Human activity is causing climate change. Since the beginning of the industrial revolution, human energy use, primarily the burning of fossil fuels, has caused concentrations of carbon dioxide and other greenhouse gases to rise substantially. The evidence shows it is extremely likely that human influence has been the dominant cause of the Earth’s warming over the past 50 years.
Lines of Evidence
This video explains how scientists have arrived at the state of knowledge about current climate change and its causes. Source
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Tracking CO2 Emissions
Carbon dioxide emissions typically reflect patterns of energy use. These graphs track the top 10 emitters of carbon dioxide globally (rankings are as of 2007). Though the United States has a much smaller population than China, the two countries have had similar total annual energy-related emissions because the United States has had higher average emissions per person than China.
Sources of Carbon Dioxide
The vast majority of carbon dioxide emissions come from energy use. In the United States, transportation is the leading contributor of energy-related emissions, followed by industrial, residential, and commercial emissions.
Within the Industrial sector, emissions come from energy use associated with manufacturing, such as iron and steel production, chemical production, and refining (85%) and non-manufacturing activities, such as agriculture, mining, and construction (15%).
Within the Residential sector, emissions come from space heating and cooling (39%), major appliances (16%), water heating (13%), lighting (11%), TVs and computers (7%) and other uses (14%).
Within the Commercial sector, emissions come from space heating, cooling, and ventilation (30%), lighting (19%), refrigeration and cooking (8%), office equipment (8%), water heating (4%), and other uses (31%).
Considering Other Factors
Other factors besides emissions of greenhouse gases can influence the Earth’s climate. However, the scientific evidence shows human-influenced emissions are the primary driver of recent climate trends.
Variations in Solar Output
The recent warming trend cannot be attributed to an increase in energy from the sun. Although solar output may have increased slightly during the first few decades of the 20th century, satellite measurements conclusively indicate that the average amount of energy output from the sun has not increased since the late 1970s, and probably has decreased slightly.
Variations in the Earth’s Position and Orientation
Slow variations in the Earth’s orbit around the sun lead to small changes in the amount and distribution of solar energy reaching the Earth’s surface. Over many thousands of years these subtle energy variations lead to the Ice Ages. However, these changes are far too slow to explain recent warming trends.
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. Volcanoes also add carbon dioxide to the air, but humans are now putting much more carbon dioxide into the air than volcanoes.
Additional Resources from the National Academies
Climate Change: Evidence & Causes is a free, 36-page booklet produced by the U.S. National Academy of Sciences and The Royal Society that describes what is well-established and where understanding is still developing in the area of climate change. It includes a Q&A, climate basics, and a figure gallery.
The materials in the Koshland Science Museum’s Earth Lab exhibit are based on reports of the National Research Council and works of the U.S. government and have been vetted for scientific accuracy by a panel of expert advisors.