Warmest twelve-month periods on record. June 2011-May 2012 is the record-setter. View bigger. (NOAA)

NOAA’s National Climatic Data Center also reports today that:

* the year-to-date period (January-May) has been the warmest on record, 5 degrees above average

* the spring period (March-May) was warmest on record in the U.S., crushing the previous warmest spring (1910) by 2 full degrees and an impressive 5.2 degrees above the 1901-2000 average.

* the month of May was 2nd warmest on record, 3.3 degrees above average.

Year-to-date temperatures compared to normal (NOAA)

“The 12-month period encapsulated the second warmest summer, fourth warmest winter, and the warmest spring on record,” NOAA said.

Every single state (in the Lower 48) was warmer than normal during this stretch, except for Washington state, which was near normal.

States in red had their warmest 12-month June-May period on record (NOAA)

Commentary: Global warming link?

It’s natural to wonder whether these warm weather records are related to increasing concentrations of greenhouse gases in the atmosphere from the burning of fossil fuels.

There is most likely a connection, but we have to be a little careful about stating this without qualification since the continental U.S. represents just around two percent of the Earth’s surface.

The best way to evaluate global warming is to examine global scale indicators over long time frames rather than small areas of the globe over short time frames.

Having said that, it’s reasonable to surmise the U.S. temperatures are warmer than they would’ve been had greenhouse gas levels not gone up. It’s well-established that as long as greenhouse gas levels are elevated and rising, the chance of setting warm weather records at all scales - local, regional, continental, hemispheric and global - increases.

(Not to mention, global temperatures have been warm. April was fifth warmest on record globally )