Global warming is the prolonged heating of Earth’s climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere.
Since the pre-industrial period, human activities are reckon to have increased Earth’s global average temperature by about 1 degree Celsius (1.8 degrees Fahrenheit), a number that is currently increasing by 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade. Most of the current warming trend is extremely likely (greater than 95 percent probability) the result of human activity since the 1950s and is proceeding at an unusual rate over decades to millennia.
Glaciers are melting, sea levels are rising, cloud forests are dying, and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years.
We frequently call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts. All of those changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere, changing the rhythms of climate that all living things have come to rely on.
What will we do—what can we do—to slow this human-caused warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the fate of the Earth as we know it—coasts, forests, farms, and snow-capped mountains—hangs in the balance.
Understanding the greenhouse effect
The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere catch heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.
Sunlight shines onto the Earth's surface, where the energy is soaked up and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.
Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.
Top 10 causes of Global Warming
Power Plants
Forty percent of U.S. carbon dioxide emissions stem from electricity production. Ninety-three percent of the electric industry emissions result from burning coal. According to the EPA coal-fired power plants, municipal and medical waste incineration account for two-thirds of U.S. mercury emissions.
Transportation
EPA reports state that thirty-three percent of U.S. emissions come from the transportation of people and goods.
Farming
Industrial farming and ranching releases huge levels of methane and carbon dioxide into the atmosphere. Farming contributes forty percent of the methane and twenty percent of the carbon dioxide to worldwide emissions.
Deforestation
Deforestation to use wood for building materials, paper and fuel increases global warming in two ways -- the release of carbon dioxide during the deforestation process and the reduction in the amount of carbon dioxide that forests can capture.
Fertilizers
The use of nitrogen-rich fertilizers increases the amount of heat cropland can store. Nitrogen oxides can trap up to 300 times more heat than carbon dioxide. Sixty-two percent of nitrous oxide released comes from agricultural by-products.
Oil Drilling
Burn-off from the oil drilling industry impacts the carbon dioxide released into the atmosphere. Fossil fuel retrieval, processing and distribution accounts for roughly eight percent of carbon dioxide and thirty percent of methane pollution.
Natural Gas Drilling
Touted as a cleaner fuel source, natural gas drilling causes massive air pollution in states like Wyoming; the hydraulic fracturing technique used to extract natural gas from shale deposits pollutes ground water sources as well.
Permafrost
The melting of permafrost releases tons of trapped green house gases which further speeds up the melting of more permafrost. Scientists calculate that approximately five-hundred gigatons of carbon is trapped in the Siberian permafrost alone. A single gigaton equals one billion tons.
Garbage
As trash breaks down in landfills, it releases methane and nitrous oxide gases. Approximately eighteen percent of methane gas in the atmosphere comes from waste disposal and treatment.
Volcanic Eruption
Volcanoes expel large quantities of carbon dioxide when they erupt. Volcanoes have an overall small effect on global warming and an eruption causes a short-term global cooling as ash in the air reflects greater amounts of solar energy.
Effects of Global Warming
- Disappearing glaciers, early snowmelt, and severe droughts will cause more dramatic water shortages and continue to increase the risk of wildfires.
- Rising sea levels will lead to even more coastal flooding.
- Forests, farms, and cities will face troublesome new pests, heat waves, heavy downpours, and increased flooding. All of these can damage or destroy agriculture and fisheries.
- Disruption of habitats such as coral reefs and alpine meadows could drive many plant and animal species to extinction.
- Allergies, asthma, and infectious disease outbreaks will become more common due to increased growth of pollen-producing ragweed, higher levels of air pollution, and the spread of conditions favorable to pathogens and mosquitoes.