Actually, I wonder if it wouldn't be hard to plant all those trees. I'm not so sure you could max out the number up here in New England, given that you would not only have to plant the new trees but completely stop all development. Country wide would we not only have to halt all suburban growth in naturally forested areas but also cover, say, Montana entirely with trees?
There's better ways to do that that kill multiple birds with one stone. Revegetating the fringes of waterways is a huge one - cuts down on soil loss, helps clean the water, etc. Restoring drained swampland might seem counterintuitive since they put out a fair chunk of methane due to the anerobic environment, but there's still a lot of carbon locked up in them, plus they're breeding grounds for fish, water quality filters, and they buffer floodwaters quite effectively.
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JohnnyCacheStarting DefensePlace at the tableRegistered Userregular
edited May 2007
how much globally warmer has it gotten?
Also, what horrible things happen when it heats up? I hear there is a chance of CGI wolves.
Also, what horrible things happen when it heats up? I hear there is a chance of CGI wolves.
little bit. .6C, I think. The thing is, 'warming' is a crap way to describe it. Basically, it means there's more free energy crashing around in the atmosphere, fuelling things like storms and playing around with larger climatic patterns. So its not really a case of warmer summers necessarily, but shifting climate regimes. There's different results predicted for different areas depending on the level of warming - for instance, if teh hypothesis about the gulf stream shutting down at some point ever comes to pass, Europe's going to be mighty freakin' cold in the winter.
Actually, I wonder if it wouldn't be hard to plant all those trees. I'm not so sure you could max out the number up here in New England, given that you would not only have to plant the new trees but completely stop all development. Country wide would we not only have to halt all suburban growth in naturally forested areas but also cover, say, Montana entirely with trees?
There's better ways to do that that kill multiple birds with one stone. Revegetating the fringes of waterways is a huge one - cuts down on soil loss, helps clean the water, etc. Restoring drained swampland might seem counterintuitive since they put out a fair chunk of methane due to the anerobic environment, but there's still a lot of carbon locked up in them, plus they're breeding grounds for fish, water quality filters, and they buffer floodwaters quite effectively.
They can also be used to work as natural sewage treatment plants if you regulate the amount of shit being pumped into them. Which would involve less powerful chemicals being dumped into the water supply since the load on our current waste water treatment plants would be reduced. Wouldn't even really have to be that big of a wetland to be efficient at it either.
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MrMisterJesus dying on the cross in pain? Morally better than us. One has to go "all in".Registered Userregular
Actually, I wonder if it wouldn't be hard to plant all those trees. I'm not so sure you could max out the number up here in New England, given that you would not only have to plant the new trees but completely stop all development. Country wide would we not only have to halt all suburban growth in naturally forested areas but also cover, say, Montana entirely with trees?
Just establish a rule that says if you chop down two trees you must replace it with three trees someplace else. We do a similar thing with the timber industry though I'm not too sure on the exact ratios.
Actually I would not be surprised if there wasn't a lot more space then we realize. Tree Canopy coverage from Boston to Washington is done 50% over the past century, and 25% in the past 20 years. The great forests of Europe have shrunk at least 85% since the dawn of agriculture there.
I think the important point is that if you put a pound of carbon into the atmosphere you should take efforts to take a pound of carbon out. Economic incentives that encourages carbon neutrality could go a long way towards achieving that. Planting trees is something everyone can do, and not terribly difficult, that's why I personally like it. And it's something I think a lot of people can get behind. "Plant a tree, save the world" sounds a lot better then "Tax the Rich! Death to Big Oil!". It's individual action rather then a governmental one. That's really the main reason so many conservatives deny global warming. It's because if they admit it's there, it requires a government solution, and government is bad. But if you put a solution in front of them that requires individual action: Cut down your personal usage, do what you can to make the environment better, more of them would jump on that. Distant solutions like Saving the Rain Forest, or melting ice glaciers, are not exactly measurable or personable. It's hard to hold things like the accountability of the money sent for such things. And they feel like they have some obligation towards the effects of economic policies, which are already a terrible mess. "We'll save the world by making the cost of energy so high, that people will stop using it." Going out and planting trees is simpler, something real, measurable. Based on each person's individual carbon lifestyles they can plant more or less, based on how much they think they're personally polluting the environment.
And even if Global Warming were not happening... then, well there is no harm other then having planted some trees. As an economist I recognize the opportunity cost of that (Well that land could have been used for something else, along with the labor), but there isn't a direct cost. All global warming policies would likely have a direct cost along with an opportunity cost, and this one just has that opportunity cost. Besides, a tree has value, which is something you can't say for a 15% tax on coal.
Aside from the waste issue that I personally think could be managed, haven't regulations/standards/policies made building and operating nuclear plants borderline prohibitively expensive?
Doesn't that have the countering disadvantage of spreading mosquitos and lyme disease and all that other bad stuff though?
Not necessarily. You'd have to spray for mozzies for convenience if nothing else (man, the little bastards are bad here this year), but the good tends to outweigh the bad. Also, when I say swamp, I don't necessarily mean 'huge jungly fetid bayou'. There's a few small-town jurisdictions in the US using carefully managed wetlands to purify town water already. They basically look like prettier rice paddies, and the water moves just enough to keep the mosquito larva from doing well. The main drawbacks are that they take up a lot of space, and are pretty useless in arid climates.
and is that tree thing even true? He didn't even say what kind of trees...
That's a good point, too. You don't want to be whacking in giant stands of one species, or using something that's not native to the area. If you want to talk about carbon emission offsets through creating more green biomass, you're probably better off thinking of it in terms of acres of woods per thousand people or something. Local small-scale projects would be the best way to go about it; people who know what's native to the area and where it will do the most good to plant.
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JohnnyCacheStarting DefensePlace at the tableRegistered Userregular
Why don't we have nuclear power and electric cars again? that's what fills me with rage.
No one wants the nuclear waste stored near them.
So? Didn't we just conquer afganistan?
That's is excellent.
I say we cram Tora Bora to the gills with nuclear waste then erect a giant Abraham Lincoln statue on top.
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JohnnyCacheStarting DefensePlace at the tableRegistered Userregular
edited May 2007
Seriously. It all comes out of a hole in the ground in Australia, anyway - why don't we have the robots put the waste back in the mine as they take new uranium out?
I don't necessarily mean 'huge jungly fetid bayou'. There's a few small-town jurisdictions in the US using carefully managed wetlands to purify town water already. They basically look like prettier rice paddies, and the water moves just enough to keep the mosquito larva from doing well. The main drawbacks are that they take up a lot of space, and are pretty useless in arid climates.
Hokay--I was just flashing back to a talk we got from a parent at my Jr. High, where she pointed out in passing that the 'save the wetlands' campaigns in the Bay Area had downsides.
And that these samples have resolutions in the thousands of years? Which means they tell us pretty much dick about our current hundred-year warming period,
I was under the (possibly mistaken) impression that most people agree the earth is getting warmer, but there's no consensus on the cause, the relevance of humans, or how significant it is.
Oh one last thing. Just to point out the hypocrisies of everybody else, New Scientist isn't a peer-reviewed scientific journal EITHER so at this point NOBODY has given evidence to suggest Global Warming does or does not exist.
Good thing I wasn't trying to argue a point about the actual science there then, wasn't it? That link is there because its a handy-dandy debunk centre. Also, NS, while not peer reviewed, is considerably higher quality than, say, the Sydney Morning Herald. You still have yet to cut and paste in any journal abstracts you've read lately that support your 'scientists are out for money and get off on scaring people' position. Its not hard to post peer-reviewed stuff here, I've done it myself.
Just in case he's actually looking, it would be nice to at least point out the metareview of peer-reviewed studies that found that the vast majority of climate-related research either implicitly or explicitly accepted the global warming consensus, and that the rest didn't deal with it at all (i.e., no research found implicitly or explicitly rejected the consensus).
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Irond WillWARNING: NO HURTFUL COMMENTS, PLEASE!!!!!Cambridge. MAModeratormod
I really don't think that there would be quite so much gripe against green practices if the people who regulate those practices weren't mind-bogglingly incompetent.
The people they have trying to regulate the construction industry, for instance, seem to not actually know anything about construction OR the environment.
Why don't we have nuclear power and electric cars again? that's what fills me with rage.
No one wants the nuclear waste stored near them.
And no one wants to use the waste in reactors. Which can be done, it just has the annoying side effect of producing fuel that can be used in bombs..
Is this true? I was under the impression it was a real bitch to refine plutonium or uranium to weapons-grade states. It seems like if the byproduct of breeder reactors was weapons-grade fissionable material the military would be all over incenting breeding reactors for power generation (under their close supervision).
Why don't we have nuclear power and electric cars again? that's what fills me with rage.
No one wants the nuclear waste stored near them.
And no one wants to use the waste in reactors. Which can be done, it just has the annoying side effect of producing fuel that can be used in bombs..
Is this true? I was under the impression it was a real bitch to refine plutonium or uranium to weapons-grade states. It seems like if the byproduct of breeder reactors was weapons-grade fissionable material the military would be all over incenting breeding reactors for power generation (under their close supervision).
It can be used to produce weapons fuel, but it isn't automatically weapons grade. I think it still gives you plutonium, but the purity is too low (40%?) to easily make a nuclear bomb directly from it. You could make a dirty bomb from it, or you would need to do more processing to make a viable nuke.
However, all of the non-poliferation stuff makes getting material which is close to bomb ready less than optimal. But Carter was stupid to outright ban breeder reactors because of this, since the obvious solution is to have local and international oversight. And his "setting an example" is bunk because many other nations reprocess the fuel anyways.
Why don't we have nuclear power and electric cars again? that's what fills me with rage.
No one wants the nuclear waste stored near them.
And no one wants to use the waste in reactors. Which can be done, it just has the annoying side effect of producing fuel that can be used in bombs..
Is this true? I was under the impression it was a real bitch to refine plutonium or uranium to weapons-grade states. It seems like if the byproduct of breeder reactors was weapons-grade fissionable material the military would be all over incenting breeding reactors for power generation (under their close supervision).
It is indeed quite difficult. Arguably, its the most difficult part of the process. When you hear about Iran trying to make nukes (whether they are or not) their goal would be refining the uranium or plutonium to weapons grade quality. This is a very tricky and energy intensive process. If you get the weapons grade stuff its not that difficult to build a bomb with it, thats the easy part that can be figured out on paper.
Why don't we have nuclear power and electric cars again? that's what fills me with rage.
No one wants the nuclear waste stored near them.
And no one wants to use the waste in reactors. Which can be done, it just has the annoying side effect of producing fuel that can be used in bombs..
Is this true? I was under the impression it was a real bitch to refine plutonium or uranium to weapons-grade states. It seems like if the byproduct of breeder reactors was weapons-grade fissionable material the military would be all over incenting breeding reactors for power generation (under their close supervision).
It is indeed quite difficult. Arguably, its the most difficult part of the process. When you hear about Iran trying to make nukes (whether they are or not) their goal would be refining the uranium or plutonium to weapons grade quality. This is a very tricky and energy intensive process. If you get the weapons grade stuff its not that difficult to build a bomb with it, thats the easy part that can be figured out on paper.
As the North Koreans showed with their botched bomb, there is still some finesse to putting it all together in the end though. If one of the shaped charges on a bomb fouls up the material won't reach critical mass and it will fizzle. And making a bomb with reactor grade plutonium is even more difficult and I am not sure if it has ever been proven in practice to work.
also, rooftop, uh, greenery. Can't be trees, though, but other green stuff.
Yes they can, it just requires more structural support due to the weight of the tree and 3 feet depth of soil. Seedum is generally used for greenroofs that aren't going to be accessible since it is hardly beautiful and only needs something around 3 inches of soil and so isn't much heavier than a standard roof given the strength of trusses and W shapes and factored loads and all of that stuff which goes into the structural design. They also double the life of a standard BUR roof past the 50 year mark and are self sustaining after 3 years of maintenance. Chicago has subsidies for green roofs and requires that a building use either that or materials to lower a building's heat island effect/albido (so white roofing rather than black tar, etc.). It isn't alone, but it was the first major metropolitan city to do it in America and possibly worldwide, so nyah @ NYC and California.
Not disagreeing, but I recall rain making green roofs insanely heavy being one of the major difficulties, so yeah, using the right kind of plants (non-tree, for most roofs) is key.
The conclusion from the climate model was that only planting tree's in the tropic will actually help prevent Global Warming. Planting trees in the USA would actually cause increased Global Warming. Because even though the trees will reduce carbon levels in the atmosphere they act as insulators holding heat on the planets surface that would otherwise be reflected back into space.
The conclusion from the climate model was that only planting tree's in the tropic will actually help prevent Global Warming. Planting trees in the USA would actually cause increased Global Warming. Because even though the trees will reduce carbon levels in the atmosphere they act as insulators holding heat on the planets surface that would otherwise be reflected back into space.
That would be true if the entirety of continental america was covered with a bright white icecap, and you replaced it with green trees. But that's not so, you're replacing green grassland with...green trees. People really do check their brains at the door when these debates open up
There are other problems with treeplanting programs, and many more efficient ways to offset C emissions, but that's one of the silliest reasons to avoid them.
Hi, I'm an environmental scientist. Skepticism is rad, but regional newspaper articles and US Senate documents are terribly poor sources for any scientific argument.
Oh I'm sorry, I guess I'll start referencing you as a source next time around. Good thing to know I can no longer trust anyone or anything other than environmental scientists that believe what you do. I'm going to ignore the ones that don't.
As opposed to someone making the claim they've read 10 times as much about global warming as anyone else, then lists a bunch of newspaper articles?
Hmm... there appears to be a credibility gap.
Word.
I would link straight to God but apparently he's unreachable at this time. Please try again later.
Perhaps, as was suggested, you could find some peer reviewed scientific articles.
Because it isn't helping your credibility when you are asked for reliable research to back your position and you reply with sarcastic bluster.
I notice the second to last link happens to be The Great Global Warming Swindle video which was infamous for misrepresenting the opinions of the scientists it interviewed.
The conclusion from the climate model was that only planting tree's in the tropic will actually help prevent Global Warming. Planting trees in the USA would actually cause increased Global Warming. Because even though the trees will reduce carbon levels in the atmosphere they act as insulators holding heat on the planets surface that would otherwise be reflected back into space.
That would be true if the entirety of continental america was covered with a bright white icecap, and you replaced it with green trees. But that's not so, you're replacing green grassland with...green trees. People really do check their brains at the door when these debates open up
There are other problems with treeplanting programs, and many more efficient ways to offset C emissions, but that's one of the silliest reasons to avoid them.
I thought white surfaces caused the world to heat up whilst dark ones caused it to cool down, due to the heat in the atomosphere being the main thing that mattered. Least that was the impression I got from SimEarth's Daisyworld - and why the heating/cooling periods were in a cycle - ice caps recede and less heat is reflected into the atmosphere, causing the world to cool, which in turn causes the ice caps to grow etc.
Whilst we're on the topic of climate control theories from computer games, is there any reason a solar shade wouldn't work? Seem to remember a couple of years back there was some scheme to use a large space based mirror to heat up parts of Russia and make them more habitable. There anything wrong with the concept or is the engineering on an epic scale factor the main issue.
also, rooftop, uh, greenery. Can't be trees, though, but other green stuff.
Yes they can, it just requires more structural support due to the weight of the tree and 3 feet depth of soil. Seedum is generally used for greenroofs that aren't going to be accessible since it is hardly beautiful and only needs something around 3 inches of soil and so isn't much heavier than a standard roof given the strength of trusses and W shapes and factored loads and all of that stuff which goes into the structural design. They also double the life of a standard BUR roof past the 50 year mark and are self sustaining after 3 years of maintenance. Chicago has subsidies for green roofs and requires that a building use either that or materials to lower a building's heat island effect/albido (so white roofing rather than black tar, etc.). It isn't alone, but it was the first major metropolitan city to do it in America and possibly worldwide, so nyah @ NYC and California.
Not disagreeing, but I recall rain making green roofs insanely heavy being one of the major difficulties, so yeah, using the right kind of plants (non-tree, for most roofs) is key.
It isn't that much, actually. If you made the roof accessible for garden parties and the like it would need to support a 100 pound/square foot live load assembly area by code which would generally cover the wet weight of 6-18" deep soil's (needed for flowering plants) dead load over the square feet of non-patio space. If you aren't making it accessible then the extra cost of supporting 3" deep soil in the structure is recouped through lengthened roof life so less replacements and the insulating effect that it has on the building's top envelope which is a big plus as well. They're beyond economically sound, you just have to think ahead and design it into the building.
Well, in good news, CO2 emissions dropped 1.3% last year, even though the economy grew (by 3.3%). It's the first time carbon emissions have gone down while the economy was improving since 1990.
The conclusion from the climate model was that only planting tree's in the tropic will actually help prevent Global Warming. Planting trees in the USA would actually cause increased Global Warming. Because even though the trees will reduce carbon levels in the atmosphere they act as insulators holding heat on the planets surface that would otherwise be reflected back into space.
That would be true if the entirety of continental america was covered with a bright white icecap, and you replaced it with green trees. But that's not so, you're replacing green grassland with...green trees. People really do check their brains at the door when these debates open up
It is up to you Aussies to bioengineer some sort of tree capable of surviving in and taking over your poisonous back yard.
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There's better ways to do that that kill multiple birds with one stone. Revegetating the fringes of waterways is a huge one - cuts down on soil loss, helps clean the water, etc. Restoring drained swampland might seem counterintuitive since they put out a fair chunk of methane due to the anerobic environment, but there's still a lot of carbon locked up in them, plus they're breeding grounds for fish, water quality filters, and they buffer floodwaters quite effectively.
Also, what horrible things happen when it heats up? I hear there is a chance of CGI wolves.
I host a podcast about movies.
So . . . you'd need to cover an area the size of Pennsylvania with dense forest.
And then either keep planting an area the size of Rhode Island or maybe Maryland every year or else make suburban development illegal.
little bit. .6C, I think. The thing is, 'warming' is a crap way to describe it. Basically, it means there's more free energy crashing around in the atmosphere, fuelling things like storms and playing around with larger climatic patterns. So its not really a case of warmer summers necessarily, but shifting climate regimes. There's different results predicted for different areas depending on the level of warming - for instance, if teh hypothesis about the gulf stream shutting down at some point ever comes to pass, Europe's going to be mighty freakin' cold in the winter.
You wouldn't have to keep planting the same amount every year, its not a straight offset.
This is certainly an intuitive issue...
and is that tree thing even true? He didn't even say what kind of trees...
I host a podcast about movies.
They can also be used to work as natural sewage treatment plants if you regulate the amount of shit being pumped into them. Which would involve less powerful chemicals being dumped into the water supply since the load on our current waste water treatment plants would be reduced. Wouldn't even really have to be that big of a wetland to be efficient at it either.
Doesn't that have the countering disadvantage of spreading mosquitos and lyme disease and all that other bad stuff though?
Actually I would not be surprised if there wasn't a lot more space then we realize. Tree Canopy coverage from Boston to Washington is done 50% over the past century, and 25% in the past 20 years. The great forests of Europe have shrunk at least 85% since the dawn of agriculture there.
I think the important point is that if you put a pound of carbon into the atmosphere you should take efforts to take a pound of carbon out. Economic incentives that encourages carbon neutrality could go a long way towards achieving that. Planting trees is something everyone can do, and not terribly difficult, that's why I personally like it. And it's something I think a lot of people can get behind. "Plant a tree, save the world" sounds a lot better then "Tax the Rich! Death to Big Oil!". It's individual action rather then a governmental one. That's really the main reason so many conservatives deny global warming. It's because if they admit it's there, it requires a government solution, and government is bad. But if you put a solution in front of them that requires individual action: Cut down your personal usage, do what you can to make the environment better, more of them would jump on that. Distant solutions like Saving the Rain Forest, or melting ice glaciers, are not exactly measurable or personable. It's hard to hold things like the accountability of the money sent for such things. And they feel like they have some obligation towards the effects of economic policies, which are already a terrible mess. "We'll save the world by making the cost of energy so high, that people will stop using it." Going out and planting trees is simpler, something real, measurable. Based on each person's individual carbon lifestyles they can plant more or less, based on how much they think they're personally polluting the environment.
And even if Global Warming were not happening... then, well there is no harm other then having planted some trees. As an economist I recognize the opportunity cost of that (Well that land could have been used for something else, along with the labor), but there isn't a direct cost. All global warming policies would likely have a direct cost along with an opportunity cost, and this one just has that opportunity cost. Besides, a tree has value, which is something you can't say for a 15% tax on coal.
Well, I doubt they'd turn retention ponds into wetlands so the issue would be a bit more distant from civilization.
I host a podcast about movies.
No one wants the nuclear waste stored near them.
That's a good point, too. You don't want to be whacking in giant stands of one species, or using something that's not native to the area. If you want to talk about carbon emission offsets through creating more green biomass, you're probably better off thinking of it in terms of acres of woods per thousand people or something. Local small-scale projects would be the best way to go about it; people who know what's native to the area and where it will do the most good to plant.
So? Didn't we just conquer afganistan?
I host a podcast about movies.
That's is excellent.
I say we cram Tora Bora to the gills with nuclear waste then erect a giant Abraham Lincoln statue on top.
I host a podcast about movies.
Hokay--I was just flashing back to a talk we got from a parent at my Jr. High, where she pointed out in passing that the 'save the wetlands' campaigns in the Bay Area had downsides.
Why bother? If we want to irradiate subjegated natives, we already have Yucca Mountain.
Not really.
http://gristmill.grist.org/story/2006/10/26/20495/240
Wrong.
3rd paragraph:
http://www.realclimate.org/index.php/archives/2007/02/quick-pre-spm-round-up/
While true, it has been explained:
http://gristmill.grist.org/story/2006/11/4/14560/6189
took out her barrettes and her hair spilled out like rootbeer
Just in case he's actually looking, it would be nice to at least point out the metareview of peer-reviewed studies that found that the vast majority of climate-related research either implicitly or explicitly accepted the global warming consensus, and that the rest didn't deal with it at all (i.e., no research found implicitly or explicitly rejected the consensus).
Well in fairness, Nevada really is a shithole and we're not going to make it much worse.
And no one wants to use the waste in reactors. Which can be done, it just has the annoying side effect of producing fuel that can be used in bombs..
The people they have trying to regulate the construction industry, for instance, seem to not actually know anything about construction OR the environment.
You really liked Parliament Square, didn't you.
Is this true? I was under the impression it was a real bitch to refine plutonium or uranium to weapons-grade states. It seems like if the byproduct of breeder reactors was weapons-grade fissionable material the military would be all over incenting breeding reactors for power generation (under their close supervision).
It can be used to produce weapons fuel, but it isn't automatically weapons grade. I think it still gives you plutonium, but the purity is too low (40%?) to easily make a nuclear bomb directly from it. You could make a dirty bomb from it, or you would need to do more processing to make a viable nuke.
However, all of the non-poliferation stuff makes getting material which is close to bomb ready less than optimal. But Carter was stupid to outright ban breeder reactors because of this, since the obvious solution is to have local and international oversight. And his "setting an example" is bunk because many other nations reprocess the fuel anyways.
It is indeed quite difficult. Arguably, its the most difficult part of the process. When you hear about Iran trying to make nukes (whether they are or not) their goal would be refining the uranium or plutonium to weapons grade quality. This is a very tricky and energy intensive process. If you get the weapons grade stuff its not that difficult to build a bomb with it, thats the easy part that can be figured out on paper.
As the North Koreans showed with their botched bomb, there is still some finesse to putting it all together in the end though. If one of the shaped charges on a bomb fouls up the material won't reach critical mass and it will fizzle. And making a bomb with reactor grade plutonium is even more difficult and I am not sure if it has ever been proven in practice to work.
Not disagreeing, but I recall rain making green roofs insanely heavy being one of the major difficulties, so yeah, using the right kind of plants (non-tree, for most roofs) is key.
http://www.forbes.com/2007/04/20/solutions-energy-bala-opinion-cx_ag_0420bala.html
The conclusion from the climate model was that only planting tree's in the tropic will actually help prevent Global Warming. Planting trees in the USA would actually cause increased Global Warming. Because even though the trees will reduce carbon levels in the atmosphere they act as insulators holding heat on the planets surface that would otherwise be reflected back into space.
That would be true if the entirety of continental america was covered with a bright white icecap, and you replaced it with green trees. But that's not so, you're replacing green grassland with...green trees. People really do check their brains at the door when these debates open up
There are other problems with treeplanting programs, and many more efficient ways to offset C emissions, but that's one of the silliest reasons to avoid them.
I notice the second to last link happens to be The Great Global Warming Swindle video which was infamous for misrepresenting the opinions of the scientists it interviewed.
Whilst we're on the topic of climate control theories from computer games, is there any reason a solar shade wouldn't work? Seem to remember a couple of years back there was some scheme to use a large space based mirror to heat up parts of Russia and make them more habitable. There anything wrong with the concept or is the engineering on an epic scale factor the main issue.
It isn't that much, actually. If you made the roof accessible for garden parties and the like it would need to support a 100 pound/square foot live load assembly area by code which would generally cover the wet weight of 6-18" deep soil's (needed for flowering plants) dead load over the square feet of non-patio space. If you aren't making it accessible then the extra cost of supporting 3" deep soil in the structure is recouped through lengthened roof life so less replacements and the insulating effect that it has on the building's top envelope which is a big plus as well. They're beyond economically sound, you just have to think ahead and design it into the building.
http://www.washingtonpost.com/wp-dyn/content/article/2007/05/23/AR2007052301510.html
It is up to you Aussies to bioengineer some sort of tree capable of surviving in and taking over your poisonous back yard.