The Greenhouse Gas Emissions Reduction Act (Maryland Code, Environment Article §2-1203) requires the Maryland Department of the Environment to prepare and publish an updated inventory of statewide greenhouse gas emissions on a three-year cycle. This dataset covers the inventory years of 2006, 2011, 2014, 2017 and 2020.

Maryland's greenhouse gas emissions inventory tracks emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) occurring in the state and from out-of-state electricity generation consumed in the state. These gases have differing lifetimes in the atmosphere and differing warming impacts. The Global Warming Potential (GWP) is a measure of the warming impact of a particular gas over a particular time horizon. GWP values allow for aggregating emissions of the different greenhouse gases into a single metric, known as carbon dioxide equivalent, and reported in the inventory in million metric tons (MMTCO2e).

As required by the Climate Solutions Now Act of 2022, MD's GHG inventory reports emissions with a GWP considered over a 20-year time horizon. Emissions are also presented using a GWP over a 100-yr time horizon, consistent with conventional national and international inventory protocols. The 20-yr GWP emissions are to be used in evaluating progress towards Maryland's GHG reduction goals.