Dianna made a goof. This should say the rate of temperature change is 1.5 degrees C per century. The temp on the graph clearly did not rise 1.5 degrees C in 29 years.
Many people do not understand the concept of 'rate of change.'
You are 100% correct!
“Many people do not understand the concept of ‘rate of change.’
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When I was in the Navy one of my buddies had a saying,”The only thing constant here is the rate of change and even that has been known to vary.”