Ok so apparently it is an article, not a bulletpoint of the other article as the ui would suggest. According to the article, some model made a while ago predicts we should only be at 1.3% warming this year and not 1.5%. That missing 0.2% is whats the mistery, so kind of misleading headline, especially if you put it in a place that doesn't make it look like an article at all. I only found out because I accidentally clicked on it.
Maybe they wrote the headline that way under the assumption that climate-change deniers wouldn't read past it (?)
Of course, here's the bottom line:
Beyond this, they're just zeroing in on variables such as volcanoes, weather patterns, ship emissions, clouds, etc. So that is apparently what the somewhat misleading headline characterizes as a "mystery".