evidence: According to a new NOAA analysis, the warming trend during that period was somewhat smaller than the longer-term (1951-2012) trend, but it wasn’t zero. And with the latest data calibrations and the most recent two years of global temperatures added to the series—including record-warm 2014—the warming experienced since 1998 is on par with the rate observed in the second half of the 20th century. [...] The long-term trend—change over the course of a century or more—is what defines "global warming," not the change from year to year or even decade to decade. Rising emissions of carbon dioxide and other greenhouse gases since the Industrial Revolution explain most of the overall warming trend over the past century, and the rate of emissions has not slowed significantly in the recent past. So what else has been going on in the climate system over the past decade that could account for the pause in Earth’s surface warming trend? [...] One of the most well-known natural climate oscillations—the El Niño-Southern Oscillation (ENSO) cycle—causes swings in sea surface temperatures in the tropical Pacific. Although ENSO originates in the equatorial Pacific Ocean, a strong El Niño or La Niña event is capable of bumping global temperatures upward or downward for a year or two. Since the last major El Niño event in 1997-1998, a series of La Niña events have dominated the tropical Pacific, resulting in a prolonged cooling of sea surface temperatures that has also likely stalled the rise in global temperatures.