[Wonder Warthog]

"Depends on your selected time scale"

True. And I was referring to the actual CO2 measurement data (Mauna Loa), not the combined curve of ice-core plus Mauna Loa, which does look exponential.

[Old Professer]

As one might expect comparing inferred data to measured data.

[M. Dodge Thomas]

Over a short period this sort of change looks almost linear, as in the Mauna Loa data:

But….

IMO, there’s little point in arguing over the shape of the CO2 curve – it’s obvious that there has been a recent increase in the level of atmospheric CO2 and a recent increase in the rate of change, and the reasons are well established, in this regard we are quibbling over details.

The meaningful discussion is “What are the implications of this change”.