Rates of warming observed in the Lower 48 states over two periods. Top: from 1912-2011. Bottom: from 1970-2011. (Climate Central)

Interactive report website: The Heat is On: U.S. Temperature Trends

From 1970 to 2011, the rate of climate warming in the contiguous U.S. was three times greater than it was for the last 100 years as a whole. The century-long warming trend (1912-2011) of 0.127 degrees (F) per decade (1912-2011) stepped up to 0.435 degrees per decade (1970-2011).


Top: Cenury long temperature record in Md. Bottom: How Maryland’s warming since 1970 compares to other states. (Climate Central)

* Maryland’s warming rate tripled from 0.176 degrees per decade (1912-2011) to 0.508 degrees per decade since 1970.

* Virginia’s warming rate quadrupled from .107 degrees per decade (1912-2011) to .456 degrees per decade since 1970


Top: Cenury long temperature record in Va. Bottom: How Virginia’s warming since 1970 compares to other states. (Climate Central)

Warming rates in the mid-Atlantic fell somewhere in the middle:

* Maryland‘s century-long warming rate ranked 20th among the 48 states, and 17th since 1970.

* Virginia’s century-long warming rate ranked 29th, and 24th since 1970.

The least warming occurred in the Southeast U.S. where a few states even have a slight (non-statistically significant) century-long cooling trend (Arkansas, Georgia, and Alabama) but warming since 1970.

Related: Global warming in America: Arizona’s heating up the fastest, Florida the slowest

The report emphasized the varying rates of warming across the states, with some states warming many times faster than others.

“...between 1912 and 2011 the top 10 fastest-warming states heated up 60 times faster than the 10 slowest-warming states,” the report said.

The differences between states have decreased since 1970 as the warming has occurred more consistently across the Lower 48.

The report does not include explicit projections of the future but conveys an expectation warming will continue due to the dominating role of increasing greenhouse gas on the course of temperatures.

Just last week, NOAA announced the last 12 months had been the warmest on record in the U.S. along with the spring (March through May) period and first five months of 2012.

But Climate Central cautioned against simply extrapolating present warming into the future due to the full range of factors operating on the climate:

....natural variability and the future emissions -- of both heat-trapping greenhouse gases and cooling aerosol pollutants -- will shape future rates of warming.

. . .

Methodology notes

The analysis was conducted using temperature data from NOAA’s National Climate Data Center U.S. Historical Climate Network (U.S. HCN), version 2. NOAA says the data, originating from 1221 stations, undergo extensive quality control measures and adjustments to account for “historical changes in station location, instrumentation, and observing practice.” Its methods remove warming resulting from urbanization.

. . .

Climate Central is transparent in noting the rates of warming reported are somewhat dependent on choices of starting points for the analysis. It explains:

Just as in every statistical analysis of trend patterns, the magnitude of the trend can depend strongly on the starting point. For example, the 1930s were an unusually warm decade in much of the U.S., so if we had started there, the warming trends would have looked weaker over subsequent decades. The 1970s were a relatively cooler period in some parts of the U.S., making some of the 40-year trends especially striking.