Answer
313 degrees C.
Work Step by Step
Assume the amount of gas (n) and the volume are both unchanged. Use the ideal gas law.
The value of P/T remains constant.
$$\frac{P_1}{T_1}=\frac{P_2}{T_2}$$
$$T_2=T_1\frac{P_2}{P_1}$$
$$T_2=(273.15+20.0K)\frac{2.00atm}{1.00atm}=586.3K\approx313^{\circ}C$$