Would anyone care to speculate as to why a city tree absorbs more CO2 than its cousin from the sticks? I wouldn’t have thought that proximity makes that big of a difference. Admittedly I know little of climate science, but I thought the carbon buildup in the atmosphere was an even, gaseous layer, somehow. Perhaps a more important question is this: how far does Co2 travel? Short of hanging a Redwood on my tailpipe, how close does a tree need to be to help expunge the CO2 I’m spewing out?
I’ll second the shade explanation. Keeping the sun off your roof makes a huge difference, and even shading the exterior walls will help. I don’t have A/C at all and really notice the different that a few well-placed plants can make.
Deciduous trees can be particularly useful, since they’ll shade you in the summer and let the sun through in the winter.
But does A/C really make *that *much of a difference? I’m talking about the 15 times figure, it seems to me that shade alone can’t account for a that much of an increase in carbon absorption.
I wouldn’t put it past the NAF to use a worst-case scenario. I’d think a modern house with good insulation in the roof/attic wouldn’t get nearly the same benefit of a shading tree. But for an old house I could believe it.
I think you’re missing the point on carbon absorption. The same amount of carbon gets absorbed no matter where the tree lives. But a tree that shades your house reduces the need for electricity and therefore reduces the amount of CO2 produced.
Here’s a thread from another forum talking about how many kg of CO2 are produced in getting a kWh of electricity. It looks like about .5 to .9 kg/kWh.
Let’s say a good-sized tree absorbs 1,000 kg of CO2 over its 20-year life. (Obviously some are less and some are much more… but the original stat didn’t define what kind of tree).
Let’s say your central AC uses 3.5 kWh and runs 10 hours per day at that rate and 60 days per year. That’s about 2,000 kg of CO2 in electrical per year
Let’s say the tree cuts the AC usage by 10% over its 20 year lifespan. It’s now saved you enough electricity to prevent the release 10,000 kg of CO2, 10x more than than the 1,000 kg it absorbs.
Now, I’m pulling most of those numbers out of the air. You can see that there are millions of estimates involved that are going to be different for every tree, house and region in the world. But the basic premise that planting trees near your house can reduce your energy bill (and therefore reduce carbon emissions) is true most of the time.
