El Niño — the periodic warming of the eastern tropical Pacific that reshapes weather around the world — appears to have grown stronger in recent decades than at any point in roughly the past millennium. That is the conclusion of a new study that reads ocean history from coral skeletons in the Galápagos Islands.
The research, led by University of Michigan paleoclimatologist Julia Cole and published in Science on August 27, found that El Niño events have been more intense over the past 40 years than in the previous 1,000.
Reading the ocean’s past in coral
Corals lay down yearly growth bands, much like tree rings. The chemistry of each band records the temperature of the water when it formed. By measuring ratios of oxygen isotopes and of strontium to calcium, scientists can reconstruct past sea surface temperatures year by year.
Writing in The Conversation, Cole explained that the team drilled cores from living corals, some 8 to 10 feet tall, around the remote northern islands of Wolf and Darwin. They also examined fossil corals found along shorelines, some up to 4,500 years old. According to Tech Times, the core reconstruction draws on 13 coral formations covering about 900 years, with the oldest sample dating to around the year 1100.
What the team found
Tech Times reports the study found El Niño events are now more than 36% stronger than before industrialization in the mid-1800s, with a 16% increase in the last 40 years alone.
“We don’t see a time in the past where El Niños have been as strong as today, and we show that the strength of El Niño changes in parallel with the warming of global temperature,” Cole said.
Cole argues the intensification is closely connected to human-caused global warming, which would suggest more extreme events as the planet keeps heating up.
Why El Niño matters
Strong El Niño years have caused enormous damage. Cole notes that the 1982–83 event triggered a marine heat wave that killed more than 95% of Galápagos corals and, by some estimates, cost the global economy as much as $4 trillion. The 1997–98 event has been linked to about 23,000 deaths.
The catch
Not everyone reads the coral signal the same way. Tech Times reports that Michael Mann of the University of Pennsylvania and John Bruno of the University of North Carolina argue the coral data may reflect general background warming of the ocean rather than changes in how El Niño itself behaves.
There is also a wider scientific debate. The Intergovernmental Panel on Climate Change’s Sixth Assessment Report found no consensus among climate models that El Niño is systematically intensifying, although newer models do project increases. The record also comes from one island group, so it captures the eastern Pacific in detail rather than the whole ocean.
Still, the study adds a long, year-by-year record to a question scientists are still debating.
Sources
- Source: WLRN / The Conversation — Galápagos corals show El Niño events are more extreme now than in past 1,000 years
- Source: Tech Times — Climate change has made El Niño 36 percent stronger, thousand-year coral record shows
- Source: Science — Climate change is strengthening El Niño, coral records suggest