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
No comments:
Post a Comment