Nitrous oxide, commonly known as laughing gas, is a major greenhouse gas.
Though it doesn't get much press these days, an international team of scientists in Antarctica analyzing ancient air trapped in bubbles in Taylor Glacier discovered there was a 30 percent increase in atmospheric nitrous oxide at the end of the last ice age.
Using the ratio of gas isotopes like a fingerprint, scientists identified terrestrial and marine microbes that produced the nitrous oxide. Terrestrial microbes had a head start, but in the end they both produced gas in equal amounts. As the earth warmed, the microbes produced even more nitrous oxide which in turn helped warm the environment further. This led to the end of the ice age and the melting of giant ice sheets.
What happened at the end of the last ice age is similar to what's happening now with global warming. Atmospheric nitrous oxide went from about 200 parts per billion at the peak of the ice age to 260 at the end. Today it's over 300, primarily from human agriculture. Global warming is predicted to increase the number of low-oxygen zones in many of the world's upper oceans, which will also increase the numbers of nitrous oxide producing microbes.
Not only that, nitrous oxide also destroys ozone.
"Isotopic Constraints on Marine and Terrestrial N2O Emissions During the Last Deglaciation" (Nature)