I agree it 's an uphill battle getting the world to work together and develop practical strategies and if humanity relied on the UN to act it is a waste of time.
Fortunately China has risen at a good time as my money is on them to come up with a technological solution.
But if China doesn't have a breakthrough within 2 decades and emissions keep rising IMO its game over as we will have triggered a positive feedback mechanism such as the release of billions of tonnes of methane from thawing arctic tundra.
Regarding the lag time for ice to melt, schools sometimes have a demonstration during science week when a large block of ice is put on display and kids try to guess how long it takes to melt. They are usually surprised to find something like a 100kg block can take several weeks to completely melt.
When you suggest scientists are rattling on about ice requiring a catch up period to create a 10m sea level rise in order to mirror the situation in the past with similar temperatures, that explanation seems to be common sense as the Antarctic ice shelf is very thick and would require a good 100 years to melt.
But from the perspective of geological time 100 years is the blink of an eye.
Many say we cant imagine our situation at the turn of the century, but IMO if we dont get our CO2 level at or under 400ppm by 2040 its game over because there is no way the Arctic tundra will stay frozen for 2 more decades.
So regarding your question about my proposed solution for unified action. This is my hypothetical answer outlining 3 options;
a. Given many UN members are corruptible it would be relatively cheap to offer every member10 million dollars to pass a 100% resolution so that for 10 years every nation will forsake their defense budget and allocate the money to a research and development program to fast tack a large scale CO2 capture scheme. Maybe a fund of 10 trillion would do the trick. The mantra could be the world is at war against climate change so we are together this time!
b. If option a falls flat then the next possible hypothetical is for investors around the world be offered shares in an infrastructure fund to fast track projects such as nuclear fusion that is currently expected to be available by 2050 but to get it up a decade earlier and use the energy to again capture CO2. Shareholders will get a dividend etc if successful.
c. If options a and b fail then we could have the CIA approach where they operate covertly as they do in South America and start a monster firestorm that burns a vast area of the Amazon during the dry season.
The world will be in such a shocked state that Greta and 10 million volunteers will get into Sth. America and replant the whole Amazon basin to forest while a a child army from around the world stops the farmers from planting the area to soybeans!
This will be such a huge success that Greta will volunteer to be the planet's first environmental dictator and with the help of a massive under 21year old world environmental army they will take over the world and to show they are serious to try and execute former UN members for attempting to take away their future!
