What’s El Niño Up To Now?

noaa-wwtw-elninox500El Niño is here. It’s a big one.  And it has consequences both global and regional!

El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO). It characterizes the ocean part of ENSO, a phenomenon that is described by Pacific Ocean sea surface temperatures (SST) along the equator and atmospheric pressure patterns.  When the Pacific equatorial SST are notably hotter than average (like this year), that is an El Niño, and if colder, a La Niña.

El Niño is a big deal because the equatorial Pacific Ocean is an immense expanse, and temperatures along the equator have a strong influence on global wind and weather patterns. El Niño with its hot SST tends to result in high global temperatures.  It also tends to reverse some of the rainfall patterns across the Pacific ocean basin, so that many areas in the Western Pacific, that are usually quite wet, suffer droughts, and areas of South and Central America and the southern United States may all have high rainfall years.

This year’s El Niño is coming on top of what were already record breaking global temperatures

This map (upper right) from the National Atmospheric and Ocean Authority (NOAA) shows that almost the whole world (apart from the Northeast and Northernmost Atlantic) is already either much warmer than average (compared to 1980-2010), or even at record breaking levels.  The graphic shows 2014 and 2015 demonstrating that if there ever was a real pause in the rate of global warming, it is over now!  And these graphics comparing January-August periods include the first six months of 2015, before El Niño really got going.  Temperature anomalies during the fall and winter are likely to be even more extreme because El Niño, already very obvious in this map across the tropical Pacific, will be reaching its maximum development.

This has lots of important implications for weather patterns in the United States.  In the Northeast, we can expect a warm dry autumn.  This should give way to a more or less normal winter, with some potential for heavy snow at times.  It is not expected to be a repeat of the last two winters with their outbreaks of cold arctic air!

Source: NOAA

El Niño should have even more important effects for other parts of the US.  In California, suffering under its fourth year of drought and record high temperatures, the expected boost to rainfall holds both promise and peril.  It is very likely that the drought will be eased, especially in the southern half of the state where increased rainfall is most likely.  But the drought, the wildfires, and the dry baked ground, all make flooding problems more likely.  The heavy rains of a strong El Niño, as this one is expected to remain through fall and into the winter, may exact a heavy price for any drought relief it brings.

In addition, the warm temperatures predicted across the Sierra and other mountains could cause more of the winter precipitation to come as rain instead of snow.  This past year, the snow pack was only 5% of normal, the lowest it’s been in over 500 years (Belmecheri et al. 2015)!   If the mountains get lots of rain this winter, but it still results in a below-average snowpack, that doesn’t help alleviate the drought because the gradually melting snowpack is normally one of the largest summer reservoirs in California’s water supply.

And of course, El Niño is most often a one-year phenomenon, and does not ensure that the long-term drought is really over.  Indeed, a strong El Niño is often followed by a strong La Niña year, which can be associated with a lower than average rainfall in the Southwest.

This has also been a brutal fire season along the west coast from California to Alaska and throughout much of the Intermountain West.  Extreme heat and dry fuels have made for a deadly combination that has worsened each year as heat and drought persists.  While some areas, especially along the coast, have received some recent help from autumn rains, fires are still raging in many areas.

Alaska in particular had over 5 million acres burned, the second worst fire season ever after 6.6 million acres burned in 2004.  These extensive burns are of particular concern because of the potential to melt permafrost and release carbon that has been stored there for thousands of years.  In general, fire cycles intensifying due to warming global temperatures release net carbon from forest stands into the atmosphere.   Even though forests may regrow over centuries, the increasing intensity and frequency of burns can further accelerate global warming over the next several decades.

Southern California may get some relief from fire impacts too if heavy rains come this winter, but the prediction of a warmer and dryer than average winter for much of interior Alaska and the Intermountain West suggest that intense fire seasons could continue to be a major problem in some regions.

Global climate models suggest that climate change may greatly increase the frequency of very strong El Niño and La Niña events during the rest of this century.  However, not all lines of evidence agree and this is still an area of very active research (Cai et al. 2015).  These are very important issues to resolve because strong events have such large ramifications in global weather with major economic consequences as well.



Category: What's With the Weather

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