It's far from obvious that CO2 emissions from excavating millions of tons of sand and earth would be dwarfed by the savings in the transit emissions of high-tonnage freight ships, which, unless I'm much mistaken, represent by far the most efficient means of transportation humanity has ever come up with.
OTOH, I assume there weren't many bulldozers in the mid 19th-century (I actually have no idea how suez was built). But, it's not really reasonable to just throw human power at something and declare it CO2-friendly.
And here's the bottom line. For better or for worse, externalities don't actually count. You can piss in the pool. People banding together and deciding otherwise - when their ancestors have gotten most of the pissing their hemisphere will ever need to do out of the way, and the rest of the world is still clawing their way out of abject poverty - is... maybe well-intentioned, but don't hold your breath. Poverty is really fucking awful. People on their way out of it will not tolerate if their governments try to put on the brakes because they watched an Al Gore movie. It's just not going to happen.
The good news is that the consequences likely aren't going to be too severe. We're not facing extinction (that many other species are is irrelevant, that ship sailed a long time ago). Florida goes away, sure. Indonesia loses a lot of it's land area. It's not going to happen overnight, people are not going to drown. They will move to higher ground. And at the end of it all, you have a world population that's not poor. That's a good trade, and I have every confidence in humanity's ability to manage whatever other consequences follow, we're pretty damn good at making tough decisions once we have something to lose. But right now, that's just not the case, except in the developed world.