<http://schema.org/alternativeHeadline>
"Laughing gas is a potent greenhouse gas that receives none of the attention or regulation of CO2, CFCs, or other heat trappers."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mnn.com/earth-matters/climate-weather/blogs/the-quiet-greenhouse-gas-nitrous-oxide>