Conversation so far:
what are known contributors to the green-house effect
The largest source of greenhouse gas emissions from human activities in the United States is from burning fossil fuels for electricity, heat, and transportation.
what percentage does transportation contribute to green-house effects
Transportation made 28.9 percent of 2017 greenhouse gas emissions.
what percentage does agriculture contribute to green-house effects
Greenhouse gas emissions from agriculture from livestock such as cows, agricultural soils, and rice production, made up 9.0 percent of 2017 greenhouse gas emissions.
how much have green-house emissions increased
Since 1990, gross U.S. greenhouse gas emissions have increased by 1.3 percent.

Question: what do the gases do
Self-contained rewrite: what do greenhouse gases do