Global warming has been attributed to persistent increases in atmospheric greenhouse gasses (GHGs), especially in CO2, since 1870, the beginning of the Industrial Revolution. Nevertheless, the upward trend in global mean surface temperature (GMST) slowed or even paused during the first decade of the 21st century, even though CO2 levels continued to rise and reached nearly 400 ppm in 2013. This episode has typically been termed the global warming hiatus, or slowdown in warming. The hiatus is characterized as a near-zero trend over a certain period. The hiatus appeared during 2001-2013/2002-2012 with extremely weak interannual variability in some GMST sequences, and the slowdown in the others.