They know this because every other bold prediction they have made about snow, drought, hurricanes, tornadoes, etc ….  has turned out to be a total farce.

They pulled exactly the same stunt in 2007.

“In hindsight, probably too much was read into 2007, and I would take some blame for that,” Serreze said. “There were so many of us that were astounded by what happened, and maybe we read too much into it.”

Tricky Sea Ice Predictions Call for Scientists to Open Their Data | Wired Science | Wired.com