[abarro81]

It's just a tool for assessing the likely impact of your future actions/options - obviously the kid option becomes moot once they are born!

[IanP]

Yep, I think we probably agree on this - the figure for an extra child is calculated in a completely different way to the figure for e.g. not driving a car and they shouldn't really be compared on a single chart.   

I'd say you just need the chart to have caveats, and to make it clear what's going on. Sometimes comparing things that aren't easily comparable is a worthwhile thing to do - this is a perfect example of that. Though I agree it doesn't make sense not to have a taper applied to the future emissions.

Have to disagree here.  Unfortunately can't get full access to the original 2008 paper to look at calculations and assumptions in more detail but still can't see that simply assigning CO2 emissions from all future generations over decades and centuries hence to the lifespan of the originating parent can sensibly be compared to individual yearly reductions made by lifestyle changes.

This is irrespective of questions around assumptions such as no future change in CO2 emissions. for multiple generations hence.
 

[abarro81]

I'm not sure what you disagree with? You think that because it's not simple to directly compare these things it's not worthwhile? What if I want a way to gauge and compare the likely climate impact of life choices, and one I want to include is having a kid? You have two options that I can see: either come up with an imperfect method or just say it's too hard and give up. The former is more likely to be useful to me than the latter, even if it requires some thinking on my part and subtlety to interpret. I don't disagree that you need to be careful about how you present the results in that context, but just saying "oh we can't compare them" is no use to anyone.

I think maybe you're getting hung up on the metric used? Perhaps they would have done better to present the data using a metric like "CO2e total" (ie. total impact of the choice assuming that you make it now and then capture all future impact) rather than "CO2e/year"... but then you have to create a single scenario that doesn't apply to most people (e.g. 30 yr old living til 80) or find an easy way to present  lots of scenarios. That would seem much nicer though. Ideally you build an interactive tool that people can use where they select country, age, various lifestyle parameters and it works out the impact of choices going forwards. Much bigger project though! I'd propose that kind of idea for the next funding round if it were me... just view this as a best first effort that needs refinement. (I'm surprised someone hasn't improved on it since - maybe they have somewhere?)

[petejh]

Ian, you can see the logic by just looking at the numbers.

You can start off by acknowledging that, to quote the paper:
'until the emissions associated with desired services are reduced to zero, population will continue to be a multiplier of emissions'.

Start with that truth, then look at 3 more truths:
1. the problem of climate warming boils down to number of molecules of CO2 equivalent in the atmosphere.
2. all CO2 molecules are fungible - one person's molecules of CO2 are exactly the same as any other person's CO2 molecules.
3. the atmosphere is dumb and doesn't judge why, where or by who those molecules of CO2 were created - it will warm at the same rate if a billion vegans contribute n CO2 as if a billion meat eaters contribute the same n CO2, all else being equal.

From that, it's obvious that if reducing personal contributions of CO2 is seen as an important part of solving the problem, then an important (the most important) question to ask is what individual actions will have the most impact on the total number of CO2 molecules contributed?

When you consider that for the climate to warm by +2 degrees (+1.5 is probably dead) it's estimated we need to limit individual contributions of CO2 equiv to ~2.1t per year by 2050 (https://iopscience.iop.org/article/10.1088/1748-9326/aa7541#erlaa7541r21)

That's 28 years away. I'm presuming that figure must be predicated on a certain estimated rate of population growth...

Well consider that one human in the developed world contributes on average ~10t CO2 per year. (Canada 13t, US 16t, Australia 13t, EU 6t). Obviously that figure will taper down, you'd hope, as we advance technologies.

Multiply that average figure by 28 years to get us to 2050.

Using that logic, there being one fewer new human in the developed world can't result in anything other than a very, very significant reduction in CO2 contributed over the next 28 years. That's without the multiplier effect (which you find concerning) of any future generations' CO2 contributions added to the calculation.
But consider the likelihood that a proportion of those new humans will also have *their own* new humans over the next 28 years... The multiplier effect is at least somewhat legitimate even in the 20-50 year timeframe we're all concerned with.

There's obviously lots of emotional baggage and value judgements intertwined with all this - I think people are prone to believing *their* new human won't be the average. But purely in terms of numbers of molecules of CO2equiv contributed to the atmosphere then the figures are what they are.
That isn't to say I think anyone should stop having children. Lots of children... maybe. Personally I'd prefer to live in a world where we could all live a bit more because we'd collectively made the choice to not create too many CO2-contributors all at one point in time when our civilisation hadn't advanced technology to be clean enough to not fuck the climate - we can grow the population in 2100 when we've sorted fusion and other advances. But that's probably too idealistic.

The largest single reduction in CO2 contributions over the next two decades that any two people can make today is to have one fewer children. It makes not eating meat, not driving or taking fewer flights pale in comparison. And it helps put lifestyle choices into context when people are trying to carve out their version of what should be considered 'sustainable' or unsustainable.

[Wellsy]

Fortunately Dave Mac has had a child so we can safely slag him off for that too, praise be

[remus]

It's just a tool for assessing the likely impact of your future actions/options - obviously the kid option becomes moot once they are born!

Unless you're VERY serious about limiting your climate impact.

[IanP]

I'm not sure what you disagree with? You think that because it's not simple to directly compare these things it's not worthwhile? What if I want a way to gauge and compare the likely climate impact of life choices, and one I want to include is having a kid? You have two options that I can see: either come up with an imperfect method or just say it's too hard and give up. The former is more likely to be useful to me than the latter, even if it requires some thinking on my part and subtlety to interpret. I don't disagree that you need to be careful about how you present the results in that context, but just saying "oh we can't compare them" is no use to anyone.

I'm not sure why you don't see what I disagree with. 

One number, 58 tonnes per year takes emissions long term into the future and assigns them back to the current year, the other takes actual emissions changes now and does nothing else. 

If someone takes one less transatlantic flight each year the emissions reduction for the world will be 2.4 tonnes this year , next year the year after so on.

If someone has an extra child this year the emissions increase will be single figure tonnes this year, next year, the year after.  In 20 years the emissions increase may be around 10 tonnes (for the one extra adult assuming no change to emissions), in another 10 years they may have a child and there may be some further increase, but we're still miles off the 58 tonnes a year.   

It's not that these things are difficult to compare, they measure different things so aren't comparable.  If you want to compare back assigned future emissions impact surely you can only compare that to back assigned future emission reductions impact.  It might be more difficult to do and explain but as you say we shouldn't give up just because its difficult 

edit: or just don't all the messing about with back assigning future emission, just say that having a child increases your emissions by (say) 5 tonnes a year for the next 20, 10 for the next 20-30, 15 for the next 30-50 etc

I guess everyone else is bored of this now so we probably should agree to disagree.

[abarro81]

I wasn't sure whether you disagreed with the idea of comparing the things per se, or only the methodology and metric/unit used.

I'm still unclear in that regard - half that post says you shouldn't compare them, half says you can but you don't like the methodology.

My point is that making a comparison of total impact is useful, even if it can be misconstrued. I agree there are obvious improvements to methodology that might significantly impact the figures. There may be a better unit for it than the one they used, and applying a learning rate to emissions would be more realistic and would fix the issue of assigning things too far in the future as they'd become negligible faster.

If you want to compare back assigned future emissions impact surely you can only compare that to back assigned future emission reductions impact.

If I understand you right, this is what I suggested:

Perhaps they would have done better to present the data using a metric like "CO2e total" (ie. total impact of the choice assuming that you make it now and then capture all future impact) rather than "CO2e/year"...

but as I understand it, it gives you the same answer - just all numbers are multiplied by the number of years left to live for the notional person in question. Again the real fix is the learning rate for emissions.

[Paul B]

Isn't the overall question here (to IanP) whether you fundamentally agree or disagree with the headline that not having a child has the biggest impact?

[IanP]

Isn't the overall question here (to IanP) whether you fundamentally agree or disagree with the headline that not having a child has the biggest impact?

I agree that having a child has the biggest impact but don't agree that the the 58 tonnes a year figure , i,e, 6x the yearly adult emissions, can be sensibly compared to the figures for other reduction numbers quoted. 

[abarro81]

Perfect, tweak the method to account for emissions declining and we're done!

[IanP]

Perfect, tweak the method to account for emissions declining and we're done!

I wasn't sure whether you disagreed with the idea of comparing the things per se, or only the methodology and metric/unit used.

I'm still unclear in that regard - half that post says you shouldn't compare them, half says you can but you don't like the methodology.

You can't compare them because the methodology is different - one is 100s of years of future emissions divided into the 50 year lifespan of a person (basically), the other is actual emission changes for a single year.   They simply mean different things so you have to look at different way of calculating one or the other if you want to compare them.

 

[petejh]

Isn't the overall question here (to IanP) whether you fundamentally agree or disagree with the headline that not having a child has the biggest impact?

It's not 'not having a child', it's having one fewer children. Big difference. It doesn't suggest having kids is the wrong choice, it suggests that the consideration to maybe not have *more* kids should enter into mainstream thinking. In the same way as what diet, what travel, what energy we all consume has begun to enter mainstream thinking.

Couple thinking about a second child consider sticking with one, couple thinking about a third stick with two, thinking about a fourth stick with three etc.

Those actions would have huge impacts on CO2 emissions. That it's the individual choice with by far the largest impact should be more widely known imo.

[Paul B]

It's not 'not having a child', it's having one fewer children. Big difference.

Fewer than one is zero (which is where I'm at, not because of an environmental choice). I'm not suggesting it's the 'wrong choice' either I'm just asking instead of arguing about the specific number and how it's quantified if Ian has any issue with 'one fewer' being the biggest impact an individual can make?

Edit: I haven't got access to the journal, but the abstract of the referenced study is in the NSFW tags:

NSFW  :

Much attention has been paid to the ways that people’s home energy use, travel, food choices and other routine activities affect their emissions of carbon dioxide and, ultimately, their contributions to global warming. However, the reproductive choices of an individual are rarely incorporated into calculations of his personal impact on the environment. Here we estimate the extra emissions of fossil carbon dioxide that an average individual causes when he or she chooses to have children. The summed emissions of a person’s descendants, weighted by their relatedness to him, may far exceed the lifetime emissions produced by the original parent. Under current conditions in the United States, for example, each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions. A person’s reproductive choices must be considered along with his day-to-day activities when assessing his ultimate impact on the global environment.

[IanP]

Perfect, tweak the method to account for emissions declining and we're done!

But people aren't doing that, they're arguing that this is a useful comparison

It's been done here, not vouching for its veracity, and it does seem to take a very positive view on impact of emission reduction policy but it comes up massively different figures.

https://www.vox.com/future-perfect/2020/2/13/21132013/climate-change-children-kids-anti-natalism

[abarro81]

You can't compare them because the methodology is different - one is 100s of years of future emissions divided into the 50 year lifespan of a person (basically), the other is actual emission changes for a single year.   They simply mean different things so you have to look at different way of calculating one or the other if you want to compare them.

Perhaps this is just different starting assumptions on what question the paper is trying to answer. If the Q is "what immediate impact does choice X have on GHG emissions" then clearly their approach isn't useful. But you can compare them if the starting question is "what impact does choice X have on future GHG emissions"; in fact you have to compare them to answer than Q. If you don't think that's a valid starting question you'll have to explain why, it seems fine to me.

Now, assuming you are ok with that as a question that we're trying to answer:
1. Calculate the impact of each choice on future emissions, assuming some notional person (e.g. a 30 yr old living for 50 yrs). They should have used some kind of deflator for future emissions (ideally different ones for different choices - e.g. car travel might be assumed to decarbonise faster than air travel), but we're stuck with what they did.
2. Either present those figures, as I suggested, for a certain assumption or convert them into a slightly different unit e.g. CO2/yr-of-life-left rather than CO2-total. The first choice might have made more sense, and might meaningfully affect how people feel about the numbers, but perhaps they thought the latter was more relatable somehow. The important bit is that it wouldn't make any difference to the maths - it's just whether you choose to divide all your numbers by 50 or not.


RE your second post - you're back to having me confused about whether you can't get your head around the validity of a comparison per se or just the methodology (which we all agree leaves a lot to be desired!).
That study from the link looks like it might well be a big improvement (from a skim!), and obviously still has kids as far more damaging than eating meat, but by a different order of magnitude. Good find, although you'll have to admit that the fundamental approach of comparing them makes sense if it's to mean anything!

[Bonjoy]

But people aren't doing that, they're arguing that this is a useful comparison

It clearly is though.
I think everyone understands that it's nigh on impossible to perfectly compare in one metric the emissions of a discrete event/action, with those of an action which sets off an open ended probabilistic chain reaction. But they can also hold in their head the obvious implications on differences in scale by looking at this apples/oranges comparison, and that is useful. Especially useful in a media environment where you are way more likely to hear about the (valid) problems of demographic decline in developed economies, than the unit cost of each extra CO2 producer.

[Johnny Brown]

each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions

I don’t feel I need to explore the methodology here because this so is clearly not a useful answer to any sensible question.

[abarro81]

each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions

I don’t feel I need to explore the methodology here because this so is clearly not a useful answer to any sensible question.

Not useful or not likely to be accurate? It's very useful if accurate... The problem is that it's not likely to be accurate if we assume that we get anywhere near net zero goals!

[Bonjoy]

The less accurate, the less useful. But it depends what point is being made. If the point is only that each child you choose to have is almost certainly going to result in more CO2 in the atmosphere than any other choice you make, by quite some way, then the accuracy is only critical in so far as arguing about it dilutes the strength of the point being made.

[Wellsy]

I wonder how much more CO2 Dave's beef patty diet uses than his regular diet, which is probably pretty heavy on eggs, meat etc already.

[mrjonathanr]

It’s very useful. Now that I realise how much CO2 I have saved by not having another 6 children, I’m pretty much free to have any carbon footprint I want, it’s a carbon free bonanza.

[Bonjoy]

If you were going to apply tappers to projected emissions, then surely you should also be factoring in the reduced carrying capacity of a CC degraded world over time. Surely it's fairly predictable that population is going to decline in many parts of the world due to climate change, regardless of birth rate...

[abarro81]

Bonjoy: I guess I was trying to understand if JB was just questioning the accuracy or was questioning the usefulness even if it were accurate (e.g. it would be accurate to say that that swimming to France emits less GHG than flying, but it's not a useful answer to any sensible question!)

[IanP]

each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions

I don’t feel I need to explore the methodology here because this so is clearly not a useful answer to any sensible question.

Not useful or not likely to be accurate? It's very useful if accurate... The problem is that it's not likely to be accurate if we assume that we get anywhere near net zero goals!

Not accurate as you say, not useful because it doesn't the define the period that the 9441 tonnes is emitted over (200, 300, 500 years?) and then it arbitrarily applies all those emissions back into the 50 year lifespan of the orginator as a yearly number.   Why not just divide by the total emission period?