Did you know it snows CO2 when it's cold? Noticed in the comments at WUWT today:
...when CO2 cools it falls from the atmosphere, it’s a low lying gas, higher levels of CO2 falling from the atmosphere are being recorded at ground level observatories beside a volcano and all other measurements are calibrated around the planet to assure the correct measurement of “atmospheric CO2” is recorded…
Sparks is wrong, of course. CO2 is a well-mixed greenhouse gas. And it doesn't easily "fall from the atmosphere". From Wikipedia (this is basic stuff):
Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520 kPa). At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below −78.5 °C (−109.3 °F; 194.7 K) and the solid sublimes directly to a gas above −78.5 °C. In its solid state, carbon dioxide is commonly called dry ice.