By Jim Steele

A year ago, when passing through Huntsville, Alabama, I had the great good fortune to sit down with Roy Spencer and John Christy for a pleasant extended lunch. As we were leaving John gifted me his new book, “Is It Getting Hotter in Fresno…or Not?” The city of Fresno might not resonate with most people but having studied the effects of climate on ecosystems in California for 30 years, I knew it would be an invaluable contribution to my understanding. On the cover is young boy staring to the heavens, so I also hoped that meant that John would explain climate change at the recommended level of a 6^th grader to better reach the general public.

But climate change is complex, and can’t be explained by any simplistic, single magical control knob. A better title for his book would have been “How Honest Scientists Adjust Temperature Data and Evaluate Trends.” The young boy on the cover represented John’s life as a “weather geek” with an unwavering desire to understand climate and weather since middle school. Throughout the book, Christy’s uncompromising integrity is obvious as he devotes several chapters to explaining how and why temperature data MUST be adjusted before any comparisons between weather stations can be meaningfully evaluated. He readily admits however those adjustments are part science and part an art form, requiring a thorough knowledge of the landscapes surrounding each weather station. Without understanding those landscape effects Christy warns “the adjustment procedure is heavily influenced by what the scientist expects. So rather than objective information, we have pre-determined information>”

You might need to read twice the chapters on why temperature adjustments are needed, but I suggest you do. It points out how different landscapes, natural or altered, affect the weather. That will help you separate good adjustments from bad adjustments. Christy saw firsthand how each change in the location of Fresno’s weather station brought it to a new landscape. He witnessed the effects growing urbanization on various areas of the region. Too many climate skeptics readily assume all adjustments are driven by a political bias. Indeed, without a thorough knowledge of the surrounding landscape changes, applying a one-size-fits-all algorithm and the expectation that any warming must be driven by rising CO2, will certainly bias temperature adjustments.  But good skeptical climate scientists, like John Christy, understand there are several important variables affecting weather, and good adjustments must be made.

While Fresno’s weather holds little interest for most, especially if they have never been there, I was eager to read John’s analyses. Fresno is just 60 miles southwest of Yosemite National Park, whose climate I had studied as part of my research on northern California’s ecosystems and wildfires. Fresno is a growing city surrounded by grasslands of the San Joaquin Valley 300 feet above sea level, where lost wetlands and irrigation affect temperatures. In winter Fresno is affected by tule fogs, while Yosemite’s forests are buried in snow at 4000 feet. Nonetheless, like Christy’s analysis of Fresno’s temperature trends, the US Historical Climate network determined the maximum temperatures of Yosemite have not been warming, in contrast to significantly rising minimum temperatures. A similar lack of warmer maximum temperatures since 1930 has been reported for all northern California.

Using Christy’s adjustment methodologies, maximum Fresno temperatures declined as did Yosemite’s between 1930 and 2010, while minimum temperatures behaved very differently, steadily warming. After accounting for urbanization effects, he concluded, “I have more confidence that the natural climate of Fresno has not warmed over the past 130 years and the upper bound of the natural TMAX (maximum temperatures) would be about +0.05 °F/decade.” And despite the uptick since 2010, there has been no statistically significant daytime warming in Fresno.

In contrast there has been a significant rise of 0.51°F /decade in the minimum temperature. As illustrated in the lights of the satellite photo, the current location of Fresno’s weather station (KFAT) is the Fresno airport located in the heart of Fresno’s increasing urban heat island. Due to human alteration of that landscape, KFAT is now 6°F warmer than in the late 1880s. Clearly maximum and minimum temperatures are being driven by different dynamics. Thus, they should be analyzed separately as Christy has done. Averaging maximum and minimum temperatures creates a misleading average as would averaging apples and oranges.

Finally, Christy examines trends in extreme temperatures using various thresholds. One such analysis examined the number of days per decade when maximum temperatures exceeded 99.5°F (orange bars). As would be expected from the trend analysis, extreme hot days have been increasingly less common since 1880. Although there has been a recent uptick, but still there were more hot days in the 1930s. And as a growing urban heat island would also predict, the number of days when minimum temperatures dipped below 32.5°F, has been steadily decreasing (blue bars).

For everyone interested in how temperature trends are constructed, I highly recommend Christy’s book. His thorough examination of Fresno’s temperatures suggests there is no climate crisis. But for people living in Fresno’s city limits, efforts to reduce the stifling heat caused by urban heat islands, would be money well spent.