2013 is declared "one of the warmest on record" without a push from El Niño - a key driver of hotter years

What will happen to global warming when we get the next big El Niño?

I'd like to declare a new season.

The back end of January is now the traditional time when we find out that the year we just had was one of the hottest on record.

I've no idea what we'd call this season, but it's upon us once again and it's becoming repetitive. It's been going on for a decade or more.

It's like Groundhog Day, but without the jokes and cuddly marmots.

The National Oceanic and Atmospheric Administration's National Climate Data Center says 2013 was the fourth warmest year on a record going back to 1890.

NASA says it was the seventh. For Australia, 2013 was our hottest ever.

Also at this time of year, climate science denialists feverishly yell at anyone within range of a newspaper opinion column or conservative media pundit that global warming stopped in 1998.

The World Meteorological Organization (WMO) averages the three main data sets of global temperature – the UK's Met Office, NASA's and one from the National Oceanic and Atmospheric Administration's National Climatic Data Center.

This WMO ranking actually has 1998 as the third hottest year on record, behind 2005 in second place. The hottest year was 2010, when temperatures were – on average – 0.56C above the long-term average of 14C.

NOAA's annual analysis of the global climate adds ocean temperatures and land temperatures together to make 2013 the fourth warmest on record.

In 134 years of records, NOAA says nine of the 10 warmest years have all happened since the turn of the century – with 1998 the exception. There has not been a single year in the last 37 that's been cooler than the long-term average.

Yet still climate science denialists claim global warming has paused or stopped.

Professor John Quiggin, an economist at the University of Queensland and member of the Climate Change Authority (which the Australian Government is in the process of closing down) has little patience for the warming deniers.

"Only someone completely ignorant of time series statistics could make such a claim," he says.

One thing that climate science denialists rarely point out is a key reason why 1998 was so warm (but not the warmest anymore) was that it coincided with a particularly strong El Niño.

We have not had a strong one of those since 1998, but what will happen when we do?

An El What-o?

There is a climate phenomenon known as the El Niño–Southern Oscillation (ENSO) that can impact on weather events across the planet.

Meteorologists and climatologists describe ENSO as being in three states – neutral, negative (El Niño) or positive (La Niña).

In simple terms, when ocean temperatures in the central and eastern parts of the tropical waters of the Pacific Ocean are unusually high, that's an El Niño.

It increases the chances of drought in eastern Australia and it tends to deliver hotter years globally.

This graph from NASA shows the correlation between global temperatures and La Niña years (blue bars) and El Niño years (red bars) with neutral years in gray. The lines show the trends in temperature for each.

Graph showing how temperatures continued to rise even when El Niño and La Niña events skew temperatures warmer or colder in any one year. Image: NASA

There have been three El Niño events since 1998, but they have all been considered weak.

Australia's Bureau of Meteorology says ENSO is currently neutral but adds that some computer models suggest there might be signs of an El Niño developing later this year, but the BoM urges caution.

A very strong La Niña event in 2010/11 delivered the wettest two-year period on record in Australia, which included the devastating Queensland floods.



What if 2013 had been an El Niño year?

Prof Matt England, deputy director of the Climate Change Research Centre at the University of New South Wales, told me it was important to understand that without human-caused global warming, 2013 should have been one of the coolest years on record, not one of the warmest.

In 2013, we had a neutral ENSO, we are not far out of a solar minimum where the energy from the sun is low and we also know pollution from aerosols that cool the planet has been very high. With all these factors together, I would not have been surprised if 2013 was the fourth coolest year on record. But of course, we should not be surprised because of the extra greenhouse gases in the atmosphere.



He said his own studies have shown in today's climate, a strong El Niño can raise the average surface temperatures across the globe by as much as 0.15C. For context, the ten warmest years according to NASA are separated by less than 0.1C.

Prof England again.

If 2013 had been an El Niño, we would have been smashing the record for the warmest year on record.



He said the biggest certainty for the future of El Niños is that as a climate phenomenon, it will change. He said any evidence of an increase in the number of El Niño was "not good news".

What might human emissions do to El Niño?

So England says any increase in the number of El Niños in the future would be bad news. Unfortunately that bad news has already started to drop on the doormat.

For many years, climate scientists have been looking to answer the key question – how will human-caused climate change affect El Niños?

A new study published last week in the journal Nature Climate Change found we will likely get twice as many extreme El Niño events under climate change. The study concluded.

With a projected large increase in extreme El Niño occurrences, we should expect more occurrences of devastating weather events, which will have pronounced implications for twenty-first century climate.



A study published last year found that even the nature of the El Niño would change. Published in the same journal, the study found that rainfall patterns driven by El Niño in the western Pacific (less rain) and the central and eastern Pacific (more rain) would actually intensify.

Prof England explains: