To date, most reporting on climate has focused on the possibility of catastrophic warming due to carbon dioxide and other greenhouse gases released into the atmosphere. The assessment of climate change risk has essentially been distilled to a single metric: the global average surface temperature. That reality was evident at the 2015 United Nations Climate Change Conference in Paris, where the central negotiating point was whether the global temperature rise should be limited to 1.5 °C or 2 °C. Indeed, a 2016 opinion piece by Simon Lewis (University College London and the University of Leeds, UK) states that, “by endorsing a limit of 1.5 °C, the [Paris] climate negotiations have effectively defined what society considers dangerous.”
But the reality of humans’ impact on climate is exceedingly complex.2 Even if greenhouse gas emissions could be elimi- nated completely, other harmful anthropogenic sources of cli- mate change would remain. And even if global average tem- peratures were contained, human impacts on climate would manifest in other potentially dangerous ways.
One often overlooked human factor is land use. Deforestation, dry land farming, irrigated agriculture, overgrazing, and other alterations to the natural landscape can disrupt Earth’s natural balances and change weather patterns. As with the addition of CO2into the atmosphere, the effects can last for decades or longer and affect regions distant from the original offense. Given continued rapid population growth, they threaten to be irreversible.
by SCE-INFO, 3 juillet 2019 in ScienceClimatEnergie
De nombreux médias l’ont annoncé, tout comme le site MétéoFrance : la barre des 45 °C aurait été franchie pour la première fois en France vendredi 28 juin 2019. On a atteint 45,9 °C à Gallargues-le-Montueux, à l’ouest du Gard, à 16 h 20. Ce serait une première en France depuis que l’on fait des mesures de températures. Température exceptionnelle? Sans remettre en cause le réchauffement global de la basse troposphère, ni l’augmentation de la fréquence des vagues de chaleur constatée par le GIEC, certaines remarques doivent être faites concernant ce record de température.
Avant de sombrer dans le catastrophisme, il est important de “garder la tête froide” et de considérer les quelques points suivants :
1. Une telle température a peut-être déjà été atteinte dans le passé proche, mais n’a tout simplement pas été mesurée. N’oubliez pas qu’il n’y avait pas autant de thermomètres il y a cent ans. Par exemple, en 1865, il n’y avait en France que deux observatoires astronomiques effectuant des observations météorologiques quotidiennes (voir ici). Aujourd’hui, les stations météorologiques professionnelles du réseau de Météo-France, appelé réseau Radome, ne sont que de 554 pour le France métropolitaine. Il faudrait évidemment plus de stations pour monitorer les 643 801 km² de territoire. Aujourd’hui, cela fait une station pour 1162 km2.
2. Pendant l’été 1930, une vague de chaleur a traversé la France, comme l’atteste le petit article de journal ci-dessous (Figure 1) retrouvé dans “The Telegraph” (Brisbane). Les températures sont données en Fahrenheit et 122 Fahrenheit correspondent à 50°C. Bien que l’article ne donne pas les détails de la mesure (il faut donc rester prudent) nous voyons que de telles vagues de chaleurs se sont déjà produites dans le passé. Voyez également ce qui s’est passé en 1900, 1911, 1921 et 1934 ici.
Based on a globally averaged statistic, some scientists and several politicians claim we are facing a climate crisis. Although it’s wise to think globally, organisms are never affected by global averages. Never! Organisms only respond to local conditions. Always! Given that weather stations around the globe only record local conditions, it is important to understand over one third of the earth’s weather stations report a cooling trend (i.e. Fig 4 below ) Cooling trends have various local and regional causes, but clearly, areas with cooling trends are not facing a “warming climate crisis”. Unfortunately, by averaging cooling and warming trends, the local factors affecting varied trends have been obscured.
It is well known as human populations grow, landscapes lose increasing amounts of natural vegetation, experience a loss of soil moisture and are increasingly covered by heat absorbing pavement and structures. All those factors raise temperatures so that a city’s downtown area can be 10°F higher than nearby rural areas. Despite urban areas representing less than 3% of the USA’s land surface, 82% of our weather stations are located in urbanized areas. This prompts critical thinkers to ask, “have warmer urbanized landscapes biased the globally averaged temperature?” (Arctic warming also biases the global average, but that dynamic must await a future article.)
This study aims to estimate the affect of urbanisation on daily maximum and minimum temperatures in the United Kingdom. Urban fractions were calculated for 10 km × 10 km areas surrounding meteorological weather stations. Using robust regression a linear relationship between urban fraction and temperature difference between station measurements and ERA‐Interim reanalysis temperatures was estimated. For an urban fraction of 1.0, the daily minimum 2‐m temperature was estimated to increase by 1.90 ± 0.88 K while the daily maximum temperature was not significantly affected by urbanisation. This result was then applied to the whole United Kingdom with a maximum T min urban heat island intensity (UHII) of about 1.7K in London and with many UK cities having T min UHIIs above one degree.
This paper finds through the method of observation minus reanalysis that urbanisation has significantly increased the daily minimum 2‐m temperature in the United Kingdom by up to 1.70 K.
As ever, the real issue with UHI is the change in the effect over time. Has, for instance, the effect of UHI increased in London and other cities increased over the last century, or was it just as great in 1919?
What we do know is that, generally speaking, towns and cities have both expanded over time, and seen increasing development in terms of roads, buildings, traffic and economic activity.
Indeed, these same tendencies also apply in small towns and what may appear to be relatively rural sites.
We also know that many of the sites used by the Met Office in their UK temperature series are urban and airport locations.
I’ve been saying for years that surface temperature measurements (and long term trends) have been affected by encroachment of urbanization on the placement of weather stations used to measure surface air temperature, and track long term climate. In doing so we found some hilariously bad examples of climate science in action, such as the official USHCN climate monitoring station at the University of Arizona, Tucson:
I have published on the topic in the scientific literature, and found this to be true based on the science we’ve done of examining the USHCN and applying the siting methodology of Leroy 2010.
In Fall et al, 2011 we discovered that there was a change to the diurnal temperature range (DTR). It decreased where stations had been encroached upon, because of the heat sink effect of man-made materials (asphalt, concrete, bricks, etc.) that were near stations.
A field experiment was performed in Oak Ridge, TN, with four instrumented towers placed over grass at increasing distances (4, 30, 50, 124, and 300 m) from a built-up area. Stations were aligned in such a way to simulate the impact of small-scale encroachment on temperature observations. As expected, temperature observations were warmest for the site closest to the built environment with an average temperature difference of 0.31 and 0.24 °C for aspirated and unaspirated sensors respectively. Mean aspirated temperature differences were greater during the evening (0.47 °C) than day (0.16 °C). This was particularly true for evenings following greater daytime solar insolation (20+ MJDay−1) with surface winds from the direction of the built environment where mean differences exceeded 0.80 °C. The impact of the built environment on air temperature diminished with distance with a warm bias only detectable out to tower-B’ located 50 meters away.
The experimental findings were comparable to a known case of urban encroachment at a U. S. Climate Reference Network station in Kingston, RI. The experimental and operational results both lead to reductions in the diurnal temperature range of ~0.39 °C for fan aspirated sensors. Interestingly, the unaspirated sensor had a larger reduction in DTR of 0.48 °C. These results suggest that small-scale urban encroachment within 50 meters of a station can have important impacts on daily temperature extrema (maximum and minimum) with the magnitude of these differences dependent upon prevailing environmental conditions and sensing technology.
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.
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)
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.
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.
La géologie, une science plus que passionnante … et diverse