Overcoming La Nina, 2011 to Rank As 10th-Warmest Year

Global temperatures in 2011 will likely rank as the 10th-warmest on record, according to the World Meteorological Organization (WMO). If this ranking holds up once data from November and December come in, it would mean that 13 of the warmest years since record-keeing began have all occurred during just the past 15 years. 

Still, the 2011 figures would mark a dip from last year, which was tied as the warmest year on record. Some people might think this means that planet is no longer warming, but that wouldn't be a valid conclusion in any case. Global warming doesn't mean the globe will literally be warmer each year than it was the year before. It's an overall upward trend over a period of decades: no individual year means much by itself.

What's remarkable, in fact, is that temperatures in 2011 did not cool off more than they did. The the fact that they didn't may be just another indication that manmade global warming is really happening.

For much of this year, an unusually intense La Niña event — the strongest in at least 60 years — took place in the tropical Pacific Ocean. La Niña, which is part of a natural climate cycle, is characterized by a large area of cooler than average sea surface temperatures near the equator. Through a series of interactions between the ocean and air above it, these cooler waters can help reconfigure global weather patterns. In 2011 alone, La Niña has been implicated in everything from the (still ongoing) Texas drought to historic flooding in eastern Australia and southern Asia this year.

Anomalies in global average surface temperatures for La Niña and other years. Credit: WMO.

According to the WMO, La Niña typically lowers global average surface temperatures by between 0.10°C to 0.15°C compared to the years preceding and following them. “2011's global temperatures followed this pattern, being lower than those of 2010, but were still warmer than the most recent moderate to strong La Niña years,” the WMO stated in a press release. 

The WMO chart above illustrates this by showing global average surface temperature departures from average during La Niña and other years. It's clear that this year was likely the warmest year with a strong La Niña event.

This raises an intriguing question: Is warming, due in part to manmade greenhouse gases, such a dominant trend now that natural climate cycles like La Niña are no longer as big of a player in determining trends in yearly average temperatures?