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A blanket around the Earth By NASA.gov, adapted by Newsela staff on 01.09.17 Word Count 945 TOP: Exhaust plumes from cooling towers at the Jaenschwalde lignite coal-fired power station, which is owned by Vatenfall, April 12, 2007, at Jaenschwalde, Germany; Sean Gallup/Getty Images. BOTTOM: A layer of greenhouse gases acts as a thermal blanket for the Earth, absorbing heat and warming the surface to an average of 59 degrees Fahrenheit. NASA. Most climate scientists agree the main cause of the current global warming trend is the human-aided increase of the "greenhouse effect." This warming effect results when the atmosphere traps in heat radiating from Earth toward space. Certain gases in the atmosphere block heat from escaping. Some gases remain for a long time in Earth's atmosphere, and they do not respond physically or chemically to changes in temperature. Scientists say these gases are "forcing" climate change. Gases such as water vapor, which do respond physically or chemically to changes in temperature, are called "feedbacks." This is because they can either worsen the effects of climate change or help diminish these effects. Gases That Contribute To The Greenhouse Effect Water vapor, the most abundant greenhouse gas, acts as a feedback to the climate. Water vapor increases as the Earth's atmosphere warms, but so does the possibility of clouds and precipitation, making these some of the most important feedback mechanisms to the greenhouse effect. This article is available at 5 reading levels at https://newsela.com. 1 Carbon dioxide (CO2) is a minor but very important component of the atmosphere. It is released through natural processes such as respiration and volcanic eruptions. It is also released by human activities, such as deforestation, land-use changes and burning fossil fuels. Humans have increased CO2 concentration in the atmosphere by more than a third since the Industrial Revolution began. The increase in CO2 is the most important long-lived "forcing" of climate change. Methane is a hydrocarbon gas produced both through natural sources and human activities, including the decomposition of wastes in landfills and rice cultivation. It is also released in large quantities by domestic livestock, like cows and sheep, and through related agricultural practices. On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide. Nitrous oxide is a powerful greenhouse gas produced by soil cultivation practices. It is commonly a byproduct of commercial and organic fertilizers. It also enters the atmosphere after we burn fossil fuels such as gasoline. Nitric acid, a chemical used to make cleaning products and explosives, also releases nitrous oxide. Chlorofluorocarbons (CFCs) are entirely man-made. They were once used in many consumer products, but they are no longer as prevalent as they once were. In the 1970s, scientists started to realize CFCs were destroying the ozone layer. Starting in 1987, many countries came together and agreed to reduce CFCs. They are also greenhouse gases. How Human Activities Create A "Natural Greenhouse" On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the process of burning coal or oil combines carbon with oxygen in the air to make CO2. The clearing of land for agriculture and businesses, the raising of livestock and other human activities have all increased concentrations of greenhouse gases. The consequences of changing the natural atmospheric greenhouse are difficult to predict. Still, certain effects seem likely. On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not. Warmer conditions will probably lead to more evaporation and precipitation overall. However, the climates of individual regions will vary, with some becoming wetter and others dryer. A stronger greenhouse effect will warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing further to sea level rise. Meanwhile, some crops and other plants may respond favorably to This article is available at 5 reading levels at https://newsela.com. 2 increased atmospheric CO2. The plants may grow more vigorously and use water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities. The Role Of Human Activity The Intergovernmental Panel on Climate Change is a group of 1,300 independent scientific experts from countries all over the world under the supervision of the United Nations. In its Fifth Assessment Report, the group concluded that there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet. Our modern civilization depends upon industrial activities. These activities have helped raise atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years. Over the past 50 years, scientists have observed a sharp increase in Earth's temperature. The panel concluded there's a better than 90 percent probability that human-produced greenhouse gases caused that increase, too. They said the rate of increase in global warming is very likely to be unprecedented within the past 10,000 years or more. Solar Irradiance It's reasonable to assume that changes in the sun's energy output would cause the climate to change. The sun is the fundamental source of energy that drives our climate system. Indeed, studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850. At that time, Greenland was largely cut off by ice from 1410 to the 1720s and glaciers advanced in the Alps. However, evidence shows that current global warming cannot be explained by changes in energy from the sun. Since 1750, the average amount of energy coming from the sun either remained constant or increased slightly. If the warming were caused by a more active sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That's because greenhouse gases are trapping heat in the lower atmosphere. This article is available at 5 reading levels at https://newsela.com. 3 Quiz 1 According to the article, it is very likely that human activity is the cause of climate change. Which paragraph from the section "The Role Of Human Activity" BEST supports the idea outlined above? 2 3 4 Which section from the article BEST explains how it is unlikely that changes in the sun have caused climate change? (A) "Gases That Contribute To The Greenhouse Effect" (B) "How Human Activities Create A Natural Greenhouse" (C) "The Role Of Human Activity" (D) "Solar Irradiance" How do fossil fuels affect the climate? (A) They cause various gases to be released from the atmosphere, leading to smog and pollution. (B) They increase the amount of carbon dioxide in the air, contributing to the greenhouse effect. (C) They lead to the use of more coal and oil, the mining of which damages Earth's surfaces and oceans. (D) They can be used to promote agriculture, leading to an increased demand for water and carbon dioxide. Which of the following answer choices would BEST describe scientists' reaction to climate change over the years? (A) concerned by increasing temperatures and searching for ways to reduce the greenhouse effect (B) panicked at the dramatic temperature increases and working with different countries to pass laws about emissions (C) interested in temperature changes and convinced that current trends in climate change indicate the arrival of an ice age (D) worried that the sun will be affected by the same human activities that led to the greenhouse effect This article is available at 5 reading levels at https://newsela.com. 4