Are observations of Arctic sea ice in accord with what the IPCC forecasts says they should be? And as such is the ice reducing in an exponential or linear way?
For instance, from https://www.scientificamerican.com/article/how-the-ipcc-underestimated-climate-change/:
Projection: The IPCC has always confidently projected that the Arctic ice sheet was safe at least until 2050 or well beyond 2100. Reality: Summer ice is thinning faster than every climate projection, and today scientists predict an ice-free Arctic in years, not decades.
And then is this prediction based on the curved line on the left (found here)
or the straight one on the right (found here)
(both are from NSIDC data):