when I was 21 years old I had all this
physics homework physics homework
requires taking breaks and Wikipedia was
relatively new so I took a lot of breaks
there I kept going back to the same
articles reading them again and again on
glaciers Antarctica and Greenland how
cool would it be to visit these places
and what would it take to do so well
here we are on a repurposed Air Force
cargo plane operated by NASA flying over
the Greenland ice sheet there's a lot to
see here but there's more that is hidden
waiting to be uncovered what the
Wikipedia articles didn't tell me is
that there's liquid water hidden inside
the ice sheet because we didn't know
that yet
I did learn on Wikipedia that the
Greenland ice sheet is huge the size of
Mexico and it's ice from top to bottom
is two miles thick but it's not just
static the ice flows like a river
downhill towards the ocean as it flows
around bends it deforms and cracks I get
to study these amazing ice dynamics
which are located in one of the most
remote physical environments remaining
on earth
to work in glaciology right now is like
getting in on the ground floor at
Facebook in the 2000s our capability to
fly airplanes and satellites over the
ice sheets is revolutionizing Glaciology
it's just starting to do for science but
the smartphone has done for social media
the satellites are reporting a wealth of
observations that are revealing new
hidden facts about the ice sheets
continuously for instance we have
observations of the size of the
Greenland ice sheet every month going
back to 2002 can look towards the bottom
of the screen here to see the month and
the year go forward you can see that
some areas of the ice sheet melt or lose
ice in the summer other areas experience
snowfall or gain ice back in the winter
the seasonal cycle though is eclipsed by
an overall rate of mass
that would have stunned a glaciologist
50 years ago we never thought that an
ice sheet could lose mass into the ocean
this quickly since these measurements
began in 2002 the ice sheet has lost so
much ice that if that water were piled
up on our smallest continent it would
drown Australia knee-deep how is this
possible
well under the ice lies the bedrock we
used radar to image the hills valleys
mountains and depressions that the ice
flows over hidden under the ice sheet
are channels the size of the Grand
Canyon that funnel ice and water off of
Greenland and into the ocean the reason
that radar can reveal the bedrock is
that ice is entirely transparent to
radar you can do an experiment go home
and put an ice cube in the microwave it
won't melt because microwaves or radar
pass straight through the ice without
interacting if you want to melt your ice
cube you have to get it wet because Mike
because water heats up easily in the
microwave that's the whole principle the
microwave oven is designed around radar
can see water and radar has revealed a
vast pool of liquid water hidden under
my colleague Olivia seven stories
beneath her feet here she's used a pump
to bring some of that water back to the
ice sheet surface just six years ago we
had no idea this glacier aquifer existed
the aquifer formed when snow melts in
the summer sun and trickles downward it
puddles up in huge pools from there the
snow acts as an igloo insulating this
water from the cold and the wind above
so the water can stay hidden in the ice
sheet in liquid form year after year the
question is what happens next
does the water stay there forever it
could or does it find a way out to reach
the global ocean one possible way for
the water to reach the bedrock and from
there the ocean is a crevasse or a crack
in the ice when cracks filled with water
the way
the water forces them deeper and deeper
this is how fracking works to extract
natural gas from deep within the earth
pressurized fluids fracture rocks all it
takes is a crack to get started well we
recently discovered that there are
cracks available in the Greenland ice
sheet near this glacier aquifer you can
fly over most of the Greenland ice sheet
and see nothing no cracks no features on
the surface but as this helicopter flies
towards the coast the path that water
would take on its quest to flow downhill
one crack appears than another and
another are these cracks filled with
liquid water and if so how deep do they
take that water can they take it to the
bedrock and the ocean to answer these
questions we need something beyond
remote sensing data we need numeric
models I write numeric models that run
on supercomputers a numeric model is
simply a set of equations that works
together to describe something it can be
as simple as the next number in a
sequence 1 3 5 7 or it can be a more
complex set of equations that predict
the future based on known conditions in
the present in our case what are the
equations for how ice cracks well
Engineers already have a very good
understanding of how aluminium steel and
plastics fracture under stress it's an
important problem in our society and it
turns out that the engineering equations
for how materials fracture are not that
different from my physics homework so I
borrowed them adapted them for ice and
then I had a numeric model for how
crevasse can fracture when filled with
water from the aquifer this is the power
of math it can help us understand real
processes in our world I'll show you now
the results of my numeric model but
first I should point out that the
crevasse is about a thousand times
narrower than it is deep so in the main
panel here we've zoomed in to better see
the details you can look to the smaller
panel on the right to see the true scale
for how tall and skinny the crevasse is
as the aquifer water flows into the
crevasse some of it refreezes in the
negative 15 degrees Celsius ice that's
about as cold as your kitchen freezer
but this loss can be overcome if the
flow rate in from the glacier aquifer is
high enough in our case it is on the
aquifer water drives the crevasse all
the way to the base of the ice sheet a
thousand metres below from there it has
a clear path to reach the ocean so the
aquifer water is a part of the three
millimeters per year of sea level rise
that we experience as a global society
but there's more the aquifer water might
be punching above its weight the ice
flows in complex ways in some places the
ice flow is very fast there tends to be
water at the base of the ice sheet here
in other places not so fast usually
there's not water present at the base
there now that we know the aquifer water
is getting to the base of the ice sheet
the next question is is it making the
ice itself flow faster into the ocean
we're trying to uncover these mysteries
hidden inside the Greenland ice sheet so
that we can better plan for the sea
level rise it holds the amount of ice
that Greenland has lost since 2002 is
just a small fraction of what that ice
sheet holds ice sheets are immense
powerful machines that operate on long
timescales in the next 80 years global
sea levels were rise at least 20
centimeters perhaps as much as one meter
and maybe more our understanding of
future sea level rise is good but our
projections have a wide range it's our
role as glaciologists and scientists to
narrow these uncertainties how much sea
level rise is coming and how fast will
it get here we need to know how much and
how fast so the world and its
communities can plan for the sea level
rise that's coming thank you
[Applause]