Source: Why is Reuters puzzled by global warming's acceleration? ClimateConsensus-The97% blog by John Abraham and Dana Nuccitelli, Hosted by the Guardian.
Expanded quote: by Dana Nuccitelli:
"When people say 'no warming in 15 years', they're cherry picking the timeframe to begin in an abnormally hot year. It's like arguing that your car must have broken down because it hasn't moved in the 15 seconds while you've been stopped at a red light. The argument selects a short timeframe that's not representative of the whole."
Notes: Nucitelli explains that we are in time period since 1998 when the ocean is heating up more quickly than the surface.
The confusion on this subject happens because humans live at the Earth's surface, so we tend to focus on surface temperatures. Over the past 10–15 years, Earth's surface temperature has risen very slowly. Thus, some people, especially in the media, mistakenly think that global warming recently stopped.
However, only about 2 percent of global warming heats the air, whereas about 90 percent of global warming goes into heating the oceans (the rest heats ice and land masses). Over this same time period, the warming of the oceans – and the warming of the Earth as a whole – accelerated.
Since 2000, a series of La Niña events transferred more global warming heat to the oceans. As a result, the surface temperatures remained relatively cool. During the 1990s, there were more El Niño than La Niña events, which triggered more surface air warming. One of the strongest El Niño events of the 20th century happened in 1998, which not coincidentally was 15 years ago.
Image Source: www.fhwa.dot.gov