A new analysis of global temperature data extending from 1880 to the present was published by Thomas Karl and coworkers, from the National Oceanographic and Atmospheric Administration, the
Global agreement is needed. This post reports that global warming has continued unabated for at least the last fifty years, raising average temperatures of the atmosphere and the ocean. Since this is truly a global problem it is necessary that all the nations of the world come together to implement meaningful reductions in annual rates of emission of greenhouse gases. The United Nations-sponsored negotiations involving all nations of the world are under way now, with the goal of reaching agreement on the way forward at a meeting to be held at the end of 2015. The harms from global warming already underway will only grow worse by 2100 and beyond if an agreement is not reached. All nations need to agree on limiting emissions, with the goal of transitioning to a decarbonized energy economy by about 2050. Major efforts by all nations will be needed to reach this goal.
Karl and coworkers examined three sources by which temperature averages could have provided erroneous results in AR5. An important feature of this reassessment is the use of new data sets for temperatures that were not available when AR5 was prepared. First, by far the largest number of observation stations in the world is land-based. But over the last one and one-half centuries their number has grown, and the physical settings of older stations have changed. Karl and coworkers reassessed land-based measurements accordingly, including incorporating new data sets not previously used. This process roughly doubled the number of reporting stations. An important feature of this improvement is far more authoritative reporting from the
The earlier data, such as those presented in AR5 as given by Karl and coworkers in their Supplementary Materials appendix, show a reduction in the rate of increase in global average temperature between 1950-1999 and the interval 1998-2012, from 0.101 ± 0.026 ºC/decade, to 0.039 ± 0.082 ºC/decade. It is important to note, as climate scientists have recognized, that the single temperature value recorded for 1998 was exceptionally high (see second graphic below) because it was affected by an unusually intense El Nino event. This has the effect of artificially elevating the starting point for the 1998-2012 data range, thus lowering the steepness of the trend line for this period.
The reevaluation of Karl and coworkers shows that these two temperature rates are now very similar, namely 0.113 ± 0.027 ºC/decade and 0.086 ± 0.075 ºC/decade, respectively. Thus their reevaluation shows that for the recent interval thought to experience the “hiatus”, the rate of increase of global temperature is more than double than that found earlier in AR5.