Stephen Gill, Senior Scientist for NOAA’s Center
for Operational Oceanographic Products and Services Group.
As a senior scientist, Mr. Gill has been involved
in the things you would expect a senior scientist
to be involved with:
strategic planning, budget initiatives,
technical and scientific directions for the office.
And he also develops science and technology
plans for programs involving tide,
currents, sea level measurement and vertical data.
But in addition to that,
Steve has also served as the NOAA lead author
for the US climate change science program
synthesis and assessment product on coastal
sensitivity to sea level rise in the Mid-Atlantic
and, in fact, was NOAA’s lead contributor to the panel
that provides guidance for incorporating sea level
change into engineering, planning and design projects.
He has served on several climate-related technical
peer review panels
including several national government review panels
for the IPPC Working Group 2 chapters and panel studies.
Now, we’ve asked Steve to come here this evening
to talk to you a little bit about climate change
and its impacts on sea level rise.
Steve is the man to go to at NOAA.
Okay, it’s really pleasure to be here, everyone.
I’m very happy to do this.
This is my second time around and –
of this presentation on sea level,
and there’s several updates from my last presentation,
and there’s a lot of exciting research
going on at the present time.
So it’s a very exciting time for sea level change
and sea level rise
and since I last presented a couple of years ago,
increasing awareness is pretty intense
in terms of sea level change and its impacts on our coasts.
So the outline of my talk,
I’m going to just briefly talking about a few things
that I’ve outlined here
in terms of what is global sea level change.
What are some of the causes of sea level change?
What are the attributes
that go into the makeup of sea level change?
Then I’m going to be looking at some present
and projected rates of global sea level rise out to the next –
through the next century followed on by
looking at how we measure sea level rise.
What kind of measurement systems do we use?
Well, we use tide gauges and then we use satellite
altimetry to measure rise around the globe.
And, finally, I’m going to close with a comparison of sea level
rise scenarios that were recently developed
by our national climate assessment
and looking at that versus observations.
So I always like to start by putting it into perspective,
and this is the perspective I like to give in terms
of what we’re looking at in terms of global sea level rise.
And that is the earth is a water planet.
Depends on your perspective.
You can look at one side of the globe
and you can see the US there. Look at another you’ll see Asia.
But if you look at coming in from the Pacific,
you can see that from this perspective
that hemisphere is all ocean.
So the earth is a water planet. It’s our life blood.
Whatever happens to the water cycle
and the global sea levels, global circulation changes
ultimately affect every one of us.
So the global water cycle is a very complex system,
a closed system if you will in terms of the water
in all its various forms.
It can be in the air. It could be within the land.
It could be flowing out of rivers,
in the lakes and in the ocean and in the form of ice.
So this provides –
the schematic provides all those complex components,
and so water could be locked up in any one of those
various components of the cycle at any given time.
And certainly during the Ice Ages most of that global water,
a large portion of it is locked up into the ice
and thus the global sea levels are low.
And when global sea levels rise with warming,
most of that water is in turn in the oceans
and a less amount is locked up into the frozen modes
in ice and glaciers.
So we’re going to be talking about some of these components
and how they interplay.
So fundamentally the causes of sea level change.
Well, what could cause the global sea level
to change like that?
Well, certainly the Ice Ages are one
and so that’s a large amount of rise and fall
due to the periodic Ice Ages.
And so when we look at the actual physics
of what can change the volume of the ocean
to cause it to rise and fall,
one of the first ones is thermal expansion.
And that means that as the water warms, it expands.
That’s a fundamental component, physical component of water
is that when you warm it, it expands.
And so as the global oceans warm, they expand.
Typically that’s what’s been causing sea level to rise
over the last century with increasing components
that are modeled to happen on the following components
down below, which are Greenland Ice,
Antarctic Ice, Mountain Glaciers,
Water Storage and other variations.
So if we just look at Greenland Ice,
it can account for maybe seven meters total.
If all of Greenland icecap melted,
that would cause the global oceans to rise seven meters.
That’s a lot of water locked up in that ice mass.
Antarctic ice mass is even more impressive.
If that all melted at once, it would add 60 meters
to the elevation of the global oceans.
Mountain glaciers are less than that, about half a meter
if they all melted at once and contributed,
which they are indeed melting very fast,
would contribute another half a meter
to global ocean sea levels.
And then there’s terrestrial water storage variations,
what’s locked up in the ground, what’s locked up in lakes
and rivers and reservoirs and so forth?
And that’s less than half a meter, a minor contribution,
and there’s other minor ones too: halosteric,
which is essentially the change in the ocean density.
The amount of salt in the oceans,
the density of the water itself
can have some minor impacts in terms of sea level.
So that equation down below is just summing all those up.
The total sea level at any given time
is the components of those upper attributes.
So if we look at the Ice Ages
so this is a graph of thousands of years before the present,
like 400,000 years before the present time
and you can see the variation in the Ice Ages
where the scale here
is in meters so from 0 to 140 meters of change,
so there’s pretty significant change in global sea levels
due to the Ice Ages.
And on the right-hand scale with the yellow –
with the red circle,
that’s our present day that we’re at this portion
of our Ice Age of variability,
and so we’re on the upper portion of that curve
at the present time.
Now if you just look at what was in that previous graph
in terms of the circle, well,
here’s the last 18,000 years before the present time.
So sea level’s been slowly rising
and then it’s been leveling off
since around 5,000 or 6,000 years ago.
It was leveled off and here we are at the present time.
So, again, that’s 120 meters on that scale there
that it’s been rising, 18,000 meters before now,
and now we’re talking about meters it lies
at the present time about this glacial maxima.
So, again, looking at that red circle,
where are we within that red circle right now?
Well, here’s the observational record based on tide gauges
and satellite measurements from 1880 to the present.
It sort of spans the observational record
from our tide gauges on the left-hand side.
So since 1880, the sea level’s risen about 25,
a little less than 25 centimeters from 1880.
You can see on the left-hand side
there’s a very large band of gray,
and that means this larger uncertainty in the data
going back in time.
And then on the upper right-hand side there’s two curves there.
You can see the orange and gray curve,
and superimposed upon that is that reddish curve,
the satellite measurements. So since the early 1990s,
we’ve had concurrent systems of tide gauges and altimeters.
We’ll talk about those measurement systems
a little bit later.
So what contributes?
You know, how do these things contribute to sea level rise?
Now, we mentioned Greenland before in our equation
so here’s Greenland and that mass balance for Greenland.
Here’s the latest research and observations in the graph
on the right-hand side that since 1958,
Greenland has been seeing the acceleration
in its loss of mass.
You can see that starting in 1958
it actually increased in mass around 1974-1975
and since then is decreasing, seemingly accelerating.
So, again, you can see that it increased
and then it started decreasing.
So there’s longer-term cycles in these variations
and we’ll talk about that more later.
But, certainly, over the last couple of decades,
there’s been increasing loss in the Greenland.
Here’s a similar figure more in terms of research,
not observations, of Antarctic Ice Mass.
And again since 1974, not a very long time series but indications
are that there is increasing loss of mass
on the West Antarctic ice sheet.
The information and measurement systems for Antarctica
are a much shorter record than even Greenland,
so we don’t have a huge long record.
We have a tide gauge record going back to the mid-1880s.
But you can see some of these measurement programs
for loss of ice mass in Greenland and Antarctica,
the precise ones, have only started recently,
but they do indicate increasing loss at some accelerated rate.
And glacier mass since the 1940s so we all know
and have heard about glaciers retreating.
These are the landlocked glaciers
that we’re all familiar with in Alaska and so forth
and Scandinavia that are melting.
And here you can see the loss of the glaciers
over time up until 2010.
We don’t have much of a record before the 1940s,
but we do see that we have a number of glaciers
being measured is about constant now
and we do see cumulative mass loss there as well.
So everything’s pointing to mass loss from glaciers,
from Antarctic Ice Mass and from Greenland Ice Mass.
So let’s look now at sea surface temperature.
So, again, we talked about thermal expansion.
Well, here’s just a graphic for the average sea
surface temperature in 2011 for the globe,
and that’s pretty much what we think.
What we’ve measured is that there’s warmer waters
along the equatorial band and cold water at the poles
and so that’s reasonable.
And then if you notice off of New Guinea north of Australia,
there’s a hotspot there.
That’s where some of the warmest waters on the globe
are is just north of there.
And that also comes in play in terms of its impact
on sea level as well that we’ll see later.
So that’s just a snapshot of the variability of the globe
just for one year.
So here’s a time series looking at sea surface temperature
across the measurements over the decades.
Now you can see
that there’s much more uncertainty prior to 1940,
and then after that, we have more precise measurement systems
but you can see that increase.
There is that anomalous feature there in 1940.
Some of that feature is due to instrument change,
but a lot of it is just due to decadal oscillations
is what the research suggests
is that we have decadal oscillation,
climate oscillations in our data that we measure and see.
And in the background there’s a long-term trend
due to the global warming,
but indeed there are specific decadal oscillation.
The El Niño-La Niña ENSO oscillation
is one that we hear of that comes into play
that causes some of these variations over time
in these sea surface temperature measurements as well.
But, overall, it’s increasing over the period
of measurement record.
And here’s a graphic of the spatial distribution
of the trend in ocean surface temperature from 1959 to 2008.
So you can see not only is there lots of variation
but there’s spatial variations in terms of these trends.
So the previous slide showed
that composite average global information,
but here’s a graphic showing the distribution of these trends.
So it isn’t the globe and all the ocean waters
have the same exact trend over time.
There’s lots of variability.
There’s a key one in the North Atlantic.
You can see that sea surface temperature trends
are larger there than they are
for many of the other areas around the globe.
There’s no real negative trends.
Around Florida you can see some negative trends
and off the West Coast of the US
and then, of course, down in Antarctica
that there’s negative trends as well.
But for the most part, those are positive trends spatially.
And combined with that we can look at the ocean heat content
and that is the amount of heat that the oceans have in them.
And the more heat they have in them across
the vertical profiles of the ocean,
that means they have more thermal expansion
that could result in changes
in circulation patterns and so forth.
And this is the ocean heat content monitoring
that goes on from three different groups:
The JAMSTEC, J-A-M-S-T-E-C, is a Japanese group,
an environmental group,
the Cicero is an Australian group
and then the NOAA group.
So all three independent agencies
are seeing the same upward trend in ocean heat content
since the mid-1950s in terms of
when they’ve done systematic measurements over time.
So that’s the other indicator
that there’s a trend in ocean warming.
So what does that mean in terms of our global sea level
projections into the future?
So this is a schematic based upon, you know,
IPCC is the Intergovernmental Panel of Climate Change,
which puts out reports. The last one was 2007.
They actually have another one,
the assessment going on right now that’s under peer review
and global review by various countries.
And so over on the right-hand side
you can see IPCC 2007 AR4.
Well, that was that fourth assessment
and those values there in different colors
are the different,
you know, at that time when they put out the report.
Sea level was going to rise anywhere from 20
to 60 centimeters by 2100.
Since that 2007, there’s been a whole lot of updated
peer-reviewed research
and looking at different variations
and plausible scenarios and plausible climate changes.
And most of the peer-reviewed research since 2007 calls
even for increased sea level rise by 2100,
anywhere from 60 to up to 160, 180 centimeters by 2100.
So it sort of reflects the latest research
and some of the latest findings that are going on.
These are more or less looked at as maximum values.
We’ll see what the next IPCC report comes out with in …
I think it’s going to come out next year.
And probably those values that you see by the AR4 nomenclature
there will probably increase upwards by all indications.
So let’s turn now to measurement of sea level.
So I mentioned tide gauges.
There’s a network of worldwide tide gauges
and so we measure water levels by long-term tide gauge records.
And so our Tide Station at the Presidio, San Francisco,
right near the Golden Gate, that tide gauge right now
is housed in a former Coast Guard base.
It’s a NOAA marine sanctuary right now
that we have a long-term tide gauge.
It’s been there since 1854 measuring continuously.
Over to the right you can see the sea level record
from that gauge.
This is monthly mean sea levels filtered from its annual means,
but it shows an increasing trend
upward of two millimeters per year relative to the land.
So tide gauges measure sea level relative to the local land.
It’s a relative sea level measurement,
and that means that tide gauges can’t distinguish by themselves
between land movement vertically and sea level change globally.
It measures both together, so a tide gauge measures
a combination of vertical land motion
and global sea level change.
We connect tide gauges to the land
by doing annual differential levels with survey
and the tide gauge sensors, sensor zeros,
to benchmarks on the land.
And that way we can tie them into a common reference datum
over time and measure what the sea level
is doing relative to the local land.
So long-term tide gauges are very important
in terms of the tide gauge record.
So here’s an example of a long-term record
for Baltimore, Maryland.
Again, it’s a trend upward of three millimeters per year
over time if we do a linear fit to the data.
And that trend is 3.08 millimeters per year
plus a -.15
millimeters per year standard error in that trend,
but the linear trend does a pretty good job of fitting that.
There’s lots of other oscillations
that you can see in the record
that are due to a whole variety of climate oscillations
and other effects, oceanographic effects,
but in general the linear fit does a pretty good job.
Now here’s an interesting one.
Now, again, remember that tide gauges measure
sea level relative to the land.
Well, sea level is falling relative to land up in Juneau,
Alaska, and Sitka, Alaska, in those glacial fields.
That means that sea level is falling
because there’s vertical uplift of the land.
That’s the strongest signal
and it overwhelms any global sea level rise,
and that’s because the glaciers have melted recently
in geologic time.
The release of those glaciers and the weight of the glaciers,
which is significant on the land,
is causing the land to rebound.
It’s rebounding from the off-weight of the glaciers.
And so this is the place you want to buy shorefront property
if you want to go up there and get some new land.
It’s a pretty impressive rate:
12.92 millimeters per year in these upper fields.
This is the same thing happening in Scandinavia.
Anywhere we’re losing these land glaciers the land
is tending to rebound from loss of the glaciers.
It’s a phenomenon we’ve see around the globe.
So here’s the opposite example for Grand Isle,
Louisiana, again sea level relative to the land.
Sea level is rising at 9.24 millimeters per year.
That’s much higher than the global average
for the past century or even recently.
And so even here the opposite effect is happening.
It’s that there’s local vertical land subsidence,
so we’re measuring global rise and vertical land
subsidence at Grand Isle.
And we know that in Southern Louisiana
and that area around where the Mississippi River
comes out into the Gulf of Mexico
that that land has lots of regional subsidence
just because it’s an old coastal plain, an old delta.
And we know that the sediments
are not being replenished into that delta.
They're being channeled through the river and out to see.
And we also know there’s been lots of recent withdrawal
of natural gas
and oil in the substraits all around that delta,
and that’s been causing varying rates of vertical land
subsidence over time in Grand Isle.
So they're particularly susceptible to storms
and to increasing sea level rise
because they’ve been losing lots of coastal wetlands and islands
and so forth fairly recently.
So they're very susceptible due to this additive effect
of vertical land subsidence and global rise.
So here at my organization we look at these trends
and analyze these trends, and we have a website:
tidesandcurrents.noaa.gov down at the bottom there.
And so that is a look at the trends around the globe
from long-term tide station records.
These are compiled internationally
by the Permanent Service for Mean Sea Level
located in England. We’ve taken the data
and put it in a presentation mode for the globe.
You can see most of the arrows are going upwards,
and most of them indicate sea level rise relative to land
at all these tide stations just to give you an indication.
And here is a blowup of just the US itself.
Again, most of the arrows are going upwards.
You can see down at Grand Isle, Louisiana, the Gulf of Mexico.
You have some arrows in Texas.
You have some red and yellow arrows
of these larger rates of sea level
rise relative to the land.
And that is simply due to the land subsidence component
being active.
Some other areas are the lower Chesapeake Bay
has abnormally high rates
and there’s subsidence going on there around
the Hampton Uproads area in Norfolk, Virginia.
But then you notice up in Alaska in the Gulf of Alaska
those arrows are going down.
And so that’s a combination of some areas of this vertical
rebound of the land due to loss of the glaciers.
And some of it is due to tectonic movement
due to recent earthquake deformation around Koyukuk
and those areas is that the earthquakes have been moving
the land vertically at different rates
caused by just the aftereffects of the movement of the land
during these times of these massive earthquakes.
It’s still responding to the 1964 earthquake
in that area in the Gulf of Alaska.
Now to use the global tide gauge information
to make sense out of it,
what they do is they correct it for vertical land motion
using various land motion models, using GPS measurements.
You can attempt to correct the tide gauge records
and correct it for vertical land motion,
and what’s left should be global sea level change.
And so this is a composite of all the tide gauges
around the word, a very noisy graph.
But if you look at the mean, the heavy white curve,
that comes out to be a rate of 1.8 millimeters per year
over the last century. Again, that’s from 1900 to 2000
and so that’s pretty much the given rate
that’s been quoted in the peer reviewed literature
is 1.7 to 1.8 millimeters per year for the last century.
There’s indications that may be increasing,
but that’s the given rate measured by the tide gauges
over the last century.
And it’s a composite of sea level measurements
around the globe, the long-term tide station
records as corrected for vertical land motion.
The next measurement system that’s used quite a bit
is the altimeter,
the satellite altimeter missions.
They started – the ones that we’re using started in 1992
with the TOPEX-Poseidon. A US and French mission went up
and this is a microwave altimeter,
a microwave sensor that is measuring down
to the sea surface from its satellite orbit.
And after you correct for the satellite orbits
and put it all in a common bill for reference training,
you can look at long-term changes in sea level over time.
Over to the right is the ground track.
It expands from 60 degrees south to 60 degrees north,
so it is not a true global system.
But, indeed, it contains information
on most of the world’s oceans.
So each one of those tracks,
you can see that there’s crossover points.
At each one of those crossover points,
you can construct a time series since 1992 and from that,
you can look at these time series
and you can look at long-term changes in the sea surface
over time at each one of those crossover times.
They become open ocean tide gauges, if you will,
because you’ve got a time series out of the record.
So here’s a composite graphic in the change
in global sea level over time since 1992 when missions began.
So we have some overlapping series because these satellites,
these TOPEX satellite,
they really only have a lifespan of five to six to seven years
and then we have to send them to another mission.
And then you can see they overlap
and they compare them to make sure they agree.
They send up another one overlap in time and compare
and then they go on with the new one.
So it’s very important that we keep up these
overlapping series of satellite altimeter missions
because we’re now starting to accrue a long-term record.
But this graphic suggests that sea level has been rising
about 2.9 millimeters per year since 1992.
Again, that’s higher than the 1.8 millimeters per year
that we’ve been seeing over the last century
from the tide gauges.
And this suggests that there’s been an increase
over the last couple of decades.
But the record’s to short to really say
that that’s a long-term climate change
or is it some oscillation that’s happened
that’s causing this perceived increase?
And, indeed, if you look at all those crossover points,
you can see there’s a large spatial variability
in those trends.
So the previous plot was the composite of the total globe,
but here is the trends on each one of those grid points
and so there’s lots of variability in that spot.
Remember we had a high temperature in 2011,
sea surface temperature above Australia and New Guinea?
Well, there’s the sea surface trends.
They're some of the highest over 10 millimeters per year
in that location.
But there’s also areas with negative trends
off the West Coast and Gulf of Alaska.
There’s fairly small trends in sea level
rise since 1992 measured by the altimeter.
And up in the North Atlantic
there’s some areas there where sea levels seem to be rising.
So not only is there very variability over time,
that composite that we just saw,
but there’s also variability spatially.
And so we’re looking keenly at how these distributions
are changing over time,
whether there might be some shifts,
where these trend maxima are.
There might be some of these global oscillations
that are causing certain areas of the ocean
to rise increasingly over others.
We’re looking at the areas near Greenland
for sure in terms of ice melt and so forth,
so there’s lots of variability.
But the global average of all those measurements that you see
is about 2.9, 3.0 millimeters per year
but there’s large variability.
So let’s move on now.
You know, we’ve talked about the measurements
and the projections.
Well, the national climate assessment
has been taking place,
and this is the latest update of the nation’s
consensus in terms of the various agencies
and various academic folks
coming together to look at their projections and scenarios
in terms of what’s happening with the climate
and what are some of the mitigation activities
that might take place and so forth
and what does climate change mean for the US?
So the national climate assessment is ongoing.
I think it’s just finishing up the peer review.
A public comment period will go into a peer-reviewed period
and so forth.
But in preparation for the national
climate assessment document, NOAA led a cross-country effort
in terms of a sea level rise scenario document
and they produced that
and that link is down below there
if you want to look at that report
and they came up with some global sea level rise scenarios.
These aren’t projections. This is just scenario
depending on what basis of risk you might want to take.
They come up with four scenarios.
So on the left-hand side from 1900 to 2000
is the measurement record
and then the four different scenarios
take place by the year 2100.
You have the high scenario of two meters.
You have a couple intermediate
so 1.2 and .5 and the lowest is .2.
So the lowest of .2 is essentially just an extension
of the present trends over the last century.
If you keep on going on average, you’ll have 20 centimeters
or .2 meters by 2100.
Intermediate high and intermediate low scenarios
take into account different climate models
and different rises
based upon increasing melting of the ice masses
that we talked about before.
And the highest of two millimeters,
that’s basically when all heck breaks loose, if you will,
if you have really high rates of –
plausible rates of ice melt from Antarctica from Greenland.
It could go up to two meters by 2100
but that’s a lot of things would have to take place
and come into play for that to happen.
So it just gives you, depending on what risk you want to take,
the lowest to the highest plausible rate
from .2 to 2 meters. So the reality is suggesting
it’s likely to be within there somewhere.
But these scenarios and these projections
underlie the uncertainty
and the response of the oceans to climate change.
You can’t just say give me the intermediate rate of 1.2
plus or minus .2 meters. _____
the uncertainty is in the bounds of these scenarios themselves,
so we really don’t know how it’s going to play out yet.
Over time more data and more research
you tend to pinpoint these down. You can narrow down uncertainty
bounds and narrow down scenarios by 2100,
but it takes more data and more observations
and more modeling to do that.
So I want you to pay attention to that green box I’ve outlined
so that’s the present time, if you will,
and we’re using that to track, okay,
these scenarios start in 1992.
Well, what’s happening to the observations?
Are they going to follow these trends?
Where are we going to fall in these trends?
And so we want to use these in trends of a climate indicator.
What’s going to happen
and how can we best track that over time?
So this is just, again,
remember this previous slide with that green box?
Well, here’s that green box scaled up.
On the left-hand side is the change since 1992
and we’re looking at four different scenarios,
those smooth curves.
And then we’re looking at the tide gauge data in red
and we’re looking at the temperature data
in the North Atlantic in the blue
and so there’s lots of variability
in the observational record at this scale
starting with this 1992 scenarios
and so you see this variability.
This variability is noise in the record
and it’s going to continue.
These sea level scenario trends are just curve linear data
that’s from 1992 out to 2100. The models don’t really say
that it’s going to follow these smooth curves.
And, indeed, all the data indications
are it’s not going to follow smooth curves.
There’s going to be lots of variability.
What we’re doing for the indicators
is this is just a plot for the Gulf of Maine.
Well, we’re going to break up the coast
into 11 different areas,
and we’re going to plot up 11 different plots
showing what the tide gauges are doing in that region
and what the altimeters are doing in that region.
And we’re going to continue to grow this plot over time
and see how we’re tracking, how the observations
are tracking within the scenario curves.
How are they doing? Are they increasing?
Are they higher? Are they lower? What is that noise doing?
So at some point in time, if you look at the previous plot,
we think that the sea level acceleration
should overwhelm that background noise
and you should start to see increased acceleration
in the observations themselves
if the models and projections play out.
So that’s what we’re doing with the indicators.
We’re looking at the variability,
looking at how it changes over time and what might happen.
So I just want to summarize now in terms of what we talked about
that we do know that global sea level has varied
and will continue to vary substantially over history,
especially in response to the Ice Ages.
We’re talking hundreds of meters of change due to these Ice Ages.
And we do know that the global tide gauge measurements,
tide gauges suggest that over the last century global sea
level rose approximately 1.8 millimeters per year.
Now with the satellite altimeter data
it’s showing 3 millimeters a year approximately
and that suggests a change,
but we don’t know if that’s a climate signal
or a decadal oscillation signal that’s happening.
We do know there’s lots of noise in the observations.
We saw there’s lot of noise spatially over time,
so sometimes it’s hard to see trends out of the noise.
Using climate models and new projections of ice mass loss,
we do know that future projections suggest sea level
will rise anywhere from 50 to 180 centimeters by 2100.
I mean that’s a pretty good range,
but at that low end 50 centimeters
if pretty significant if you live in a coastal zone.
We do have relative local sea level change
that’s measured by long-term tide gauges, right,
relative to the land.
And what we’re doing is working with folks
that look at these measurements,
and you can combine with a global sea level
rise projection
to estimate local impacts for planning purposes.
We’d look at what’s happening now, local relative to the land,
and ride that upon your chose scenario,
whichever you choose to use and what your risk is,
and look at what might happen by 2100.
And, finally, I’ve talked upon the optional data –
the observational data are very noisy
compared to those climate scenario curves,
and they show significant variability
over decadal timescales
as well as significant regional variability.
So it’s a hard puzzle to look at right now
and so it’s an interesting time because the models, of course,
show that sea level rise has to accelerate pretty quickly
from now to the end of the century
if we’re going to meet those climate scenarios
and those climate projections.
So that concludes my talk.
It’s been a pleasure. I hope it was clear.
I hope it helped you out a little bit.
I’m certainly available anytime for questions.
Bruce has my contact information.
Hi, Steve. Actually we have some terrific questions
now from our climate stewards.
I got a couple of notes during my –
when I facilitated our last month’s webinar,
I was a little short with the questions
so I want to make sure we get some questions in
because we do have some time.
And then everyone who’s on the line,
please stay on the line.
We have some important announcements.
So the first question that we have,
Steve, let’s see if I get down over here,
is there was a question about a gray band on Slide
No. 13, I believe.
And Elizabeth Cooke is asking what that band represented,
yes, as it doesn’t appear to be there
or it appears much lower after 1960.
That’s right so that’s the uncertainty
in the measurements so going back in time,
the instrumentation was less precise.
They didn’t have the modern electronic instrumentation
and more precise instrumentation that was used
so it’s partially instrumentation.
It’s partially because we didn’t have
that many measurement points to get that global average.
So it was a combination of not as many data points to use
in the average and less accurate instrumentation
is the cause for the gray band.
So that’s the uncertainty bands around that average curve
that you see in the heavy orange curve.
Ahh, interesting. Now, another question.
Janet Orr has a question.
How is the ice in Greenland and Antarctic mass loss calculated?
It says “analyzing specific sample locations over time
or is it interpreted from size changes or both?”
These days one of the big measurements,
you know, I’m not an expert in that.
But one of the big ones is using altimeter data,
using satellite-based measurements
of looking down in the area of ice coverage
and then I think also about measurement cores.
They take lots of sampling over time of repeat ice cores
and looking at the cores and looking at the content
of the vertical core drillings themselves.
Okay and we have a question from Eve Cursey and she is
– was wondering if you might be able to explain on Slide No.
25 there appear to be a somewhat significant dip in 2011
in the data and was wondering,
yes, what that might be attributed to if it’s known.
Right so yes, from what I’ve seen,
that is due to changes in these global climate oscillations
that I talked about earlier,
and so there was a major shift in I forget
if it was the Pacific decadal oscillation.
But there was a major oscillation
that occurred during that timeframe
that caused this sea level anomaly to go down
and then rise back up again. So, previous to that in 1992,
there weren’t any major oscillations.
You can see there were some oscillations
going on around a linear trend,
and this was the first appearance
of this major global oscillation.
So the earth has a very complex system
of these coupled oscillations in the atmosphere
and oceans that have caused these oscillations to occur.
Oh, okay. Now we have a question from Leanna Gertzer,
and she asks the thermosteric expansion,
is that one meter a maximum based on the properties of water
or a projection from expected temperature change?
Oh, I think that’s just a, yes,
I’m not sure to answer your question precisely.
That one-meter potential I think is a maximum physical property,
if you will, the maximum amount of expansion
possible given a plausible thermal expansion
of the waters without boiling.
But, certainly, it’s a plausible maximum amount
given global warming and ocean warming.
Okay, another question asked by Vickie Peterson
is has anyone researched whether the major ocean currents
such as the Gulf Stream or I forget the major current
going off Japanese … Kashiro?
Kashiro Current.
Kashiro Current, yeah, whether or not those have
or are projected to shift either in position or depth
or speed given that with temperature changes
within the ocean basins?
Right, well, they're being monitored closely.
There’s lots of oscillations, again, a very complex pattern
and they’ve been starting to monitor
those closely via satellite measurements,
very high precise monitoring of these current systems over time.
And so, yes, there is potential for them to change
and they have been oscillating different modes.
But there’s other reasons for them to change.
They're driven by wind, global wind patterns and so forth.
So as the global wind patterns change
and drive those differently, they’ll have an effect.
The changes in density of the water over time
will have an effect on those surface currents,
so there’s a lot of things that can make them change
and oscillate in ways
that aren’t intuitively obviously proven
from any long-term trends.
So I guess the news is they are being monitored
closely now via satellite. And so as that puzzle unfolds,
we can start to relate those changes
to perhaps to climate change.
Okay and Howard Dimmick, he has a question which I believe
he says is related to one of your very early slides
showing sea level rise relative to the Greenland,
Antarctic and other regions.
He’d like to know where is the arctic sea ice
included in your chart or is it included in your chart?
Well, arctic sea ice itself if it isn’t landlocked,
you know, not on land has a minimum effect if that ice melts
because it’s all a compensating effect of the ice
floating on water.
It doesn’t change the elevation of that water.
It’s all either locked in ice or not,
so melting of that doesn’t drastically change
a sea level per se if it’s floating ice.
Okay, actually Dale Glass would like to know
if you have some kind of visualization or slide
or if you can share a scenario of what our coast
might look like here in the Mid-Atlantic
if there is a 50-, 100- or 150-centimeter rise by 2100.
Dale wants to know if her house will become oceanfront.
Well, I’m moving to West Virginia myself.
I live in Maryland. [Laughs]
Seriously, though,
Bruce showed you before a digital coast weblink,
a sea level rise viewer.
So they’ve been updating that viewer
to provide that kind of insight of overlaying various rates
of sea level change relative to the land topography.
And so I would go to that website
to see what it shows for your location.
Again, that’s just a –
it doesn’t say what’s going to happen.
It’s just a scenario, a builder.
If it did happen, here’s how much land at present
would be covered, inundated by sea level,
so go to that website and see if it covers your location.
Okay, now Janet Orr would like to know
what is the best source of data about impact of sea level
rise on very large riparian systems such as the Amazon,
Mississippi beyond wetlands interactions.
Beyond wetland interaction?
Yes.
Well, that gets to the hydrologic cycle
I think is what you’re alluding to, if I’m not mistaken,
and that has to do with the amount of rainfall
in that cycle,
the amount of runoff and those kinds of areas.
In terms of sea level rise it’s not something,
but in terms of the hydrologic cycle
and what happens there, we do know, for instance,
I just got through working a story
with lake levels falling in the upper Great Lakes
and that’s because of the decrease
and inflow from over the last several years
it’s been fairly low in terms of snow
mass melting in the spring and rainfall.
So those lake levels are very low now
and will continue to be in the future
unless the short-term climate turns around
and they have more rainfall and snowmelt
in the springtime in those lakes.
So we do know a very complicated hydrologic cycle
locally and over watersheds
it’s very important ultimately for those lake levels
and for river levels and river flow.
Right. Karen Metka has a very interesting question
about are you aware of some of the common misconceptions
that are being spread by the skeptic community
relating to sea level rise?
Well, there’s been lots of them.
I think most of the controversy I’ve heard are
“it’s all a government conspiracy”.
But from my standpoint, I’m a measurement person
so I’m looking at measurements from all of our tide stations.
And I’m looking at measurements from altimeter systems
and so I can only go in terms of what’s been happening.
And we know it has been rising over the last century
and a half,
and we do know that the climate models,
the international consensus climate models,
call for increased warning and increased sea level change.
So my job now is to simply track, okay,
as I mentioned we’re looking at an indicator.
Well, here’s what we’re measuring.
Here’s what the models say. How well are they comparing?
So over time we’ll find out in terms of how it plays out.
But, certainly, sea level has been rising globally
and will continue to,
and the models show that it will accelerate.
And indications over the last couple of decades
are indeed that’s happening but there’s very short,
you know, we suffer from short-term measurements.
So the question is what’s overarching climate change
versus what’s natural oscillations?
The indications are from the models
that this background warming
will overtake any of the natural oscillations and result
in increased sea level rise towards the next century,
so we’ll see how that plays out.
Wow, this is really interesting. Your last answer has, in fact,
been a perfect segue for the next two questions.
And I think that we should finish
with these last two questions
and then we’ll continue with some project announcements.
The first question is so how do –
this is from Nanette Mulero.
How do the projections for 2100 compare with the up-and-down
trends that you presented for the last several hundred
or several thousand years or even possibly longer?
I know that there was actually a really interesting article
in the New York Times about this somewhat recently,
but I’d love to hear your perspective.
Well, the indications are that what’s happening now with,
you know, from what we’re looking at
in terms of the climate models and so forth
is that this increase in a short amount of time
can be anomalous of what’s been seen.
But the record in the past is hard to reconstruct,
but the indications are that what’s happening over
the last couple of centuries in terms of the amount of rise
and certainly the climate projections in the models
are unprecedented in terms of its rate
over the last thousands of years.
So the rate being much faster than we had seen
before compared to other,
I guess, epochs that we’ve noted.
I mean certainly you can see in the record that I showed.
I’ll just go back here at the beginning.
Oops, sorry.
[Laughs] It’s okay, Steve.
So it shows – this one from the last 18,000 years
shows a flattening out.
Well, between this one and it’s been flat recently,
but within that circle this rise is thought to be anomalous
compared to what’s been happening along that flat curve
for the last several thousand of years.
So it amounts to a blip in terms of the global sea level
change over the Ice Ages
but in terms of its impact along the coast it’s not a blip.
It’s a serious event.
Okay and the second question then,
just what will be our final question
for this evening for announcements,
you might take – this is from Theresa Eastburn
and she’d like to know
if you could discuss briefly some of the natural changes
that typically result from oscillation such as ENSO and NAO
and I’m actually not familiar with NAO, are you?
North Atlantic Oscillation.
Okay.
Yeah, these are climate oscillations
and a lot of these things have to do with our weather, too,
because it depends on where the jet stream is at any given time.
We’re going through a cool period on the East Coast here.
We’re having some great weather in the 60s and 40s at night
and 60s in the day
and so we’re having a great spring here.
I don’t want to – I’m not looking forward
to the hot and humid July and August.
I’m having some great weather,
but it has to do with the placement of the jet streams
and a pattern of persistence in the jet streams and so forth.
And that’s an example of an oscillation.
The ENSO oscillation has to do with a change in the El Niño-La
Niña oscillations changing of the wind patterns
along the equator
and how they move water back and forth along our coast.
And that has a lot to do with changing water temperatures,
so there’s lots of spatial and time during oscillations
and they're all linked. They're globally teleconnected.
The atmosphere and the oceans are a coupled system
and it’s a very complex system that we don’t fully understand.
We call them “oscillations”.
That doesn’t mean they're periodic.
We see lots of ENSO La Niña-El Niño oscillations,
but they aren’t all the same all the time
and they don’t happen periodically like clockwork.
Okay, well, thank you so much, Steve,
for your time this evening.