Modeling the 2000-2012 Global Warming Hiatus

Global temperature increases have been stalled since 2000. Meanwhile, the extreme summer droughts of 2011 and 2012 left many US farmers in ruins. Most climate models failed to project these phenomena correctly. US researchers now took a new attempt on finding a solution.

The hiatus in global warming since the year 2000 gives climate skeptics and climate deniers tail wind for making the case against human-caused global warming. At the same time, the extreme summer droughts of 2011 and 2012 left many US farmers in ruins. The US Department of Agriculture (USDA) estimates, more than 40 % of all US farms and almost 60 % of all US crop land were affected by severe or extreme drought, causing a record-breaking $17.3 billion in crop losses, according to the Federal Crop Insurance Program (FCIP).

Most climate models failed to predict this hiatus in global temperature rise that occurred from 2000 to 2012, despite increasing CO2 levels. Instead of a flat temperature curve, models projected an unaltered increase. Scientists from Scripps Institution of Oceanography in San Diego, CA, now present a new attempt to model this recent hiatus – with success. Yu Kosaka and Shang-Ping Xie used the Geophysical Fluid Dynamics Laboratory Climate Model 2.1 (GFDL CM2.1), but in addition to prescribing radiative forcing, they also used recorded instead of modeled sea surface temperatures from the eastern tropical Pacific. This resulted in a remarkably accurate projection of the past temperatures, especially after 2000. Their model “reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012. Their findings suggest the current hiatus is based on a “La Niña-like decadal cooling”, natural climate variability. Their model configuration also projected the current hiatus and a number of seasonal and regional anomalies, such as the recent prolonged drought across the US. Although similar conditions can occur again, the authors say, the long-term warming trend is “very likely” to continue.

Their results are published online at nature.com (subscription required for full view).

Edit (July 10, 2015):

Researchers found the extra heat content has been stored in the oceans. Veronica Nieves, Josh Willis, and Bill Patzert, researchers at NASA’s Jet Propulsion Lab (JPL) found that most of the additional heat content is stored in depth between 100 and 300 meters (300 – 1,000 ft). Their results are published in yesterday’s issue of Science Magazine (subscription required for full text).

Open Access summary: http://earthobservatory.nasa.gov/IOTD/view.php?id=86184&src=twitter-iotd