Both climate alarmists and so-called sceptics seem to agree that the recent devastating floods can be attributable, at least in part, to the La Nina conditions in the Pacific Ocean. Where the two groups differ is that alarmists are claiming or implying that human activity has also had a significant influence.
First we had Neville Nicholls, of Monash University and a former IPCC author, reported in various News Corporation outlets saying that while the link between the current “extreme La Nina event” and global warming was not clear, the record sea surface temperatures could not be disputed:
The only issue we do have with global warming is that the changes we see around Australia are partly to do with the oceans around Australia warming – it’s a pattern of La Nina – and this year they’re hotter than they’ve ever been.
Then on January 12, in a report titled “Scientists see climate change link to Australian floods”, Reuters quoted Matthew England, of the University of New South Wales:
I think people will end up concluding that at least some of the intensity of the monsoon in Queensland can be attributed to climate change … The waters off Australia are the warmest ever measured and those waters provide moisture to the atmosphere for the Queensland and northern Australia monsoon.
The same report paraphrases Kevin Trenberth, another IPCC Lead Author:
He said a portion, about 0.5C, of the ocean temperatures around northern Australia, which are more than 1.5C above pre-1970 levels, could be attributed to global warming.
You could be forgiven for getting the impression that a warmer atmosphere has caused the oceans to warm. Although only Trenberth is paraphrased as explicitly saying as much, the others seem to want to imply this.
Maybe their caveats and clarifications didn’t make it into print, or maybe there were none to begin with. Maybe they have forgotten their high school physics.
The simple fact is that according to the laws of physics, it is impossible for the atmosphere to warm any more than the top millimetre or two of the oceans. If the sea surface is made turbulent by winds then maybe a little more water will be heated, but when the ocean calms this heat will be quickly lost.
Warm air, like warm water rises. Think hot-air balloons. Cool air and cool water fall; just ask anyone who lives near the bottom of a large hill or mountain about winter nights.
If warm air touches the cold ocean then the top layer of water will warm. The air touching the water loses its heat and won’t rise because it’s now cooler than the air above. Likewise the top layer of water would be warmer than water beneath it, so it won’t fall. The warming process basically ceases before it has properly begun.
Nor can carbon dioxide warm the atmosphere directly. The radiation that it bounces back towards the Earth is absorbed in the first few thousandths of a millimetre of the ocean surface and almost immediately disappears in evaporation.
Maybe some volcanoes beneath the oceans cause a little warming but sunlight is the principal source of heat and it penetrates to around 100 metres in clear water. Clear skies and calm conditions could cause the warm oceans, just as they previously have done on the Great Barrier Reef.
It’s a very different story when the heat goes from the oceans to the air.
When warm ocean water comes in contact with cooler air, the water loses heat and the air gains heat. The water in contact with the air is now colder than the water beneath it, so it falls away and is replaced by warmer water. The air in contact with the water is now warmer than the air above it, so it rises and is replaced by cooler air. The process continues because warm water keeps being exposed to cooler air.
On top of that the heat content of water is 3300 times that of air. This means that the heat stored in one metre depth of water is equivalent to the amount of heat that could be stored in air to a height of 3300 metres above the same area as the water. In practice it doesn’t work that way because temperatures won’t be constant in those volumes of water or air, but the principle is correct and shows why a little warm water can heat a lot of air.
The same principles can even account for the warming since the middle of the last century.
The IPCC, CSIRO and Bureau of Meteorology all agree that El Nino conditions have dominated since 1976-7. La Nina events, such as the recent one, have become rare.
El Nino conditions occur when there’s little or no easterly wind in the Pacific and top 100 metres of the ocean warm, especially in the centre and western half of the ocean, and then this water in turn warms the air above. That air rises and is carried away from the tropics and ultimately warms much of the world.
La Nina conditions occur when the easterly winds push the warm surface water right across the Pacific, allowing cooler water to rise in its place. The heat is concentrated in the western Pacific, around the islands in south-east Asia. While the sea there still warms the air and it rises, the circulation takes it back above the equator to the eastern Pacific where it sinks. Because this air doesn’t spread from the equator and doesn’t act against intrusions of cold Polar air, the average global temperature is lower than with an El Nino.
The whole El Nino and La Nina system has operated for at least 125,000 years, so there’s nothing new here. Scientists haven’t found a cause of the abrupt shift in 1976 but there’s no reason to believe that it was anything other than natural. The rise in average global temperatures started shortly after that shift, driven both by warmer air and by the reduction in rainfall meaning that more energy from the sun could contribute to temperature and less to the evaporation of surface water.
Simple physics shows us that human activity is not to blame for the recent warming of the oceans around northern Australia and the same physics can account for the rise in average global temperatures that have been blamed on human activity.
The question that now bothers me is whether some of our luminaries of climate science have forgotten their basic physics or whether the media organisations distorted what they were told. Both alternatives are unhelpful and quite alarming.
John McLean is a member of the New Zealand Climate Science Coalition