Urban warming 'as important as AGW'

Tuscon, Arizona (Credit: © John Miller / Fotolia)

Whilst the possible warming from AGW in the last 100 years can be measured in tenths of a degree, a new study suggests that warming from urbanisation may be even more significant:

In the first study to attempt to quantify the impact of rapidly expanding megapolitan areas on regional climate, a team of researchers from Arizona State University (ASU) and the National Center for Atmospheric Research has established that local maximum summertime warming resulting from projected expansion of the urban Sun Corridor [the four metropolitan areas of Phoenix, Tucson, Prescott and Nogales] could approach 4 degrees Celsius. This finding establishes that this factor can be as important as warming due to increased levels of greenhouse gases. Their results are reported in the early online edition (Aug. 12) of the journal Nature Climate Change.


“The actual contribution of urban warming relative to summertime climate change warming depends critically on the path of urbanization, the conversion of natural to urban landscapes, and the degree to which we continue to emit greenhouse gases,” said Alex Mahalov, a co-author and principal investigator of the National Science Foundation grant, “Multiscale Modeling of Urban Atmospheres in a Changing Climate,” which supported the research.

“As well as providing insights for sustainable growth of the Sun Corridor and other rapidly expanding megapolitan areas, this research offers one way to quantify and understand the relative impacts of urbanization and global warming,”said Mahalov, the Wilhoit Foundation Dean’s Distinguished Professor in ASU’s School of Mathematical and Statistical Sciences. (source)

The abstract is here.

Up to 44% of warming due to Urban Heat Island effect

UHI effects

A new paper in the Journal of Geophysical Research reveals that as much as 44% of recent warming may be due to the Urban Heat Island effect, caused by increasing urbanisation around temperature measuring stations. The study looked at over 460 individual stations in East China:

The trends of urban heat island (UHI) effects, determined using OMR [observation minus reanalysis] and UMR [urban minus regional] 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. (source – abstract only)

There is no reason to doubt the fact that similar contamination of the surface record would be occurring elsewhere. Which helps to explain why the surface record diverges so noticeably from the satellite record, and why the satellite record should always be favoured.

[Also little Jimmy Hansen doesn’t get to carry out his special kind of “data cleansing” either – Ed]

h/t Hockey Schtick

Urban areas "getting hotter faster"

The UHI hard at work

So reads the headline on the ABC website, as if it’s something we don’t know. Obviously, as cities increase in size, the Urban Heat Island (UHI) effect will also increase. However, the latest “research” bolts this on to the IPCC’s incorrectly exaggerated warming predictions, to give some even scarier scenarios:

Dr Richard Betts, a climate scientist at the UK’s Met Office, and colleagues, report their findings in the journal Geophysical Research Letters [although I cannot find the article there right now].

Betts and colleagues found not only do cities retain more heat than rural areas do but hot cities will grow even hotter as the climate warms and cities grow.

By mid-century, night-time temperatures in cities could rise by more than 5.6°C, they say.

At stake are the comfort and health of people who live in cities around the world, especially those who don’t have access to air-conditioning.

“If you’ve been exposed to hot temperatures during the day and you expect relief over night, that becomes increasingly difficult as temperatures at night get warmer,” says Betts. “We have to prepare to live in a warmer world.”

In a concrete jungle, roads and buildings absorb sunlight and trap heat, which also flows as waste out of cars, air-conditioning units and even just the breathing of millions of people crammed into a busy grid of streets.

As a result, cities create their own, warmer microclimates – a phenomenon called the urban heat island effect.

Unfortunately, this is another GIGO* case, where the results from the IPCC’s incomplete models, which vastly overstate the sensitivity of the climate, are plugged into further models of UHI effects (which may or may not be accurate). However, satellite temperatures are continuing to diverge from the IPCC’s predictions, which means that research based on them is the stuff of fairytales.

Read it here.

* Garbage in, garbage out

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