Hi, this is Lyle from NASA's Jet Propulsion Laboratory.
Today we're going to be talking about sea level rise
and the way that NOAA and NASA
are working to help us understand changes
that are happening in our atmosphere and in our ocean.
We're going to start by talking about sea level
and sea level rise,
and we'll start by talking about tides and water levels.
So the first thing we need to understand is what tides are.
The water level of the ocean seems to always be changing.
Tides appear as the regular rise and fall
of the sea surface.
This animation shows the relationship
between the vertical and horizontal components of tides.
As the tide rises, water moves toward the shore.
This is called a flood current.
As the tide recedes, water moves away from the shore.
This is called an ebb current.
The movement of water toward and away from the shore
is illustrated by the movement of the green seaweed.
Tides are actually long-period waves
that move through the ocean
in response to the gravitational forces
exerted by the moon and the sun.
Here we see the moon and Earth,
and we're looking at Earth from the North Pole.
You can see that red dot that represents the North Pole.
There are two yellow dots.
One represents me here in California,
and the other one is on the east coast of the United States.
And gravity from the moon pulls on the ocean,
creating a bulge of water on one side of Earth.
While the Earth rotates about a common center of gravity
between Earth and the moon, it wobbles and creates a bulge
on the opposite side of Earth.
As Earth rotates, places on the surface
will move through these high tide and low tide regions.
Here's an example of sea level changing
between high tide and low tide.
You'll notice on the left, during low tide,
much more of the beach is visible
as well as more of the bottom of the pier,
while on the right side, less of the beach is visible
and more of the pier supports are covered by water.
The line of debris on this beach marks the extent of high tide.
There are multiple debris lines
from high tides of differing heights.
Sea level is measured and recorded
at monitoring stations around the world.
Here you can see an example of a simple monitoring station,
while here you can see what is called
a sentinel monitoring station.
The sentinel looks different
because it is built to withstand a category 4 hurricane.
In addition to sea level monitoring stations,
we measure sea level with satellites.
This allows us to get a global picture of sea level.
We verify our satellite measurements
with the ground stations.
This is done using radar.
A satellite sends a radar signal towards the surface of the ocean
and times how long it takes for that signal to return.
In this global image, you can see
areas of higher water in brown and lower water in blue.
This monthly tide chart shows the difference
between high and low tide during one month
at Battery Park in New York.
These are normal changes in the sea level
that we expect to see on a daily and monthly basis.
The blue line shows the predicted tide levels,
and the red line shows what was measured.
In October of 2014,
the first quarter and last quarter moon phases
came at the beginning and the middle of the month.
During those times, we experienced
higher low tides and lower high tides,
while the full moon and new moon fell on the 8th and 24th.
During those times, we experienced
higher high tides and lower low tides.
So why do we measure and predict water levels?
I'll give you a moment to think about that.
The NOAA air gap system is a tool that measures the clearance
between the water surface and the bridge.
Air gap measurements are updated every six minutes
to account for changes in the water level and bridge height
due to traffic, air temperature, and other factors.
Data on the air gap, along with real-time data
on water conditions like tides, currents, and winds
help ship captains safely enter and leave U.S. ports.
This information is critical for ship captains
to safely navigate a ship under a bridge.
Hereyou can see theUSS New York
clearing the Huey P. Long Bridge
on June 27th of 2009,
by a margin of only 2.1 feet.
In addition to knowing water levels for the air gap system,
predicting storm surge is also important.
Storm surge is water from the ocean
that is pushed toward the shore
by the force of the winds swirling around a hurricane
or a storm.
Here you can see how having water level information
allowed storm surge warnings to be made
before Superstorm Sandy approached the Northeast.
This allowed people to evacuate affected areas
before the storm arrived, potentially saving many lives.
You can see here how storm surge impacted an area
along the east coast after the storm.
The rise and fall of the tides on a daily basis
and the changes on a monthly basis
are something that we expect to see.
Now we're going to talk about sea level rise.
NOAA calculates relative sea level trends
at U.S. and global stations
for local, regional, and global trend comparisons
generated from water level observations
collected for a minimum of 30 years
from 128 U.S. and 240 global long-term water level stations.
When looking at this map,
what do you notice about sea level trends?
You may see that around most areas in the U.S.,
sea level is rising.
This map shows sea level indicators for Baltimore.
The yellow arrow indicates
that sea level in this area is rising.
This is an example of mean sea level measured
at one of the oldest U.S. tidal stations in Baltimore
from 1902 to 2006.
By looking at this graph of the last 104 years,
you can see that mean sea level has risen
approximately 35 centimeters, or 13 inches.
Earth is a water planet
with 70% of its surface covered by water.
This image is meant to illustrate
that while we call our planet Earth
and typically look at views of the planet
with a focus on the continents,
it is mostly covered with water.
We saw that sea level was rising in Baltimore,
but what about sea level rise on a global scale?
If you saw data that looked like this,
what would you do with it?
We looked at one location, Maryland,
and saw evidence of sea level rise.
But to know if it's happening worldwide,
we need to look at data from many locations
and get an understanding of what is happening to sea level
on a global scale.
The data that you see here is a measurement
of global mean sea level change from each year, 1993-2009.
I want you to take a moment and plot these data points
and look for any trends or patterns that you see.
You might have noticed that your data points
don't line up nicely to create a linear graph,
but they do suggest a trend in the rise of sea level.
By looking at this data,
we can see that sea level on a global scale is rising.
What might account for the nonlinear graph?
Global sea level rise has changed
over the past 400,000 years.
It has varied substantially over history,
especially in response to the Ice Ages.
But in recent history, circled in red,
it has been pretty steady.
Starting around 7,000 years ago, sea level became quite steady --
again, the area circled in red.
But over the last century, sea level has been rising.
Global tide gauge measurements from tide gauges
suggests the global sea level rose
approximately 1.8 millimeters per year over the last century.
All of the areas you see highlighted in red
are at risk due to sea level rise.
We've had roughly a foot of sea level rise
in New York City in the past century.
That's measured at a tidal gauge near Battery Park,
just off the southern tip of Manhattan.
The total amount of water on Earth isn't increasing,
but the volume of liquid that fills the ocean basins
is growing, raising the elevation of the sea's surface
and spilling ocean water onto low-lying land.
So, what is causing the increase?
The extra volume of seawater comes from two places.
Clearly, melting of ice sheets and glaciers on land
adds more water to the sea.
Less obviously, water expands as it warms,
so the more heat energy the ocean absorbs,
the more space its water requires.
Global sea level is currently rising
as a result of both ocean thermal expansion
and glacier melt, with each accounting for about half
of the observed sea level rise
and each caused by recent increases
in global mean temperatures.
From 1961 to 2003,
sea level rose due to thermal expansion and glacier melt
at a rate of about 1.11 millimeters per year.
Between 1993 and 2003,
the contribution to sea level rise
increased from both sources to 2.79 millimeters per year.
So not only is sea level rising,
it is rising at a faster rate than in the past.
Now what I'd like to do is take a closer look
at the causes of sea level rise,
both ice melt and thermal expansion.
Here you can see the measured mass of glaciers declining
as they have melted over the past several decades.
Like other data, the graphs aren't straight lines,
but you can see trends in what's happening.
Where do you think the largest ice sheets and glaciers
are found?
The largest glaciers and ice sheets are found
in Greenland and Antarctica.
Here we can see the Greenland ice sheet
and its measured mass declining.
Here we can see the reduction in mass
of the West Antarctic ice sheet as it has melted.
These two regions, Greenland and Antarctica,
have the potential to cause a great rise in sea level
if they were to fully melt.
If the Greenland ice sheet completely melted,
we would see a rise of 7 meters.
If West Antarctica's ice sheet melted,
it would be an additional 7 meters of sea level rise.
If the East Antarctica ice sheet melted,
it would result in 70 meters of sea level rise.
However, the most significant contributors
to sea level rise within the current climate
are not the Greenland and Antarctic ice sheets.
What are they?
The mass balance for the Antarctic ice sheet
may represent only about 10% of the current contribution
to sea level rise coming from glaciers.
The Greenland ice sheet may be contributing about 30%
of all glacier melt to sea level rise.
That means Greenland and Antarctica only account for
about 40% of sea level rise coming from ice melt.
In contrast to polar regions,
the network of lower latitude small glaciers and ice caps,
although making up only about 4% of the total land ice area,
or about 760,000 square kilometers,
may have provided as much as 60%
of the total glacier contribution to sea level change
since the 1990s.
The contribution to sea level rise
from lower latitude ice caps and glaciers
is apparent in these before and after pictures
of Lillian Glacier in Olympic National Park.
This first image was taken in 1905.
Note the red arrows marking the boundaries of glaciers.
Compared with a picture taken in 2010.
You can see the red arrows
indicating the former extent of the glacier.
Anderson Glacier is a similar example.
Again, note the extent of the edge of the glacier,
marked by the red arrows in this picture taken in 1936.
And compare that with a picture taken in 2004.
We talked about glaciers, which are on land,
but not about sea ice. Why not?
Well, sea ice displaces water, and as it melts,
does not contribute to sea level rise.
You can see this melting ice block
does not add to the volume,
and thus does not raise the sea level.
Glaciers, however, when they melt,
add water to the ocean basins, thus raising sea level.
As we discussed before, glacier and ice sheet melt
is only part of the reason ocean level is rising.
As fluids such as water are heated,
they want to maintain a constant pressure.
In order to do that, they expand and increase in volume.
That's thermal expansion.
In the ocean, that results in sea level rise.
In this system, when the heat lamp is turned on
and the water increases in temperature,
the increase in volume will cause the water
to be pushed up through the straw.
Annually, we observe a sea level rise of about 3.1 millimeters.
0.2 millimeters comes from the Greenland ice sheet melt.
Another 0.2 millimeters comes from Antarctic ice sheet melt.
0.8 millimeters comes from glaciers and ice cap melt,
while nearly half, 1.6 millimeters,
comes from ocean thermal expansion.
This means the water is heating up.
Where is the heat coming from?
Satellites and weather stations on land show
that average air temperature at the surface is going up.
Consequently, we see an increase in the number of heat waves
and the area affected by drought.
Thermometers on ships and floating buoys
show that air near the ocean surface
is getting warmer as well,
increasing its ability to evaporate water.
In turn, we see an increase in heavy precipitation events
and flooding on land.
Measurements from satellite and weather balloons
show that the lowest layer of the atmosphere,
where we live, where airplanes fly,
and where weather occurs, is warming.
Greenhouse gases are building in this layer,
trapping heat radiated from Earth's surface,
and raising the planet's temperature.
Satellite sensors and thermometers on ships and buoys
show that the temperature of water
at the ocean's surface is rising.
Warm surface waters can damage coral reefs,
reducing opportunities for fishing and tourism,
and leave coasts vulnerable to storm surges and erosion.
It turns out the ocean can absorb a lot of heat,
and as a result, those increases in air temperature we just saw
lead to an increased water temperature.
Let's take a look at how it's able to absorb so much heat.
I have a guest here with me today
that can tell us a lot more about climate change,
Josh Willis.
Now, you're an oceanographer here at JPL, correct?
Well, I'm an oceanographer, but I study sea level rise
and global warming and really how the ocean fits into
that whole global warming picture.
It turns out that 80% to 90% of the heat from global warming
is actually going into the oceans.
So the oceans are really the big Earth heat bucket.
That's where all the heat winds up going.
The oceans can absorb
1,000 times the amount of heat as the atmosphere
without really changing their temperature all that much.
And the reason is because of something called heat capacity.
Let's imagine that this balloon represents
the whole Earth's atmosphere.
So now my candle, my little lighter here represents the sun,
so let's add some heat to it and see what happens.
Whoa!
So obviously the heat capacity of air is very low
because it didn't absorb any heat at all.
That's right.
Almost as soon as we put the candle to the balloon,
it exploded, and the reason is because
since the air inside the balloon
couldn't really absorb the heat that fast,
all the heat went toward melting the rubber.
As soon as the rubber melted, the balloon explodes.
Ah, okay, cool.
Now that's a good demonstration of the heat capacity of air.
How about the heat capacity of water or the oceans?
Yeah, let's do the oceans.
How about a water balloon, Steve?
- Sounds great. - All right.
All right, Steve, so this balloon filled with water
represents the oceans,
and my lighter here represents the sun.
Let's put some heat on it and see what happens.
Wow.
Obviously it's absorbing a great deal of heat.
Right, so you feeling the heat there, Steve?
I am.
All right, the balloon really isn't,
because it turns out that the water can absorb so much heat
that it takes the heat away from the skin of the balloon
before the rubber can melt, so the balloon doesn't pop.
Excellent example.
So the water has a tremendous ability to absorb heat,
and if that's an analog for our oceans,
that means our oceans are absorbing a lot of heat as well.
That's right. They sure are, Steve.
LYLE: As global temperatures warm, scientists expect
that the rate of sea level rise will increase.
Researchers are working to unravel the details
that will allow them to predict how much the seawater
at different depths in the ocean will warm and expand.
Scientists are also working to understand
how ice sheets on Greenland and Antarctica will react
to higher global temperatures.
If the downhill motion of these ice sheets accelerates,
sea level could rise abruptly.
So where is this heat coming from?
Since the beginning of the Industrial Revolution,
the concentration of carbon dioxide in the atmosphere
has increased by 39%.
Some of this extra carbon dioxide has been absorbed
by oceans, soils, and trees,
but the rest will stay in the atmosphere
for thousands of years.
This is significant for our climate,
because carbon dioxide is the most important gas
for controlling Earth's atmospheric temperature.
Carbon dioxide and other atmospheric gases
control Earth's temperature through the greenhouse effect.
Without a greenhouse effect, the temperature on Earth
would be much colder than it is now.
But an increase in CO2 traps heat in the atmosphere,
leading to the increases in temperature that we've seen.
So, what is the source of this additional CO2?
A majority of CO2 is created by energy production
from fossil fuels that we are demanding
to support our lifestyles.
Automobile traffic, air travel,
and coal and natural gas power plants are contributors.
Before we look at some of the impacts of rising sea level,
what do you think some of the potential impacts are?
Let's think about New York City,
the most populated city in the United States,
with over 8.4 million residents living there.
Now imagine this.
With 28 centimeters, or 11 inches, of sea level rise
predicted by the 2020s, there's a 1% chance of flooding
in the dark blue areas every year.
And with 79 centimeters, or 31 inches, of sea level rise
predicted by the 2050s,
there's a 1% chance of flooding
into the light blue areas every year,
impacting a huge number of people and businesses.
In addition to sea level rise impacting New York City,
the southeastern United States faces a great risk
from sea level rise.
Watch how much land is covered by water
with a 5-foot rise in sea level,
a 10-foot rise in sea level,
or a 15-foot rise in sea level.
Now imagine a 20-foot rise in sea level.
Sea level rise is already impacting some coastal areas.
Here you can see a home that has been made unlivable
as higher and higher sea level has eroded away
the surrounding ground, exposing septic tanks
and washing away building supports.
In American Samoa, there is only a small amount of land
between the steep mountains and the water's edge,
so you can't just back up a village a few hundred feet
when the sea level rises and be okay.
In landscapes like this, you quickly lose usable land
with sea level rise.
This is a small village in American Samoa
that will suffer major impacts with sea level rise.
American Samoa shows the severeness of the issue,
especially since there is nowhere for people to go.
The light blue line shows the current shorelines,
and the dark blue shows land, streets, and houses
that will be covered by a rising ocean.
In this simulation, note the sea wall here
that's used to protect against storm surge.
With a simulated sea level rise, you can see there's no longer
any protection for those houses
when it comes to an approaching storm surge.
As relative sea level rise increases,
it no longer takes a strong storm or a hurricane
to cause coastal flooding.
Flooding now occurs with high tides in many locations
due to climate-related sea level rise,
land subsidence, and the loss of natural barriers.
Nuisance flooding, which causes such public inconveniences
as frequent road closures, overwhelmed storm drains,
and compromised infrastructure,
has increased on all three U.S. coasts
between 300% and 925% since 1960.
The effect of rising sea levels
along most of the continental U.S. coastline
are expected to become more noticeable
and much more severe in the coming decades,
likely more so than any other climate change-related factor.
Any acceleration in sea level rise
that is predicted to occur this century
will further intensify nuisance flooding impacts over time
and will further reduce the time between flood events.
The city of Norfolk, Virginia, is already experiencing
the effects of sea level rise.
Streets that used to flood only occasionally
now fill with seawater every time there's a full moon.
The Federated States of Micronesia in the Pacific
has 30,000 citizens living on atolls that are vanishing
due to sea level rise from climate change.
Today they have drinking water shortages,
and food security is in peril.
The population of coastal watershed counties
in the U.S. and territories, including the Great Lakes,
makes up more than 50% of the nation's population
and contributed more than $8.3 trillion
to the 2011 U.S. economy,
but depend on healthy coasts.
Expected health impacts of sea level rise
include a decline in seafood quality,
shifts in disease patterns,
and increases in rates of heat-related morbidity.
So let's review.
By monitoring, we know that sea level is rising.
It's rising due to ice melt being added to the oceans
but also because of thermal expansion of water.
Ice is melting and water is expanding
because of increased temperatures.
Increased temperatures are connected
to a rise in CO2 in the atmosphere,
and a rise in CO2 is linked to human activity.
So what can we do about it?
We use energy to heat and cool our homes.
Moderating thermostats,
insulating homes as much as possible
can help reduce the increase of CO2.
We use electricity to power appliances.
Think about what's being left on
and being turned off when you leave the house.
Consider phantom charges
and using a power strip to turn off appliances.
We use cars for the majority of travel
rather than taking public transportation, carpooling,
or using alternative transport such as bikes or walking.
So those are some of the things that can be done,
but be thinking about what else can be done
and who else can make a difference.
For one of your follow-up activities,
you'll be calculating your carbon footprint
to see how much carbon you're contributing to the environment.
Thanks for joining me today.
From all of us at NOAA, NASA,
and the Jet Propulsion Laboratory,
have a great rest of your day.
Bye-bye.