Yes, it is a fact.
Why, however, skepticism about it is increasing. Well, some people are just plain misinformed, and the press is to blame: Global-Warming Denial Hits a 6-Year High. As the author of that piece says, "Journalists take heed: Your coverage has consequences. All those media outlets who trumpeted the global warming "pause" may now be partly responsible for a documented decrease in Americans’ scientific understanding".
Others, however, are just plain stupid, and/or certifiable: Donald Trump’s Climate Conspiracy Theory.