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  • >> This is a view of the earth that you probably not familiar

  • at looking at all the time,

  • looking down over the North Pole.

  • Here you've got the Arctic Ocean,

  • it's about 14 million square kilometers, and it's surrounded

  • by land on all of its sides, but then you have these regions

  • where water can flow in and out in here

  • through the Bering Strait, into the North Pacific, and then here

  • through Fram Strait and the Davis Strait

  • into the North Atlantic.

  • In the winter, the temperatures across the ocean on average get

  • down to about minus 30.

  • And because of these cold temperatures,

  • the sea waters freeze and it forms a layer

  • of ice known as sea ice.

  • And over average, the ice is about 2,

  • 2 and half meters thick,

  • and below it is kilometers of the ocean.

  • And in the winter, that ice completely fills the Arctic

  • basin and even reaches

  • out through the Bering Strait into the Bering Sea.

  • Now in the summer, that ice cover starts to retreat

  • as the temperatures get warmer and in the summer.

  • The average temperature across the Arctic Ocean is

  • around 0 degrees, and this video

  • that you've been watching here shows the summer September ice

  • extent minimum.

  • It's from the National Snow and Ice Data Center in the USA,

  • and some of you might be familiar

  • within the press every year around September,

  • you see headlines about we've reached another minimum arctic

  • sea ice extent, and it's a downward trend

  • since the satellite records began in 1979.

  • So, and then you often get kind of speculation

  • about when the arctic ice cuff is going to be ice-free

  • in this summer, and whether the Northwest Passage will be open.

  • And we can go back to PowerPoint now.

  • The [background noise], this is in the melting and freezing

  • of the ice [inaudible], that the ice kind of changes.

  • The ice is also moved around by the wind, it's dynamic.

  • And what you're looking at here is a video

  • that I took while I was on an ice company arctic.

  • And its two icebergs, basically being blown by the wind

  • and they crush in together, there's actually the sound

  • that you could hear, just before they lowered the volume,

  • was the sound of actually the ice [inaudible], the ice pushing

  • up against each other.

  • So as the ice is being moved around,

  • it's forming these ridges and it's thickening dynamically.

  • The other thing that happens as the ice moved is

  • that it splits apart, and again this was a picture I took during

  • an ice camp.

  • We've gone in for dinner into our mess tent and came out,

  • kind of-- just as the sun was setting and we were greeted

  • by this view about 100 meters from where we were camping.

  • The ice plain we were on had actually split in two,

  • so we're quite glad it hadn't happened straight on the center

  • of our camp, but it was an amazing view

  • and what happens here in the winter, because the warm--

  • the ocean is a lot warmer than the atmosphere.

  • It would lose heat to the atmosphere

  • and then ice-- new ice will form.

  • So these areas of open water become production areas

  • for the formation of ice.

  • So those figures I shared, or that animation I showed you

  • at the beginning, with the ice extent changing from year

  • to year, it's changing for 2 reasons,

  • one because it's melting or it's refreezing,

  • and the other thing 'cause it's changing dynamically.

  • So we don't just need to know how the area is changing,

  • we also really need to know how the ice thickness is changing,

  • 'cause then we can work out how the ice volume maybe changing.

  • Now sea ice has kind of an important role

  • in our climate system.

  • Something that you maybe familiar with it is this--

  • is the idea of the ice-albedo feedback mechanism.

  • So albedo is ma-- measure of the amount

  • of solar radiation that's reflected back in to space.

  • So sea ice covered by layer

  • of fresh snow has a very high albedo, about 0.9.

  • That means it reflects more radiation back into space

  • than the open water does and absorbs more radiation.

  • So when you have more [inaudible] from water,

  • more radiation is absorbed, you get more heating that can go

  • on to melt more ice and so on.

  • And of course the converse is true.

  • When you have more ice cover,

  • you get more radiation reflected,

  • and you can get cooling.

  • But this is isn't the only way the sea ice affects our climate.

  • It forms on the ocean so it forms a barrier

  • between the atmosphere and the ocean.

  • On the open ocean, the winds can free, they can't move the water,

  • but this isn't the case in the Arctic.

  • So that's another effect that it can have on,

  • on our climate system.

  • The third thing is that when it melts,

  • it adds fresh water into the ocean.

  • When it freezes, it add salt into the ocean.

  • So that can affect the density of the water,

  • but it's not just sea ice that's an important component

  • of the fresh water in the Arctic.

  • Now this diagram here describes a kind

  • of simple structure of the Arctic Ocean.

  • The sea ice actually fits in a very cool fresh layer

  • and that's separated from warm, salty Atlantic waters beneath,

  • by I think called the halocline.

  • So "halo" means salty and "cline" means slope.

  • It's a steep density gradient that's controlled by salinity

  • that separates these 2 very distinct water masses.

  • Now, I siad the sea ice forms contribution to that fresh water

  • in the top, but it's not just that.

  • In the beginning, you saw the map of the Arctic

  • and it was surrounded by continents.

  • And as you move in to the summer, these--

  • the rivers in those continents thaw and the river runoff runs

  • into the Arctic Ocean, and that provides another source

  • of fresh water, will also got cha--

  • changes from fresh water from precipitation and evaporation,

  • and also exchanges through those outlets that I showed you

  • into the North Pacific and North Atlantic.

  • And this diagram here is taken from a paper

  • and it shows the mean distribution

  • of that liquid fresh water in the Arctic.

  • And you'll notice it-- the red colors,

  • basically show we've got more of that fresh water

  • and that's predominantly in the Western Arctic.

  • So here you've got Greenland,

  • and this is the Canadian archipelago.

  • This is an area, notice the Canada basin

  • and it contains the Beaufort Gyre,

  • which is something I'm going to talk a bit more about later on.

  • Now we're interested in the storage and distribution

  • of this fresh water because if it is released even in parts,

  • it has the potential to disrupt the thermohaline circulation,

  • which then could have a knock-on effect

  • to our climate in Northern Europe.

  • So this slide is basically to summarize UCL's heritage

  • with working wit the European Space Agency to use satellites

  • to look at the changes in the Arctic.

  • This photo here was taken of the remote sensing group

  • at the Mullard Space Science Laboratory which is also known

  • as MSSS-- MSSL, and it's part of UCL.

  • This photo was taken about 20 years ago,

  • but actually our heritage with this kind of work starts,

  • even earlier than that, around the early 1980s, 1982 to 1983.

  • MSSL let us study for the European Space Agency,

  • looking at the feasibility of using satellites

  • to monitor changes in the Arctic.

  • But it wasn't really until the launch

  • of the Earth remote sensing satellites, which name is ERS1.

  • That was launched in 1991.

  • We can use data from 1993 onwards.

  • It wasn't until those satellites we launched

  • that we're actually able to have observations over the Arctic.

  • Previously, the satellites didn't go up that high,

  • we can actually see-- take data from there,

  • and it was really work done during this time

  • by Seymour Laxon who is sitting in the audience here

  • that pioneered the method that we used to calculate

  • or estimate sea ice thickness from space.

  • And I'm going to go on to the next few slides

  • and describe actually what this technique is

  • and how we're actually doing it.

  • So all of those satellites you saw were on the last slide,

  • and you carry an instrument known as a radar altimeter.

  • So the first bit of that is radar.

  • Now radar's a really useful tool for Earth observation.

  • This diagram here shows the opacity of the atmosphere

  • to different wavelengths of radiation.

  • And I'm sure you're all familiar with the idea

  • that an x-ray can see through your skin

  • and it can make a map with your bones.

  • Well, radar can see through our atmosphere.

  • It can see through the clouds and it can monitor what's going

  • on at the surface of the earth.

  • So that's why we use that frequency in Earth observation.

  • It also doesn't rely on having daylight,

  • which if you're using sort of an invisible wavelength,

  • then when it's dark, you're not going to see anything.

  • So it's useful for getting year-round measurements

  • over the earth.

  • Now the second word I mentioned was an altimeter.

  • Now this slide describes the measurement principle

  • for an altimeter.

  • And if you cast your mind back to your school days,

  • I'm sure you'll remember the relationship speed equals

  • distance over time, and that's basically what we're doing here.

  • The altimeter transmits a pulse of radiation, it travels to down

  • to the surface of the earth, it reflects to the surface,

  • and travels back up to the satellite.

  • And we measure the time taken for that pulse of radiation

  • to travel from the satellite to the earth and back again.

  • Now we know how fast the radiation is traveling.

  • We know the time, so from that we can work out the elevation

  • of the satellite above the surface that we've looking at.

  • So over the Arctic Ocean, we have the--

  • those areas of open water, the leads.

  • So we measure the elevation to the leads,

  • and then we measure the elevation

  • to the ice slopes next to them.

  • And if we take the difference between those measurements;

  • we can calculate the free board of the ice, so that's the amount

  • of ice, that sticky arc above the ocean surface.

  • Now, to kind of simply explain what we do next

  • to estimate ice thickness from this measurement,

  • the ice is floating and roughly nine tenths

  • of the ice is below the water level.

  • In reality, it's a little bit more complicated from this,

  • we have to take into consideration things

  • like the snow depth and density that's sitting on the top

  • of the ice and how it weights the ice down.

  • We have to consider the ice density

  • and the water density as well.

  • But that basically describes the principle of the measurement

  • and what were looking at.

  • Now, as I said today, I want

  • to present you our most recent results,

  • and I don't really have time to go into what we've looked

  • in the past, and though Seymour and myself had looked

  • at how the Arctic ice thickness has been changing,

  • but today just going to take the measurements over the ocean,

  • and this was actually started a couple of years ago

  • when we started looking at these ocean graphic measurements

  • on their own, and we noticed something was going on.

  • Now this is a video that's being made using our data.

  • The reds mean that the sea surface height is getting

  • higher, and we were looking at data between 1995 and 2010,

  • and what we could see is the sea surface height getting higher

  • and higher.

  • This area is in the Western Arctic, that area I pointed

  • out to you earlier where you get the largest storage

  • of fresh water.

  • So obviously after seeing this in the--

  • our data, we wanted to find out what was going on.

  • So our first port of call was to get and actually have a look

  • in the literature, and see what other people had been observing.

  • Now this figure here is from some work by [inaudible]

  • and what they've done is taken in situ measurements,

  • say measurements that should be made for being

  • on the Arctic Ocean, so from a ship or being in ice kind

  • of pool having a mooring floating around