El Nino is intensifying as planet warms, study says

El Nino episodes are intensifying as the planet warms, according to a study published Thursday in Science that used coral skeleton records stretching back 1,000 years.

The research found that swings linked to the El Nino-Southern Oscillation, or ENSO, were considerably smaller during the pre-industrial period from 1000 to 1850, began rising in the late 19th century and showed “striking amplification” over the past 40 years.

ENSO variability is now roughly 36% greater in the equatorial eastern Pacific Ocean than in the pre-industrial era, largely because of stronger El Ninos, the paper found. The figure does not mean El Ninos themselves are 36% stronger, because it measures variability across the wider ocean-atmosphere system in both warm and cool directions.

Julia Cole, a University of Michigan professor and the paper's first author, said very strong El Ninos in the eastern Pacific are unusual in the context of the last 1,000 years and stand above the pre-industrial level.

Researchers used living and fossilized corals from the Galapagos Islands, off Ecuador's west coast, to build windows of monthly temperature records across the past millennium. The chemical makeup of coral skeletons reflects the conditions in which they grew, including the ratio of strontium to calcium and forms of oxygen inside the skeleton.

The team tested the observed changes against climate models simulating the pre-industrial period and found the increases were larger than anything produced from natural causes alone.

“That strengthening parallels global warming, so it appears to be related to the warming of the planet caused by human production of fossil fuels,” Cole said.

Andrew Dessler, a climate scientist at Texas A&M University who was not involved in the research, said the findings reinforced the need to move away from fossil fuels.

The research does not propose physical mechanisms for the observed changes. Cole said the corals show a trend that is happening, but “they're not a time machine to the future.”