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The Earth’s climate has undergone natural variations over time. However, the Intergovernmental Panel on Climate Change (IPCC) concluded that human activities have contributed significantly to the change observed in recent decades. The planet surface absorbs some of the incoming solar radiation which is then converted into heat, while the rest is radiated back to the space at longer wavelengths (infrared, Houghton et al., 2000, IPCC 2007). There are naturally occurring compounds in the atmosphere known as greenhouse gases or GHG: water vapor (H₂O), carbon dioxide (CO₂), ozone (O3), methane (CH₄) and nitrous oxide (N₂O), which capture part of the energy radiated by the Earth and return it back, warming the atmosphere and the Earth’s surface (IPCC, 2007). This phenomenon is known as greenhouse effect; without it, the Earth would be 33 °C colder, on average (Houghton et al., 2000; IPCC 2001).

IPCC has defined climate change as "... any change in climate over time, whether due to natural variability or as a result of human activity." This definition differs from that proposed by the UN Framework Convention on Climate Change (UNFCCC): "... a change in climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and whichs is in addition to natural climate variability observed over comparable time periods" (IPCC, 2007).

Climate change is accelerated by increased GHG levels in the atmosphere (NAS, 2001; IPCC 2007). Although GHGs are emitted by natural processes (e. g. microbial reactions, volcanoes and seawater evaporation, among others; NAS, 2001), human activities (fossil fuel combustion, production of coolants, deforestation, land-use changes, biomass burning, etc.) release additional quantities of GHGs, in addition to others that do not occur naturally, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and halons, commonly used in refrigeration, air conditioning and, the latter, as fire extinguishers (IPCC, 2007). CO₂ is considered the most important GHG because of its prolonged life in the atmosphere (between 5 and 200 years); its radiative forcing (1.3-1.5 Wm^-2) –an indicator of its climate-change potential-; and the significant rise in its concentration in the atmosphere (38% higher than in preindustrial times); its warming potential is set as 1.0 to be used as reference for determining the potential of other GHGs (NAS, 2001, IPCC, 2007).

Mexico contributes about 1.5% to CO₂ emissions from fossil fuel consumption and combustion worldwide, far from the countries with the highest GHG emissions: the United States of America and China (IEA, 2008). Although there are important differences in the magnitude of emissions by country, GHGs are dispersed in the atmosphere and climate change is occurring globally, hence affecting the whole planet (IPCC, 2007). The main changes associated with global warming are the rise in sea level and temperature (air and sea surface), changes in rainfall patterns, reduction in the extension and thickness of the ground ice layer (glaciers) and ice caps, and changing patterns of atmospheric and oceanic circulation (increased frequency, persistence and intensity of El Niño-Southern Oscillation; Magaña, 1999; NAS, 2001; IPCC 2007).

It is anticipated that the mean surface temperature in Mexico in 2020 may be 1.5 to 2.5 °C higher than today’s and would reach 2 and 4 °C by the year 2080. The sea temperature will also rise: in the Caribbean, Gulf of Mexico and Pacific it could rise between 1 and 2 °C from 2020. As for rainfall, studies suggest that winter rainfall could decrease in 15 percent in some parts of the country and 5 percent in the Gulf, and the onset of the rainy season could be delayed in many parts of the country. The number of severe storms may increase causing floods and landslides. In contrast, more extreme and prolonged droughts are expected to occur (Semarnat-INE, 2006). According to a study included in the Third National Communication to the United Nations Framework Convention on Climate Change, the types of vegetation that could undergo the greatest changes in area are grasslands, shrubland and oak forests (Semarnat-INE, 2006). The effects on human populations are also important. About 20 million persons are settled in high flood-risk areas in Mexico, making them vulnerable to the effects of extreme hydro-meteorological events (Magaña & Gay, 2002).

At a global scale, projections indicate that the CO₂ concentration in 2100 could range between 540 and 970 parts per million and that the rise in the planet’s mean surface temperature will be of 1.8 to 4 °C in the last decade of the twenty first century. Increases in temperature are likely to occur in high latitudes while decreasing by up to 20% in subtropical regions by 2100. Projections foresee that the global mean sea level will rise between 18 and 59 cm by the end of the century, although with regional variations (IPCC, 2007).

Given this scenario, measures are required at national and international levels. In this context, Mexico has signed and ratified (in 1992 and 1993, respectively) the UN Framework Convention on Climate Change (UNFCCC), whose objective is to achieve stabilization of GHG concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system (UNFCCC, 2009). The Kyoto Protocol emerged as a UNFCCC instrument; it proposes the quantified reduction in emissions along with flexible mechanisms to achieve it. Mexico signed the protocol in 1998 and ratified it in 2000 as a “non-Annex I” country (developing countries; UNFCCC, 2009). Countries are currently working on fulfilling their commitments under the UNFCCC and the Kyoto Protocol, which came into force in February 2005 (UNFCCC, 2009).

Mexico has fulfilled its international commitments and has even taken the lead in developing programs and studies on climate change. It has presented four national communications including GHG emission inventories. Additionally, it has studies and programs dealing with climate-change mitigation technologies in forestry and energy through a long list of programs and initiatives. Prominent among them are the Trust Fund for Electric Energy Savings (FIDE, for its acronym in Spanish), use of cleaner fuels, promotion of renewable energy and programs to preserve and manage forest ecosystems to foster the conservation and restoration of forest areas that capture carbon. Furthermore, the creation of the Mexican Committee for Projects to Reduce Emissions and Capture Greenhouse Gases was published in the Federation Official Gazette in January 2004 (DOF, 2004) and the GHG Mexico program (Mexican pilot program for calculating and reporting GHGs) was created in August 2004. The latter is a joint agreement between the Ministry of Environment and Natural Resources (Semarnat), the Commission on Private-Sector Studies for Sustainable Development (CESPEDES, for its acronym in Spanish), the World Resources Institute (WRI) and World Business Council for Sustainable Development (WBCSD; Semarnat et al., 2005). Mexico also issued the Special Climate Change Program, the aspirational goal of which is "... to achieve a 50% reduction in GHG emissions by 2050, relative to those emitted in 2000. Thereby, Mexico aims to contribute to a possible scenario of stabilization of GHG concentrations in the atmosphere at a level not exceeding 450 parts per million of carbon dioxide equivalent (CO₂e) ... " (Poder Ejecutivo Federal, 2009).

References

DOF. Acuerdo por el que se crea con carácter de permanente la Comisión intersecretarial denominada Comité Mexicano para Proyectos de Reducción y Captura de Emisiones de Gases de Efecto de Invernadero. México. 2004.

Houghton, R. A., D. L. Skole, C. A. Nobre, J. L. Hackler, K. T. Lawrence y W. H. Chomentowski. Annual fluxes of carbon from deforestation and regrowth in the Brazilian Amazon. Nature 403:301-304. 2000.

IEA.  2008. CO2 emissions from fuel combustion 2008 Edition. France. 2008.

IPCC. Climate Change 2007: The Physical Science Basis. Summary for Policymakers. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. 2007.

Magaña, V. O. (ed.). Los impactos de El Niño en México. Centro de Ciencias de la Atmósfera UNAM, Segob. México. 1999.

Magaña, V. O. y C. Gay. Vulnerabilidad y adaptación regional ante el cambio climático y sus impactos ambientales, sociales y económicos. Gaceta Ecológica 65: 7-23. 2002.

NAS. Climate Change Science. An Analysis of some key questions. National Academy Press. USA. 2001.

Poder Ejecutivo Federal. Programa Especial de Cambio Climático 2009-2012. Versión para consulta pública. México. 2009.

Semarnat, CCE, CESPEDES, WRI y WBCSD. Programa GEI México. 2005. Disponible en: http://www.geimexico.org/acerca.html Fecha de consulta: agosto de 2005.

Semarnat-INE. México Tercera Comunicación Nacional ante la Convención Marco de las Naciones Unidas sobre el Cambio Climático. México. 2006.

UNFCC. Parties & Observers States. Ratification Status. 2009. Disponible en: http://maindb.unfccc.int/public/country.pl?country=MX