Imagine a damaged boat in which it would be necessary to use all the power of the machines to pump the water from the holds. But first-class passengers want to continue using the air conditioning and other facilities, while second-class passengers are only concerned about being upgraded to first. Soon everyone is sinking, having used or attempted to use the air conditioning for a few more hours, instead of all being saved. On a normal boat, a captain takes the necessary measures to prevent sinking. Here the passengers insisted on being their own bosses.
The current approach to the environment, climate change and other pressing challenges of our time (disarmament, regulating the greed that drives the free market economy, etc.) is that of tribes fighting over usufruct and ownership of a sinking ship, of a burning forest and a ticking time bomb.
The heads of state behaved like the chiefs of great tribes. Some may be wiser than others, but they have little influence over other tribes, sometimes even over their own tribe.
Global problems can only be dealt with by transnational institutions. In a global world, heads of state should play the role of provincial governors who administer local affairs and defer decisions to a transnational authority when the fate of the whole world is at stake.
Nobody wants it? GOOD. So swim now.