Re: Cities are getting hotter: Study -- Global Warming, Climate Change

From: Ian St. John (istjohn_at_noemail.ca)
Date: 07/20/04 

Date: Tue, 20 Jul 2004 16:28:22 -0400

Psalm 110 wrote:
> http://timesofindia.indiatimes.com/articleshow/745542.cms
>
> Cities are getting hotter: Study
>
> AGENCIES[ FRIDAY, JUNE 18, 2004 11:28:20 PM ]
>
> PARIS: Sweaty summer nights in the city are going to get even sweatier
> in the future thanks to climate change, according to a study by a top
> British expert.

Probably, though not necessarily. There is no guarantee that climate change
is uniform. In fact, we know it won' t be. And some ciites may benefit from
a cooler climate due to change in ocean currents. Or they may be hurt by
increased cold. Global warming is just the *trigger* for changes in climate.

>
> Cities are hotter than the surrounding countryside because they
> receive more heat through traffic pollution.

False. The two main factors are albedo and reduced air flow to even out the
differences. The latter is the most significant.

> Tarmac and concrete store
> up heat efficiently during daytime and release it gradually over the
> course of the night,whereas fields and forests give up their stored
> heat quickly.

This affects nightime temperatures vs daytime, not really the peak
temperature.

>
> This effect, called the ''urban heat island'', will greatly intensify
> if the gloomiest scenarios about global warming come true, according
> to Richard Betts of the Met office's Hadley Centre for Climate
> Prediction.

I don't see the connection. Urban heat islands exist and they are no
enhanced by global warming noticeably.

>
> A doubling of carbon dioxide (CO2) in the atmosphere could triple the
> intensity of the heat island effect, according to his study, reported
> in New Scientist.
>
> In the case of London, there have been only 20 nights in the past 30
> years when the minimum temperature failed to fall below 20 degrees C.
> Under Betts' scenario, this would happen six times more often,
> equivalent to an extra three nights per year, with the risk of
> inflicting ''quite significant effects'' on human health. A prolonged
> heatwave in Europe last August caused at least 20,000 deaths.

Ahhh. So this is about nighttime lows, due to reduced IR emissions? I think
that this may overestimate the direct GH effect relative to other factors
and may generalise a bit much which is why it is more of a 'more probable'
event rather than a complete change. Climate change is basically about the
odds of particular weather, which fits though it is a bit incorrect to
generalise it to all cities. I suspect that it is more of a claim that heat
waves ( defined by their nighttime lows) will increase over the whole
planet.

>
> Global warmingis the term usedfor agradual heating of the Earth's
> surface by greenhouse gases -- carbon pollution from oil and other
> fossil fuels that traps the Sun's heat instead of letting it radiate
> safely back out into space.

And it is the reduction in nighttime emission as well as a slight increase
in daytime heat absorbion that would be the key to this claim. However it is
to be noted that the claim has been generalised in this post more than I can
agree with. The conditions will vary locally just too much to make such
broad generalisations. More park space could continue to decrease the UHI
effect as it has over recent decades by opening up the city to more wind and
by increasing the traspiration cooling of green spaces.

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