Climate change 'new normal,' lessons from Sandy - UN chief

* Ignore climate change at your own peril, says UN's Ban

* U.N. building sustained flood damage in superstorm

By Michelle Nichols

UNITED NATIONS, Nov 9 (Reuters) - Extreme weather sparked by climate change is "the new normal" and Superstorm Sandy that ravaged the U.S. Northeast is a lesson the world must pursue more environmentally friendly policies, U.N. Secretary-General Ban Ki-moon said on Friday.

The United Nations headquarters closed for three days when former hurricane Sandy slammed the Northeast on Oct. 29 as a rare hybrid superstorm, killing at least 121 people, swamping seaside towns and leaving millions without power.

"We all know the difficulties in attributing any single storm to climate change. But we also know this: extreme weather due to climate change is the new normal," Ban told the 193-member U.N. General Assembly.

"This may be an uncomfortable truth, but it is one we ignore at our peril. The world's best scientists have been sounding the alarm for many years," he said. "There can be no looking away, no persisting with business as usual ... This should be one of the main lessons of Hurricane Sandy."

New York City Mayor Michael Bloomberg endorsed President Barack Obama for a second term after Sandy struck, citing Obama's record on climate change and saying he believed the Democrat would adopt more policies to curb greenhouse gases in a second term. Obama won re-election on Tuesday.

The head of U.N. security, Gregory Starr, said last week that U.N. headquarters sustained severe damage when Sandy produced heavy flooding in basement levels of the world body's Manhattan complex along the East River.  Flood damage forced the relocation of a U.N. Security Council meeting on Somalia last week from its normal chambers to a temporary building inside the U.N. campus.

U.N. delegations sharply criticized the United Nations' management on Monday for an almost "total breakdown in communications" with the world body's member states after superstorm Sandy struck.

"Our global services were provided without interruption," said Ban. "However, it is clear that in focusing so much on operations and infrastructure, we fell short when it came to communications."

"We learned that too many email addresses were out of date or otherwise incorrect," he said. "And in the broadest sense, we should have done more to update member states, staff alike and wider audience at large about the impact and implications of the storm."

Michael Adlerstein, who heads a $1.9 billion renovation of the United Nations due to be completed in 2013, has said Sandy would not delay the overhaul of the U.N. complex.