However, it often can be misleading to fit a linear trend line through historical data and draw firm conclusions from it. Referring to Figure 1 again, we have fit two additional trend lines through the historical temperature data—a quadratic and a cubic trend. Using these three trend equations, we have extrapolated temperature anomalies from 1991 to 2050, and we observe a wide range of temperature difference, depending upon which historical trend is used. Thus, historical data may not determine a unique trend and can be highly misleading in predicting future temperature changes.