NASA and international university researchers claim that humans have thrown off the balance between the Earth's rotation, surface air temperatures and movements in its molten core through our contribution of greenhouse gases.

Those included in the study were Jean Dickey and Steven Marcus from NASA's Jet Propulsion Laboratory, along with Olivier de Viron, from the Universite Paris Diderot and Institut de Physique du Globe de Paris in France.

It is well known that an Earth day consists of 24 hours, which is the time it takes for the Earth to make one full rotation. Over a year's time, seasonal changes occur due to energy exchanges between fluid motions of the Earth's atmosphere, the oceans and solid Earth itself, which changes the length of a day by about 1 millisecond. In addition, the length of a day on Earth can vary over longer timescales such as interannual timescales (two to 10 years) or decadal timescales (10 years).

But Earth’s oceans or motions of its atmosphere cannot explain the variances in the length of day over longer timescales. Instead, longer fluctuations are explained by the flow of liquid iron within Earth's outer core, which interacts with the mantle to determine Earth's rotation. This is also where the Earth's magnetic field originates, and because researchers cannot observe the flows of liquid iron directly, the magnetic field is observed at the surface.  

Studies have shown that this liquid iron "oscillates in waves of motion that last for decades," and have timescales that resemble long fluctuations in Earth's day length. At the same time, other studies have shown that long variations in Earth's day length are closely related to fluctuations in Earth's average surface air temperature. 

In this study, the NASA/university team of researchers has linked Earth's rotation, surface air temperatures and the movement in its molten core. They did this by mapping existing data on yearly length-of-day observations and fluid movements within Earth's core against "two time series of annual global average surface temperature." One dated back to 1880 from NASA's Goddard Institute of Space Studies in New York, and the other dated back to 1860 from the United Kingdom's Met Office.  

According to the study, temperature changes not only occur naturally, but are also affected by human activities. So researchers used computer climate models of Earth's oceans and atmosphere to generate changes made by humans. Then, these temperature changes caused by human activities were removed from the overall total observed temperature records. What they found was that old temperature data coordinated with data on Earth's day length and movements of its core until 1930, but after that, surface air temperatures increased without corresponding changes in movements of the core or day length. According to the study, this deviation after 1930 is linked to increased levels of the human contribution of greenhouse gases.  

But the new temperature data that the researchers generated (which subtracted human activity from the equation) had a temperature record that coordinated with Earth's core movements and day length, showing how human activity has thrown the Earth's climate off balance. 

"The solid Earth plays a role, but the ultimate solution to addressing climate change remains in our hands," said Dickey. 

Dickey is unsure as to why these three variables correlate, but hypothesized that Earth's core movements might interfere with the magnetic fielding of charged particle fluxes, which may affect cloud formation. This affects how much sunlight the Earth absorbs and how much is reflected back into space. 

"Our research demonstrates that, for the past 160 years, decadal and longer-period changes in atmospheric temperature correspond to changes in Earth's length of day if we remove the very significant effect of atmospheric warming attributed to the buildup of greenhouse gases due to mankind's enterprise," said Dickey. "Our study implies that human influences on climate during the past 80 years mask the natural balance that exists among Earth's rotation, the core's angular momentum and the temperature at Earth's surface." 

This study was published in the Journal of Climate.