Welcome to Just Have Another Think. Our bi-weekly look at the ecological, environmental and social
impacts of the climate emergency. The increase in atmospheric warming from all the greenhouse
gas emissions we humans have created since the beginning of the industrial revolution
would quite possibly have already wiped out our species and most other land-based animals if it
wasn't for one major feature of our planet - the oceans. Our oceans are very big indeed, I think we
can all agree on that. They cover 71% of the surface of earth at an average depth of about
12 000 feet or just under 4 000 metres, and by the way if you're wondering where the deepest bit is
it's a place quite appropriately called Challenger Deep at the southern end of the Mariana Trench, in
the Western Pacific. This abyss of water reaches a depth of thirty six thousand two hundred feet
that's eleven kilometres or nearly seven miles straight down. The water in our world today is
all the water that has ever existed and all the water that will ever exist on our planet,
and 97% of it is currently held by our oceans. According to this 2019 IPCC report,
these vast bodies of water have absorbed about a third of all the carbon dioxide we've emitted
since 1750 and more than 90% of the resulting extra heat in the overall earth system.
Water is actually very good at absorbing CO2 but the reactions that take place on an ocean
wide scale as a result of CO2 absorption are enough to give you a headache! So I took a couple
of paracetamol about half an hour ago and now I'm ready to dive in - if you'll forgive the pun!
Here's what happens as carbon dioxide is dissolved in water. CO2 plus H20 becomes H2CO3, which is
carbonic acid. That's fairly basic chemistry that I vaguely remember from school. And if you stick
one of these ph probes into a glass of sparkling water you do indeed get a ph value on the acidic
side of neutral. But in our oceans that's just the beginning of the process. Carbonic acid molecules
can release one of their hydrogen ions to make a bicarbonate. Then the bicarbonate can release
another hydrogen ion to become a simple carbonate. At normal temperature and alkalinity levels
carbonates can combine with calcium that's leached out from rocks and organisms and soils and been
transferred via rivers into our oceans. Calcium and carbon, unsurprisingly, make calcium carbonate
and that's what forms the shells of shellfish and the vast skeletal structures that coral polyps can
grow on. About a century ago the surface of our oceans had an average ph value of about 8.25
which as this chart shows is clearly on the alkaline side of neutral. The ocean surface
today has an average ph of about 8.14 which on the face of it really doesn't sound all that
different does it? But the ph scale is logarithmic which is scientific jargon that means that on this
scale two is no longer one more than one, it's ten times more than one, and three is ten times more
than two and a hundred times more than one and so on and so on. So a reduction from eight point
two five to eight point one four on the ph scale actually represents a 30 decrease in alkalinity.
But ph 8.14 is still alkaline, so what's the problem? Well according to our scientists that move
towards acidity is a significant shift because the reaction of CO2 and water is reversible
and that reversibility depends entirely on temperature and alkalinity. As CO2 concentrations
increase and more and more of the free hydrogen ions become available, the simple carbonates
that were previously happy to hook up with calcium to make shells and coral skeletons
now tend to favor combining back up with the more abundant hydrogen ions to go back to being
bicarbonates. That's just the way nature is - it takes the course of least resistance. To show how
this complicated mechanism works the science bods created a fancy graph that they call a Bjerrum Plot.
The vertical axis shows another logarithmic scale - this one is of concentrations of carbonic acid
bicarbonate and simple carbonate. The horizontal axis shows the ph values ranging from very acidic
over here to very alkaline over here. So when the water is very acidic you get mostly carbonic
acid with just a little bit of bicarbonate going on down here. When the water reaches
ph neutral the bicarbonate combo becomes the dominant reaction. And then as the water moves
into alkaline territory the simple carbon end of the reaction becomes the most prevalent.
It's in this alkalinity 'goldilocks zone' that calcium carbonate structures in our oceans
can be created, which is good news for shells and corals and all of that. If we draw a vertical
line down at ph levels from around 100 years ago and then another one at today's ph level
you can start to see the direction of travel as more and more CO2 gets dissolved into the oceans.
Simple carbonate levels go down, and bicarbonate levels go up. That means less carbon available
to combine with calcium to make calcium carbonate which in turn means that shellfish and corals are
less able to grow or repair themselves. What isn't known with any certainty is just how much more CO2
is going to be emitted in the coming decades as a result of human activity, but if we continue our
current way of life then according to the ipcc we can expect a further lowering of average ph values
of about 0.3 to 0.4 by 2100. That'll drop the average ph level of our oceans down to about 7.8
which is very likely indeed to have a hugely negative impact on the overall system. A 2014
study by The Royal Society carried out a survey of phytoplankton called pteropods in the waters along
the Washington- Oregon- California coast in August 2011. Even a decade ago researchers found that 53%
of onshore pteropods and 24% of offshore pteropods had what they call severe dissolution
damage. The Royal Society study estimated that the incidence of severe pteropod shell dissolution
owing to anthropogenic ocean acidification has doubled in near-shore habitat since pre-industrial
conditions across this region, and is on track to triple by 2050. Now, like most things that go on in
our atmosphere and ocean there are other variables that may be influencing the process. For example,
some argue that as the waters get warmer then the metabolisms of organisms like phytoplankton
get faster, and that means they take up more carbon dioxide as they grow more quickly, which would
potentially be a good thing. But other studies, like this one from the American Geophysical Union,
suggest that the nutrients that phytoplankton need to grow are supplied from deeper waters and as the
oceans get warmer there's more temperature separation between the different depths
and so there's less mixing of the layers that make these nutrients available. That could actually be
causing phytoplankton CO2 uptake and growth to decrease, which leaves more CO2 available
to be dissolved into the water. All that extra heat energy in the oceans doesn't just contribute to
this relentless carbon and calcium cycle either. It has its own set of direct consequences too.
The IPCC say that marine heat waves are very likely to have doubled in frequency since 1982
and are also increasing in intensity as a result of the extra energy available. Around 90% of
all marine heat waves that occurred between 2006 and 2015 have been attributed to the absorption of
heat from the atmosphere caused by our greenhouse gas emissions. These events present all sorts of
problems. They certainly have the potential to cause catastrophic bleaching of coral reefs. In
fact according to this IPCC chart the risk to coral reefs is very high as temperatures
continue to rise but the impacts are also being seen in kelp forests and seagrass meadows and to
a certain extent in mangrove forests too. Seagrass meadows cover about 0.2 % of the ocean floor
but they capture 10% of the so-called blue carbon that gets dissolved into the ocean each year
and they can store that carbon for thousands of years. This 2020 paper at nature.com found
that the kelp forests on the Australian coastline were storing 30% of all blue carbon around
Australia and 3% of the global total. If we get above two degrees Celsius of warming, which looks
more and more likely as every day goes by, both these resources are in big trouble. And if we
stray towards three degrees of warming then we're severely jeopardizing coastal mangrove forests
which right now hold more carbon per unit area than all types of land-based forests on the planet.
It doesn't just end there though. Ocean warming is fundamentally altering the habitats of all marine
life. Since 1950 a large number of fish species that live in the top 200 metres of the sea have
been migrating from the warming equatorial regions towards the poles at a rate of between 15 and 30
kilometres every year, which over the course of 70 years has in some cases resulted in a displacement
of more than 2 000 kilometres that's great if you live in Greenland, but not so good for the
millions of people in equatorial regions who rely on those species for their food and livelihood.
And as the oceans get warmer the volume of the water increases, because that's what water does
when you heat it up. Around 680 million of the world's most vulnerable people live in low-lying
coastal zones - a number that's predicted to reach more than a billion by 2050. Another 65 million are
indigenous to small island developing states and if that all feels a long way away then remember
that half the world's mega cities are situated on coasts or alongside inland river estuaries
taking the total at risk from rising sea levels to 2 billion. We're already seeing the damage that
hurricanes, cyclones and storm surges are causing in many parts of the world. Once we get past
two degrees of warming then century level events will become decadal events and in some cases even
more regular than that, costing our economies several trillion dollars every single year
in damage reparation and resulting in a level of emergency human migration that will dwarf the
numbers of refugees from recent conflicts in the middle east. This map, based on real-world IPCC data
shows the areas of the world already experiencing hundred-year events every year. They're the ones
with the black circle. The purple, orange and yellow circles are areas where these events will become
annual during the middle and second half of this century if we stay on our current trajectory. If
you've tried getting property insurance on the U.S. eastern seaboard or in some of those Australian or
Japanese coastal areas, you'll no doubt already be very well aware that the financial institutions
have factored these events into their business models and are bracing themselves for the worst.
And that's why so many of our climate scientists and environmental groups are suggesting that the
question our governments should be asking is not whether we can afford to put in place
multi-trillion dollar green recovery plans, but whether we can afford not to. So that's your
midweek food for thought this week folks. I'll be back with a new episode of Just Have Another Think
in two weeks time, and I'll see you for our regular Just Have a Think program this Sunday. Bye for now.