Why can't Carbon Dioxide be liquid at 1 atm?
This is the phase diagram from a better source:



The pressure axis is the vertical one at the left. One bar (which equals 0.986923 atmospheres) is near the bottom, as shown on the diagram. So carbon dioxide is a gas at all temperatures above −78.5 °C when the pressure is one bar. Solid carbon dioxide (dry ice) sublimes at one bar (about one atmosphere), i.e., goes directly from solid to gas.

If you want liquid carbon dioxide, you need a temperature, pressure pair in the liquid region, e.g., −40.0 °C and 20 bar.