• The lowest layer of the atmosphere, known as Troposphere, contains those gases which are, to a great extent, responsible for Earth’s temperature, and therefore responsible for generating conditions to support life.

• The Greenhouse Effect occurs when an atmosphere is able to absorb infrared radiation through gases, such as carbon dioxide (CO2), water vapor, ozone (O3), nitrous oxide (N2O), methane (CH4) and chlorofluorocarbons (CFCs). Atmospheric concentrations of such gases are so small that they are referred to as trace gases.

• The Earth catches basically visible radiation from the sun which reaches the surface. The surface warms up and emits long wave radiation in turn, which is absorbed by greenhouse gases in the atmosphere, thus producing a warming up of the surface (Figure 1). This process keeps earth’s surface temperature approximately 14ºC higher than it would otherwise be.

Figure 1. Greenhouse Effect

Traducción figura: La radiación solar….: Solar radiation passes through the atmosphere; La mayor parte de la ….: Most radiation is absorbed by the surface of the Earth, thus warming it up.; Una fracción de la radiación…: A fraction of solar radiation is reflected by the Earth and the atmosphere.; Atmosphere; Tierra: Earth., Una parte de la radiación infraroja atraviesa la atmósfera, mientras…: Some infrared radiation passes through the atmosphere, while some is absorbed and redirected back in random directions by clouds, warming the earth’s surface and the lowest layer of the atmosphere (Troposphere).

• From an increase in atmospheric concentrations of greenhouse gases, rises in temperature can be expected since greater infrared radiation absorption occurs. This phenomenon generates the Global Climate Change.

• It has been detected that CO2 concentrations increase year by year. It is estimated that such an increase is mainly due to fossil fuel burning emissions, which are not balanced with CO2 sinks (photosynthesis in vegetation). In other words, 6000 million tons of carbon per year are estimated (one ton of C (cabon) equals 3,666 tons of CO2), from which approximately 3000 million remain and accumulate in the atmosphere (Figure 2 and Table 1).

Figure 2. Carbon Cycle

Traduc. de la figura:
Ciclo del carbono: Carbon Cycle; Atmosfera: Atmosphere; Fotosíntesis: Photosynthesis; Respiración: Breathing; Suelo: Soil; Deforestaciön: Deforestation ; Descomposición: Decomposition; Co2 Contribuye al efecto….: Co2- Contributes to greenhouse effect and is a key factor in determining earth’s surface temperature; 6000 Mton….: 6000MtonC/year are released , 3000 MtonC/year remain in the atmosphere. Incendios forestales: Forest fires; Industria: Industry; Combustibles fósiles: Fossil Fuels; Procesos dependientes de …: Processes depending on temperature and precipitation; Procesos químicos y biológicos: Chemical and Biological Processes; Océanos: Oceans

a) Atmospheric warming potential expresses relative significance of greenhouse gases in relation to CO2 in a given time span This is due to the different periods in which gases remain in the atmosphere, so the warming potential is a function of how efficient the gas is to absorb infrared radiation, and how long it remains in the atmosphere. For example, in a 20 year time span, methane can retain 62 times more infrared radiation than CO2.

Figure 3 (a) shows CO 2 concentrations over the past 1000 years from ice core records, (D47, D57, Siple and South Pole) and (since 1958) form the Mauna Loa and Hawai measurement sites. The increase in CO 2 concentrations as from the onset of industrialization is evident and has followed closely the rise in CO 2 emissions from fossil fuel consumption (See the period from 1850 on in the small table).

• On the other hand, growth rates in the late 1980s, the decrease in the early 1990s, and recent increase are shown in Figure 3 (b). The smooth curve shows the same data, but variations lasting less than ten years or so were eliminated.

Figure 3. Historical CO 2 Concentrations

Source: Summary for Policy Makers and other summaries. Part of the IPCC Report for the First Meeting of the Conference of the Parties to the Framework Convention on Climate Change

Traducción figura 3a : Concentración CO2 …: CO 2 Concentration (ppmv); Sipla, South Pole, Mauna Loa, Fossil CO 2 emissions, Promedio a lo largo de cien años: 100 year Average; Años : Years

Traducción figura 3b: : Tasa de crecimiento de las concentraciones CO 2 (ppmv/año): CO 2 Concentration growth rate (ppmv/year); Año: Year

• Thorough analyses of historical records (as from 1860) on temperature and precipitation indicate that in the late XIX century a rise in temperature started to be noticed both in the Northern and Southern Hemispheres, matching an increase in CO 2 atmospheric concentrations, shown in Figure 3. This increase in temperature reached its peak in the late 1930s (Figure 4). In the following decades, global temperatures decreased slightly until the late 1970s to continue with their mounting trend.

• World climate data on the past two decades suggest that air temperature for Earth's surface exceeded 1930 maximum values. This heat wave extended to the Northern and Southern Hemispheres and has resulted in an increase in mean global temperature of approximately 0.5ºC as from mid last century.

Figure 4. Climate Anomalies from 1860 to 1994

Traducción figura 4 . Anomalias en grados C…: Anomalies in ° C; Años: Years