Stop the Hiatus!

     There have been several hiatuses in global warming since 1880

One of the main points of evidence cited by climate change skeptics has been the hiatus in global warming observed since  1998.  For fifteen years mean annual temperatures stayed at very high levels but never exceeded the mean annual temperature the earth reached in 1998.  Climate change skeptics said that this hiatus in warming debunked the idea that the earth was warming in response to the accumulation of CO2 in the atmosphere.

Finally, in 2014, global annual temperatures reached a new record high.  

Looking at the instrumental record of global temperatures since 1880, its apparent that there have been several hiatuses (hiati?) during the last 130 years.  A very long hiatus in the rise of global temperatures occurred from the 1940s into the late 1970s, a period of almost 40 years when global temperatures never exceeded record high temperatures set in the early 1940s, and another hiatus occurred at the end of the 19th century and into the early 20th century.

There are several reasons why temperatures on a warming earth should rise and then intermittently pause, rather then warming by steady increments each year.  Perhaps the most important reason is that global warming is affecting both the atmosphere and the oceans, and the oceans can absorb huge amounts of thermal energy without greatly warming.  By some measures about 90% of the global warming that has occurred over the last century has occurred in the oceans.  The huge amounts of ocean warming have so far acted to mitigate warming in the atmosphere.

Another possible reason for the observed hiatuses in global warming may have to do with the inherent randomness of year to year weather variations.  A new climate modeling study shows that natural weather variability will tend to produce periods of hiatus in global warming even as the Greenhouse forcing increases each year due to CO2 buildup in the atmosphere.

Either way, global warming eventually will kick in again and terminate the hiatus.  The new record global temperature set in 2014 suggests the hiatus in global warming seen since the start of the new millennium is over.  If so, the Earth will start warming again, and will return to setting ever higher temperature records in the coming years.