by Geoffrey Sherrington, December 20, 2018 in WUWT
The ‘urban heat island’ arises because air temperatures measured in urban cities can be different to those of the rural city surroundings. Thermometers were and still are more often found in cities than surroundings. City temperatures have a synthetic, man-made component that needs to be subtracted to match the surrounding rural temperatures, which are the items of interest for climate studies.
Failure to subtract the UHI effect will lead to false results for temperature trends such as those used to claim global warming. The question arises whether rural and urban temperatures have adequate accuracy to provide reasonable results after the subtraction. This essay argues that historic Australian rural temperature records are unfit for this purpose; that global temperature records are likely to be similarly inadequate; and that as a consequence, all past estimates of UHI derived from land surface temperatures by thermometry are invalid or questionable.
In short, all past estimates of UHI magnitude before the satellite era are incorrect for reasons given. The actual rates of global temperature changes over the past century are likely to be wrong by a significant amount, of similar magnitude to the global warming claimed at about 1°C per century.
More recent estimates are being made with temperatures from instruments on satellites, which help the future path to better understanding.
by Anthony Watts, August 6, 2018 in WUWT
h/t to Dr. Ryan Maue
In Spain, has been following my lead on the poor quality of weather stations that produce record-high temperatures. I recently pointed out how the tentative all time high temperature in Africa could very well be due to being at an airport. I also pointed out that high temperature records in the Los Angeles area could be a product of poor siting. Such as this station on the roof of the Santa Ana fire station:
by G.E. Kyriakodis and M. Santamouris, June 2018, in UrbanClimate
Large scale implementation of cool asphaltic and concrete photocatalytic pavements
Extensive monitoring strategy of in situ measurements in the area
Surface temperatures reduction up to 7.5 °C and 6.1 °C respectively in the summer period, while the peak drop was up to 11.5 °C
The maximum air temperature reduction could reach 1.5 °C.
Ageing phenomena may reduce substantially and up to 50% the mitigation potential of cool asphaltic materials.
by Willie W.H. Soon et al., May 22, 2018 in EarthScienceReviews
Most estimates of Chinese regional Surface Air Temperatures since the late-19th century have identified two relatively warm periods – 1920s–40s and 1990s–present. However, there is considerable debate over how the two periods compare to each other. Some argue the current warm period is much warmer than the earlier warm period. Others argue the earlier warm period was comparable to the present. In this collaborative paper, including authors from both camps, the reasons for this ongoing debate are discussed. Several different estimates of Chinese temperature trends, both new and previously published, are considered. A study of the effects of urbanization bias on Chinese temperature trends was carried out using the new updated version of the Global Historical Climatology Network (GHCN) – version 4 (currently in beta production)
by Anthony Watts, April 25, 2018 in WUWT
Beijing has undergone several important urbanization development stages since late 1978. Linked with urbanization, the so-called “urban heat island effect” is a key problem caused by urban land expansion. Such changes in air temperature in Beijing inevitably have an impact on the daily lives of its inhabitants, and is therefore of considerable interest to scientists and the wider public alike.
Dr. Xiaojuan LIU and Associate Professor Guangjin TIAN from the School of Environment, Beijing Normal University, used the mesoscale Weather Research and Forecasting model coupled with a single urban canopy model and high-resolution land cover data to analyze the spatial and temporal patterns of summertime urban warming influenced by three stages of urban land expansion during 1990-2010 across Beijing. They found that urban-induced warming increased with urban land expansion, but the speed of warming declined slightly during 2000-10.
by A. Watts, February 23, 2018 in WUWT
How cities heat up
The way streets and buildings are arranged makes a big difference in how heat builds up, study shows
CAMBRIDGE, Mass. – The arrangement of a city’s streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide city planners and officials with new ways to influence those effects.
Some cities, such as New York and Chicago, are laid out on a precise grid, like the atoms in a crystal, while others such as Boston or London are arranged more chaotically, like the disordered atoms in a liquid or glass. The researchers found that the “crystalline” cities had a far greater buildup of heat compared to their surroundings than did the “glass-like” ones.