By Paul Homewood
A study was published a couple of months ago, concerning the effect of urbanisation on UK temperatures:
ABSTRACT
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.
https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.896
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 have analysed temperature trends at Heathrow and Oxford since 1948 (when Heathrow’s data starts). As they are only 40 miles apart, there should be little difference in trend.
Significantly though, we find that the trend at Heathrow is much greater than at Oxford, 0.028C v 0.021C a year. In other words, Heathrow is warming faster than Oxford, at a rate of 0.7C per century.
https://www.metoffice.gov.uk/public/weather/climate-historic/#?tab=climateHistoric
This discrepancy can only be due to the increasing local effect of the airport. Over the years, Heathrow and most other airports around the world have transformed from being little more than grass fields to highly developed infrastructures with buildings, car parks, tarmac runways and, of course, jet planes forever taxiing around.
It may of course also be the case that urbanisation has also been pushing up temperatures at Oxford as well, and therefore that the airport effect is even greater than 0.7C.
What is clear is that the Met Office should stop using any sites where urbanisation or airport effect is a factor.
Globally the issue is also a major one, given the predominance of urban and airport sites.
via NOT A LOT OF PEOPLE KNOW THAT
May 6, 2019 at 05:18AM
Iowa Climate Science Education 