Days to become longer under global warming, but not by much

Global warming caused by increasing carbon dioxide in the atmosphere will lengthen the day, say a group of Belgian scientists, although this will only be by milliseconds, they say.

The researchers, from Belgium’s Royal Observatory and the Catholic University of Louvain in Belgium, used 14 different computer models to analyse the effect of increasing atmospheric carbon dioxide by 1% per year for 70 years – although they did not include the effects of other greenhouse gases.

Scientists can currently measure the length of day (LOD) to an accuracy of 1/100,000th of a second – 10 microseconds, and have found that the Earth’s rotation is affected by the movement of its non-rigid components – the oceans, atmosphere and core.

“The major effect is associated with the change in the zonal wind, which increases the LOD of some microseconds per year; this effect is compensated of about one third by the mass distribution change,” say the scientists. “The oceanic current change induces an additional increase of the LOD at the level of some tenths of microsecond per year.” Other changes associated with global warming which have an effect on day length include variations in surface pressure over land masses and average surface pressure over the ocean.

However, although the change in day length will initially be so small as to be indistinguishable from naturally occurring variations, say the researchers, on a scale of decades or longer, the phenomenon would be measurable, with an increase of around 11 microseconds per decade during this century.

The results of the research will be detailed in a paper to be published this month in the American Geophysical Union’s Geophysical Research Letters.

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