The slope of the temperature data did change when the Arctic opened.
When the oceans are warm and the Arctic opens during the warm season, it snows much more and the warming cycle bounces off of the upper limit. That causes the slope of the temperature data to change. No warming for seventeen years does follow and no warming for a hundred years will follow and more than that will follow into the next cold period similar to the Little Ice Age.
I took this plot from John Nielsen-Gammon's "Climate Abyss" ,Global Temperature Anomaly Forecasts, January 2013, and added the dotted lines to show the new slope for recent data. The actual data is unchanged. There is a link to "Climate Abyss" on my LINKS Page.
