The Intergovernmental Panel on Climate Change (IPCC) was created by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 for the purpose of studying and openly disclosing technical and socioeconomic information, and the relevant impact of the risk factors of the human population so that mechanisms for adaptation and mitigation of global climate change effects might be created.
In February 2007 IPCC published the results of the Fourth Assessment Report on the planet's Climate Changes, called IPCC-AR4 (Alley et. al., 2007). The results show a global average increase of temperature, between 1.8ºC and 4.0ºC until the year 2100. This increase might be even greater (6.4ºC) if the population and the economy continue to grow rapidly and if we maintain the intensive consumption of fossil fuels. A more reliable estimate, however, indicates an average increase of 3ºC, if we assume that the levels of carbon dioxide will stabilize at 45% above the now present average. It also points out, with over 90% reliability, that human activity is responsible for most of the temperature increase observed in the last 50 years.
Changes in the amount of greenhouse effect gases and aerosol, solar radiation, and in the characteristics of the Earth's surface alter the balance of energy of the climate system. These changes are stated in terms of radiative forcings, which are used to compare how human contribution and natural factors work to influence the warming or cooling of the climate system. Radiative forcing is a measure of the influence that a factor has in altering the balance of incoming or outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism. Since the Third Assessment Report (TAR) new observations and related modeling of greenhouse gases, solar activity, land surface properties, and some aspects of aerosols have led to improvements in the quantitative estimates of radiative forcings.
The concentration of carbon dioxide (CO 2 ), methanol (CH 4 ), and nitrous oxide ( N 2 O ) in the atmosphere has significantly increased as a result of human activity since 1750. This increase is primarily due to the burning of fossil fuel and changes in land use, whereas methane and nitrous oxide are primarily due to agriculture.
The most important greenhouse gas resulting from human activity is carbon dioxide. Its concentration in the atmosphere has been increasing in the last 650,000 years, from 180 ppm to 300 ppm. However, there has been a more accentuated increase since the pre-industrial era, rising from 280 ppm to 319 ppm in 2005, being the largest increase in the last decade, between 1995 and 2005.
It is very likely that the increase in methane concentration in the atmosphere is due to anthropogenic activities, predominantly agriculture and the use of fossil fuels. Methane concentration went from 715 ppb in the pre-industrial era to 1,732 ppb in the beginning of the 90's and to 1,774 ppb in 2005. Growth rates have declined in the last decade, being nearly constant until 2005. And lastly, nitrous oxide, which also had an increase in its concentration in the atmosphere, primarily due to agriculture, went from a pre-industrial value of 270 ppb to 310 in 2005, with the growth rate being practically constant since 1980.
The understanding of human activity influences on climate warming or cooling has improved since the last assessment report, leading to greater certainty that human activities since 1750 have contributed to the increase in concentrations of greenhouse effect gases in the atmosphere. The combined radiative forcing due to increases in carbon dioxide, methane, and nitrous oxide, and its rate of increase during the pre-industrial era is very likely unprecedented in more than 10,000 years. The radiative forcing of carbon dioxide increased 20% between 1995 and 2005, and it is the largest change in at least the last 200 years.
The increase in concentration of greenhouse gases and their effects are better understood in this report due to improved in situ measurements using satellites, ground-based measurement stations, and more comprehensive modeling, though there are still uncertainties concerning this complex system as far as its present and future behavior.
Considering global average temperatures of the Earth's surface and oceans since 1850, the ten warmest years in history are from 1995 to 2006. The increase rate between 1850 and 1899 was 0.57 ºC, while between 2001 and 2005 it went up to 0.95ºC, an average of 0.76 ºC for the period.
Analyses of ocean characteristics have shown climate changes along the years. Among them are changes in Artic ice temperatures, changes in precipitation distribution, ocean salinity, wind patterns, and extreme weather events such as droughts, heavy precipitation, heat waves, and the intensity of tropical cyclones.
The warming of oceans and the atmosphere, along with glacier melting, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without the anthropogenic element, and it is obviously not due to natural causes alone.
Continuous emission of greenhouse gases could cause warming and lead to many changes in the global climate system in the 21 st century. The most probable estimates of temperature increase on the surface take into account the extremes scenarios of high emissions (A2) and low emissions (B2), which have been used in the Third Assessment Report. Only the analyses of extreme climate use the generated projections from the Fourth Report. The more optimistic estimate (B1) indicates an increase of 1.8 ºC and the more pessimistic (A1F1) indicates an increase of 4 ºC (Fig. 1).
Fig.1: Solid lines are multi-model global averages of surface warming (relative to 1980-99) for scenarios A2, A1B, and B1, shown as continuations of the 20 th century simulations. The shaded area denotes a strip more or less one standard deviation for the individual annual averages of the models. The orange line represents the model in which concentrations were held constant at year 2000 values. The grey bars on the right indicate the best estimate (solid line within each bar) and the likely range assessed for the six scenarios of the Special Report on Emission Scenarios (SRES) – IPCC 2000. The assessment of the best estimate and likely ranges in the grey bars includes the Atmosphere-Ocean General Circulation Models (AOGCMs) on the left of the figure, as well as results from a hierarchy of independent models and observational constraints.
Observational evidences of continents and oceans indicate that several natural systems have been affected by regional climate changes, especially temperature increase. Preliminary indicators show that certain human systems have already been affected by droughts and floods. Biological systems are vulnerable to climate changes and some will be irreversibly damaged.
The Executive Summary of observational studies of climate variability and global and regional modeling of future scenarios of climate changes for Brazil and South America, publicized by the Climate Studies and Weather Forecast Center of the National Space Research Institute (CPTEC/INPE), in collaboration with the Department of Atmospheric Science of the University of São Paulo (USP/IAG) and the Brazilian Foundation for Sustainable Development (FBDS), show the average projections for Brazil, taking into consideration the results of A2 and B2 models.
According to this report, between the years 2071 and 2100 the temperature could vary by between 4 and 8ºC in the Amazon for A2 and 3 scenarios, and by 5ºC for B2 scenario, with great spatial variability. In the Northeastern region the warming could reach 4ºC in an A2 pessimistic scenario and 2 to 3ºC on a B2 optimistic scenario. In the A2 scenario the warming in the Mid-West and Southeast could vary by 4 to 6ºC, while the B2 scenario shows 2 to 3ºC rate. In the South, scenario A2 indicates a 3 to 4ºC warming in the A2 scenario and between 2 and 3ºC in the B2 scenario. Though the warming is greater in the tropical region of South America as for the several regional models employed, the projections of these models differ on where the greatest warming (over 8ºC) occurs: in the Eastern or Western Amazon, depending on the regional model used (Marengo et al. 2007).
Climate change impact magnitudes were more carefully studied in this Fourth Report due to a larger amount of available information, and also to other places coverage.
Poor communities, in particular those in high risk areas, can be the most vulnerable. They usually have a more limited adaptation capability and are more dependent on climate sensitive resources, as the local access to water and food. In places where extreme climate events become more intense and/or more frequent, the economic and social costs of those events will be higher, and this increase will be substantial in the more directly affected areas.
Studies confirm that Africa is one of the most vulnerable continents to climate variability and change, due to multiple tensions and low adaptation capability. We are noticing some adaptation to the present climate variability; however it might not be enough for future climate changes.
These changes could affect the sustainable development of most developing countries in Asia , since they are added to the already existing pressures on natural resources and the environment, associated to fast urbanization, industrialization, and economic development. The availability of water in Central, South, East, and Southeast Asia , especially in large hydrographical basins, could decrease.
Projections for Brazil are consistent in both the Third and Fourth Report models. However the uncertainties are greater concerning rains, especially in the Southeast and Mid-West. As for precipitation on a continental scale, the Northeast is the region which shows the most certainty in future climate projections for 2071-2100. The Northeastern semi-arid could become a desert in a hotter climate in the future. This could affect regional subsistence farming, forcing population migration, thus creating waves of “climate refugees”.
Bibliographical references
Adger, N. et al. Mudança do Clima 2007: Impactos, Adaptação e Vulnerabilidade à Mudança do Clima: Sumário para os Formuladores de Políticas . 26/04/2007. Avaliado da Internet: http://www.cptec.inpe.br/mudancas_climaticas/ .
Alley, R. et al. Contribuição do Grupo de Trabalho I para o Quarto Relatório de Avaliação do Painel Intergovernamental sobre Mudanças do Clima : Sumário para os Formuladores de Políticas . 26/04/2007. Avaliado da Internet: http://www.cptec.inpe.br/mudancas_climaticas/ .
Marengo J, A.; Nobre, C. A.; Salati, E.; Ambrizzi, T.: Caracterização do clima atual e definição das alterações climáticas para o território brasileiro ao longo do Século XXI: Sumário Técnico [online]. 26/04/2007. Avaliado da Internet: http://www.cptec.inpe.br/mudancas_climaticas/ .
NAE 2005a: Mudança de Clima, Vol. I: Negociações internacionais sobre a mudança de clima; vulnerabilidade, impactos e adaptação à mudança de clima. Cadernos NAE, Núcleo de Assuntos Estratégicos da Presidência da República, NAE-SECOM 2005. Brasília, 250p.
