What can be said about the report by the National Academy of Sciences? What is the largest energy source in the US today?

W: Mr. Welch, do you think there is any doubt now that global warming exists?
M: Let me put it this way. A few determined skeptics don’t accept it, but the over-whelming majority of scientists do. The report the National Academy of Sciences issued was very balanced. They noticed some uncertainties, for example, when and where impacts might be felt and to what degree. But the conclusion was that the earth is warming. This change is induced by human activity and it will get worse.
W: Do a few degrees of warming really matter?
M: The earth is warmed by I degree Fahrenheit in the last 100 years, more in some places, like the Arctic, where there has been an increase of 4 to 5 degrees since the 1950s. Polar bears are having a terrible time there and may be extinct by the end of this century. Already, we are seeing changes in Alaska, where roads are buckling in places and some major pipelines no longer fit together. Cold water fish that used to be found off the Alaskan Coast are no longer there.
W: Can a new energy policy help?
M: Energy policy is climate policy since fossil fuels are the main sources of green-house gases, so the question becomes: Where do we get our energy? In the United States, 51％ of electricity comes from coal, 20％ nuclear, 16. 5％ natural gas, 7％ hydroelectric, 3％ oil and the rest, renewables, geothermal, wind, and solar.
W: How much power can we realistically expect to derive from renewable sources?
M: 10％ by 2020 is realistic or with a considered effort, 30％ by 2050. Without major breakthroughs, it’s hard to get beyond a third, because most renewables are intermittent. You need better ways of storing the energy.