- Climate change matters to life on land,
but the oceans, they're so big.
They'll be fine, right?
(buzzing) (dinging)
When we talk about climate change,
we don't usually talk about the oceans.
Instead one of the first things we hear about
is global temperature.
That's air temperature up here where we live.
Air temperature is measured every day
by thousands of weather stations round the whole world.
Using thermometers about two meters,
or just over six feet off the ground.
When we stitch together all of those records
we get global average temperature.
The most commonly used measure
of how fast our planet is warming.
Air temperature is such a common measure of climate change
that when all the countries in the world got together
in December 2015 to hammer out the Paris Agreement,
they decided to use global temperature
to define it's targets.
The nations that signed the Paris Agreement
agreed to hold the increase in global average temperature
to well below two degrees Celsius,
that's about three and a half degrees Fahrenheit,
above pre-industrial levels.
But is global air temperature really the best measure
of how fast our planet is warming?
Many scientists would say, "No!"
Ever since the industrial revolution
carbon dioxide has been building up in the atmosphere.
It's a direct result
of using coal, oil, and natural gas for our energy.
Carbon dioxide and other gases like it
are wrapping an extra blanket around the planet,
trapping heat inside the climate system
that would otherwise radiate out to space.
Where is this heat going?
Over 90% of it hasn't been going into the atmosphere
where it can be measured by weather stations.
No, it's been going into the ocean.
And the world's oceans are warming
at much faster rates than previously thought.
Both at the surface and at depth.
How much hotter have they gotten?
As one article recently put it, ocean heat accumulation
is the equivalent of one, two, three, four,
five Hiroshima bombs
exploding every second since 1990.
Why do we care about a warmer ocean?
These record breaking ocean temperatures
we've seen in recent years
have been fueling stronger hurricanes.
They've been altering our weather pattens
and they have been profoundly affecting marine ecosystems.
Record warm ocean temperatures in 2016
exacerbated by a strong El Nino,
devastated the Great Barrier Reef.
Heat stress damaged the algae living in the coral,
resulting in bleaching.
Bleached coral can bounce back
but it takes years and most of it is lost forever.
After the 2016 event,
Australian scientists went to assess the damage.
They estimated that two thirds of the whole northern part
of the Great Barrier Reef is now dead.
You can understand why one scientist called it
the saddest research trip of his life.
Even if the world meets that two degree target
set by the Paris Agreement,
only a fraction of the world's coral reefs
that hold an amazing 25% of ocean species
are forecast to survive by the end of the century.
And it isn't just about the coral.
Around the world warmer temperatures
have been linked to increased risk of disease
in a whole range of fish, shellfish,
and even marine mammals like seals and dolphins.
Marine species are on the move too.
Trying to change where they live
to keep up with warming temperatures.
The tiny organisms that form the base of the food chain
are clocking in the fastest changes,
a poleward shift of 100 kilometers
or over 60 miles per decade for zooplankton
and over 400 kilometers,
that's 250 miles per decade for phytoplankton.
The US National Climate assessment concludes
that these changes will alter the distribution
and the abundance and the productivity
of many marine species.
This is a concern, not just for natural systems,
but for us as well,
because according to the United Nations
about a billion people around the world depend on fish
for their primary source of protein.
Most of these people live in poor developing countries.
If the marine food web falls apart, so does theirs too.
And the phytoplankton we were just talking about,
they also produce about half of the oxygen that we breathe!
And not just us,
most living organisms need oxygen to survive,
and it turns out that warmer water holds less oxygen.
So the warmer the ocean
the lower the amount of dissolved oxygen in the ocean.
It's estimated that for each degree Celsius,
or 1.8 degrees Fahrenheit that the world warms,
oxygen levels in the ocean will go down by 2%.
Now for some parts of the ocean it isn't really a big deal.
But where it really matters are the oxygen minimum zones
that lie off the coasts, just under
many of the most productive fishing areas in the world.
As climate changes these oxygen minimum zones
are expanding sideways and upwards.
This is shrinking valuable habitat for fish
effecting commercial fisheries and the local economy.
Recent die offs during temporary low oxygen events
off the coast of Oregon and the Gulf of Mexico
show how sensitive fish and shellfish can be
to oxygen levels.
And the number of dead zones around the world,
so called because most organisms can't live there
because there isn't enough oxygen,
they've been doubling each decade since the 1960s
due to both pollution and warming.
All of this sounds bad enough,
but there's one more big problem
to complete the trifecta of devastating ways
that climate change affects the world's oceans.
We know the ocean is taking up
more than 90% of the extra heat in the climate system,
but did you know the ocean is also taking up
about a quarter of all the carbon we produce
from burning fossil fuels every year?
Since the dawn of the industrial revolution
oceans have absorbed 550 billion tons of carbon dioxide.
That's the amount of carbon that would be stored
in about 150 billion trees.
Once carbon dioxide dissolves into the ocean
it turns into carbonic acid.
This lowers the pH level of the ocean making it more acidic.
That's why this problem is known as Ocean Acidification.
Why do we care?
Because a more acidic ocean
makes it more difficult for phytoplankton,
those same phytoplankton we talked about earlier
that make up the base of the food chain
and produce half the oxygen we breathe,
and makes it harder for them to form their shells
and for coral to form their skeletons too.
Acidification reduces the amount
of calcium carbonate in the water.
That's the mineral
that's one of the key building blocks for shells and reefs.
Sea creatures that do grow shells can even see them dissolve
if conditions are acidic enough.
And today the ocean is 30% more acidic
than it was 200 years ago.
We don't live in the ocean,
but we care about it all the same.
Whether it's the stunning beauty of dolphins leaping
or sea life in coral reefs swaying in the tide,
or whether it's acknowledging
the irreplaceable and fundamental services
that the ocean provides
to maintain human life on this planet,
the potential consequences of climate change
for the ocean are enormous.
Ocean heat content, oxygen levels and acidification,
these all join global air temperature
as indicators that are vital
to track the health of our planet
and the impact that human activities are having
on one of our most important resource.
(buzzing) (dinging)
(melodic music)
Thank you for watching Global Weirding.
Be sure to check out globalweirdingseries.com
every other Wednesday for a new episode.
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See you next time.
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