How bad is the warming world going to get?

From the always-direct Straight Dope:

Sea levels just two meters higher will displace 2.5 million people from Miami, 1.8 million from Mumbai, more than a million each in New York and New Orleans, etc. We’re already exacerbating this problem — i.e., in ways beyond our economic addiction to fossil fuels. More people are moving to coastal cities, leading to construction on land previously left undeveloped precisely because of flood risk. In some places, increased population can overtax the groundwater, causing cities to subside — literally sink as water is pumped from below. Sunny seaside Jakarta, with a metro area now home to 30 million, is expected to drop six feet by 2025 — an inopportune development, one might say, what with oceans on their way up.