Background Paragraph: Current Situation : Currently the heating effect of extra greenhouse gases (since the start of the industrial revolution) is equal to about . Thus the recent period has recorded parallel increases in concentration of carbon dioxide and average global temperature. As more greenhouse gases are put into the atmosphere the temperature will increase further. There are certain effects of a warmer Earth (discussed more in optional section), which could accelerate the process, even if no more greenhouse gases are put into the atmosphere (an unlikely prospect for the foreseeable future). 
Story: Last week, an exact clone of Earth appeared next to our current Earth. Scientists have come to call this new planet, Terra. Terra has the exact same cities, civilizations and history as Earth. Scientists are completely baffled as to how this planet exists, but it undeniably does. The only difference between Earth and Terra is that the citizens of Terra output half as many greenhouse gases into the atmosphere as citizens of Earth do. 
Question: Does Terra have more or less concentration of carbon dioxide than Earth?
less.