[Paula J. Brown, Arthur T. DeGaetano]
A paper published today in the Journal of Applied Meteorology and Climatology finds, contrary to global warming theory, that “little change has occurred in dewpoint and specific humidity” in the U.S. over the 80 year period from 1930 to 2010. The paper also finds “trends in relative humidity show little change for the period 1947 – 2010.” Thus, the paper contradicts the theory of a runaway greenhouse effect allegedly due to positive feedback from increased atmospheric water vapor and specific humidity.
U.S. hourly surface observations are examined at 145 stations to identify annual and seasonal changes in temperature, dewpoint, relative humidity and specific humidity since 1930. Due to numerous systematic instrument changes that have occurred, a homogeneity assessment was performed on temperatures and dewpoints. Dewpoints contained higher breakpoint detection rates associated with instrumentation changes than temperatures. Temperature trends were tempered by adjusting the data, while dewpoints were unaffected. The effects were the same whether the adjustments were based on statistically-detected or fixed-year breakpoints. Average long-term trends (1930 – 2010) indicate that temperature has warmed, but little change has occurred in dewpoint and specific humidity. Warming is strongest in spring. There is evidence of inhomogeneity in the relative humidity record that primarily affects data prior to 1950. Therefore long-term decreases in relative humidity, that are strongest in winter, need to be viewed with caution.
Trends since 1947 indicate that the warming of temperatures has coincided with increases in dewpoints and a moistening of specific humidity. This moistening is especially pronounced during the summer in the Midwest. Nationally, trends in relative humidity show little change for the period 1947 – 2010 during which these data are more homogeneous. However, moistening has occurred throughout the central U.S. while other regions have seen drying. Urban-related warming and drying trends are present in the data but their effect is minimal. Regional changes in landuse and moisture availability are likely influencing trends in atmospheric moisture.