Global Temperature in 2014 and 2015 - by James Hansen et al.

Abstract.  Global surface temperature in 2014 was +0.68°C (~1.2°F) warmer than the 1951-1980 base period in the GISTEMP analysis, making 2014 the warmest year in the period of instrumental data, but the difference from the prior warmest year (2010), less than 0.02°C, is within uncertainty of measurement.  The eastern two-thirds of the contiguous United States was persistently cool in 2014, cooler than the 1951-1980 average in all seasons.  Record warmth at a time of only marginal El Niño conditions confirms that there is no “hiatus” of global warming, only a moderate slowdown since 2000.  Global temperature in 2015 may further alter perceptions.  We discuss the prospects for the 2015 global temperature in view of the seeming waning of the current weak El Niño.

Update of the GISS (Goddard Institute for Space Studies) global temperature analysis (GISTEMP)(Fig. 1), finds 2014 to be the warmest year in the instrumental record.  (More detail is available at data.giss.nasa.gov/gistemp/ and columbia.edu/~mhs119/; Figs. 2-3 here are available on the latter web site.)  The three warmest years in the GISTEMP analysis, 2014, 2010, and 2005 in that order, can be considered to be in a statistical tie because of several sources of uncertainty, the largest source being incomplete spatial coverage of the data.  Similarly, the next warmest years in our analysis, 1998, 2002, 2003, 2006, 2007, 2009, and 2013, can be taken as a statistical tie for the 4th through the 10th in our analysis.  The 15 warmest years all occurred since 1998 (including 1998).  Year-to-year temperature fluctuations in Fig. 1 are caused mainly by natural oscillations of tropical Pacific sea surface temperatures as summarized by the El Niño-Southern Oscillation (ENSO or Niño) index (lower part of Fig. 1), which we discuss further below.

Residents of the eastern two-thirds of the United States and Canada might be surprised that 2014 was the warmest year, as they happened to reside in an area with the largest negative temperature anomaly on the planet, except for a region in Antarctica, as shown by the map in the upper left of Fig. 2.  The North American cold anomaly in

2014 contrasts with the other two warmest years, 2010 and 2005, when North America and almost all land areas had annual temperatures above the 1951-1980 climatology (Fig. 2).  The cold pattern in North America persisted through all four
season in 2014 (Fig. 3).


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