First of all, it looks like you are quoting a completely different article to defend the graph you posted. Not sure if that's intentional, but it's misleading just the same.
Now lets see what one of the researchers (John Turner) actually said about the study you are quoting here:
"In the second half of the 20th century, “the place that’s warmed the most was the Antarctic Peninsula,” said John Turner, a researcher with the British Antarctic Survey. “It’s a real hotspot of warming across the Earth.”
Now, however, Turner and a team of fellow scientists with the survey are out with a rather unexpected new finding in the journal Nature — one likely to be seized on by climate change skeptics, doubters and deniers. Since about 1998, the research finds, the Antarctic Peninsula has reversed this famous trend and cooled down again, and done so fairly significantly.
Yet Turner stresses this doesn’t mean climate change isn’t happening — only that natural variability in the region is quite large, and has recently kicked into gear for rather complex reasons. “This switch from a very very marked warming to a modest cooling is purely a local factor, and not saying anything like ‘global warming has stopped,’ ” Turner said.
Indeed, the Antarctic Peninsula has still warmed in the long run, said Eric Steig, an Antarctic researcher at the University of Washington, Seattle — whose comment on the study accompanies its publication in Nature on Wednesday. Two decades of reversal aren’t enough to change that. So it’s important to keep a sense of perspective.
“It hasn’t cooled nearly as much as it had warmed before,” Steig said."
https://www.washingtonpost.com/news/energy-environment/wp/2016/07/20/the-antarctic-peninsula-is-cooling-but-climate-skeptics-shouldnt-get-too-excited/