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2013 was the second-hottest year without an El Niño since before 1850

 
El Niño Events

El Niño events like this one cause temporary warming of the atmosphere, but 2013 was hot without an El Niño event.

 

Powered by Guardian.co.ukThis article titled “2013 was the second-hottest year without an El Niño since before 1850” was written by Dana Nuccitelli, for theguardian.com on Thursday 6th February 2014 14.00 UTC

According to the global surface temperate data set compiled by Kevin Cowtan and Robert Way, which achieves the best coverage of the rapidly-warming Arctic by filling in data gaps between temperature stations using a statistical method called kriging, 2013 was the 5th-hottest year on record (since 1850). The top three hottest years (2010, 2005, and 2007) were influenced by El Niño events, which cause short-term warming of the Earth’s lower atmosphere.

Over the past decade, we’ve seen less warming at the surface and more warming in the oceans. This has been in large part due to a change in Pacific Ocean cycles. We’re currently in a cycle that tends to produce more La Niña than El Niño events, which has resulted in the oceans accumulating more heat, leaving less energy than normal to warm the atmosphere. This in turn has led to the widespread myth that the slowed rate of increase of global surface temperatures means we no longer have to worry about global warming, or that its consequences won’t be as bad as expected.

The fundamental flaw in this argument is that it neglects a key fact: cycles are cyclical. In the ’80s and ’90s when the Pacific Ocean was in the previous phase of this cycle, we saw more El Niño events and more warming of global surface temperatures than the average of climate models projected. However, we can separate out the short-term El Niño and La Niña influences from the human-caused global warming component in the simple manner first suggested by Texas state climatologist John Nielsen-Gammon, shown in this animated graphic:

Global surface temperature data from Cowtan & Way, separated into El Niño (red), La Niña (blue), and Neutral (black) years for 1966–2013, with linear trends plotted for each category.
Global surface temperature data from Cowtan & Way, separated into El Niño (red), La Niña (blue), and Neutral (black) years for 1966–2013, with linear trends plotted for each category.

The El Niño/Neutral/La Niña years here are categorized using a slightly modified approach from the one described in this post last year. In essence, a year with a significant surface cooling influence from a La Niña event is put in the La Niña category, the same for El Niño, and a year with no significant influence is put in the Neutral category.

For each of these three categories, the linear global surface warming trend for 1966–2013 is 0.16°C per decade. That is our long-term underlying global surface warming trend, caused almost entirely by human influences. Note that the colored data points tend to fall close to each of their respective trend lines. This tells us that, for example, an El Niño year today is about 0.6–0.7°C hotter than an El Niño year in the 1970s, and the same is true of Neutral and La Niña years.

What’s also interesting is that despite being a Neutral year, 2013 was hotter than 1998, which saw one of the strongest El Niño events on record. This tells us that humans have caused as much global warming over the past 15 years as a powerful El Niño event. The difference is that an El Niño is a temporary event, while human-caused global warming is permanent, unless we can quickly pull a lot of carbon dioxide out of the atmosphere.

Temperature Anomaly

Cowtan & Way global surface temperature data, with the powerful El Niño year of 1998 in red and the Neutral year of 2013 in blue.

 

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