El Niño of 2015 and the End of Global Warming Hiatus: Insights from a Semi-Empirical Model of Global Mean Surface Temperature

Global mean surface temperature (GMST) has steadily risen since the mid-19^th century, and at the same time experienced significant variations on interannual and decadal timescales. Various mechanisms have been proposed to explain such variations, ranging from the Pacific decadal oscillation to volcanic eruptions. In this study, we construct a simple, physically-based model of GMST variations that incorporates greenhouse gas emissions, ENSO forcing, and stratospheric sulfate aerosols. The model closely reproduces the history of GMST changes since 1880 with the mean squared error about 0.05°C for the past 60 years, much smaller than the typical error of GMST observations. It also accurately captures decadal GMST variations, including the global warming hiatus in the early 21^st century.

This model can be used to understand the causes of the observed GMST variations and requires little computational resource. For example, our results confirm that weak El Niño activity, rather than volcanic eruptions, was the major cause of the hiatus, while the rapid temperature rise since 2014 is due to atmospheric heat release during 2014-2016 El Niño conditions concurrent with the continuing global warming trend. The model can be also used to make predictions for next-year GMST in the short term, and the future climate projections in the long term. The implications of this simple model for paleoclimate reconstructions and GCM performance evaluations will also be discussed.