Thursday, 12 June 2014

Countdown to El Nino

Photo: Clive Simpson
Meteorologists and climate scientists say the world is likely to enter another El Niño weather event by this autumn upsetting 'normal' weather and driving up global temperatures further.

El Niño’s most notable characteristic is the presence of extra-warm surface water in the central and eastern equatorial Pacific ocean which tends to lead to greater average global temperatures.

Climate scientists saw a chance for 2014 to be a record temperature year even before news about the likely development of El Niño conditions - simply because temperatures continue to tick upwards.

“I would have predicted a likely top five if asked at the beginning of this year and the incipient/potential El Niño strengthens that,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, one of the leading agencies that tracks global temperatures and ranks them by year.

“We saw record global temperatures in 1998, 2005 and again in 2010 when ongoing global warming was positively reinforced by El Niño events,” he added.

“There is a good chance we will see a global temperature record this year or next if a substantial El Niño event takes hold.”

Data from ocean observing satellites and other ocean sensors indicate that El Niño conditions appear to be developing in the equatorial Pacific Ocean.

Conditions in May 2014 bear some similarities to those of May 1997, a year that brought one of the most potent El Niño events of the 20th century.

The maps above show the ten day average of sea surface height centred on 2 May 1997 (left), and 3 May 2014. Darker shades indicate where the water is warmer and above normal sea level. Shades of blue-green show where sea level and temperatures are lower than average. Normal sea-level conditions appear in white. The 1997 map is from data collected by the TOPEX/Poseidon satellite, while the 2014 data is from the Ocean Surface Topography Mission/Jason 2 satellite.

During an El Niño, easterly trade winds in the Pacific falter and allow giant waves of warm water - known as Kelvin waves - to drift across from the western Pacific toward South America.

Surface waters in the central and eastern Pacific become significantly warmer than normal, altering weather patterns and affecting fisheries along the west coasts of the Americas. El Niño can also have a significant influence on weather and climate far from the tropics.

Sea surface height is a good indicator of the amount of heat stored in the water. As the ocean warms, the surface rises; as it cools, its falls. This is due to thermal expansion and contraction; the molecules in warmer water are farther apart than in cooler water.

Above-normal sea surface heights in the equatorial Pacific indicate El Niño conditions, while below-normal heights indicate La Niña.

“What we are now seeing in the tropical Pacific Ocean looks similar to conditions in early 1997,” said Eric Lindstrom, oceanography programme manager at NASA.

“If this continues, we could be looking at a major El Niño this autumn. But there are no guarantees.”

Observations from a network of sensors within the Pacific Ocean support the satellite view, showing a deep pool of warm water that has been sliding eastward since January.

The years 1997/98 brought El Niño out of the scientific literature and onto the front pages and evening newscasts. It was one of the strongest El Niño events observed, with extreme weather impacts on several continents.

North America had one of its warmest and wettest winters on record, particularly in California and Florida. Peru, Mexico, and the rest of Central and South America endured devastating rainstorms and flooding. Indonesia and parts of Asia saw disastrous droughts.

Scientists at the Climate Prediction Center of the National Weather Service (NWS) announced in early May that they foresee a 65 percent chance of a transition to El Niño in the summer of 2014.

"There remains uncertainty as to exactly when El Niño will develop and an even greater uncertainty as to how strong it may become," NWS reported.

All this might just be bad news for climate change skeptics. We've all heard by now the claim that global warming has ‘stopped’ or is ‘slowing down’ but this assertion often takes the very warm year of 1998 as the starting point.

By deliberately beginning with a hot year it can be made to look as though global temperatures aren't rising so fast.

Global temperature anomalies from 1950-2013 from World Meteorological Organisation, with years beginning with El Niño conditions in red and years beginning with La Niña conditions in blue.

You could think of annual global temperature variations as like waves on a rising tide. The rising tide is global warming and the waves are the shorter-term natural fluctuations related to phenomena like El Niño (or its flip-side La Niña), which warm (or cool) the globe by fractions of a degree.

The reality is that, as the World Meteorological Organisation (WMO) notes, each of the last three decades has been warmer than the previous one - culminating with 2001-2010 as the warmest decade on record.

Every time the world sets another temperature record, the global warming ‘slow down’ message becomes less compelling and as we enter another El Niño the climate change skeptics may finally be running low on options.

Either they finally accept the overwhelming body of evidence that global warming is real or they can come up with a new cherry-picked counter argument. Have a guess which one they'll choose - for now, at least?

The Lighthouse Keeper is written by Clive Simpson - for more information, commission
enquiries or to re-publish any of his articles click here for contact information

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