With 2014 likely to be declared the world's hottest year on record, the last thing the planet needs is a climate shift to turbo-charge the global warming already under way.

While it's an early call, a measure of surface temperature differences in the Pacific shifted to a positive reading in the five months to November, according to the US National Oceanic and Atmospheric Administration – the longest such run in almost 12 years.

Climate experts are watching to see if a shift in a Pacific temperature gradient signals a period of accelerated warming is about to begin. Credit:Brianne Makin

Known as the Pacific Decadal Oscillation, the El Nino-like pattern typically lasts 15-30 years and is understood to operate as an accelerator on global surface temperatures during its positive phase – and a brake during its negative phase – as the ocean takes up fluctuating amounts of the extra heat being trapped by rising greenhouse gas emissions.

"It certainly could be an early sign of a change but you'd probably want to see another year or two before it's a genuine phase shift," Matthew England, a professor at the University of NSW's Climate Change Research Centre, said. "This could be the start of another ramping up of warming."