David Paul Morris/Bloomberg via Getty Images

High temperatures in California in 2014 helped drive widespread drought there.

This past year was the hottest since at least 1891, the Japan Meteorological Agency (JMA) said on 5 January. According to the JMA, the average temperature in 2014 was 0.27 °C warmer than the 1981 to 2010 baseline average.

This was not unexpected: in December, the United Nations' World Meteorological Organization released a preliminary analysis of temperatures from January through October 2014 pointing to a record-setting year. The UK Met Office said at the time that its data were in agreement. The US National Oceanic and Atmospheric Administration, which is set to release its final analysis on 16 January, is expected to report the same finding.

The warmth in 2014 is also notable for another reason: the absence of El Niño. Three years that were previously considered to be the hottest in the global record — 2010, 2005 and 1998 — got a boost from the weather pattern known as the El Niño Southern Oscillation, which pushes up air temperatures.

El Niño is marked by the warming of surface waters in the eastern equatorial Pacific Ocean. It occurs when oceans are warm and Pacific trade winds are weak, allowing heat from the waters to be pumped into the atmosphere.

Although Pacific temperatures were high in 2014, atmospheric conditions did not allow El Niño to form. “It is surprising to have record heat in a year without strong El Niño,” says Michael Oppenheimer, a climate scientist at Princeton University in New Jersey. It is a reminder that the Earth is heating up quickly, he adds.

The new high comes after more than a decade during which the rate of temperature rise slowed. This so-called warming hiatus began around 1998, following a particularly strong El Niño that year. Between 1951 and 2012, the average global temperature rose by 0.12°C per decade, compared with just 0.05 °C for the period from 1998 to 2012.

Although El Niño is generally thought to warm the climate, some researchers have suggested that 1998’s strong El Niño changed heat absorption in the Pacific, contributing to the warming slowdown¹.

Other researchers disagree that this period of slower temperature rises should be termed a hiatus. “The theory is that rather than a hiatus, the warming temperatures have been collecting in the bases of oceans instead,” says Anthony Barnston, chief forecaster at the International Research Institute for Climate and Society at Columbia University in New York. “But it was harder to tell because we couldn’t measure this well.”

The record warmth in 2014 does not indicate a major change in the continuing warming trend, scientists say. “It’s important to remember that we’re talking about a very small difference between this record and the last,” says Oppenheimer. The JMA's data show 2014's high to be 0.05°C higher than the previous record.

Still, he says, “this should chasten sceptics who have used the past decade’s temperatures to deny that climate change is happening. It’s a reminder that variability happens in both directions, up as well as down.”

Journal name:

Nature

DOI:

doi:10.1038/nature.2015.16674

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1. 
   David McRae • 2015-01-15 12:40 AM

   [i]"should chasten sceptics who have used the past decade’s temperatures to deny that climate change is happening"[/i] Please Nature, do not call science deniers "sceptics". Scepticism is key to science, promoting inquiry, investigation, measurements and investigations of new measurements. Denial is the prior acceptance of some "fact" and rejection of any evidence and study. We've got 2 examples in the comments - 100% of the comments to date. One rejects the reported evidence as not consistent with what he thinks he sees locally. The other brings up the debunked Urban Heat Island Conspiracy, the crank conspiracy that global temperature measurements only use urban thermometers that show warming and do not include rural, remote, or polar measurements that they assert show no warming. (Just in case you're wondering, non-urban measurements are included and show same warming as urban) Rejection of published evidence and manufacturing one's own data is not sceptical behaviour.

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2. 
   Andy Holguin • 2015-01-13 06:37 PM

   As a scientist and southern California fisherman I can attest that although El Nino did not fully rear its head it did nod in our direction. The waters off southern California were uncommonly warm all summer heading into the fall. Warm water pelagic species were found off southern California like we have not been seen in decades. If other El Ninos have caused atmospheric temperatures to rise in the past it is highly likely we are seeing a similar event tied to El Nino, even a weak El Nino, rather than Global Warming. There definitely seems to be a bias in the reporting of atmospheric temperatures. When it raises for known and unknown reasons, it is heralded by all the news media and climate scientists as further proof of Global warming, in years when it doesn't rise, as it was predicted to rise, all one hears is a deafening silence.

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3. 
   James Rust • 2015-01-10 02:00 AM

   The prediction in this paper 2014 is the warmest year in recorded history is from data from the Japan Meteorological Agency. I suspect their data is from temperature measurements across the planet from temperature measuring stations. These stations, as shown in the United States, are subject to elevated temperatures because stations once in rural areas have been absorbed into urban areas due to the urbanization of the planet's population. This is called the urban heat island effect. Satellite temperature measurements are less subject to these distortions. The University of Alabama (Huntsville) collects satellite data through the work of Prof. Roy Spenser. This data is available on the Internet. The recently posted data shows 2014 was the third warmest year in the period 1979 to the end of 2014. Warmer years were 1998 and 2010. The data is given as the change from the 30-year satellite average temperature over the period 1981 to 2010. The year 1998 had a temperature of 0.420 degrees C, 2010 had a temperature of 0.400 degrees C, and 2014 had a temperature of 0.275 degrees C. The 17-year period from 1998 to the end of 2014 contains 204 months. The satellite data shows over this time period there were 50 months with higher temperatures than individual 12 months in 2014. Examining the graph of temperatures from 1998 to the end of 2014 shows no warming taking place over the 17-year period. Over this 17-year period atmospheric carbon dioxide increased more than ten percent above the pre-industrial level. This is an indication increasing atmospheric carbon dioxide has a negligible impact on global warming (climate change). James H. Rust, Professor of nuclear engineering (ret.)

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