Wednesday, July 27, 2011

New paper finds urban heat islands cause up to 44% of total recorded warming

A paper published today in the Journal of Geophysical Research finds that urban heat islands account for up to 44% of the recorded warming in cities in east China over the period of 1981-2007. An urban heat island is a metropolitan area which is significantly warmer than its surrounding rural areas. As extensively documented by the project, poor siting of weather stations in the US near urban heat islands results in a false warming trend in which "9 of every 10 stations are likely reporting higher or rising temperatures because they are badly sited." This shows why Phil Jones was worried that the Chinese Meteorological Agency was not playing along to prop up the AGW fallacy by recording temperatures at airports (highly biased by the urban heat island effect) in favor of unbiased rural areas. Without knowledge of the urban heat island effects on a global basis, it is unknown how much of the claimed 0.7C rise in temperature since 1850 is simply an artifact of poor siting rather than actual warming. Alarmists including the IPCC dismiss the urban heat island effect as insignificant, but as this paper and many others show, the effect causes very significant upward biases in recorded temperatures.
Metropolises warmed ~1.4C compared to surrounding rural areas ~0.4C over the period 1981-2007


Observed surface warming induced by urbanization in east China

Key Points:

The rapid urbanization has significant impacts on temperature over east China
A new method was developed to dynamically classify urban and rural stations
Comparison of the trends of UHI effects by using OMR and UMR approaches

Xuchao Yang et al

Monthly mean surface air temperature data from 463 meteorological stations, including those from the 1981–2007 ordinary and national basic reference surface stations in east China and from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) Reanalysis, are used to investigate the effect of rapid urbanization on temperature change. These stations are dynamically classified into six categories, namely, metropolis, large city, medium-sized city, small city, suburban, and rural, using satellite-measured nighttime light imagery and population census data. Both observation minus reanalysis (OMR) and urban minus rural (UMR) methods are utilized to detect surface air temperature change induced by urbanization. With objective and dynamic station classification, the observed and reanalyzed temperature changes over rural areas show good agreement, indicating that the reanalysis can effectively capture regional rural temperature trends. The trends of urban heat island (UHI) effects, determined using OMR and UMR approaches, are generally consistent and indicate that rapid urbanization has a significant influence on surface warming over east China. Overall, UHI effects contribute 24.2% to regional average warming trends. The strongest effect of urbanization on annual mean surface air temperature trends occurs over the metropolis and large city stations, with corresponding contributions of about 44% and 35% to total warming, respectively. The UHI trends are 0.398°C and 0.26°C decade−1. The most substantial UHI effect occurred after the early 2000s, implying a significant effect of rapid urbanization on surface air temperature change during this period.

1 comment:

  1. Confirms what I have been saying since 2002.
    Here at 19°S 146°E, almost everyone is aware of the UHI effect, even if they don't call it that.
    A few houses in the wrong configuration, handful of ACs in the intervening space, and it hits you. Summer afternoons, you don't need gas to cook on the barbeque. May not be so obvious in temperate climates, but it will be there all the same.
    Across the world, a large number of surface stations have disappeared over the last 20 years, and most of these were rural. A bitumen or concrete driveway replacing a dirt road, stations being moved closer to buildings to shorten the data cable links when digital replaces analog ... it all makes a difference, and is not necessarily an exclusively urban phenomenon.
    One caretaker with time on his hands and a flair for gardening, or a few cheap ACs in the vicinity, have also been known to produce the effect, and most changes push the temperature up rather than down.
    IMHO this one's as bad as the Hockey Stick scam.
    I'm not surprised one of the usual suspects was "worried".
    Martin Clark