A glaciologist is investigating the linear relationship between the annual rate of ice melt, $M$ mm, and the mean surface temperature, $T$ degrees Celsius. Which of the following is not a possible value for the calculated product moment correlation coefficient, $r$?

• $-0.92$
• $\frac{\pi }{4}$
• ${\log }_2(2.5)$
• $\cos (4)$