“Since the beginning of the industrial revolution, concentrations of greenhouse gases from human activities have risen substantially. Evidence now shows that the increases in these gases very likely (>90 percent chance) account for most of the Earth’s warming over the past 50 years. Carbon dioxide is the greenhouse gas produced in the largest quantities, accounting for more than half of the current impact on Earth’s climate.”
-National Research Council
Explore how CO2 concentration and global average surface temperature have changed over the past century using the interactive below.
Historically, over half of all global carbon dioxide emissions have been generated by just ten countries. Since energy-related CO2 emissions constitute the vast majority of total emissions, emissions rise as energy demand increases. The following graph shows trends in energy-related CO2 emissions from top emitters. The countries shown were the top ten contributors to total energy-related CO2 emissions in 2007.
Though the United States has a much smaller population than China, the two countries have had similar total annual energy-related emissions. This is because the United States has had higher average emissions per person than China. The following graph shows trends in emissions per person for top-emitting countries. The countries shown were the top ten contributors to total energy-related CO2 emissions in 2007. Note that several other countries had higher emissions per person in 2007 than those shown here.
Though the United States has traditionally been the greatest CO2 emitter, other nations are quickly catching up. The gap is closing as other nations’ populations grow and their economies consume more energy.
In 2007, 97 percent of the CO2 that the U.S. added to the atmosphere came from energy-related uses. These emissions totaled over 6 billion tons of CO2 in 2007, accounting for approximately 20% of total global energy-related emissions. Which sector (residential, commercial, industrial, or transportation) is responsible for the most energy-related emissions? Within each sector, what uses account for the greatest emissions?
Click below to explore U.S. CO2 emissions by use.
The residential sector energy use consists of the energy used to maintain private households. Common uses of energy include: heating and air conditioning; operating major appliances, including refrigeration and clothes dryers; water heating; and lighting.
The commercial sector energy use consists of energy used by businesses, government, public works, and other private and public organizations. Common uses of energy include heating, air conditioning, and ventilation; lighting; office equipment; and water heating.
The industrial sector energy use consists of all energy used by facilities and equipment used for producing, processing, or assembling goods. This sector includes manufacturing such as iron and steel production, bulk chemical production and refining, as well as non-manufacturing such as agriculture, mining, and construction.
The transportation sector consists of all vehicles whose primary purpose is transporting people and goods from one physical location to another. This includes cars, trucks, air, rail, bus, and shipping. This sector burns most of the world’s petroleum.
Natural Processes Cannot Account for the Recent Change in Temperature
Variations in Solar Output
The recent warming trend cannot be attributed to an increase in energy from the Sun. Though solar output may have increased slightly during the first few decades of the twentieth century, satellite measurements conclusively indicate that the average amount of energy output from the Sun has not increased since the late 1970s.
Variations in Earth’s Position and Orientation
Slow variations in Earth’s orbit around the Sun lead to small changes in the amount and distribution of solar energy reaching Earth’s surface. Over many thousands of years these subtle energy variations lead to the Ice Ages. However, these changes are much too slow to explain recent warming.
Volcanic eruptions spew many small particles into the atmosphere. These particles reflect sunlight, and large eruptions can reflect enough solar energy back to space to cool the Earth’s surface by a few tenths of a degree. However, since these particles fall back to the Earth’s surface over a few years, the cooling effect does not last indefinitely. Massive eruptions may only slightly reduce annual global temperatures and temporarily mask the warming trend.