Climate change, also know as global warming, is the gradual increase in overall temperature of the earth’s atmosphere due to the greenhouse effect caused by increased levels of greenhouse gases (GHGs).
The Greenhouse Effect
The greenhouse effect is a natural phenomenon essential to life as we know it. The sun’s energy, in the form of solar radiation, penetrates through the atmosphere. Some of that radiation is reflected straight back into space, bouncing off lighter colored areas (e.g. clouds, ice caps, and deserts) while some is absorbed by the earth’s darker areas (e.g. land and oceans). Water vapor and carbon dioxide act as a blanket around the earth, keeping the earth at habitable temperatures. Adding additional GHGs, such as methane, nitrous oxide and chlorofluorocarbons, causes the blanket to become thicker, trapping extra solar radiation and increasing the global surface temperature, hence the name global warming.
Figure: The Greenhouse Effect
Where are these GHGs coming from?
Since the beginning of the industrial revolution, human activities – primarily from burning fossil fuels – have caused a rapid increase in the concentration of several important GHGs in the earth’s atmosphere. Over the last 50 years, levels of CO2 in the atmosphere have risen 25 percent; levels of methane, an even more potent greenhouse gas, have more than doubled. While naturally occurring levels of GHGs keep temperatures on earth stable, climate scientists now agree that these human-caused emissions are having discernible impacts on global climate. Scientists estimate that the earth’s atmosphere can safely handle around 350 parts per million (ppm) of carbon dioxide. We’re already at 387 ppm and that number is rising quickly.
Carbon Dioxide (CO2) – Fossil fuels such as coal, gasoline, diesel, fuel oil and natural gas, destroying forests, and converting wildlands for farmland and housing
Methane (CH4) – Agriculture, landfills, wetlands, and thawing permafrost
Nitrous Oxide (N2O) – Fertilizer use and fossil fuels
Chlorofluorocarbons – Refrigerants including CFCs
The figure below shows the global anthropogenic GHG emissions from 1970 – 2004.
Figure: Global Anthropogenic GHG Emissions (IPCC AR4 Synthesis Report, 2007)
For the full version of the IPCC AR4 Synthesis Report, click here.
For more information on GHGs, visit the National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center website.
How long do GHGs stay in the atmosphere?
Our GHG emissions today can stay in the atmosphere for decades, centuries or even millennia. In addition, not all GHGs are created equal. Some are much more potent than others. This concept is called global warming potential (GWP), which is a relative measure of how much heat a greenhouse gas traps in the atmosphere. The table below shows the lifetime and 100-year GWP of the most prevalent GHGs.
Table: Greenhouse Gas Lifetimes and 100-Year Global Warming Potentials (IPCC AR4 WG-I Report, 2007)
For more information on GHG lifetimes and GWP, click here.
What does the increase of GHG emissions mean for life on earth?
With the increase of these heat-trapping gases, global temperatures are expected to rise by 1-1.5°F over the next few decades. While this may seem insignificant, these small changes in temperature can have devastating global effects. For example, climate change is linked to a growing frequency of extreme weather events such as:
Increased frequency and intensity of storms,
Wildfires, droughts, and floods,
Rising sea levels,
Substantial changes in habitats, including an expansion of range of many diseases and pests, and
Decreased snowpack and losses from polar and glacial icepacks.
The figure below details other impacts from global warming.
Figure: Examples of Impacts Associated with Global Average Temperature Change (IPCC AR4 Synthesis Report, 2007)