Is the world polluted beyond redemption?

Chris Smith put this to climate scientist Doug Crawford-Brown from the University of Cambridge...

Doug - Yeah. The first thing I'll say is we just don't know, either on the IPCC or on the UK Climate Change Risk Assessment Committee, we don't know the exact timing of this. It's probably something around 2050 to 2080, somewhere in that range. There are some people, even in the scientific community who think we're already there, we're already seeing inconvenience in the weather. I don't happen to be one of those people. I do happen to be one of those people who think that by 2050 and 2080 will really start thinking about this. I'm already making a list of people who have been climate deniers so that in 2050 and 2080 I can roll that list out and say, "whatever were you thinking of." But, of course, most of them are about my age and they'll be dead by that time so I'll have no glee at all.

Chris - You're clearly a glass half full man aren't you?

Doug - Yeah.

Chris - Andrew.

Andrew - Yeah, I was just wondering, linking back to the last question as well. If the icecaps were to melt completely, what change would that make to the global sea level?

Doug - Well it raises it by hundreds of metres.

Andrew - Hundreds of metres?

Doug - Hundreds of meters, yeah. So you flood almost all the coastal areas.

Chris - Of course, not the North Pole because that's floating ice, which means it's already displaced it's own mass already so that's not going to change a lot. But what's on Greenland? I mean Greenland alone adds, potentially quite a big rise in sea level, just Greenland, doesn't it Doug?

Doug - Tens of metres, yeah.

Chris - Yeah, and the Antarctic's interesting. I read a paper where they were actually looking at the gravitational effect of having that much mass, even though in the Antarctic the ice is on land so it's not displacing water. It is nonetheless, gravitationally active so it attracts a big bulge of water around the bottom of the planet holding the water down there, so it's not washing around up here and, therefore we have artificially lower levels of sea than we would otherwise have were that to be released. And, if we melt that, obviously then that water's going to redistribute and we'll see higher sea levels. Georgia...

Georgia - Trump wants to build a wall between the USA and Mexico. If a wall that big could you just build one around Greenland and just keep all the water in there?

Doug - Mexico, by the way, have said they're going to build the wall to keep Trump out of Mexico.

Chris - But what's the carbon footprint of that concrete, because 40 percent, isn't it, of CO2 emissions worldwide are just making cement?

Doug - That's right, there's a large carbon footprint to making cement. However cement, when put into buildings and so forth, then reabsorbs carbon dioxide. So, about half of that will be reabsorbed during the process of making something.

Chris - But you've still got to run the furnace to boil up the limestone in the first place.

Doug - I have no idea how big the carbon footprint is of the Mexican wall.