Does purchasing emissions offsets make a car zero emissions?

It doesn't make it zero emmisions. However it is a good thing to do.

 

Trees do not consume Nox, Sox, or hydrocarbons. Actually, trees as a carbon sink is a ymmv.

OTOH, trees are *great* for lots of reasons, so go ahead !

 

Nope.
It's like buying a baby calf to offset that steak dinner.
Might be a good thing to do, but it doesn't make you a vegan.

 

How many trees are they planting for your $25?

My understanding is that it takes a heck of a lot of trees to offset 1 year of average driving. Perhaps someone on here may know?

 

There is no simple answer, it depends on the exact details of the carbon offset. The term of art is "additionality". You might Google that and see if you can make sense of what you are reading.

The short answer is that almost no offsets that are offered commercially have true additionality, and that for those that do, it is rare to be able to measure the additional impact with any accuracy. Almost all offsets are, in effect, a nice charitable donation, not a pound-for-pound literal offset of atmospheric carbon releases.

Briefly, a carbon offset has "additionality", if, by giving these people your money, you actually truly and permanently remove some additional carbon from the atmosphere that would not otherwise be removed (or prevent the release of additional carbon that would otherwise be released).

Most of the offsets you can buy have no "additionality". Here in the US, most offset sellers are simply retailers of "green tags" (renewable energy certificates) and, to a pretty close approximation, result in no additional avoidance of emissions. (Because: Voluntary-market green tag revenues typically do not, and in may instances, cannot, factor into the decision to build and run more renewable energy power generation).

I realize I'm running through this pretty fast -- you'll have to do some homework, possibly starting with using the search function here, with some of the terms above, because I know I've laid this all out on PriusChat before.

For trees, in particular, you can say a few things.

First, an acre of US Southern Pine absorbs roughly one ton of carbon per year over the lifetime of the forest. (That's from the EPA). So if you take a bare field that would not otherwise turn into forest, plant pine trees, and wait 100 years, you'll sequester about 100 tons of carbon, as long as that forest remains standing. Once the forest is mature, decay offsets growth, and it sequesters no new carbon. If the forest dies, then ... no offset. The carbon goes back into the atmosphere. If it dies, then in the long run, all you've done is taken your carbon problem and passed it down to some later generation.

A Prius driven 15,000 miles would consume 300 gallons of gasoline, emittting under 1 ton of carbon.

So from the example above, to claim an eventual offset of 1 ton of carbon, you'd need to plant 1/100th of an acre of trees, or a plot roughly 20'x20' or call it (EDIT: 7) meters on a side or so. So, plant that a plot that size, a plot that would not otherwise turn to forest on its own (due either to climate or human land-use), plant it with (in my example) pine seedlings, make a sincere pledge to maintain it to eternity, and you can claim to have (eventually) sequestered the carbon emitted by your Prius this year.

So, beyond a doubt, for $25, that's the essence of what this company is doing.

An accurate statement would be something like this: "By planting these trees, and maintaining this forest forever, we (eventually) sequester a ton of carbon".

Now, there are obviously a few problems with this.

One, you have to maintain it forever. (To understand this, you have to know that the additional C02 emitted by burning fossil fuel results in a very-long-lived increase in atmospheric C02. Roughly speaking, for every pound of C02 you emit into the atmosphere, you might as well consider a third of a pound to be permanent, because it'll still be around when your Nth generation descendants are dealing with it. Not those exact atoms, but the increased carbon in the atmosphere. It's the fact that it is so long-lived that is generating our problem -- if it were rapidly re-absorbed by Nature, the total buildup in the atmosphere would be tiny.)

So if I plant some trees, grow a forest, then (e.g.) the climate dries out so much that the forest dies back, the net result in the long run is zero.

Two, even if this works for you, you realize it can't be used to solve any significant portion of the entire problem. The example I like to use is the US. We emit 2.5 gigatons of carbon per year. So, on a per-year basis, all we need to do is find 2.5 giga-acres of land, plant southern pines, and we can continue our carbon-intensive lifestyle free of guilt. That's new land, not currently growing forests. Problem is, the entire land area of the US is only 2.2 giga acres.We'd new a whole brand-new country, just to grow the trees to offset our current emissions. (Then, after 100 years, we'd have to chop that forest down, carefully store the wood where it wouldn't rot, and do it all over again, if we wanted to keep burning fossil fuels at that point).

Three, you also have to realize that sequestering emissions on a scale that matters can't possibly cost just $25 per ton of carbon. If it could be done, we'd be idiots not to pass a tax, set that sequestration in motion, and be done with this issue.

So that's the scoop. You are safe if you consider this to be a reasonable charitable donation. Depending on the details, you might even be able to consider this a true offset -- in other words, the combined act of driving your car and donating the money might truly be carbon-neutral. But I wouldn't count on it. Probably, what you are buying is a 20x20 foot plot of newly planted trees, along with the promises that a) that plot wouldn't grow trees if we didn't plant them there, and b) a sincere promise to preserve that plot of forest forever.

That latter promise is clearly unenforceable. That's why I've stopped believing in many mitigation measures, like using "white roofs" to increase the earth's albedo, reducing soot emissions, reducing methane emissions, if they are done as a substitute for reducing carbon emissions overall. Because that's a sucker's game. The atmospheric carbon lasts far longer than any roof, soot, or methane will. Or, in this case, probably, forest. So all those do is use short-term measures to mask out long-term problem. So we can feel OK, even as we in fact increase the size of the problem that the next generations will have to deal with. Here's a nice thought-provoking discussion here, by an atmospheric scientist. It changed my thinking about these types of issues.

RealClimate: Losing time, not buying time


Bottom line is, at present, there is no substitute for simply not burning fossil fuels in the first place. Planting some additional forest is good in its own right, do it for that reason. But don't kid yourself about the offset.

 

I like trees too. Sounds good to me.
In another thread, we were doing CO2 calcs, if all fossil fuels on planet are burned. Since I think we are heading in that direction, the best hope I see is long term sequestration. Years ago I visited Redwood forest in your backyard, New Zealand. Apparently they stole seeds from California 100 years ago (and rainbow trout too). I suggest a similar project.

 

What Chogan wrote.

I think I'd say that the key point of his post is that carbon offsetting has exactly the same issues as trying to reduce production: there is some that can be done cheaply, even positively, but eventually it'd become increasingly expensive, so why not simply invest the money in reducing carbon production instead?

You might be able to invest the money in energy-saving measures at home and then re-invest your profits. (Tough if you're at your parents' house and you can't do a deal with them. )

There are charities that help supply people in developing countries with more efficient heating and lighting systems. They can help reduce deforestation (e.g. more efficient stoves to reduce use of wood) and use of fossil fuels (e.g. replacing kerosene lamps with solar) with possible additional benefit of increasing wealth or quality of life by reducing consumption and/or energy costs.

 

We're going to have to plant a few billion more trees to make up for the last few hundred years of deforestation. Even then, that doesn't begin to address the emissions epidemic. Offsets are at best a way to ease our guilt.

 

hundreds? more like millenia... we start cutting trees and deforestation the moment we started planting grains.

 

Note that the Green Fleet website is rather clear cut. They are planting as much as possible, stressing that reducing emissions should be pursued as strongly as possible (donation or not). What they have done is try a quantify how much a donation helps to the extent that a lot of folks are looking for some guideline for a donation. Note the following quote from their statement online:

"Remember that carbon offsets are only part of the solution for tackling climate change - you also need to avoid and reduce greenhouse gas emissions wherever possible."