntary Speed Limits

The US administration insists that any plan to reduce greenhouse gas emissions be voluntary and devised by individual countries rather than a worldwide agreement or treaty. Other countries, especially European countries, consider voluntary measures ineffective. They argue if efforts to curb climate change should be voluntary then why not have a voluntary income tax in the US or voluntary speed limits? Voluntary efforts cannot end global climate change, the energy crisis or the exponential growth of the population.