Carbon dioxide (CO2) is at the center of efforts to manage climate change. Many identify CO2 as the leading cause of calamitous environmental destruction, but how does this naturally occurring substance wreak such havoc on our environment?For over 100 years the scientific community has been warning us of the dangers of global warming caused by CO2 emissions from fossil fuels. In 1896 S. Arrhenius, published the paper "On the influence of carbonic acid in the air upon the temperature of the ground." More recently a plethora of scientific studies have corroborated these early concerns. (In a forthcoming post we will review some of the scientific evidence for global warming).
CO2 and Other GHGs
CO2 is a naturally occurring chemical compound. CO2 is part of the respiration of plants and animals and it is produced through the decay of carbon based material from plants and animals. Some natural processes, such as volcanoes and geysers, also add CO2 to the atmosphere.
Although CO2 gets most of the attention there are other naturally occuring greenhouse gases (GHGs). Water vapor is by far the most important GHG. It evaporates mostly from the ocean, and it causes earth's surface to be about 30°C warmer (out of the 36°C of warming caused by all greenhouse gases combined). Methane is produced by bacteria in wetlands and bogs, cattle, rice paddies, termites, landfills, and coal mining. Nitrous oxide is produced from microbes in the soil and the ocean. Halocarbons such as refrigerants are used in air conditioners and tropospheric ozone, produced in smog.
The Greenhouse Effect
Naturally occuring GHGs like CO2 warm and regulate the earth's temperature through the greenhouse effect. Warming occurs because the GHGs, although transparent to incoming solar radiation, absorb infrared (heat) radiation from the Earth that would otherwise escape from the atmosphere into space. GHGs re-radiate some of the heat back towards the surface of the Earth.
Normally almost half of energy emanating from the sun is trapped in our atmosphere. This natural phenomenon is what we call the greenhouse effect, GHGs warm the earth so that it is conducive to life, if there were no GHGs the temperature on earth would fall below –18 C.
GHGs and Global Warming
The unnatural addition of GHGs to the atmosphere is known as global warming. This unnatural build-up of GHGs in the troposphere (the lower part of the atmosphere about 10-15 kilometres thick) is trapping additional heat. The amount of heat in the troposphere depends on concentrations of GHGs and the amount of time these gasses remain in the atmosphere. CO2 remains in the troposphere between fifty and two hundred years.
CO2 and Human Activities
Anthropogenic (human-produced) CO2 is mixing with naturally produced CO2 and influencing the earth's radiation balance. The two main human activities that increase the amount of carbon dioxide in the earth's atmosphere are fossil fuel burning and land clearing. The burning of fossil fuels adds about 6 gigatons of carbon to the atmosphere each year.
Prior to the industrial revolution, atmospheric CO2 concentrations had not changed appreciably for over 850 years. That changed around 1850 when human processes began emitting significant quantities of GHGs. Pre-industrial levels of CO2 were approximately 270 and according to scientists at the Mauna Loa observatory, as of 2008, CO2 levels in the atmosphere were at 387 parts per million (ppm). This represents an increase of approximately 40% since the industrial revolution and the highest levels of CO2 in at least 650,000 years.
The US national oceanic and atmospheric administration research has corroborated other findings that indicate CO2 is accumulating in the atmosphere faster than expected. Their review suggests that levels of CO2 emmisions are on the increase, from 1970 to 2000, the concentration of CO2 rose by about 1.5ppm each year, but since 2000 the annual rise has surged to an average 2.1ppm. "Researchers suggest the trend could mean that the earth is losing its natural ability to absorb billions of tonne of CO2 each year."
CO2 emissions from cars and industry are a major cause of what we refer to as global warming. These increasing CO2 emissions cause about 50-60% of the global warming. Human activities have released an amount of CO2 that exceeds the amount sequestered in biomass, the oceans, and other sinks. About 22% of the current atmospheric CO2 concentrations exist due to these human activities. Fossil fuel combustion for energy generation causes about 70-75% of the anthropogenic CO2 emissions. The remaining 20-25% of the emissions are caused by land clearing and burning and by emissions from motor vehicle exhausts.
Other GHGs Associated with Human Activity
According to Ocean World, about two thirds of the methane emissions into the atmosphere come from human activity, mostly from the northern hemisphere. Methane concentration was 1783 parts per billion in 2004, which was 155% larger than pre-industrial concentrations. The rise in methane appears to have leveled off, and concentrations have increased only 5 parts per billion since 1999. Methane does not remain long in the atmosphere, about 8 years (Fischer et al, 2008). However methane is 22 time more effective in absorbing infrared radiation than CO2.
Nitrous oxide (N2O) is also a byproduct of burning fossil fuels at high temperatures. About one-third of the emissions into the atmosphere come from human activity. N2O concentrations were 319 parts per billion in 2004, which was 18% larger than pre-industrial concentrations. Its lifetime in the atmosphere is about a century.
US GHG Emissions
Although the US is only 4.6% of the world's population, American energy use accounts for 24% of all the world's energy. According to the Statistical Review of World Energy 2005 89.4% of energy consumption in the US is derived from burning fossil fuels.
The average American uses almost 31 kilowatt-hours (kWh) per day, or 1.3 kilowatts (kW) continuously. Most of that electricity is produced by burning fossil fuels. In certain other fully modern countries (England, France, Germany, Japan), the per-capita average ranges from 0.6 to 0.8 kW. At the other end of the scale, in developing countries where, even if some cities are electrified, rural areas are generally without power, the number is much lower: Mexico uses 0.14 kW, Thailand 0.10, and Peru 0.05. India is way down, at 0.037. China is around 0.07.
While most GHG emissions derive from industrial processes in developed countries like the US, GHGs from developing countries are rising. At the current rate, anthropogenic carbon dioxide emissions are expected to double in this century.
GHGs contribute to the greenhouse effect and many anthropogenic GHGs are on the increase. In the next post we will review the effects that they are having on the earth and its inhabitants.
Next: The Effects of Global Warming / Debunking CO2 Myths and the Science of Global Warming / Action on Global Warming.
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