Editor’s comments

In the State of the Climate in 2008, it was reported that based on experimental observations it appears that the global temperature rise has slowed in the decade after 2000. The trend for January 1999 to December 2008 is +0.07±0.07°C per decade, much less than the 0.18°C per decade recorded between 1979 and 2005.

A number of studies have attempted to explain the apparent pause. A new study attributes the slowdown to an increase in ocean heat uptake and reports that most of the excess energy was absorbed in the top 700 m of the ocean, 65% of it in the tropical Pacific and Atlantic oceans.

The new study, which is based on observations and computer models, showed that natural La Nina weather events in the Pacific around the year 2000 brought cool waters to the surface that absorbed more heat from the air.

According to a Reuters article, Kevin Trenberth, of the U.S. National Center for Atmospheric Research, has said that warmth is spreading to ever deeper ocean levels and that pauses in surface warming could last 15-20 years. A very recent observational-based reanalysis of the time evolution of the global ocean heat content for 1958 through 2009 has shown that ocean heating has continued during the recent upper-ocean-warming hiatus, but the heat has been absorbed in the deeper ocean. In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend.

The latest observed global temperature anomalies from the Climate Research Unit and the Hadley Centre of the UK Met Office based on HadCRUT4 data.