Nothing occupies global warming deniers more than trying to prove that the U.S. temperature record — a tiny portion of the global temperature record — is not reliable.  Now NOAA’s National Climatic Data Center has issued an excellent Q&A, “Is the U.S. Temperature Record Reliable?” that should settle that question for any objective observer.

The NCDC paper proves we should all be delighted that deniers like Anthony Watts and Steve McIntyre spend so much time on this:  It is clearly a fruitless effort that consumes time which they might otherwise spend spinning out more potent disinformation.

Consider this definitive NCDC graph comparing the U.S. temperature record since 1950 “using 1221 stations in NOAA’s Historical Climatology Network (USHCN)” [red line] with “the 70 stations that surfacestations.org classified as good or best” [purple line].

No discernible difference!

Imagine all the effort Watts and his cohorts at surfacestations.org and WattsUpWithThat have expended examining some 70 percent of the 1221 stations around the country — and all they ended up proving is that the best stations give the exact same output as all the rest of the stations!

NCDC explains exactly what this chart means:

We would expect some differences simply due to the different area covered:  The 70 stations only covered 43 percent of the country with no stations in, for example, New Mexico, Kansas, Nebraska, Iowa, Illinois, Ohio, West Virginia, Kentucky, Tennessee or North Carolina. Yet the two time series, shown [above] as both annual data and smooth data, are remarkably similar. Clearly there is no indication from this analysis that poor station exposure has imparted a bias in the U.S. temperature trends.

And this result matches a previous analysis:

Q. How has the poor exposure biased local temperatures trends?

A. At the present time (June 2009), to the best of our knowledge, there has only been one published peer-reviewed study that specifically quantified the potential bias in trends caused by poor station exposure (Peterson, 2006). The analysis examined only a small subset of stations — all that had their exposure checked at that time — and found no bias in long-term trends.

But what about all of those photos Watts et al. have assembled of temperature stations in dubious locations?

Q. Does a station with good exposure read warmer than a station with poor exposure?

A.  Not necessarily. Many local factors influence the observed temperature: whether a station is in a valley with cold air drainage, whether the station is a liquid-in-glass thermometer in a standard wooden shelter or an electronic thermometer in the new smaller and more open plastic shelters, whether the station reads and resets its maximum and minimum thermometers in the coolest time of the day in early morning or in the warmest time of the day in the afternoon, etc. But for detecting climate change, the concern is not the absolute temperature — whether a station is reading warmer or cooler than a nearby station over grass — but how that temperature changes over time.

And so in spite of the best efforts of the deniers, the American public should have every confidence in the US temperature record and the rather painfully obvious conclusion that the planet is warming:

Q. Is there any question that surface temperatures in the United States have been rising rapidly during the last 50 years?

A. None at all. Even if NOAA did not have weather observing stations across the length and breadth of the United States the impacts of the warming are unmistakable. For example, lake and river ice is melting earlier in the spring and forming later in the fall. Plants are blooming earlier in the spring. Mountain glaciers are melting. Coastal temperatures are rising. And a multitude of species of birds, fish, mammals and plants are extending their ranges northward and, in mountainous areas, upward as well.

Some may question whether the climate scientists at NCDC should spend time on this sort of report.  I think it is good to take on the deniers when it can be done in a simple, straightforward manner.  I think the entire report is worth reading.  It is a model of how real climatologists work.

As a model of how real climatologists don’t work, you can turn to the response to the NCDC paper that Watts published on WattsUpWithThat.  For reasons that should baffle everyone, he gives the task to Roger Pielke, Sr.   I’m not going to waste time rebutting his rebuttal.  It is so unserious that Pielke doesn’t even reprint the devastating figure above.  Then again, Pielke is a “climatologist” who thinks that the long-term 30-year trend in shrinking Arctic ice is somehow refuted by data “since 2008″  (see “Roger Pielke Sr. also doesn’t understand the science of global warming – or just chooses to willfully misrepresent it“).

Kudos to NCDC for this analysis.