But he also told lawmakers that he views nuclear power and coal as critical parts of the nation's energy mix and said he was optimistic that ways can be found to make coal a cleaner energy source by capturing its carbon dioxide emissions.

Chu, nominated by President-elect Barack Obama to head the Energy Department, appeared before the Senate Energy and Natural Resources Committee where he received immediate support from both Democrats and Republicans.

Committee chairman, Sen Jeff Bingaman, a Democrat, said Chu has "the insight and vision" to press Obama's energy policies at the department. Bingaman said he saw no serious opposition to Chu's nomination and that a committee vote approving his selection would like occur later this week.

Chu, a Chinese-America who has been director of the Lawrence Berkeley National Laboratory since 2004, told senators that climate change is "a growing and pressing problem" and the nation's dependence on oil represents a threat to the US economy and security.

Of the risks from global warming, Chu said: "It is now clear that if we continue on our current path, we run the risk of dramatic disruptive changes to our climate system in the lifetimes of our children and grandchildren."