Tuesday, December 31, 2013

El Nino, hurricanes, climate change: a year-end update

It’s easy to overlook the El Nino phenomenon when we haven’t had one for a couple of years.

The latest forecast from the National Oceanic and Atmospheric Administration is that El Nino neutral conditions will continue at least through summer, but that chances of a new El Nino increase then. The last significant El Nino was nearly four years ago. 

El Nino is that oscillating climate pattern that has dramatic impacts on rainfall and drought, storm frequency and strength, wind patterns and many other parts of the climate picture. When the pattern is on the warm side, it’s called El Nino, and when conditions are cooler, it’s La Nina.

A strong El Nino  involves unusually warm equatorial waters south of Hawai`i and toward the American coast. In the Islands, the main concerns are that it can be associated with more hurricanes, and with drought in winter, when we normally count on rainfall to make up for summer dryness.

They seem to show up every two to five years. In the past two decades, we have seen them in 1991-92, 1994-95, 1997-98, 2002-03, 2004-05, 2006-07 and 2009-10. So, it’s been since the late spring of 2010, so you might say we’re due.

And indeed, the forecast suggests an increasing likelihood of an El Nino developing around the middle of 2014. Says NOAA: “Neutral is favored into the Northern Hemisphere summer 2014, with an increasing chance for the development of El Nino.” But it says some of the computerized climate models suggest it could still remain neutral.

We have had a very quiet decade thus far in Hawaiian waters on the hurricane front. Only two hurricanes made it into the Central Pacific in 2013: Flossie and Henriette, and both were largely played out by the time they made it to Hawai`i. In 2012, there was just one, Hurricane Daniel, and in 2011 and 2010, none. 

Could that change in 2014? It could. There are normally four to five named storms in our region each year, and that number rises somewhat in El Nino years. (Named storms include both tropical storms and hurricanes.)

For more on hurricane forecasts, check out this site from the NOAA Hurricane Forecast Improvement Program.  That's where the hurricane image at the top of this post is from.

Moving onto a related topic, a paper published a couple of months ago said that El Nino events
during the late 20th century have been significantly more common than in the previous half millennium.

Researchers from the University of New South Wales, the University of Hawaiʻi at Mānoa's International Pacific Research Center and the NOAA Geophysical Fluid Dynamics Laboratory, reconstructed past climate by applying new techniques to clues found in lake sediment, corals and tree rings.

They found that El Nino activity—often referred to as ENSO for El Nino Southern Oscillation-- was more active during 1979-2009 than during any other 30-year period between 1590 and 1880.

“Our results represent a significant step toward understanding where current ENSO activity sits in the context of the past,” said UH Mānoa Professor Axel Timmermann, co-author of the study.

The paper’s lead author, Shayne McGregor, said there are tantalizing clues linking El Nino to climate change, but not yet enough evidence to prove a link.

“Climate models provide no clear indication of how ENSO activity will change in the future in response to greenhouse warming, so all we have to go on is past records.

"We can improve the projections of climate models, however, by selecting those that produce past changes in ENSO activity consistent with the past records. Our new estimates of ENSO activity of the past 600 years appear to roughly track global mean temperature, but we still don't know why,” McGregor said.

Citation: S. McGregor, A. Timmermann, M. H. England, O. Elison Timm, and A. T. Wittenberg: Inferred changes in El Niño–Southern Oscillation variance over the past six centuries. Clim. Past, 9, 2269–2284, 2013. doi:10.5194/cp-9-2269-2013

© Jan TenBruggencate 2013

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