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What is the global warming hiatus, and why does it matter?

The credibility of the IPCC’s projections of 21st century climate has been called into question by a slowdown of the rate of warming in the early 21st century, relative to a more rapid rate of warming in the last quarter of the 20th century. This slowdown is referred to as the “global warming hiatus.”

Climate models can’t explain the warming from 1910-1945 or the mid-century grand hiatus

The 2013 IPCC assessment made the following statement: “the rate of warming over the past 15 years . . . is smaller than the rate calculated since 1951.” Most significantly, the observed rate of warming in the early 21st century was slower than climate model predictions. The growing discrepancy between climate model predictions and the observations has raised serious questions about the climate models that are being used as the basis for national and international energy and climate policies.

A comparison of three global surface temperature datasets is shown in Graph 1 for the period since the 1990s. The data set with the largest trend since 1998 (0.1 C per decade) is the new NOAA data set (the black line), which has a trend that is 50 per cent greater than some of the other data sets. However, even the larger NOAA trend is just below the lower end of the climate model projections for the early 21st century warming of 0.11 to 0.43 C per decade.

The warming hiatus is most clearly revealed in the global satellite data sets of lower atmospheric temperature in Graph 2.

Scientists disagree on the reasons for the discrepancies between the variations of surface temperature and the lower atmospheric temperatures. The presence of El Nino and La Nina events compounds the difficulty in interpreting trends. Scientists working with the global surface temperature datasets have predicted an 85 per cent probability that 2015 will be the warmest year on record. However, scientists working with the satellite data of lower atmospheric temperatures do not foresee 2015 as being among the warmest years.