Could Climate Change give the planet circulation problems?

Well. Not exactly. But in another sense yes. Many of you will be familiar with the Gulf Stream and will know that it is responsible for bringing warm waters from the Caribbean to the UK and allowing for those summer swimming sessions in the Cornish sea. You might be thinking at this point ‘The Cornish sea is a bit cold anyway, surely global warming will make it a bit more bearable?’. Well actually, Climate Change could potentially do the complete opposite.

The image below depicts the ‘Atlantic Meridional Overturning Circulation’ or ‘AMOC’ which is essentially an ocean current that transports warm surface water from the equator to the North Atlantic and cold water from the poles down into the deep ocean where it returns to the equator, thus completing the cycle.

thermohaline
Figure 1: The Thermohaline Circulation with the AMOC in the top right box

This circulation is the reason we benefit from the Gulf Stream (Top right in red) and consequently don’t experience -20⁰C winters like in Moscow, which is at the same latitude. This circulation is driven by the cold water (which is denser) sinking in the Arctic and so driving this ‘conveyor belt’ as one could put it. But it is not that simple!

 

Global warming as we know is causing the melting of the polar ice and is effectively diluting the sea salt around the Arctic. This, combined with the increase in sea temperatures associated with global warming means the Arctic waters are considerably less dense than they should be. If this water continues to have its density reduced it may stop sinking into the deep ocean and could stop this ‘conveyor belt’ entirely. Not only would this stop us enjoying the Cornish sea in summer, but it would have similar effects across the whole globe by stopping the Thermohaline Circulation (the name for the  big ‘conveyor belt’ that exists across the globe) as a whole. This might not seem like a big deal, but if you think of the ocean’s currents in the same way as the blood of a human you begin to realise that if they stop moving, the earth (or human) is as good as gone!

As if this couldn’t get any worse, but the deep sea ocean currents are also responsible for the long term storage of carbon, mainly from carbon dioxide (CO2). Carbon dioxide dissolves easier in cold than warm water, and the ‘conveyor belt’ allows for this continuous uptake as the carbon is circulated around the globe in the same way a conveyor belt would work. Remove this circulation and the carbon uptake is significantly reduced, leaving the remaining carbon to add to the global warming effect.

So, is it going to happen? Well, the science is still uncertain but in my opinion there is a fair chance that it is already happening. The ‘switching off’ of the oceans currents is not something that is going to happen overnight but is more likely to be a gradual process where the currents slowly get weaker and weaker before eventually shutting off completely. So we are not going to lose our Cornish summer breaks just yet, but if we continue the way we are with fossil fuel consumption, the unthinkable could happen.

Here is a very good summary of the above issues

For those who are interested in finding out a bit more about the Thermohaline Circulation, below are a few academic papers.

1.                2.             3.

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