Carbon dioxide in Earth's atmosphere Atmospheric O levels are decreasing in Earth's atmosphere as it reacts with the carbon in fossil fuels to form . Burning fossil fuels such as coal, petroleum, and natural gas is the leading cause of increased anthropogenic ; deforestation is the second major cause. In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of or about 4.3 ppm in Earth's atmosphere) were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990. In addition, land use change contributed 0.87 GtC in 2010, compared to 1.45 GtC in 1990. In 1997, human-caused Indonesian peat fires
Environmental impact of hydraulic fracturing life cycle of oil or coal. Until recently, Canadian provinces such as Alberta, Saskatchewan, and Nova Scotia produced over half of their electricity from coal combustion whereas Ontario has already completely phased out coal-powered electricity. Switching from coal- to natural gas-powered electricity can reduce carbon dioxide emissions by ~50% and also decrease the amount of NOx and SOx emitted to atmosphere. Lack of baseline data or before-and-after hydraulic fracturing sample collection and analysis makes it challenging to quantify environmental impacts (if any) resulting from hydraulic fracturing. Hydraulic fracturing fluids include proppants and other substances, which may include toxic chemicals. In