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Global warming could shorten day, report predicts

May 7, 2007
Special to World Science  

Earth’s fa­mil­iar 24-hour day may be­come about 12 hundred-thou­sandths of a sec­ond shorter due to the long-term trend of glob­al warm­ing, a new re­port con­tends.

Along­side var­i­ous en­vi­ron­men­tal dis­as­ters that sci­ent­ist pre­dict will en­sue from glob­al warm­ing—believed to be caused by emis­sions of heat-trapping gas­es due to hu­man ac­tiv­i­ties—another ef­fect would be a re­dis­tri­bu­tion of Earth’s wa­ter. This would oc­cur be­cause of changes in wa­ter tem­per­a­tures.

Fe­lix W. Lan­derer of the Max Planck In­sti­tute for Me­te­or­ol­ogy in Ham­burg, Ger­ma­ny, and col­leagues cal­cu­lat­ed the ef­fects of this re­dis­tri­bu­tion on the Earth’s spin. This in turn de­ter­mines the length of the day.

If an ap­pre­ci­a­ble amount of the weight of ocean wa­ters re­dis­tributes it­self to­ward the poles, this re­duces the ex­tent to which the plan­et as a whole bulges at the equa­tor. This then re­sults in some­thing si­m­i­lar to what hap­pens when a spin­ning skat­er pulls her arms in to­ward her­self: the spin speeds up.

Earth may witness an analogous effect, Lan­derer and col­leagues re­ported in a pa­per pub­lished March 28 in the jour­nal Geo­phys­i­cal Re­search Let­ters. The ef­fect oc­curs be­cause a rise in ocean tem­per­a­tures would raise sea lev­els, the sci­ent­ists ex­plained. A con­si­der­able amount of ocean mass may trans­fer away from deep wa­ters to shal­lower con­ti­nen­tal shelves, the sea­beds that surround con­ti­nents.

In ad­di­tion, “the con­ti­nen­tal con­fig­u­ra­tion is such that there is a lot of shelf ar­ea es­pe­cial­ly in the high­er north­ern lat­i­tudes,” near the North pole, Lan­derer wrote in an e­mail. Thus, a move­ment to­ward shelf ar­e­as means a move­ment to­ward Earth’s ax­is of ro­ta­tion, and away from the equa­tor.

By the end of the next cen­tu­ry, enough wa­ter mass could shift to short­en the length of day by about 0.12 thou­sandths of a sec­ond, Lan­derer’s team pre­dicted. They based their cal­cu­la­tions on fu­ture ocean con­di­tions pre­dicted by the In­ter­gov­ern­men­tal Pan­el on Cli­mate Change Fourth As­sess­ment.

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Earth’s familiar 24-hour day may become about 12 hundred-thousandths of a second shorter due to the long-term trend of global warming, a new report contends. Alongside various environ mental disasters that scientist widely predict will ensue from global warming—believed to be caused by emissions of heat-trapping gases due to human activities—another effect would be a redistribution of Earth’s water. This would occur because of changes in water temperatures. Felix W. Landerer of the Max Planck Institute for Meteorology, Hamburg, Germany, and colleagues calculated the effects of this redistribution on the Earth’s spin, which determines the length of the day. If an appreciable amount of the weight of ocean waters redistributes itself toward the poles, this reduces the extent to which the planet as a whole bulges at the equator. The result is similar to what happens when a spinning skater pulls her arms in toward herself: her spin speeds up. This is what will likely happen with Earth, Landerer and colleagues reported in a paper published March 28 in the journal Geo physical Research Letters. The effect occurs because a rise in ocean temperatures would raise sea levels, the scientists explained. A con siderable amount of ocean mass may transfer away from deep waters to shallower continental shelves. A continental shelf is the shallow seabed surrounding a continent In addition, “the continental configuration is such, that there is a lot of shelf area especially in the higher northern latitudes,” near the North pole, Landerer wrote in an email. Thus, a movement toward shallow shelf areas means a movement toward Earth’s axis of rotation, and away from the equator. By the end of the next century, enough water mass could shift to shorten the length of day by about 0.12 thousandths of a second, Landerer’s team predicted. They based their calculations on future ocean conditions predicted by the Intergovernmental Panel on Climate Change Fourth Assessment.