A super El Ni帽o that is gathering strength in the Pacific Ocean may have been made worse by climate change, according to new analysis of coral records that suggest El Ni帽os have become more intense as global temperatures have climbed.
The impacts of El Ni帽o 鈥� droughts, floods and storms 鈥� are already exacerbated by rising global temperatures, because a warmer atmosphere intensifies both rainfall and droughts.
But scientists have long struggled to untangle the effect of climate change on the El Ni帽o Southern Oscillation (ENSO) cycle, which drives El Ni帽o events. Part of the difficulty is that detailed observational records only began in the 1980s. A much longer timescale than that is needed to tease out a trend from natural variability.
Advertisement
at the University of Michigan and her colleagues hope corals can provide the answer. They collected living and dead corals from around the Galapagos Islands in the eastern Pacific ocean, where El Ni帽os first develop.
They used uranium and thorium dating to identify the age of the corals, then analysed the chemistry of their skeletons to track changes to sea temperatures during their lifetime. In that way, they built a time series of sea surface temperatures in the eastern Pacific spanning the past 1000 years.
El Ni帽o and La Ni帽a events are measured by changes to sea surface temperatures in the Pacific, so by building this time series, Cole and her colleagues could track the fluctuating ENSO cycle through the centuries.
鈥淭he chemistry of the coral skeleton preserves a record of the environment in which it grew, and certain aspects of the chemistry are especially sensitive to temperature changes,鈥� says Cole.
The team found that, over the past 40 years, variability in the ENSO cycle has increased by 36.5 per cent compared with the pre-industrial period. This increase in variability has been driven largely by more intense El Ni帽o events, the analysis found.
The corals collected by the team covered about half the 1000-year time period. Nevertheless, Cole is confident in the overall trend identified. 鈥淚 think we show pretty clearly that the increase in variability in ENSO is tracking global temperature closely,鈥� she says.
The findings add to an that suggests the ENSO cycle is changing in response to rising temperatures. 鈥淭he evidence is better than 50-50 that climate change is affecting El Ni帽o,鈥� says at Columbia University in New York, used tree ring data to identify an increase in El Ni帽o activity in recent years.
Although the research does not include the recent El Ni帽os in 2015, 2023 and 2026, Cole says they are consistent with the trend identified by the corals. When the current El Ni帽o peaks at the end of this year, sea surface temperatures in the east-central Pacific Ocean are projected to reach 4掳C above normal, a 60 per cent increase over the old record.
at the US National Oceanic and Atmospheric Administration (NOAA) agrees. 鈥淚f the current El Ni帽o turns out to be as strong as we expect, that past decade will have witnessed three major El Ni帽os 鈥� a sequence not seen before in the instrumental record dating back to the late 19th century,鈥� he says. 鈥淚t will add to the mounting evidence that climate change is amplifying the ENSO cycle鈥� which is a concern considering the far-reaching global impacts that ENSO has on humans and natural systems.鈥�
Science
