Task: Question Answering
Input (English): 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: A group of researches studied the green house gas emissions and their effects on Earth and people during the eighties compared to the twenties. The eighties produced way more green house gasses than the twenties did. 
Question: During which decade did Earth experience a decreased average global temperature?
Output (English): twenties.