Latest / The Climate Translation / The Shell Game

Transcript

The Shell Game · The Climate Translation

0:00
When we talk about climate change, we usually focus on the air, rising carbon dioxide,
0:14
warming temperatures, and the changing weather.
0:17
But the atmosphere isn't handling this alone.
0:21
The ocean is quietly doing a huge amount of work.
0:25
So far it is absorbed roughly a third of the carbon dioxide we as humans have released
0:32
and most of the excess heat trapped by greenhouse gases.
0:37
That buffering has slowed warming on land and bought us time, but chemistry has consequences.
0:45
Today we're going to talk about ocean acidification, the direct chemical link between the atmosphere
0:52
and the sea.
0:54
We'll look at why oceans naturally absorb carbon, what happens when that carbon dioxide
1:00
dissolves in seawater, and how small changes in chemistry can make it harder for corals
1:07
and shell-building organisms to survive.
1:11
Welcome to the podcast on Dr. Mac and this is the Climate Translation.
1:17
In earlier episodes, we've talked about the ocean as a sponge, soaking things up.
1:28
That's useful, but for ocean acidification, there's a better analogy.
1:34
Think of the ocean as a giant soda bottle.
1:37
When carbon dioxide in the air touches the ocean's surface, some of it dissolves into the water.
1:45
That happens naturally all the time, because gases tend to move from places where they're concentrated
1:52
to places where they're less concentrated.
1:55
Right now, there's a lot more carbon dioxide in the atmosphere than there used to be,
2:00
so more of it is moving into the ocean.
2:04
That process is called air-sea gas exchange, and it's one of the reasons the oceans
2:11
is such an effective carbon sink, wind, waves, and mixing constantly expose new surface water
2:19
to the air, giving carbon dioxide plenty of opportunities to dissolve.
2:26
Once carbon dioxide enters seawater, something important happens.
2:31
It doesn't just sit there as a gas. It reacts with water molecules to form a weak acid we call
2:38
carbonic acid. This is the same basic chemistry that gives soda its fizz.
2:45
When you open a bottle of soda, carbon dioxide escapes as bubbles, but when it's sealed,
2:52
that carbon dioxide is dissolved in the liquid, changing its chemistry slightly.
2:58
In a very real sense, we're slowly carbonating the world's oceans.
3:03
Now, the word acid tends to raise alarm bells, so let's be a little more precise.
3:09
The ocean is not turning into an acid. Seawater is still slightly basic,
3:15
but what's changing is the balance of chemicals dissolved in it.
3:20
Since the beginning of the industrial revolution, the average acidity of the ocean has increased by
3:27
about 30%. On the pH scale, that shows up as a very relatively small change,
3:34
but chemistry doesn't work in straight lines. Each step on the pH scale represents a large change
3:43
in the amount of hydrogen ion concentration. So a small shift in pH corresponds to a much
3:51
bigger shift in how water behaves chemically. So students often ask me if the ocean is absorbing
3:59
carbon, why hasn't it leveled off? It's because the ocean and the atmosphere are constantly
4:05
rebalancing. As long as the atmosphere carbon dioxide keeps rising, the ocean keeps taking
4:12
in more. It's following the rules of physics and chemistry, and that buffering has a real benefit
4:20
for us. By absorbing carbon dioxide, the ocean has slowed the rate of warming in the atmosphere.
4:27
Without it, climate change on land would likely be happening much faster.
4:34
But there's no free lunch when it comes to chemistry. When the ocean absorbs carbon dioxide,
4:40
it pays the price internally, through chemical change. And that brings us to the next step in the
4:46
story. Because once carbon dioxide becomes carbonic acid, it starts interacting with other chemicals
4:53
in sea water, especially the ones that marine organisms rely on to build their shells and their
5:00
skeletons. Coral reefs are often called cities in the sea. They cover less than 1% of the ocean
5:09
floor, yet they support about 25% of all the marine life. Fish shelter there, invertebrates
5:17
grow there. Entire food webs depend on the complex structures corals build. But those cities
5:25
are now facing a one-two punch. And the important thing to understand is that these punches come from
5:32
two different directions. So let's talk about heat. Corals are animals, but they don't live alone.
5:40
Inside their tissues live microscopic algae called zooxanthellae. These algae use sunlight to make
5:48
food through photosynthesis, and they share that energy with the coral. In return, the coral
5:55
gives the algae shelter in nutrients. It's a tight partnership, and it's why coral reefs can
6:01
grow in clear, nutrient-poor tropical waters. Most of the coral's energy comes from that algae.
6:10
When ocean temperatures rise even a degree or two above normal for long enough,
6:15
that partnership begins to break down. The coral becomes stressed and they expel their algae.
6:23
Without the algae, the coral loses both its color and its primary food source.
6:30
So what's left behind is the white calcium carbonate skeleton, a process we call coral bleaching.
6:39
A bleached coral isn't dead just yet, but it's starving. And if temperatures return to normal
6:45
quickly, the algae can come back. But if the heat lasts too long, the coral dies.
6:53
This is a part of the story most people have heard, but heat is only the first punch.
6:59
Even if a coral survives bleaching, it still has to build and maintain its skeleton. And that's
7:06
where ocean acidification comes in. Corals build their skeletons from calcium carbonate,
7:12
using carbonate ions dissolved in seawater as their raw material. Those carbonate ions are the
7:20
bricks of the reef. When carbon dioxide dissolves into the ocean and forms carbonic acid,
7:28
it changes the balance of chemicals in the water. Some of the carbonate ions get tied up in reactions
7:35
that make them unavailable for building skeletons. The result is that corals grow more slowly.
7:42
Their skeletons become thinner and more brittle. In extreme cases, parts of the reef can
7:47
even dissolve. And I often get students asking me, well, if corals have survived past climate
7:54
changes, why is it different this time around? It's because now corals are being hit twice at the
8:02
same time. And on a much faster timeline, heat attacks the coral's energy supply. A
8:09
acidification attacks its structural integrity. It's like trying to recover from a high fever
8:16
while also suffering from severe osteoporosis. Even if you survive the illness, your bones aren't
8:23
strong enough to support you. That combination makes recovery much harder. Reefs that bleach
8:30
repeatedly don't have time to regrow. Reefs growing in acidic water struggle to rebuild
8:38
even after temperatures cool. Storms and waves cause more damage because the skeletons are weaker.
8:45
And the consequences ripple outward. Weaker reefs protect coastlines less effectively
8:52
from waves and storm surge. Fisheries decline. Tourism suffers. Communities that depend on
9:00
reefs for food and income feel the loss directly. This is why scientists say ocean acidification
9:08
is not a future problem. It's happening now, quietly, chemically, and in ways that don't show up
9:15
on satellite images. Corals aren't just responding to warmer water, they're responding to a
9:21
fundamental shift in the chemistry of the ocean that they evolved in.
9:26
Now, at this point, let's discuss a way to break this down and make the science more understandable.
9:33
There's a great way to visualize the ocean acidification process and its impact on corals
9:41
in your very own home. And it is an experiment I have conducted in the classroom many times.
9:47
And all it takes is some vinegar and some sticks of white blackboard chalk that you can get from
9:53
the grocery store. White chalk is made of calcium carbonate. It's the same basic material corals
10:00
used to build their skeletons. What you do is break the chalk into some pieces and get a clear glass.
10:08
Add the vinegar to the glass about halfway and then drop a piece of chalk into the glass.
10:15
Almost immediately, you should see bubbles beginning to form. The chalk starts to fizz and
10:21
slowly dissolve. What you're watching is chemistry in action. The acid in the vinegar is reacting
10:28
with the calcium carbonate, breaking it down, and in the process, releasing carbon dioxide gas.
10:36
Now, while this is a great visual, let's be clear. The ocean is not turning into vinegar.
10:42
Sea water is still mildly basic on the pH scale, not acidic. But ocean acidification is about
10:50
the direction, not the extreme. As more carbon dioxide dissolves in the ocean, the chemistry shifts.
10:58
The water doesn't suddenly dissolve the coral, but it does make it harder for corals to build and
11:04
maintain their skeletons. So, a student might ask me, why don't corals dissolve like the chalk
11:11
just did? Because the ocean is a much weaker solution than vinegar. But even small chemical
11:18
changes matter when organisms are trying to build delicate structures, molecule by molecule.
11:25
It's like trying to build a brick wall while someone keeps taking bricks out of the pile.
11:31
The wall doesn't collapse instantly, but it does get weaker over time. And that's the part
11:37
that people often miss. Ocean acidification isn't a dramatic process, and a lot of times it's not
11:44
obvious. You can't see pH change from space. You can't point to a single event or place in
11:51
the ocean and say, with certainty that that was due to only ocean acidification. It's because it
11:58
works quietly, molecule by molecule, and there are a lot of interactions. But there are places where
12:04
the effects show up sooner, places that act like natural warning lights. And one of those places
12:11
is the Great Barrier Reef. The Great Barrier Reef is located in the coral sea, off the north-eastern
12:19
coast of Queensland, Australia. It stretches over 2,300 kilometers. That's about 1,400 miles.
12:26
From the tip of Cape York Peninsula, in the north, down to Bundaburg in the south.
12:32
Long-term monitoring in this area has shown that corals are growing more slowly than they did,
12:39
even a decade ago. Even when reefs survive bleaching events, their recovery is weaker.
12:46
Skeletons are thinner. Breakage from storms are more common. Another set of early warning sites are
12:53
regions with natural upwelling, like the Pacific Coast of North America. In places such as the
13:00
Pacific Northwest, Washington, Oregon, Northern California, deep ocean water, already rich in carbon
13:07
dioxide rises to the surface. As atmosphere carbon dioxide increases, that upwell water starts
13:15
to be closer to the chemical threshold that makes shell building difficult.
13:21
That's why oyster hatcheries in Washington were the first industry to feel a certification
13:27
directly. Larval oysters struggle to form shells. Sometimes failing entirely,
13:34
unless water chemistry was carefully adjusted. So why do we notice it there first?
13:40
It's because the regions are like stress tests. They experience naturally lower pH conditions,
13:46
so even small global changes push them past biological limits sooner. These places aren't
13:53
anomalies. They're previews. So what do scientists do when chemistry itself is changing?
14:00
Well, the first step is measurement. Researchers deploy sensors on reefs,
14:05
buoys, and seafloor platforms to track pH, carbonate availability, and temperature altogether.
14:13
Acidification doesn't act alone. It interacts with heat, oxygen levels, and nutrient cycles.
14:20
So next comes biological research. Some coral species and shellfish populations
14:27
show slightly higher tolerance to lower pH. Scientists are studying whether selective
14:33
breeding, assisted evolution, or microbiome manipulation can help vulnerable species survive longer.
14:41
But there's a reality check here. Those approaches don't stop acidification. They just buy
14:47
some time. There are also local mitigation strategies. Reducing pollution and nutrient runoff
14:55
helps reefs cope with stress. Protecting sea grass meadows and mangroves can locally absorb
15:02
carbon dioxide, slightly buffering nearby waters. In hatcheries, water chemistry can be adjusted
15:09
during critical life stages. All of this can help, but none of it obviously replaces the root cause.
15:17
Ocean acidification is driven by carbon dioxide in the atmosphere. As long as atmosphere at
15:23
carbon dioxide rises, the oceans will continue to absorb it, and the chemistry will continue to
15:29
change. This is why scientists are so clear on one point. There is no technological fix
15:36
that reverses ocean acidification at scale without reducing carbon dioxide emissions.
15:44
You can protect ecosystems. You can support resilience. You can slow damage locally,
15:50
but chemistry follows physics. And that brings us back to why ocean acidification matters so much.
15:58
It's not just about the corals. It's about recognizing that the ocean is responding exactly
16:03
as expected to the carbon we've added to the atmosphere. And understanding that response
16:10
helps us to see where the limits of adaptation lie.
16:22
The ocean is our life support system of our planet. It regulates climate, feeds billions of
16:27
people and quietly absorbs the consequences of what we put into the atmosphere. And right now,
16:33
it's doing exactly what chemistry says it should, taking in carbon dioxide and changing
16:39
in response. Understanding ocean acidification helps us see climate change more clearly. This
16:45
isn't just a story about hotter days or rising seas. It's about balance. It's about the chemistry
16:52
that allows corals to build reefs, shellfish to grow, and the entire food web to exist.
17:00
What makes ocean acidification so important and so unsettling is that it's largely invisible.
17:07
It doesn't announce itself with a single disaster. It works quietly, molecule by molecule,
17:13
until systems that evolved under stable conditions start to struggle. But understanding that
17:19
process gives us something powerful. It replaces confusion with clarity. It replaces
17:25
argument with evidence. And it reminds us that the atmosphere in the ocean aren't separate
17:30
problems. They're part of the same system. So the ocean is responding and how it responds depends
17:37
on the choices we make above the surface. I'm Dr. Mac and this has been the climate translation.
17:45
If you have a question about the climate that you've been too afraid to ask or if you have a
17:50
differing opinion, please let me know. I can use your viewpoints in future episodes.
17:55
You can reach me at theclimatetranslation at gmail.com. I'll see you next time.