Well, it sure sounds bad. But to most people it will be an abstract concept - what does that mean? It's like saying, "dihydrogen monoxide is the principal ingredient in acid rain". Makes water sound scary, doesn't it?
So what does a 7 meter rise in water over 1,000 years mean? Like I said, it sounds scary but is that:
a) We'll lose 3 miles of coastal land scary
OR
b) We'll be in Kevin Costner Water World scary
I don't know the answer to that. They should spell out what the actual impact will be, not make an abstract statement few people have a point of reference about.
Fortunately, 1000 years is a long time. I've read that Netherland will be able to adapt to a sea level rise of 1 meter in the next century (or maybe two centuries, which would already be a problem), but if it continues to rise at that speed, we'll have to figure out better solutions. In any case, it's going to cost a lot of money. Some minor investment now could prevent a lot of trouble in the future.
But "apres moi le deluge" seems to be the reigning attitude.
If we have 1000 years to prepare for it, it most likely means that we will gain several miles of coastal land as we discover the best places (which may well be some way out to sea) to build dikes around the (relatively few) places where it's impractical to just move the population.
The Netherlands are often mentioned as the first place to go, but that's disingenuous: Nowhere else is better prepared to slap 50cm each century on top of their existing dikes. No, it's not quite that simple, but it's orders of magnitude simpler than constructing building a dike from scratch around, say, New York City.
No, we won't be the first place to go; that'll be the Maldives. And we probably can afford the extreme expenditure necessary to increase those dikes. But wouldn't it have been better to prevent that extreme expenditure in the first place?
The "extreme expenditure" to build dikes is a lot less than the expenditure to not just stop, but revert global warming. Nobody knows if it's even possible, so we might end up wasting all that money and then still having to build dikes.
What? In the quote you included, they do spell out the bad things: the complete melting of the Greenland ice sheet, resulting in 7 meters of global sea-level rise. What's unclear about that?
A bit more subtle is what that 1-4 degrees warming means. That's not how much they think the earth will get warmer, that's what they think the threshold for the complete melting of Greenland's ice sheet is. So if we manage to limit the temperature rise to 2 degrees C, there's a good chance it won't melt completely, but if the threshold turns out to be on the low end of the range, it might still melt.
There's also nothing excessively alarmist about this. It's up-front about the 1000 year time scale.
Also, don't blame the scientists for what less-informed alarmists are shouting. Though I agree that it would be easier to inform people if there weren't a ton of people shouting nonsense.