For many years, there has been a long-term equilibrium between the energy coming from the Sun to the Earth and energy that is irradiated back to space from the planet surface. This equilibrium left the Earth’s surface temperature constant on a long term. Nevertheless, since the 19th century, this temperature has increased progressively. The vast majority of the scientific community and the general public are certain that this temperature rise is due to an unstable greenhouse gas balance. Greenhouse gases (GHG) act by retaining the infrared radiation that is reflected from the Earth surface, absorbing it and consequently keeping this energy in the atmosphere. An excessive amount of these compounds leads to an accumulation of energy resulting in higher global temperatures.
There are several compounds that can achieve this greenhouse effect. Main GHGs are:
Carbon dioxide (CO2), which is produced mainly through burning fossil fuels. Roughly 20 gigatonnes of this gas are generated from combustion. Other sources include solid wastes and vegetables. CO2 can be absorbed by plants via photosynthesis, producing carbohydrates and oxygen.
Methane (CH4) is a gas generated from the production and transport of coal, natural gas, and oil. Enteric fermentation of rumiants and manure management are also important sources of CH4. It has a higher ability for absorbing heat than CO2, and additionally can remain in the atmosphere for around a decade. Reducing methane emissions can also be considered as a measure with regard to energy efficiency, given methane is used as fuel.
Nitrous Oxide (N2O) takes part in the Nitrogen Cycle, and is produced mainly from the management of soils, sewage and animal manure, as well as from combustion of fossil fuels. N2O is also produced naturally from biological processes within soils and water.
Fluorinated gases such as hydrofluorocarbons (HFC), perfluorocarbons (PFC) and sulfur hexafluoride (SF6) are synthetic GHGs which are produced from several industrial processes. It is established that little amounts of these compounds lead to large effects on global temperature given they have a high Global Warming Potential (GWP).
The awareness of the influence of GHGs on global warming lead to the adoption of the Kyoto Protocol in 1997. This global agreement has set several GHG emission reduction objectives for each country. Until 2011, 191 states have signed and ratified the protocol, including European countries. When the protocol was agreed the EU-15 countries accepted to have, in 2008-2012 period, 8 % less emissions compared to 1990 emission levels. This overall objective has been translated into specific national emission reduction or limitation targets. New non-EU15 countries have also committed themselves to limiting their emissions.
According to 2010 data, EU-15 emissions were 11% below 1990 levels. For 2020, the 27 Member States have to reduce overall greenhouse gas emissions by 20% compared to 1990 levels. However, current climate change monitoring methods for determining the European carbon budget are not accurate enough, and are not adapted either to deal with spatial and temporal variations. Several research projects, such as CARBOEUROPE-IP and GHG EUROPE, focus on reducing the uncertainty in GHG estimations and predictions.
United States Environmental Protection Agency (EPA)
European Commission Climate Action