El Niño Southern Oscillation (ENSO) affects extreme weather; scientists are looking to the past in hopes of finding out how the phenomenon will affect the future.

ENSO can cause droughts in Hawaii and flooding in California by pushing Pacific winter storms southward. The goal of the study was to predict El Niño by tracking its behavior over hundreds of years, according to a University of Hawaii at Manoa press release.

Researchers determined El Niño's past by studying tree rings from the last seven centuries. Tree rings can tell scientists a lot about the temperature and rainfall patterns of their time.

The team is looking at 2,222 tree-ring chronologies from the tropical and mid-latitude regions to find out the secrets of El Niño. The researchers compiled a shockingly accurate picture of ENSO's activity.

The study showed El Niño was unusually active during the late 20th century compared the earlier 700 years. This shows ENSO is sensitive to global warming, and the temperature changes could be affecting its behavior.

"In the year after a large tropical volcanic eruption, our record shows that the east-central tropical Pacific is unusually cool, followed by unusual warming one year later. Like greenhouse gases, volcanic aerosols perturb the Earth's radiation balance. This supports the idea that the unusually high ENSO activity in the late 20th century is a footprint of global warming" said lead author Jinbao Li.

The changes in ESNO could show the global effects of climate change, and call attention to how serious they really are.

"Many climate models do not reflect the strong ENSO response to global warming that we found," says co-author Shang-Ping Xie, meteorology professor at the International Pacific Research Center, University of Hawaii at Manoa and Roger Revelle Professor at Scripps Institution of Oceanography, University of California at San Diego.

"This suggests that many models underestimate the sensitivity to radiative perturbations in greenhouse gases. Our results now provide a guide to improve the accuracy of climate models and their projections of future ENSO activity. If this trend of increasing ENSO activity continues, we expect to see more weather extremes such as floods and droughts," he said.