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December 07th 2009 print

Mark Imisides

DIY ocean heating

Why on earth do we attribute any heating of the oceans to carbon dioxide, when there is a far more obvious culprit, and when such a straightforward examination of the thermodynamics render it impossible.

Scarcely a day goes by without us being warned of coastal inundation by rising seas due to global warming.

Carbon dioxide, we are told, traps heat that has been irradiated by the oceans, and this warms the oceans and melts the polar ice caps. While this seems a plausible proposition at first glance, when one actually examines it closely a major flaw emerges.

In a nutshell, water takes a lot of energy to heat up, and air doesn’t contain much. In fact, on a volume/volume basis, the ratio of heat capacities is about 3300 to 1. This means that to heat 1 litre of water by 1˚C it would take 3300 litres of air that was 2˚C hotter, or 1 litre of air that was about 3300˚C hotter!

This shouldn’t surprise anyone. If you ran a cold bath and then tried to heat it by putting a dozen heaters in the room, does anyone believe that the water would ever get hot?

The problem gets even stickier when you consider the size of the ocean. Basically, there is too much water and not enough air.

The ocean contains a colossal 1,500,000,000,000,000,000,000 litres of water! To heat it, even by a small amount, takes a staggering amount of energy. To heat it by a mere 1˚C, for example, an astonishing 6,000,000,000,000,000,000,000,000 joules of energy are required.

Let’s put this amount of energy in perspective. If we all turned off all our appliances and went and lived in caves, and then devoted every coal, nuclear, gas, hydro, wind and solar power plant to just heating the ocean, it would take a breathtaking 32,000 years to heat the ocean by just this 1˚C!

In short, our influence on our climate, even if we really tried, is miniscule!

So it makes sense to ask the question – if the ocean were to be heated by greenhouse warming of the atmosphere, how hot would the air have to get? If the entire ocean is heated by 1˚C, how much would the air have to be heated by to contain enough heat to do the job?

Well, unfortunately for every ton of water there is only a kilogram of air. Taking into account the relative heat capacities and absolute masses, we arrive at the astonishing figure of 4,000˚C.

That is, if we wanted to heat the entire ocean by 1˚C, and wanted to do it by heating the air above it, we’d have to heat the air to about 4,000˚C hotter than the water.

And another problem is that air sits on top of water – how would hot air heat deep into the ocean? Even if the surface warmed, the warm water would just sit on top of the cold water.

Thus, if the ocean were being heated by greenhouse heating of the air, we would see a system with enormous thermal lag – for the ocean to be only slightly warmer, the land would have to be substantially warmer, and the air much, much warmer (to create the temperature gradient that would facilitate the transfer of heat from the air to the water).

Therefore any measurable warmth in the ocean would be accompanied by a huge and obvious anomaly in the air temperatures, and we would not have to bother looking at ocean temperatures at all.

So if the air doesn’t contain enough energy to heat the oceans or melt the ice caps, what does?

The earth is tilted on its axis, and this gives us our seasons. When the southern hemisphere is tilted towards the sun, we have more direct sunlight and more of it (longer days). When it is tilted away from the sun, we have less direct sunlight and less of it (shorter days).

The direct result of this is that in summer it is hot and in winter it is cold. In winter we run the heaters in our cars, and in summer the air conditioners. In winter the polar caps freeze over and in summer 60-70% of them melt (about ten million square kilometres). In summer the water is warmer and winter it is cooler (ask any surfer).

All of these changes are directly determined by the amount of sunlight that we get. When the clouds clear and bathe us in sunlight, we don’t take off our jumper because of greenhouse heating of the atmosphere, but because of the direct heat caused by the sunlight on our body. The sun’s influence is direct, obvious, and instantaneous.

If the enormous influence of the sun on our climate is so obvious, then, by what act of madness do we look at a variation of a fraction of a percent in any of these variables, and not look to the sun as the cause?

Why on earth (pun intended) do we attribute any heating of the oceans to carbon dioxide, when there is a far more obvious culprit, and when such a straightforward examination of the thermodynamics render it impossible.

Mark Imisides is an industrial chemist working in the private sector.