Climate - Large-scale warming is not urban
ABSTRACT Controversy has persisted over the influence of urban warming on reported large-scale surface-air temperature trends. Urban heat islands occur mainly at night and are reduced in windy conditions. Here we show that, globally, temperatures over land have risen as much on windy nights as on calm nights, indicating that the observed overall warming is not a consequence of urban development.
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ABSTRACT: Local climate changes due to urbanization have been well documented. These changes are epitomized by the concept of the “Urban Heat Island” (UHI), which represents temperature differences between urban and rural areas. In urban areas, the UHI effect is a critical factor for air quality and public health. It results in higher peak energy demand because of the use of air conditioning in Summer. Higher temperatures increase health risks to city dwellers, because increased air temperatures are associated with secondary air pollutants, such as ozone (O3). Recent research on the UHI, including theoretical models and statistical analyses, has resulted in a better understanding of climate modifications in urban areas. The purpose of this research is to further develop statistical models of local temperature changes, using Landsat-5 satellite remote-sensing data. The temperature at any location and for any land use is modeled as a function of the pattern of land uses around this location. These models are estimated with data pertaining to the Columbus, Ohio, metropolitan area (CMA). Their applicability to land-use planning and regulation is illustrated by simulating hypothetical land-use changes in part of the CMA, and computing the resulting temperature effects. The results clearly demonstrate that it is possible to reduce temperatures in residential and urban areas through a judicious siting of green areas.12/2009, Degree: PhD, Supervisor: Jean-Michel Guldmann
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ABSTRACT: We evaluate to what extent the temperature rise in the past 100 years was a trend or a natural fluctuation and analyze 2249 worldwide monthly temperature records from GISS (NASA) with the 100-year period covering 1906–2005 and the two 50-year periods from 1906 to 1955 and 1956 to 2005. No global records are applied. The data document a strong urban heat island effect (UHI) and a warming with increasing station elevation. For the period 1906–2005, we evaluate a global warming of 0.58°C as the mean for all records. This decreases to 0.41°C if restricted to stations with a population of less than 1000 and below 800 meter above sea level. About a quarter of all the records for the 100-year period show a fall in temperatures. Our hypothesis for the analysis is, as generally in the papers concerned with long-term persistence of temperature records, that the observed temperature records are a combination of long-term correlated records with an additional trend, which is caused for instance by anthropogenic CO2, the UHI or other forcings. We apply the detrended fluctuation analysis (DFA) and evaluate Hurst exponents between 0.6 and 0.65 for the majority of stations, which is in excellent agreement with the literature and use a method only recently published, which is based on DFA, synthetic records and Monte Carlo simulation. As a result, the probabilities that the observed temperature series are natural have values roughly between 40% and 90%, depending on the stations characteristics and the periods considered. "Natural" means that we do not have within a defined confidence interval a definitely positive anthropogenic contribution and, therefore, only a marginal anthropogenic contribution cannot be excluded.International Journal of Modern Physics C 01/2012; 22(10). DOI:10.1142/S0129183111016798 · 1.13 Impact Factor