Earth is the only planet in the universe that supports life, and this uniqueness is attributable to its optimal temperature and climatic conditions. Earth’s temperature is affected by variations in solar energy that reach earth, changes is earth surface as well as atmospheric reflectivity, as well as changes in concentration of greenhouse gases (EPA, 2016). Earth’s distance, rotation in its axis and revolution around sun in its orbit primarily determine change of seasons in earth, as well as its climatic patterns. Variations in light reflectivity or albedo of various surface features on earth also contribute to climate variations. Similarly, aerosols emitted into the atmosphere during volcanic eruption reflect more sunlight and help in cooling earth, while black carbon aerosols absorb more solar energy resulting in warming (EPA, 2016). Since earth’s origin there have been several warming and cooling episodes attributable to natural causes such as volcanic eruption or changes in atmospheric gaseous composition. But, it is only in the post-industrialization era that the change in earth’s temperature has been very drastic mainly due to increase in greenhouse gas (GHG) emissions, loss of heat sinks as well as carbon sinks i.e. water bodies and green cover.
GHGs allow short wavelength visible light from sun to enter earth’s atmosphere, and absorb long wave infrared radiations emitted by the heated earth’s surface. Thus, they entrap heat energy and prevent it from escaping the earth’s atmosphere. GHGs include carbon dioxide, methane, nitrous oxide, ozone, water vapor and CFCs. Water vapor concentration in the atmosphere depends on the temperature and pressure driven hydrological cycle, and ozone is only a short-living GHG, produced as a secondary pollutant from photochemical reactions of nitrogen oxides with volatile organic compound emissions (EPA, 2016). Methane, CO2, CFCs and nitrous oxide are thus considered as chief GHGs emitted from human activities including fossil fuel extraction, combustion of fossil fuel for power generation or transport, usage of aerosols or coolants, etc (EPA, 2016). Further, due to deforestation and rapid development trees that act as carbon sinks and sequester CO2 through photosynthesis are reduced. As a result of rising temperature ice caps melt, and high albedo earth surfaces are converted to low albedo surfaces. As a result more solar energy is absorbed further contributing to the heating effect. Thus the vicious cycle continues.
There is experimentally verified evidence for climate change, and the outcomes further confirm it beyond doubt. Global CO2 levels have never reached beyond 300ppm since earth’s origin 400,000 years back till 1950 (NASA, 2016). But, within a few decades of human activity it has reached almost 400ppm (NASA, 2016). Further, satellite measured data reveal less heat escape from earth to outer space, especially at CO2 absorbing wavelengths, and earth surface measurements confirm more entrapped radiation fall within the absorption spectra specific to CO2 (Cook, 2010). Together these evidences clearly prove increased anthropogenic GHG concentration is responsible for global warming. Expansion in the troposphere layer due to heating, rise in the tropopause level i.e. boundary between troposphere and stratosphere and stratospheric cooling response to earth’s surface heating are all observed as well as verified through satellite data (Cook, 2010).
The main indicators that help us know that climate change is happening include sea level rise, global temperature rise, shrinking ice sheets and decreased snow cover, extreme events and Ocean acidification (NASA, 2016). Global sea level has rose by 17cm in the last century, and the rate of level rise has been double the century’s average rate in the last 10 years alone (NASA, 2016). Since, 1970’s global surface temperature has been rising, and out of 20 warmest years that have occurred since 1980, 10 of them have occurred within last 12 years alone (NASA, 2016). Further, between 2007 and 2009 there has been very large decline in the energy output received from sun, but earth’s surface temperature continues to increase. Oceans being major heat sinks have absorbed much of the energy, and our ocean surface temperature have rose by 0.3 F since 1969 (NASA, 2016). Additionally, oceans also act as carbon sinks, absorbing excess CO2 emitted by anthropological activities. Since, industrial revolution there has been 30% increase in ocean acidification (NASA, 2016), which has also been catalyzed by the rising temperature. Between 2002 and 2006 there has been up to 60 cubic miles of ice lost in green land, and 30 cubic miles of ice lost in Antarctica. Further, retreating glaciers, and decline in both thickness and extent of Arctic ice within last several decades indicate that climate change is happening (NASA, 2016). Extreme weather events such as heavy precipitation, draught and intense storms are also outcomes of climate change and global warming.
Cook, J. (2010, July 30). Climate Science Glossary. Retrieved April 09, 2016, from
EPA (US Environmental Protection Agency). (2016, February 23). Causes of Climate
Change. Retrieved April 09, 2016, from https://www3.epa.gov/climatechange/
NASA (National Aeronautics and Space Administration). (2016, April 8). Climate change
evidence: How do we know? Retrieved April 09, 2016, from http://climate.nasa.gov/