One of nature's many amazing gifts is a thing called the latent heat of fusion. Essentially,
it means that in order to warm something up enough to change from one state to another,
like changing these ice cubes from solid ice to liquid water,
you have to shove in quite a lot of extra energy to convince the molecules to start
jiggling around in a more 'liquidy' kind of a way. So as these ice cubes take in energy
from their surroundings they warm up to zero degrees Celsius, which is the freezing point.
But they're still solid ice. In order to get them to change from solid ice to liquid water,
still at zero degrees Celsius, you have to put in an extra 334 joules of energy for every gram
of ice. And that extra energy is what they call the latent heat of fusion. But here's the thing
that blows my mind. Once you've done that, and you've got liquid water at zero degrees Celsius,
you put in another three hundred and thirty-four joules of energy for every gram and you heat that
water up from zero degrees Celsius to 79 degrees Celsius! Which is basically scolding water! And
that's why the scientists are a bit worried about this whole Arctic sea ice loss thing!
Hello and welcome to Just Have a Think. Now just for clarity no one's suggesting that the Arctic
Ocean is going to start heating up to 79 degrees Celsius - that really would be the end of us! But
the same principle of latent heat of fusion does apply in the Arctic as we just looked at in that
glass of water. As long as there's ice in the ocean then all the heat energy is going into the
ice trying to get it to turn into water, but as soon as the ice disappears then all of that heat
energy from the Sun can be devoted to warming up the water, and that will most certainly make
several degrees of difference, with all sorts of pretty catastrophic consequences. So lots of
research institutes keep a very close eye on the state of the Arctic each year, one of which is the
National Oceanic and Atmospheric Administration or NOAA in the United States. NOAA produces an annual
scorecard each December and this is their latest one. It's a comprehensively peer-reviewed document
which draws on a huge array of reference sources, all of which are now scrolling up on the screen
behind me. I'll leave a link to the full report in the comments section below so you can go have
a look for yourself, and in the course of the next two videos I'll be taking a look at some of the
highlights from the report. The report actually considers a whole host of indicators. In addition
to sea ice there are seven vital signs outlined here. Surface air temperature, terrestrial snow
cover, Greenland ice sheet, sea ice as we've already mentioned, sea surface temperatures,
marine algae, and tundra greenness. Far more than we can possibly cover in a single video,
of course. So I'm going to focus on sea ice in this week's video, and then we'll take a look
at some of the other key points in subsequent programs. The report points out that Arctic sea
ice cover varies substantially over the year, with end of winter ice cover generally being
two to three times as large as at the end of summer. Sea ice is an important element of the
Arctic system. It acts as a barrier between the underlying ocean and the atmosphere. It limits
the amount of absorbed solar energy during the summer due to its high Albedo, or reflectiveness,
and it provides a habitat for biological activity and limits human access to the Arctic Ocean. This
chart shows average monthly sea ice extent in March 2018 on the left and September 2018 on
the right. The magenta line indicates the median ice extent during the period from 1981 to 2010.
The minimum extent last year was on the 23rd of September, and this was tied with 2008 and 2010
as the sixth lowest extent on the satellite record, at one point six three million square
kilometres or 26 percent less than the 1981 to 2010 average. And the 12 lowest extents in the
satellite record have all occurred in the last 12 years. According to the report observations
of Arctic sea ice extent have shown decreasing trends in all months and virtually all regions,
with the September monthly average trend for the entire Arctic Ocean now standing at minus twelve
point eight percent per decade relative to the 1981 to 2010 average. The extent of sea ice,
in other words the surface area that it covers, is relatively easy to measure,
especially now we've got these satellites looking down on the whole shabang. But surface area only
tells us part of the story about the state of the ice. If we want to get the full picture we
need to know how thick the ice is, and how old it is. Older ice tends to be thicker and more
resilient to temperature increases in the air and water compared to younger, thinner ice. In 1985
the oldest ice comprised 16% of the ice pack. In March 2018 old ice constituted nought point
nine percent of the ice pack. That means it's gone down from 2.54 million square kilometres in March
1985 to 0.13 million square kilometres in March 2018. That's a 95 percent reduction! Measuring
the thickness of the ice is much more difficult than measuring the surface area, simply because
most of the thickness is underwater and therefore not visible. NOAA gets data from various sources,
including an altimeter called ESA Cryosat-2, which has been operating since 2010, and more recently
NASA's Icesat - which is a laser based altimeter that provides an even more accurate picture.
According to the report the thickness increase from October 2017 through April 2018 was less than
normal, resulting in a relative decline in mean thicknesses over the winter. Ice volume estimates
representative of ice extent and concentration in the central Arctic verify the below average ice
volume gained over this interval. NASA themselves also talked about Arctic ice thickness at their
own website. Here's their take on the situation. The Arctic oceans blanket of sea ice has changed
since 1958 from predominantly older thicker ice to mostly younger thinner ice. Working
from a combination of satellite records and declassified submarine sonar data, NASA
scientists have constructed a 60-year record of Arctic sea ice thickness. Right now Arctic sea ice
is the youngest and thinnest it's been since we started keeping records. So... that declassified
submarine sonar data then? Well as I've mentioned in a previous video on this subject, if you're
spending several months of the year patrolling and surveying the depths of the northern waterways you
will need to surface from time to time, and when that happens you'll find it extremely helpful if
you know how thick the ice is that your submarine is going to have to break through in order to hit
fresh air. So the US Navy make it their business to know more or less to the millimetre exactly how
thick the ice is. And thanks to Patrick McNulty, whose ocean mechanical thermal energy conversion
design we featured a few weeks ago, and he also runs a Facebook forum called Ocean Tunnels,
we have access to those declassified charts. In fact, Patrick has been able to provide charts
that allow us to look at maximum and minimum levels for every year from 2012 right up to just
a couple of days ago - March the 7th 2019. Let's look at the March charts first of all which show
the maximum coverage for each year. If you look at the colour key on the right side you can see that
the scale goes from the very dark reds at the top, indicating ice thicknesses of five metres or more,
down to the very pale purple at the bottom, which denotes thicknesses of less than half a metre. In
March 2012 the majority of ice in the open water was between 2.5 and 4 meters thick, with some 5
metre thick ice clinging to the southern coast lines. As we go through the years you can see
that the very thick ice is beginning to decline, and by the time we get to 2017 there's far less of
the yellow and red colours at the land's edge. By March 2018 those colours have all but disappeared
completely. And here's what the Arctic sea ice looked like on Thursday of this week. Not only has
the thick ice not reappeared, but if we flick back and forth briefly between this year and last year
you can also see that the open water ice, which last year was mostly in the 2 to 2.5 metre range,
is now firmly down in the 1 to 1.5 metre range. Back at the NOAA website they make a further
worrying observation... One of the more remarkable features of Arctic sea ice over the past year was
the dearth of ice in the Bering Sea through the 2017-18 ice growth season. The Bering Sea supports
a vibrant sea ice ecosystem with abundant seals, birds and other species that critically depend on
the timing of the sea ice formation and retreat. It is also an important commercial fishing region.
Ice typically begins to form in the Bering Sea around the beginning of October and expands
through the winter before melting away through the spring. According to NOAA for virtually the entire
2017- 2018 Bering Sea ice season, the extent was at a record low. During February 2018 typically
the height of the winter season the Bering Sea actually lost significant ice cover. From
the 7th of February to the 23rd of February ice extent decreased by about two hundred and fifteen
thousand square kilometres, dropping from around fifty nine percent to only around 26 percent of
normal levels. And this report from March the 7th 2019 by Andrew Friedman for the website Axios,
tells us that it's happened again this winter. For the second straight year, Friedman says,
the Bering Sea - a turbulent and bountiful stretch of the northern pacific ocean - is
virtually ice-free at a time when it should be gaining ice. This is the richest fishing ground
in the U.S. - featured in the Discovery Channel's Deadliest Catch. Friedman spoke with Rick Toman,
a scientist at the Alaska Center for Climate Assessment and Policy. Toman's view was this
one year maybe a fluke. Two years sure looks like we've crossed a threshold. Now, Zac Labe,
a PhD candidate at the University of California at Irvine, and creator of these superb graphic
representations of Arctic sea ice loss since 1979, also contributed to the Axios report,
saying 'although the past two years have brought historically low Bering Sea ice conditions,
year-to-year trends there can fluctuate considerably.' Labe goes on to say some
years may see temporary upticks in Bering Sea ice extent, but the overall climate change is
now in the driver's seat. The impact of this dramatic reduction is significant,
says Friedman. March is normally when people would be crabbing and fishing out on the ice.
That's not happening now. Communities exposed to high seas are seeing severe erosion and threats
to their infrastructure. The loss of sea ice could change ocean temperatures, salinity and
currents enough to alter the distribution and abundance of commercially valuable fish in the
region. The stakes are high here, as the Alaska pollock fisheries alone was worth 430 million
dollars in 2017. It also portends consequences for the lower 48 states and beyond. In a new
study published in 'Earth's Future' on Thursday, scientists warned that Arctic climate change is
already reverberating far outside the region. So what about the September minimum sea ice levels
again? Well, let's go back and have a look at those Navy charts from Patrick McNulty again.
This chart shows the September minimum from 2012. Obviously you can immediately see the
dramatic difference between winter maximums we looked at earlier and the summer minimums shown
here. But that's perfectly normal. What you can also tell from the colour key though, is
that back in 2012 there was still a fair quantity of that old multi-year 4 & 5 meter thick ice just
above Greenland and the Canadian archipelago. The thicknesses were similar in 2013, and then we see
quite a bit of variability in the subsequent years running up to 2017, by which time there really is
very little multi-year ice left. Then when we arrive at last September's chart. Although the
surface area coverage looks relatively large you can clearly see that it's an almost universally
thin layer less than a metre thick, and even right down to only a few centimetres out in
the open waters. This wafer-thin ice is extremely vulnerable to being broken up by severe weather.
One big storm and much of that light pink stuff may well have disappeared. Unsurprisingly then,
the greatest level of concern and anxiety - and frankly speculation - amongst the climate science
community is about if and when the Arctic will become ice-free in September, with the consequent
very rapid warming of the water that we looked at right at the start of the program. Its what's
come to be known by the climate scientists as a Blue Ocean Event or BOE. Now just for clarity,
when they say "ice-free", they actually mean a quantity of ice that's less than 1 million
square kilometres which still sounds like an awful lot of ice, but in the context of a maximum extent
of about 15 million square kilometres and an average minimum of about 6 million square
kilometres during the 80s and 90s, 1 million square kilometres is actually a statistically
insignificant quantity. And crucially, it won't be one big blob of ice in the middle of the water,
it'll be little pockets of ice here and there, much of which will be clinging to the shorelines,
leaving the vast quantity of open ocean exposed to the full force of the sun's heat. Some of the
more strident climate commentators have been predicting a blue ocean event every year for
the last several years. Well, it hasn't happened yet, and NOAA's stated rate of decline in surface
area of 12.8% a decade, that we looked at earlier, would suggest it may not happen until the end of
the century. But the Navy charts of ice thickness do seem to suggest a rather more urgent dilemma,
and given what we can see on this latest chart from just a couple of days ago,
it looks likely that this year's September minimum ice cover may well turn out to be the most fragile
and vulnerable layer of ice yet. One thing's for sure - if and when we do get a blue ocean event,
our global climate will change very rapidly and very significantly, and most likely irreversibly.
There's much more to digest from this fascinating report so, as I mentioned earlier,
we'll definitely be returning to the subject in future videos. But that's it for this week. I hope
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