I didn't suggest that angular velocity is the same as linear velocity, I asked how you were interpreting the area and velocity, and parenthetically observed that the angular velocity was constant. You say that the area is impactful - what do you understand it as meaning?

The scale is not arbitrary, it covers the range of anomalies over the chosen period, in units of temperature change in degrees Celsius, and is labelled as such, with the anomaly reference period described in the text. If you were to use absolute values then the scale would similarly cover the range of absolute values over the chosen period - there is no "unbiased" choice of data range, except perhaps that which covers all of the data in question, which this does.

As I noted, the impact of the anomalies is with reference to "normal" temperatures - it is relatively easy for anyone to see that 1 C (/K) is quite a large temperature increase, relative to "normal" temperatures. Surely you can agree that if the largest anomaly shown was 0.01 C then the graph would have far less impact, and if it was 100 C then the graph would have far more impact?