Image: Average temperatures warmed in nearly all parts of California between 1950 to 2000. Image credit: NASA/JPL/Cal State L.A Click for Larger Image
Average temperatures in California rose almost one degree Celsius (nearly two degrees Fahrenheit) during the second half of the 20th century, with urban areas leading the trend to warmer conditions, according to a new study by scientists at NASA and California State University, Los Angeles. Results of the study appeared in the journal Climate Research.
But 50 years of temperature trends hardly proves anything relevant about climate change, other than its gotten warmer in the past fifty years. 50 years in terms of our planet and the suns processes is a blink. I have to think that because NASA chose to co-author this paper with researchers at California State University, that some of the statewide “global warming as man-made problem bias” crept into the thinking for the purpose of this paper, i.e. “we need another study to show that its getting hotter so action is justified”.
What is troubling about this study is that many of California’s historical climatological stations, when done on a 100 year trend, rather than a 50 year trend, show a net cooling over the period, or a reversal of trend. The northern Sacramento Valley has very few reporting stations that go back 100 years, so I only have 4 data points, but it makes me wonder just what data the NASA/CSU study used to come to the conclusion that our area has warmed 1.1 degrees F over the last 50 years.
I’ve prepared some side-by-side graphs below of Sacramento Valley stations to illustrate that point:
My data source: U.S. Historical Climatology Network (USHCN) Data Set
Yet the NASA/CSU paper claims “The only area to cool was a narrow band of the state’s mainly rural northeast interior“. None of the stations above are in that area, but are in the North Sacramento Valley.
Even odder than that, cold and snowy Mt. Shasta, where you’d expect to hear about depleted snowpack, it’s melting glacier on the side of the mountain, and other “signatures” of “global warming” shows a significant drop in temperatures over the last 50 years. yet the NASA/CSU study for that area concludes that a 2.1 degree F rise in temperature occurred.
Granted a few data points don’t equal a complete study, but the fact that I’ve been able to find and plot in a couple of hours, several places that don’t match the trends in the NASA/CSU study calls their methodology into question. Note the cities I used are all small rural cities, but the NASA/CSU study plotted major, medium, and minor cities in California to draw their conclusions. From their own paper they admit that the areas that have grown the most have shown the greatest temperature increases:
Southern California had the highest rates of warming, while the NE Interior Basins division experienced cooling. Large urban sites showed rates over twice those for the state, for the mean maximum temperatures, and over 5 times the state’s mean rate for the minimum temperatures. Average temperatures increased significantly in nearly 54 percent of the stations studied, with human-produced changes in land use seen as the most likely cause. The largest temperature increases were seen in the state’s urban areas, led by Southern California and the San Francisco Bay area, particularly for minimum temperatures.
For example, look at Pasadena, CA once a small city itself, but in the last 100 years it became a dot in the sea of the second largest American City, Los Angeles. It’s temperature trend, unsurprisingly, is sharply upward, for both the 50 and 100 year trends. Its drowning in a sea of asphalt and concrete, is it any wonder it shows a temperature increase?
The inescapable conclusion is that the NASA/CSU study is plotting the effects of urban heat islands, and applying that trend to the entire landmass of California to reach the conclusions they have mapped onto the state map of temperature trend they present.
A simple filtering based on urban growth factors would yield a temperature map with a far different result.
To their credit though, they recognize this fact: “If we assume global warming affects all regions of the state, then the small increases our study found in rural stations can be an estimate of this general warming over land. Larger increases would therefore be due to local or regional changes in land surface use due to human activities.”
For the most part, “urban warming” has dwarfed “global warming” in its magnitude, a fact that is lost on some who look at temperature data from weather stations worldwide and treat them all equally in the quest to prove a theory.