14 DAY TRIAL // An international collaboration of experts has recently determined that air temperature can have an influence on the average duration of a standard day. The two are connected by Earth's molten core, the investigators explain.
If confirmed, the new findings could demonstrate that data about the influence humans have on the environment can be derived not only from records of the atmosphere, oceans and lands, but also from deep within the plant, thousands of miles below our feet.
In their study, scientists set out from the idea that a day has a duration that fluctuates around the 24-hour average. Winter days are milliseconds shorter than summer days, because of the way energy is exchanged between the solid Earth and the fluid motions of our planet's atmosphere and oceans.
By utilizing astronomical observations and precise geodetic methods, experts can measure all these small changes in the planet's rotation. They say that additional variations have also been discovered.
We have inter-annual (day length varies between consecutive years), decadal and multi-decadal ones, experts say. There are variations that last 80 years, or even centuries. Such an even was recorded at the beginning of the 20th century.
The length of a day was 4 millisecond off from the standard value of 24 hours. Experts recently said that this difference is too high to support a natural explanation, and set out to clear this mystery.
The flow of liquid iron within Earth's outer core was found to be the culprit, as it influences the planetary rotation by interacting with the mantle, on which all tectonic plates lie. This flow can be deduced from measurements of the planet's magnetic field on the surface.
Researchers at the NASA Jet Propulsion Laboratory (JPL), in Pasadena, California, the Universite Paris Diderot and the Institut de Physique du Globe de Paris, in France, took this a step further.
They established a link between Earth's rotation, movements in its core and the global surface air temperature. The group used two temperature records for the job, one held by the Goddard Institute of Space Studies in New York, and the other by the Met Office, in the United Kingdom.
The former extends back to 1880, whereas the British one features records from 1860 onwards.
The group than carried out a comparison: a model of the fluid planetary core movements and the averaged length-of-day observations on one hand, against the two series of temperature records.
“Researchers used results from computer climate models of Earth's atmosphere and ocean to account for temperature changes due to human activities,” the JPL team says in a press release.
“These human-produced temperature changes were then subtracted from the total observed temperature records to generate corrected temperature records,” the group explains further.
It was “found that the uncorrected temperature data correlated strongly with data on movements of Earth's core and Earth's length of day until about 1930. They then began to diverge substantially […],” they add.
“Global surface air temperatures continued to increase, but without corresponding changes in Earth's length of day or movements of Earth's core,” JPL scientists argue.
“This divergence corresponds with a well-documented, robust global warming trend that has been widely attributed to increased levels of human-produced greenhouse gases,” they conclude.
Details of the new study can be found in a paper published in the latest issue of the esteemed scientific Journal of Climate.