You can be sure, or at least hope, that the many effects of climate change will be addressed this week in Paris, and I’ve got my fingers crossed for some truly meaningful progress to be made. But there is one problem that many people remain startlingly unaware of; the effect that climate change is having on the world’s oceans.
At first glance that might not seem like much of a problem. I mean, what does the ocean do for us? Right? Well it turns out it actually does an awful lot for us humans, and all these services are at risk as the effects of rising temperatures mount up.
The ocean is actually an integral part of the climate system, taking up around 90% of excess energy in the form of heat. It still continues to take up heat to this day, and is an important factor in slowing the atmospheric warming we are so much more concerned about. This heat uptake causes the ocean water column to warm as well, and it is now detectable around the globe to depths greater than 2000m. This not only has a negative effect on ocean ecosystems, but weakens it’s ability to absorb heat in the future.
This is due to the phenomenon known as “Thermohaline Circulation”, meaning the circulation of both heat (thermo) and salt (haline) within the ocean. The mixing occurs due to differences in density, which is determined by both the temperature and salinity of the sea water. The colder and more saline the water, the greater the density. This means that colder water will sink, and will rise again as it travels the worlds ocean currents and warms.
What the increasing temperature of the oceans means is that, due to the fact that a certain volume of water can only absorb so much heat, any excess heat will be taken up by the less dense water being mixed downwards, causing the lower, colder areas of the ocean to warm. This will cause warming throughout the entire water column and the Thermohaline Circulation will become stabilised, as the increasing temperatures mean that density differences will be reduced.
This means that the mixing process will be slowed, maybe even stopped altogether if the warming continues, and the transportation of heat energy around the ocean will become much less efficient. This would make the ocean much less capable of absorbing heat from the atmosphere, as there would be fewer areas of water that are cold enough to absorb a meaningful amount. So where would that heat go now? Well… nowhere. It would remain the atmosphere above the ocean, and its warming would proceed at a much faster rate due to the loss of this regulatory system.
But ocean circulation would not be the only thing affected by the ocean warming. The intensity and frequency of extreme weather would also change, as well as the extent of the areas affected by them. Cyclones and extreme weather events pick up a lot of energy from the ocean in the form of heat. The air above the ocean’s surface contains a great deal of water vapour, and as this air rises and the vapour condenses, the heat absorbed during evaporation is released into the surrounding air. This causes an expansion of the air and a decrease in pressure, which then facilitates the rising of more air from the ocean’s surface. This process feeds more energy into the cyclone or weather system, increasing it’s intensity.
A warming ocean not only increases the amount of heat energy available to these weather events, but since the warming is occurring across the globe the energy exchange can occur over a much larger area. This means that previously unaffected areas of the world may have to rapidly adapted to dealing with these storms, and a poleward shift in the zones of maximum intensity has already been observed.
I hope you’re now thinking “Wow, this could actually really fuck things up”. Well there is more bad news to come my friends, as the ocean is not only getting warmer, it also is getting more acidic. The oceans also does us the service of removing some of our CO2 emissions from the atmosphere, and has absorbed around 28% of human-produced CO2 since the start of the industrial revolution. Doesn’t sound like much? Well it’s equal to approximately 150 billion tons of the stuff.
The trend in ocean acidification is now 30 times greater then the natural variation thanks to us, and the average surface ocean pH has dropped by 0.1 unit, which is a significant increase in acidity. While the large scale effects of acidification remain unknown, it is already clear that it is affecting marine wildlife.
Certain organisms rely on Calcium Carbonate (CaCO3) to form their skeletons or shells, and it is known that CaCO3 formation is disrupted if the environment is too acidic. This can also have indirect effects on other organisms, as some CaCO3 reliant structures, such as coral reefs, provide homes for many other forms of marine life.
It is also known to be slowing the release of sulphur from the ocean and into the atmosphere. This will directly increase the amount of atmospheric warming, as gaseous sulphur contributes to the reflection of solar radiation back into space.
But it has to end there, right?! There can’t possibly be more problems. Did you even read the title? There are many more. The last issue we’ll be discussing affects us more directly, as it has to do with our food supply. Fisheries currently generate $195 billion for the US every year, and fish is a key food source for many people worldwide. Fishing stocks have usually been quite predictable and reliable, as certain populations tend to stay in certain areas. But fish populations are beginning to move, flourish, or whither, depending on the species, due to the many effects we have already discussed.
It is estimated that around 70% of fish species are shifting their ranges, according to a major survey lead by ecologist Malin Pinsky of Rutgers University. This makes fish stocks much less predictable, and it can have surprising economic and political implications.
Over the past decade, huge amounts of Mackerel began appearing of the coast of Iceland, indicating that the populations were moving further north. Iceland took advantage of this during a financial crisis in 2009, and increased the amount of Mackerel they were catching. This was not taken well by competing fleets in the EU and Norway, who had rights to the majority of the catch, claiming that Iceland’s increased Mackerel haul was affecting their own stocks.
This prompted quite a fierce debate on the science of monitoring fish populations. Parties disagreed on the size of the whole population, whether competing fleets were even catching from the same population, and even what waters should be included in the Mackerel’s range.
Luckily, it would appear that this “Mackerel War” has come to a close, with new fishing quotas being agreed on by all parties involved. But it remains a very real example of how the changing environment of the ocean can affect the world of us landlubbers.
I hope that by now you have a good idea of the problems the ocean is facing, but I’d like to point out that there is much I didn’t mention to make this post a reasonable length. Given the prominent role of the ocean in the climate system I’m surprised we haven’t heard about this in the past, and I encourage you to go and find out more. Our ignorance of what’s going on in the ocean is what allowed things to get this bad, and once we’ve educated ourselves we need to start setting up efforts to better understand and counteract these problems.
Let’s hope this at least gets mentioned in Paris, and that someone there decides that enough is enough.
- BBC News,. (2015). Mackerel quotas agreed after dispute – BBC News. Retrieved 8 December 2015, from http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-26554619
- Lavelle, M. (2015). Moveable Feast: As fish stocks move in response to warming, regulators struggle to keep pace. Science, 350(6262), 760-763.
- Met Office,. (2015). Tropical cyclone facts. Retrieved 8 December 2015, from http://www.metoffice.gov.uk/weather/tropicalcyclone/facts#energy
- Osborn, T., & Kleinen, T. (2015). 7: The Thermohaline circulation. Cru.uea.ac.uk. Retrieved 8 December 2015, from http://www.cru.uea.ac.uk/documents/421974/1295957/Info+sheet+%237.pdf/320eba6e-d384-497d-b4fc-2d2c187f805e
- Rahmstorf, S. (2015). Thermohaline Ocean Circulation. Potsdam Institute for Climate Impact Research. Retrieved 8 December 2015, from http://www.pik-potsdam.de/~stefan/Publications/Book_chapters/rahmstorf_eqs_2006.pdf
- Stocker, T. (2015). The silent services of the world ocean. Science, 350(6262), 764-765.