Scientists thought carbon emissions had peaked. They’ve never been higher

I think you are missing a bit of nuance in the wording. The long-form would be "Prior to reviewing the latest data, scientists were confident that carbon emissions would not surpass previous levels, and continue a downward trajectory. However, latest data show that emissions are again rising above record levels"

No they aren’t.

They thought they had peaked. IE - they thought the peak was in the past. IE - they thought emissions were higher in the past than they are right now.