Higher levels of carbon dioxide may have led, over the past century, to approximately a

A) 1 degree (F) warming of the earth.
B) 10 degree (F) warming of the earth.
C) 1 degree (F) cooling of the earth.
D) 10 degree (F) cooling of the earth.

Warming

A process wherein the average temperature of the Earth's atmosphere and oceans increases, often discussed in the context of global climate change.

Past Century

"Past century" refers to the period of 100 years immediately preceding the current moment.