Question

Climatologist Michael Mann and his colleagues have graphed a thousand-year period (the famous "hockey stick" chart) that shows how __________ were more or less constant until they spiked __________.

Answer 1

Global temperatures; in the past half-century.

Step-by-step explanation:

The graph of the global temperatures in the northern hemisphere was more or less costant until it spiked very hard in the past half-century. Therefore, it is called the "hockey stick" chart because its shape resembles a hockey stick. The original graph was made, as the exercise details, by Michael Mann and his colleagues in 1999.