Ocean cooling and natural cycles
Interesting to see research published yesterday from the University of East Anglia regarding the rapid cooling of the North Atlantic around 1970.
Indeed, between 1968 and 1972, the surface temperature of oceans in the northern hemisphere fell by 0.3C.
This was a particularly interesting period during the last century, when global air temperatures were falling, at a time when the burning of fossil fuels was increasing fast in the rapidly developing parts of the northern hemisphere.
The explanation of the cooling between the mid 1940s and mid 1970s, against a background of longer term warming, has by many scientists been put down to the huge increase in sulphur and pollutant particles in the atmosphere during that time, reflecting sunlight back out in space, and hence causing a net reduction in absorbed planetary heat.
This new research concludes that the cooling, between 1968 and 1972, happened too quickly for that explanation to work.
You can read more about the research in this morning's Guardian .
Readers of this blog will know that some scientists, more sceptical about the extent to which man is altering global temperatures, have long believed that the overall drop in global temperatures between the mid 1940's and mid 1970's was at least in part due to a natural cycle in the Pacific Ocean called The Pacific Decadal Oscillation (PDO), which was in a cold phase at the time.
The PDO is detected as warm or cool surface waters in the Pacific Ocean north of 20 N. During a 'warm', or 'positive', phase, the west Pacific becomes cool and part of the eastern ocean warms; during a 'cool' or 'negative' phase, the opposite pattern occurs.
It's sometimes forgotten how important the oceans are in controlling the overall temperature of the planet. After all, 70% of the earth is covered in water.
The heat capacity of land and ocean are very different. Land heats up and cools down quickly; oceans heat up and cool down much more slowly and as such influence global temperatures over much longer time scales.
This new research illustrates a point worth repeating again. Even though most scientists believe man made greenhouse gases will cause global temperatures to rise in future, natural cycles play a crucial part too - and not all natural cycles are understood.
It's only a few months back that we learned that a drop in stratospheric water vapour is thought at least in part to be the reason why global temperatures have not risen as fast as computer models had suggested in the late 1990's.
The PDO is in a cool phase once more; and the Atlantic Decadal Oscillation usually follows several years later. The cool PDO on average lasts 25-30 years. With these natural cycles it is easy to see a situation arising where global temperatures could fall - or at least the forecast rise in global temperatures because of man made greenhouse gases over the next 10-20 years may be held back by some of these natural processes
Recent data shows that global sea surface temperatures have been falling for some months. Is it only a matter of time before global air temperatures follow?
Hello, I’m Paul Hudson, weather presenter and climate correspondent for Ö÷²¥´óÐã Look North in Yorkshire and Lincolnshire. I've been interested in the weather and climate for as long as I can remember, and worked as a forecaster with the Met Office for more than ten years locally and at the international unit before joining the Ö÷²¥´óÐã in October 2007. Here I divide my time between forecasting and reporting on stories about climate change and its implications for people's everyday lives.
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