We hear a lot about carbon dioxide emissions as the main perpetrator of human-induced climate change, there is another element that is often overlooked when it comes to a wide range of environmental and human health issues: nitrogen. Humans have more than doubled the amount of usable "reactive" nitrogen in the earth's land-based ecosystems each year through the use of fertilizers and the combustion of fossil fuels. As a consequence, we are, on average, better nourished than at any time in human history. Unfortunately, using so much nitrogen has also caused many unintended consequences that have become serious problems including another potent climate-changing gas, nitrous oxide, which is also now the most important human-produced compound that destroys stratospheric ozone.
