Has anyone done the calculation of the contribution that asphalt and concrete surfaces make to global warming?
I visited relatives that live on the other side of a hill from the "city" and it is about 10 degrees cooler there. I frequently hear weather reports that speak of temperatures being higher in cities.
Given the prevalence of pavement as a good thermal mass, I have to wonder if it isn't a significant contributor to climate change.
If pavement is a significant contributor, there are many things we could do. Planting trees along freeways to shade the pavement. Covering buildings with vines to reduce the absorbtion, etc.
Steve wrote: > Has anyone done the calculation of the contribution that asphalt and > concrete surfaces make to global warming?
Look up Urban Heat Island.
I live in one (Atlanta).
There's a slight temperature rise over surrounding areas, but it is not that much. What we do get this time of year is popup thunderstorms as the island cools in the evening.
It's a complicated effect and is more tilted towards large urban areas generating their own weather rather than any warming trend. The net global warming effect is negligible.
A larger problem in many places is that the hardened surfaces lead to faster runoff. This is particularly true of concrete, but also true in farmland areas where border woodsy/swampy areas have been cultivated...
> I visited relatives that live on the other side of a hill from the "city" > and it is about 10 degrees cooler there. I frequently hear weather reports > that speak of temperatures being higher in cities.
> Given the prevalence of pavement as a good thermal mass, I have to wonder if > it isn't a significant contributor to climate change.
> If pavement is a significant contributor, there are many things we could do. > Planting trees along freeways to shade the pavement. Covering buildings > with vines to reduce the absorbtion, etc.
Steve wrote: > Has anyone done the calculation of the contribution that asphalt and > concrete surfaces make to global warming?
> I visited relatives that live on the other side of a hill from the "city" > and it is about 10 degrees cooler there. I frequently hear weather reports > that speak of temperatures being higher in cities.
> Given the prevalence of pavement as a good thermal mass, I have to wonder if > it isn't a significant contributor to climate change.
> If pavement is a significant contributor, there are many things we could do. > Planting trees along freeways to shade the pavement. Covering buildings > with vines to reduce the absorbtion, etc.
> Regards, > Steve
No to mention the heat from all the human bodies,and appliances. There are more heat sources in a city.
> In article <gIKdnbEGUPZK2-zVnZ2dnUVZ_rDin...@comcast.com>, > "Steve" <nospam_steve...@comcast.net> wrote:
>> I frequently hear weather reports >> that speak of temperatures being higher in cities.
> Temps are ALWAYS higher in a city, because that is where ALL that power > is dissipated. Duh......
Hmmm...
On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) reaches the surface of the earth. That's about 2.6 megawatts per square mile.
I know that if that energy falls on concreate or asphalt (a good thermal mass) the heat is stored and re-released at night. If it falls on foliage it tends to get converted into chlorphyll.
It is certainly not obvious to me that this is a small effect. Especially when you consider how much of the earths surface we have covered with concrete and asphalt. Just bring up google earth and zoom in just about anywhere in the US and you will find a lot of thermal mass.
On 07/13/2008 6:52 PM, nospam_steve...@comcast.net wrote to All:
-> On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) reaches the -> surface of the earth. That's about 2.6 megawatts per square mile. ->
-> Regards, -> Steve
Ummm... There are about 1600 metres in a mile, so 1600 x 1600 or 2,560,000 square metres in a square mile. So there are about 2.6 GIGAwatts of solar energy falling on each square mile of ther earth´s surface.
> >> I frequently hear weather reports > >> that speak of temperatures being higher in cities.
> > Temps are ALWAYS higher in a city, because that is where ALL that power > > is dissipated. Duh......
> Hmmm...
> On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) reaches the > surface of the earth. That's about 2.6 megawatts per square mile.
> I know that if that energy falls on concreate or asphalt (a good thermal > mass) the heat is stored and re-released at night. If it falls on foliage > it tends to get converted into chlorphyll.
> It is certainly not obvious to me that this is a small effect. Especially > when you consider how much of the earths surface we have covered with > concrete and asphalt. Just bring up google earth and zoom in just about > anywhere in the US and you will find a lot of thermal mass.
> Regards, > Steve
but you seem to be ignoring the FACT that the suns energy is only PART of the Total Energy being dissipated in any one area. Think of ALL the electrical energy we pump into cities. Thousands of Megawatts. Where does all that energy go? It goes up in HEAT, in the cities where it is USED. That heats the AIR in those cities, and that causes a Temp Rise in cities that isn't there in rural areas. How much energy does a tree dissipate, or grass, or small animals, compared to the amount of electrical energy dissipated, per square mile, in a city? Duh......
>>>> I frequently hear weather reports >>>> that speak of temperatures being higher in cities.
>>> Temps are ALWAYS higher in a city, because that is where ALL that >>> power is dissipated. Duh......
>> Hmmm...
>> On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) >> reaches the surface of the earth. That's about 2.6 megawatts per >> square mile.
>> I know that if that energy falls on concreate or asphalt (a good >> thermal mass) the heat is stored and re-released at night. If it >> falls on foliage it tends to get converted into chlorphyll.
>> It is certainly not obvious to me that this is a small effect. >> Especially when you consider how much of the earths surface we have >> covered with concrete and asphalt. Just bring up google earth and >> zoom in just about anywhere in the US and you will find a lot of >> thermal mass.
>> Regards, >> Steve
> but you seem to be ignoring the FACT that the suns energy is only > PART > of the Total Energy being dissipated in any one area. Think of ALL > the electrical energy we pump into cities. Thousands of Megawatts. > Where does all that energy go? It goes up in HEAT, in the cities > where it is USED. That heats the AIR in those cities, and that > causes a Temp Rise in cities that isn't there in rural areas. How > much energy does a tree dissipate, or grass, or small animals, > compared to the amount of electrical energy dissipated, per square > mile, in a city? Duh......
Google "heat island".
-- -- --John to email, dial "usenet" and validate (was jclarke at eye bee em dot net)
> On 07/13/2008 6:52 PM, nospam_steve...@comcast.net wrote to All:
> -> On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) > reaches the > -> surface of the earth. That's about 2.6 megawatts per square mile. > ->
> -> Regards, > -> Steve
> Ummm... There are about 1600 metres in a mile, so 1600 x 1600 or 2,560,000 > square metres in a square mile. So there are about 2.6 GIGAwatts of solar > energy falling on each square mile of ther earth´s surface.
> dow
I stand corrected. Those nasty decimal places anyhow.
--- All the energy stored in Earth's reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine.
In 40 minutes of daylight The SUN releases upon The Earth the amount of energy that is consumed by the entire population of the planet in ONE YEAR.
Each day more solar energy falls to the Earth than the total amount of energy the planet's 6 billion inhabitants would consume in 27 years. ---
If these statistics are true, I would not be a bit surprised if the "Heat Island" effect is more significant than the greenhouse effect. Of course they are not independent, and the global effect of either are extremely hard to measure with any certainty.
-> but you seem to be ignoring the FACT that the suns energy is only PART -> of the Total Energy being dissipated in any one area. Think of ALL the -> electrical energy we pump into cities. Thousands of Megawatts. Where -> does all that energy go? It goes up in HEAT, in the cities where it is -> USED. That heats the AIR in those cities, and that causes a Temp Rise -> in cities that isn't there in rural areas. How much energy does a tree -> dissipate, or grass, or small animals, compared to the amount of -> electrical energy dissipated, per square mile, in a city? Duh......
When the sun is shining on the earth's surface, about one GIGAwatt of heat per square kilometre is produced by it. It's true that large cities consume several gigawatts of electrical power, but they have areas of many square kilometres. So the amount of heat, per square kilometre, that the electrical power produces is much less than the amount from sunshine.
The reason why asphalt gets a lot hotter than grass when the sun shines on it is mainly because water evaporates from the grass and not from the asphalt. Very dry grass does get hot, but fresh green grass does not. The same is true of other vegetation.
>-> but you seem to be ignoring the FACT that the suns energy is only PART > -> of the Total Energy being dissipated in any one area. Think of ALL the > -> electrical energy we pump into cities. Thousands of Megawatts. Where > -> does all that energy go? It goes up in HEAT, in the cities where it is > -> USED. That heats the AIR in those cities, and that causes a Temp Rise > -> in cities that isn't there in rural areas. How much energy does a tree > -> dissipate, or grass, or small animals, compared to the amount of > -> electrical energy dissipated, per square mile, in a city? Duh......
> When the sun is shining on the earth's surface, about one GIGAwatt of > heat per square kilometre is produced by it. It's true that large > cities consume several gigawatts of electrical power, but they have > areas of many square kilometres. So the amount of heat, per square > kilometre, that the electrical power produces is much less than the > amount from sunshine.
> The reason why asphalt gets a lot hotter than grass when the sun shines > on it is mainly because water evaporates from the grass and not from > the asphalt. Very dry grass does get hot, but fresh green grass does > not. The same is true of other vegetation.
Another question would be - how much energy is re-radiated back into space at night from the hot pavement. It may even reduce the warming effect compared to greenery.
