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¿Por qué se calienta la Tierra?

El cambio climático es la variación global del clima de la Tierra y se debe a causas naturales y también a la acción humana. Normalmente los cambios se han producido a lo largo de miles de años, lo que ha posibilitado que la vida en el planeta se adapte a ellos, pero en el último siglo, como consecuencia de la industrialización en el mundo desarrollado, las variaciones ocurren a una velocidad sin precedentes.

De forma natural, el dióxido de carbono y otros gases como el metano y el óxido nitroso forman una capa en la atmósfera que retiene el calor en la Tierra e impide que éste regrese al espacio, lo que haría del planeta un lugar frío y yermo en el que sería imposible la vida tal y como la conocemos.

 

Pero la industrialización y, en particular, la combustión de cantidades cada vez mayores de petróleo, gasolina y carbón, la tala de bosques y algunos métodos de explotación agrícola han aumentado el volumen de dichos gases que es liberado a la atmósfera.

Según la secretaría de la Convención sobre Cambio Climático, el mundo industrializado ha conseguido que la concentración de estos gases haya aumentado un 30 por ciento desde el siglo pasado, cuando, sin la actuación humana, la naturaleza se encargaba de equilibrar las emisiones.

Esta elevada concentración hace que la capa de gases sea «más gruesa», por lo que retiene más el calor y los rayos infrarrojos del sol, y, actuando del mismo modo que lo hace un invernadero, hace subir las temperaturas.

Si las emisiones continúan creciendo al ritmo actual, es casi seguro que a lo largo del siglo XXI los niveles del dióxido de carbono atmosférico serán casi el doble de los registrados en la era preindustrial y es posible, incluso, que se tripliquen.

Según cálculos matemáticos, la temperatura de la superficie terrestre aumentará entre 1,4 y 5,8 grados centígrados para el año 2100, cuando en el siglo pasado se registró un aumento de la temperatura de 0,6 grados. Aun cuando el aumento real sea el mínimo previsto, será mayor que en cualquier siglo de los últimos 10.000 años.

Para la mayoría de los científicos, el cambio climático o calentamiento terrestre ya ha comenzado a producirse y ven como prueba de ello un mayor registro de ciclones, huracanes, inundaciones y sequías. También han constatado que las temperaturas del aire ártico aumentaron cinco grados el siglo pasado, las cubiertas de nieve disminuyeron un 10 por ciento desde los años sesenta y cuencas hidrográficas como las de los ríos Níger y Senegal o el lago Chad bajaron entre un 40 y un 60 por ciento. Las consecuencias que se predicen varían en grado y van desde impactos significativos hasta otros catastróficos. África parece condenada a llevarse la peor parte.

En: Ciencia — Noviembre 7, 2006

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