Taking cumulative CO2 output over the past 250 years isn't fair, since the greatest increases have really happened in the past 75 years and the distribution of output would be much more diverse. A better measure would be to graph individual countries' output over that time since those lines would track each country's rise into industrial modernization. The challenge should be for the world to promote the progress of third world but support alternative energy generation - safe nuclear fission and tidal or wind to supply the power needed to bring developing nations along. Right now, coal is the simplest and cheapest option, even being the dirtiest and least efficient. India and China are the biggest contributors to the carbon sink over the past 25 years, and only China is making big strides to convert to greener sources because they both need to increase their power generation capacity greatly to support growing economy, and they have been experiencing much of the impacts of climate change you listed here including devastating flooding and agriculture killing drought.

The world needs to move to a nuclear fission future ASAP. Fission reactors designs have gotten much safer since Chernobyl and Three Mile Island, using heavy water and molten salts to control the reactions. Going smaller and modular for these reactors will enhance safety and reduce costs of construction, making them more economically feasible for developing nations to invest in. They also provide time to develop viable fusion reactors that would guarantee clean energy in an environmentally safe manner.

We have gone past the point of no return for climate change, it will be affecting us now for the next 200-300 years and we will need to adapt. But by doing fission then fusion along with some carbon capture we can start to see positive results in the next 50-75 years. It still means a difficult world for the next two to three generations but gives a future that will be brighter than it appears today.