A tipping point is something that happens to the climate system that's irreversible on
human time frames. Can't get back to the old climate state not for potentially millennia.
The one that matters for Antarctica is essentially the point at which the ice shelves are all gone.
And that will cause very rapid sea level rise above the levels of the current projections.
So the Antarctic ice sheet itself sits on continental bedrock. But the ice essentially flows
from a high point to a low point, then it hits the ocean. And so it flows onto the ocean, it floats
on the ocean, and we call that the ice shelf. The Ross Ice Shelf is a spectacular example - it's
the biggest ice shelf in the world, size of France, size of Texas, but there are ice shelves
all around the coast of Antarctica. And what these ice shelves do is they hold back the ice
flowing off the continent and they slow down the dynamic flow of ice under gravity into the ocean.
Unfortunately these ice shelves are all melting, they're all thinning because the ocean is warming
and in some places around West Antarctica it's warming a lot. The Larsen ice shelf for example,
the size of England and it it essentially disintegrated in a couple of months. Then what
happened the glaciers feeding theLarsen ice shelf sped up 10 times. So we're seeing that happen all
around Antarctica and what we think is that there will be a threshold whereby the ocean warms and
all those ice shelves are going to pretty much go at once and they're going to go very very fast,
and once they go then there's nothing to stop the rest of the ice sheet just sliding into the ocean.
Now there's another wrinkle here, another instability.
So West Antarctica essentially sits in a big bowl below sea level.
Large parts of it are two kilometers below sea level. So that warm ocean nibbles away at the
edges and gets into the soft underbelly. You can imagine you've got this ice sheet flowing into the
ocean but as it retreats into the bowl the edges of the ice sheet start to lose the grip on the
side of the bowl - it's clinging onto the edges but it's about to slip off. There's nothing for
them to hold on to anymore and so what happens is it's like a bunch of dominoes falling over.
These ice cliffs just topple. And we've seen that in Jakobshavn Glacier up in Greenland.
You know it's an incredible thing to watch these immense ice cliffs 30 kilometers long - just boom!
And if that really plays out at large scale around Antarctica,
we're grossly underestimating the amount of sea level rise from Antarctica.
Ultimately the key thing is carbon dioxide warming the climate. The natural climate cycles
which have regulated the ice ages occur exactly in step with the amount of carbon dioxide of the
atmosphere. In other words it is the pacemaker of Earth's climate and CO2, the greenhouse gases,
and Earth's temperature are totally locked. We know from ice core records and geologic records
that you have to go back three million years to see a time when our planet last had 400 parts per
million carbon dioxide on the atmosphere. "Here we have the ANDRILL drill system sitting here on
the Ross Ices Shelf. We made a hole 84 meters..." So one of the areas of research I've spent much of
my life doing is drilling sediment cores from around the Antarctic margin. We drilled back
to sediments that were three million years old to answer that question when CO2 is at 400 parts per
million or higher what happened to Antarctica? What happened to the sea ice? What happened to
the ice sheet? How warm did it get? - to give us information about the world we're heading into.
And we were able to reconstruct what was living in the Ross Sea and was algae. And we know that
this algae lives north of the Polar front these days in the Sub Antarctics. So we know that the
Ross sea was five degrees warmer then present, no sea ice, and we know that the Ross Ice Shelf
had collapsed -there is no West Antarctic Ice Sheet. And not only that we know from
other drilling projects that big parts of the East Antarctic Sheet also disappeared.
Global sea level records from around the world tell us that sea level was about 20 meters higher.
So the Paris target says we must limit global warming to less than two degrees and this is
one of the reasons. It's a Tipping Point for the Antarctic Ice Sheet. Even if we achieve
the Paris target we'll get 50 centimeters of sea level rise in a century. That's baked in
from the heat that's already in the system. People underestimate what 50 centimeters really means for
us globally. 800 million people around the world are going to be affected by high tide flooding.
That's the rising sea level but it's also the storms that are on top of that rising sea level
and so you know hurricane Sandy that wiped out big parts of Manhattan... "Water is splashing Over the
Sea walls at the tip of lower Manhatten" ...those sort of coastal flooding events will be an annual
occurrence and we can't avoid that that's locked in. So we've got to adapt to living in a warmer
world. The latest generation of ice sheet computer models incorporating this instabilities predict
up to two meters of sea level rise a century, unless we aggressively reduce our emissions.
People feel it's a hopeless situation and it's not a hopeless situation. In fact the science tells us
we still have a chance to solve this problem, get on top of it anyway, and avoid the worst.
Just in the last few years we were seeing a sea change in the world. Young
people in the streets protesting - pissed off. Politicians starting to take it more
seriously, government's starting to really make it a top priority.
We can all limit our carbon footprint hugely. It requires a Global Response. If we take action we
create a better world both in terms of how we save the climate and in terms of how we save ourselves.