Sources of Greenhouse Gas Emissions
What are the Issues?
While the majority of greenhouse gases (GHGs) are a result of producing and consuming energy, they are also tied to agriculture, land use change, and forestry activities. The majority of GHGs associated with energy production and use occur during fuel combustion that supports electricity generation, transportation, and industrial processes. The following discussion provides a synopsis specifically focused on GHG emissions that are a result of the energy supply chain — from resource extraction to the primary end uses of energy.
What are the Challenges?
Fugitive Emissions & Natural Gas Flaring
When producing oil, there are often large quantities of "associated" gas that must be separated for handling purposes. While this natural gas is sold where an infrastructure and market exists, associated natural gas may be flared (burned) or vented (released) into the atmosphere when these alternatives are not available. The venting of unprocessed gas releases methane into the atmosphere, which is a greenhouse gas. Flaring causes emissions of other greenhouse gases, including carbon dioxide, carbon monoxide, nitrogen oxides, and sulfur oxides. Other parts of the oil and gas value chain (such as refineries and pipelines) also can generate fugitive emissions through leaks, losses, and accidents.
Industry and company partnerships with governments of oil producing countries are collaborating on solutions that are substantially reducing gas flaring. These solutions include creating economic incentives to produce and deliver gas to markets and re-injecting associated gas into oil reservoirs, which enhances oil production, stores the otherwise flared gas and reduces GHG emissions. In addition, businesses, governments, investors and scientists are working together to find ways to increase carbon capture and storage at gas fields and coal mines.
Emissions from Electricity Generation
Power generation plants convert energy inputs (such as coal, natural gas, and oil) into electricity for residential, commercial, and industrial use. Both in the United States and worldwide, the generation of electricity and heating is the single largest source of CO2 emissions.
Coal remains an important and growing source for energy supply and accounts for a dominant portion (73%) of the CO2 emissions from the electricity generation sector.
Potential climate change solutions that would reduce emissions will need to take into account the particular characteristics of electricity generation, such as:
- More than forty percent of electricity demand is for the benefit of commercial and residential buildings, thirty five percent is for industry, and the remainder is for energy processing (refining) and energy transmission, including losses.
- The United States, China, and the EU are by far the largest emitters (in absolute terms) in this sector.
- Seventy percent of US electricity comes from fossil fuels such as coal, oil and natural gas.
At the global level, emissions from this sector are the fastest growing. In order to address this challenge, stakeholders are working to reduce reliance upon coal combustion and to encourage the use of alternative resources for electricity generation such as nuclear, natural gas, geothermal and renewable technologies. (The Energy Portfolio). By 2015, natural-gas-fired plants, which are cleaner burning than coal, are expected to account for 25 percent of electricity generation in the United States, with investments in such plants currently underway. Another way to reduce the emissions from energy production is to invest in energy efficiency at production facilities: technologies such as advanced combined cycle gas turbines reduce the losses that arise in generating energy.
Emissions from Industry
Industrial facilities, including those for chemical, petrochemical, cement, steel, and aluminum production, are large consumers of energy, accounting for a third of global industrial energy use and 21% of world GHG CO2 emissions. Through voluntary and regulatory initiatives, industrial users are managing their climate change impacts and are implementing a range of efficiency measures as well as technology innovations to curtail their energy footprint.
When considering solutions for reducing emissions from industry, it is important to consider the particular characteristics of this type of energy use, including:
- Industrial uses of energy are diverse, but fossil fuel combustion, electricity and heat contribute the majority of GHGs (see figure below).
- The majority of emissions from industry come from developing countries with large scale energy intensive industries, with China having the largest share.
- Emissions from industry as a relative share of overall national emissions have declined since 1990 in the United States, the EU-25, Mexico, Russia and Australia.
Emissions from Transportation
Road transport is the dominant contributor of GHG emissions in the transportation sector (see figure below), which is second to electricity generation in terms of overall GHG contributions. Some important characteristics of this segment include:
- Petroleum dominates this sector in terms of both energy demand and emissions.
- The OECD countries constitute over 50% of worldwide emissions from transportation fuels.
- Transportation is a fast growing source of emissions in several countries. In China, for example, the number of cars more than doubled between 2000 and 2006 and substantial growth in vehicle sales and demand for fuel are anticipated, which will contribute to the country’s continued growth of emissions (which is largely driven by the expansion of the power sector).
National policies which focus on improving engine efficiency and providing incentives and mechanisms to reduce demand (such as incentives for using public transportation or high-occupancy vehicle systems) could provide a long-term pathway for reducing emissions from the transportation sector. In addition, technology advances including electric hybrid vehicles and plug in electric hybrids, advanced diesel technology, and hydrogen power offer emerging platforms for reducing GHGs in this sector. Initiatives that address engine efficiency, especially consumer education programs, offer some of the most readily available GHG reduction strategies.
What are the Solutions?
Scientists contend that it is possible to reduce, delay or avoid many climate change impacts through mitigation efforts that stabilize the atmospheric concentrations of greenhouse gases.
To achieve this stabilization, the consensus among climate scientists is that worldwide emissions of greenhouse gases need to start a long-term decline within the next decade or two and realize reductions of about 50 to 80 percent by 2050 (from 1990 levels). Most scientists agree that there is no single solution - the deployment of a broad portfolio of different strategies and technologies will be necessary to stabilize carbon emissions by 2050. (The Energy Portfolio). Our global challenge is to develop the right mix of solutions that achieve these stabilization goals while continuing to support economic growth and development. Periodic "checkpoints" that assess the environmental, social and economic impacts of solutions will help us to know whether the right results are being achieved.
Robert Socolow and his colleagues at Princeton developed a theoretical approach to reducing GHGs based on "wedges" of activity. Each of the seven wedges illustrated below represents an application of current technology that would reduce carbon emissions by 1 billion metric tons per year.
The following sections detail different sets of climate change solutions that could be pursued, including: energy conservation and efficiency; cleaner emerging energies, and; energy policies, markets and incentives.