Sound Science Bite: August 26. Has "Global Warming" Been in a Hiatus?
A research paper appearing recently in the journal Science (26 June 2015, p. 1469) questioned the existence the famous so-called "hiatus" in rising global surface temperatures over the past decade and a half. Global warming "deniers" have used this hiatus to argue that global warming is a fallacy. (In one sense this should no longer be an issue as 2014 was the warmest year since records have been kept, and 2015 shows every sign of being warmer still.) The study combines new temperature records with corrected old ones to argue that warming has continued unabated.
However, there have been valid criticisms leveled at the study, but not criticisms of the theory of human-caused climate change. One of the main criticisms has to do with the choice of time periods used for temperature comparisons in the study. For example, a climate scientist argues in Science (14 August 2015, p. 691) that natural changes in the atmosphere and ocean can at times swamp the trend of warming surface temperatures. For example, the strong El Niño in 1998 marks an unusually warm year and the beginning of the disputed hiatus. The El Niño-Southern Oscillation (ENSO) cycle is one that can affect world temperatures: generally higher during an El Niño and cooler during a La Niña. Also there is the Pacific Decadal Oscillation (PDO), the positive and negative anomalies of which, this scientist showed, were related to warming and cooling, respectively. When the PDO is positive the temperature in the NW Pacific is cooler and in the NE warmer than normal. The opposite is true when the PDO is negative. The PDO is influenced by a number of atmospheric and oceanic effects, including ENSO. And there are other natural variations besides these two.
The much argued-over hiatus is a red herring, however. There is no doubt the lower atmosphere has been warming over the past 100 years (with the exception of a real hiatus between about 1950 and 1975 due apparently to human produced air pollution that reflected sunlight, pollution that is now reduced by worldwide clean air laws). This warming took off in the late 1970s. It is clear that the atmosphere-ocean system can enhance or mask global warming. The "enhance" part is scary. We are seeing the development of an exceptionally strong new El Niño, dubbed "Godzilla". Maybe you ought to get your air conditioning system checked out.