VOA常速英语:The Science of Climate Change

Climate negotiators are meeting in Durban, South Africa beginning from November 28-December 9 to discuss the planet's changing climate.

The first decade of this century was the hottest on record. 

Polar ice is melting.

Global sea levels are rising.

And the vast majority of scientists attribute the changes to greenhouse gases, both natural from water vapor and man-made from burning fossil fuels, that trap heat in the lower atmosphere. 

"Since roughly the 1850s or so, we've seen an increase globally of about eight-tenths of a degree Celsius, so that's roughly 1.4 degrees Fahrenheit," said Todd Sanford, a climate scientist at the Union of Concerned Scientists in Washington. 

A one-degree difference is not noticeable in daily temperatures,  but a one-degree change in global average temperature is significant.

"One way to put that in perspective is that in the last Ice Age when there was, you know, a mile of ice above much of North America, the temperature difference between then and now was only roughly five or six degrees Celsius," Sanford said.

Alden Meyer, the director of climate strategy and policy at the Union of Concerned Scientists, says global warming affects weather and water cycles.

"You have increased flooding and extreme downpours combined with droughts and desertification in some regions of the world.  So there's tremendous variability here, and we're seeing that with extreme weather events on the increase, not only here in the U.S. but around the world," Meyer said.

A U.N. report shows that climate change hits poorer countries hardest.

William Orme with the United Nations Development Program explains:

"They tend to be arid, they tend to be rural, and they tend to be therefore most vulnerable to extreme weather events, drought, typhoons and deteriorating productivity of their soil resources, forest resources and fisheries," Orme said.

And global efforts to curb emissions and slow change have not helped yet. Again climate scientist Todd Sanford:

"Last year saw the largest single increase in history to the largest emissions amounts," Sanford said.    

NASA satellite evidence shows solar fluctuations have only a slight impact on global temperatures.

And while the vast majority of climate scientists agree that human activities play a role in climate change, they are not certain how that affects the planet.

Fred Singer is a well known climate change skeptic. He says there is not enough evidence to link human activities, climate change and environmental impacts. 

"Supposing the other side is wrong?  They are forcing us to make tremendous economic sacrifices which will induce poverty in the world," Singer said.

Other climate change scientists counter that argument, saying greener technologies can be viable -- environmentally and economically.