Marathon Oil recognizes the concern about the potential impact of greenhouse gas (GHG) and other air emissions on global climate. At the same time, we recognize the need for reliable and affordable energy to meet long-term demand, and the important role oil and natural gas are projected to play in meeting that demand.
Marathon Oil remains committed to finding and developing oil and natural gas in a safe and responsible manner, which includes efforts to reduce GHG and other air emissions from our operations in accordance with our standards, policies and applicable regulations.
Marathon Oil understands that additional climate change laws and regulations may be implemented in the future as guided by national policy and supported by more comprehensive global agreements such as that proposed by the 2015 United Nations Climate Change Conference. Our approach to mitigating the risk of additional regulation includes understanding and mitigating our GHG emissions, evaluating climate change risk in our investment decisions and engaging with external stakeholders to understand their perspectives.
Marathon Oil periodically evaluates and implements air emissions reduction strategies and technologies for our operations, which are described in the Emissions Overview, Methodology and Mitigation Strategies section. Emissions reduction strategies and technologies are used throughout the drilling and production lifecycle, including:
Because our business is focused on producing hydrocarbon liquids, we evaluate our performance using primarily GHG and methane emissions intensity, expressed as carbon dioxide equivalent (CO2e) emissions per all hydrocarbon production.
In 2015, the Company’s gross production of hydrocarbons increased by 3 percent. However, the reduced capital spending program resulted in lower activity and production in many assets, which contributed to a 5 percent increase in our global GHG emission intensity. Global CO2 emissions increased by 8 percent, and methane emissions increased by 11 percent.
GHG emissions increased in some growth assets, and decreased or remained relatively constant in our legacy assets.
Marathon Oil's methane intensity decreased or remained relatively constant in our growth assets primarily due to improvements in gas capture and operational efficiency. In Oklahoma, methane intensity decreased by 3 percent largely due to improvements in flare systems and installation of low-bleed controllers. Continuing current practice, all new wells in Oklahoma will be outfitted with low-bleed controllers. In addition, Oklahoma set an asset-wide goal to reduce methane intensity 50 percent by 2020.
Marathon Oil also evaluates our performance as a measure of total methane emissions as a percentage of total hydrocarbon produced and total methane emissions as a percentage of natural gas produced. Our overall methane emissions ratio remains flat at 0.3 percent.
Criteria pollutant emissions, which include nitrogen oxides (NOx), volatile organic compounds (VOCs) and sulfur oxides (SOx), increased from 2014 to 2015. Criteria pollutant emission intensity increased by 22 percent. We manage our criteria pollutant emissions in accordance with applicable emissions control regulations. In countries that do not have emission control regulations, we comply with applicable World Bank Guidelines for air quality.