The commission must monitor the greenhouse gas emissions resulting from natural gas and renewable natural gas delivered by each gas company to its customers, relative to a proportionate share of the state's greenhouse gas emissions reduction goal. The commission must report to the governor by January 1, 2020, and every three years thereafter, an assessment of whether the gas companies are on track to meet a proportionate share of the state's greenhouse gas emissions reduction goal. The commission may rely on reports submitted by gas companies to the United States environmental protection agency or other governmental agencies in complying with this section.