quinta-feira, agosto 07, 2003
Aquecimento Global
Um perito do grupo intergovernamental das Nações Unidas sobre a evolução do clima afirmou recentemente que a recente (e presente) vaga de calor não prova o aquecimento global. Perante tal "heresia" alguns pretendem desmenti-lo utilizando argumentos que nada devem à ciência.
A página da Scientific Alliance, que se dedica a desmistificar este tipo de assuntos, afirma o seguinte:
Climate, which is affected by a myriad of different forces which are not fully understood, is constantly changing. Among the many factors influencing climate are: dust released into the stratosphere by volcanic eruptions, which reflects sunshine away from the Earth’s surface altering global climate cycles; El Niño and la Niña, rare weather patterns that cause temporary climate changes and extreme weather events which are frequently blamed on “enhanced” climate change; solar magnetism which at its maximum strength, as in the 10th and 11th centuries, appears to warm the world; and the greenhouse effect.
Since the industrial revolution, emissions of “greenhouse” gases from anthropogenic activity have increased, leading to the notion of climate change “enhanced” by anthropogenic activity. Anthropogenic CO2 emissions are estimated to be less than 10% of naturally-occurring emissions. Some scientists argue that any anthropogenic effects are negligible against the background of natural emissions of these same gases, whilst others argue that the difference is enough to upset the global carbon cycle’s balance.
The crux of the climate change debate focuses on the difficulties in collecting accurate historic data, confidence levels in predictive computer models, and outstanding questions over the impact of radiative forcing – variations in the Earth's orbit around the Sun, solar radiation, volcanic activity and atmospheric composition - on climate.
The complex nature of global climate places limitations on the predictive power of computer models, which themselves are dependent on the quality of data put in. This raises large question marks over the certainty of the results produced. Indeed, different models have produced different results, leading to predictions based upon wide margins of temperature changes. The Intergovernmental Panel of Climate Change (IPCC) has predicted changes between 1.5 and 5.58 degrees centigrade by 2100. Confidence in the models has not been encouraged by the fact that, even when using historical data, none of the existing models has been able to predict the present temperature correctly. The models are unable to account for the temperature rise between 1920 and 1940, the cooling to 1975 and the absence of warming in the satellite record since 1979.
Models are only as good as the data entered into them. Two different types of data are entered into the models, climate data and scenarios predicting CO2 emissions based upon assumptions of economic growth and energy use. Climate change data over the past 100 years contains many discrepancies. Surface temperature measurements disagree with recent measurements from satellites and balloons. Whist some researchers predict CO2 emission will be eight times pre-industrial values, others doubt they will even double.
These predictions are used to make further predictions on what impact such change will have. Different scenarios include melting glaciers, sea level change, species extinction, an increase in extreme weather events and even the collapse of thermohaline circulation in the ocean. Such scenarios have often been portrayed in cataclysmic terms, and a debate on what level of confidence the results can be given has been stifled.
posted by Miguel Noronha 10:20 da manhã
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