The Harvard College Ocean Sciences Club was founded in spring 2015 and devotes itself to spreading knowledge of and excitement for the ocean. Members give presentations on subjects as varied as dolphins and marine geology to students at local public schools, as well as more advanced ones to their peers at the college.

Why is this winter so damn hot?

With this winter, which is fortunately almost over, bringing record highs all across the US, this has been a commonly asked question. The obvious answer would seem to be climate change—2015 was the hottest year on record, as 2014 was the year before it. However, climate change likely can’t explain just how warm the past few months have been.

To account for how warm it has been, we have to examine a phenomenon known as el Niño. During el Niño, atmospheric pressure rises over Indonesia and Australia, and falls over South America. Correspondingly, South America becomes warmer and rainier, while the Southwest Pacific gets colder and dryer. It happens every three to eight years, and can last months to years. Between occurrences of el Niño, there are often years of la Niña, where the opposite atmospheric phenomena are observed. Because of this behavior, the full name of the phenomenon is the El Niño Southern Oscillation (ENSO).

Credit: NOAACredit: NOAA

But what does something going on in the Southern Hemisphere have to do with us?

The current El Niño is one of, if not the strongest on record. From November to January, water in the equatorial pacific had been 2.3°C warmer than average, tying it with the ‘97-’98 El Niño, the strongest on record before this year.  This pocket of warm water has a strong influence on climate through its impact on the jet stream. The jet stream, which is a flow of air high in the atmosphere, influences climate in North America, and during El Niño years its deviation causes heavy rainfall on the West Coast and warmer weather as far as the North East of the United States.

El Niño also has far-reaching global effects. The changes in atmospheric pressure and precipitation impact a huge variety of industries; the damages to South American fisheries and wheat production in Australia can raise food prices worldwide.

Unfortunately, many climate scientists warn that ENSO will likely grow stronger and more frequent with the changing climate. While the link isn’t certain, oxygen isotope data from coral samples indicates that ENSO has increased in frequency and magnitude since the industrial revolution, especially since 1950. So enjoy the warm winter, but don’t be too happy that it’s happening!

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