International efforts are under way to bring greenhouse gas emissions to zero in a manner fast enough to limit global warming to +2 degrees Celsius. That’s proving tough to do, and there are some expectations it won’t be achieved.

Some people ask where the +2 degrees comes from. One striking example of what +2 degrees means is the shaded map below of Boston, Massachusetts, in a century or two, with emissions limited and the +2 degree limit successfully achieved. That blue stuff is inundation by ocean water due to sea level rise. Naturally, if emissions are not so limited, matters will be worse.

(Click image to see a bigger picture.)

Note this is not inundation due to flooding, as from nor’easters. This is just ordinary high tide.