Tuesday, February 12, 2013

Book Review: The Ocean of Life

by Nick Cunningham

Photo: NOAA
Most of everyday discussion about climate change revolves around how many degrees the global temperature will rise over the coming decades, how severe and frequent the natural disasters will be, or how charismatic species like the polar bear will fare in a warming world.

Hurricanes and drought make it onto the front pages, but changes to the world's oceans often get overlooked. Considering that 1 billion people (1 out of every 7 people in the world) rely on fish for their primary source of protein, this is surprising.

I am currently reading a book that translates into accessible language some of the challenges ocean life faces due to climate change. The Ocean of Life by Callum Roberts made it onto my radar from The Economist, which named it one of the best books of 2012.  While there is too much to cover in one blog post, I'll cover a few of the sections that really struck me.

Getting through the beginning is a bit of a slog, as Roberts covers a gazillion years of ocean history. But, after the first chapter, the book becomes much more interesting and applicable to our current climate predicament.

For example, ocean chemistry and atmospheric chemistry tend to be linked, with gases in the air in equilibrium with gases absorbed in the ocean.  This means that all the carbon dioxide we are releasing into the atmosphere from burning fossil fuels is been taken up by the oceans. In fact, the oceans absorb about 30% of all the CO2 released. This helps us humans in terms of climate change - without that process we would be in much worse shape.

However, sucking up all that CO2 is making the ocean more acidic. On the pH scale, a measure of acidity, the ocean has dropped by 0.1 units to 8.1 since preindustrial times (pure water is 7.0 and is in the middle of the scale). So, the oceans are still pretty alkaline, but becoming much more acidic. This is already having dire consequences for ocean life. Acidity makes it difficult for 'calcifying organisms' - or anything that builds an external shell - to build their shells and skeletons. In other words, they are dying. This includes coral reefs, crabs, shrimp, lobsters, snails, other crustaceans, and countless other organisms. Much of the world's coral reefs are already becoming bleached from this process, and Roberts says some scientists are concerned that anything "built from calcium carbonate could cease to grow within our lifetimes."
Not as colorful as it used to be. (Photo: Bleached coral, NOAA)

Another troubling trend discussed by Roberts is the effect climate change is having on the flow of ocean currents, which plays a crucial role in determining the climate. The Gulf Stream brings warm water from the Gulf of Mexico, up across the Atlantic Ocean to the the Arctic. This warm water is why Europe has a mild climate even though it is at high latitudes. Paris is farther north than Montreal, but is much balmier. I was familiar with this story, but didn't realize why it happened.

The water is flowing in that direction because there is a conveyor belt that carries water around the world in one continuous loop. The conveyor belt exists because of what is known as "thermohaline circulation" - that is, movement because of disparities in temperature and salinity. As it so happens, colder water is more dense and so it tends to sink. Salty water also tends to sink lower than fresh water.

The Gulf Stream brings water to the Arctic, at which point it cools down significantly.  This causes the water to sink. Since the ocean isn't getting any bigger, the enormous amount of water being pulled down in the Arctic is offset by water being pulled up in other places. This "upwelling" occurs in key spots around the world, creating thriving fisheries (more on that below). This ocean circulation process is continuous, and is one of the determining factors of why different places have different climates.
Photo: Smithsonian

So what, who cares? Well, scientists are concerned that the Arctic may warm to the point where ocean currents do not cool when they arrive in the north. This may mean the ocean conveyor belt gets disrupted. It's difficult to model what this change would mean for climate and no one really knows what the implications are.

The ocean conveyor belt is also critical for the world's fisheries. As Roberts explains:
The ocean has two layers, surface water and the deep sea...Surface waters are warmed by sunshine. Since warm water has a lower density than cold water, this layer tends to float on top of the much cooler deep waters. There is little mixing across the boundary between the two.
Mixing happens where there is "upwelling:" water from the deep moving up towards the surface. Again, this is caused by the ocean conveyor belt. Upwelling brings nutrients from down below up to the surface, which is critical for healthy fisheries. Upwelling only occurs over 1% of the world's ocean surface, but this area represents about half of the global fish catch.

Anchovies (Photo: NOAA)
The world's largest upwelling occurs off the coast of Peru, and it is no accident that Peru has an enormous fishing sector. Anchovies are the centerpiece of Peruvian fisheries, and Peruvian anchovies account for 1/10 of the entire global fish catch! Peruvian anchovies are ground up and made into fish meal to feed other fish (so that your salmon can grow nice and fat). Peru is the world's top producer of fish meal.

Back to climate change. Our inability to reduce carbon emissions from all the fossil fuels we consume is gradually heating the planet. This is causing disruptions in the complex marine ecosystems - acidification is gradually wiping out entire species. And warming waters may throw ocean currents out of whack, putting global fisheries - and the 1 billion people who depend on them - at risk.

Check out The Ocean of Life. Good book.

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