This is a guest post from John Polkinghorne

There’s a difference between “pollutants” and “greenhouse gases”. Cars put out a few pollutants, such as nitrogen oxides, carbon monoxide, sulphur dioxide and particulate matter – which means unburnt carbon (soot) and worse. These contribute to localised air pollution and health issues. In terms of these pollutants, though, cars today are much cleaner than they were a few decades ago.

Greenhouse gases are another story. In the car engine, petrol or diesel is combusted with oxygen, to produce energy and carbon dioxide (CO2). This chemical reaction is what makes your car move, and CO2 is the inevitable product. This is different from the other nasty stuff above, where the pollutants are byproducts and can be reduced through higher-quality fuels, better filters etc.

CO2 is of course a greenhouse gas, contributing to global warming. Cars may become more efficient in the future – in fact, new cars could become 20% to 40% more efficient over the next 20+ years – but CO2 will always be generated, as it’s the main product of the chemical reaction which powers the car. And it will always be created in proportion to the amount of fuel used, so saying a car is “low emissions” is the exact same thing as saying it is “fuel efficient”. As I showed in a previous post, our fuel efficiency doesn’t seem to have improved in the last few decades.

CO2 is sometimes referred to as a pollutant, and the US Environmental Protection Agency has now classified it as such, but it’s quite different from nitrogen oxides, soot and those other grimy things. It doesn’t have much of a local effect, but it contributes majorly to global warming.

How much CO2 do our cars produce?
According to the Ministry for the Environment (New Zealand’s Greenhouse Gas Inventory 1990–2010), the road transport sector accounted for 12,514.1 gigagrams of CO2-equivalent emissions in 2010. This is a rather silly unit in my opinion – although Quagmire from Family Guy might disagree – so let’s convert it to tonnes instead. With that cleared up, road transport accounted for 12.5 million tonnes of CO2-equivalent emissions in 2010.

New Zealand’s total ‘net’ emissions (after accounting for forestry, which removes CO2 from the air) were 51.7 million tonnes. So, road transport makes up 24.2% of our net emissions. But this includes freight and other non-passenger uses. We’ve got to dig a little deeper to find how much is generated by cars. For this, I turn to the very interesting Annual Fleet Statistics published by the Ministry of Transport. Figure 1.10 shows that 65.2% of road transport emissions come from the “light passenger fleet”, which includes passenger cars and vans.

So, this suggests that cars (and vans, let’s not forget the vans, although it’s only passenger vans and not goods vans and I really can’t imagine they make up a big chunk of this) are producing 65.2% x 12.5 million tonnes = 8.15 million tonnes of CO2-equivalent emissions in New Zealand each year.

That’s a little under two tonnes per man, woman or child in the country. It’s more than your car weighs, and it’s about 15.8% of our country’s net emissions total.

John P Emissions

What does this mean for you?
The average NZ car uses 10 litres of fuel to drive 100 kilometres, although this can be quite a bit higher or lower depending on the car, the driver and the traffic. Petrol produces around 2.3 kilograms of CO2-equivalent emissions for every litre – which is about three times as much as the petrol itself weighs, incidentally.

Every 100 kilometres you drive, then, you’re producing 23 kilograms of CO2. The average car drives some 12,000 km a year, producing 2.8 tonnes of CO2.

As consumers, the best thing we can do to reduce our contribution to global warming is to change our transport habits. Better driving makes a small difference, more efficient cars can make a bigger difference. Carpooling is better still, and public transport is much better than that. I’ll look at public transport emissions in my next post.

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  1. And the ETS charge is a measly 0.4c a litre, not making any difference at all to demand for petrol. And no influence at all on central Govt as it poors billions into RoNS. The Emissions Trading Scheme is a complete shambles that doesn’t achieve anything.

    1. Agreed on all points. But even with a high carbon price, ETS charges would be too low to have much effect on petrol sales. A carbon price of NZD $100/tonne would only increase the price of petrol by 20 to 25 cents. Because demand for petrol and diesel is fairly inelastic, we can’t rely on ETS charges to wean ourselves off fossil fuels. That will take either very high oil prices, or some proactive thinking by governments and councils to make the alternatives more viable.

      By which I really mean public transport, not electric cars. If I was the government I’d be putting money into public transport, infrastructure and services.

    2. Land use patterns can make a big difference here. Higher density means less driving which means lower emissions. Manhattan has incredibly low emissions on a per capita basis.

      1. That’s true to a degree – although one of the biggest impacts of density on energy consumption is through more efficient heating/cooling. Some research by Ewing showed that a one standard deviation increase in density reduces household electricity consumption by approximately 20%, holding other factors (such as household size and preferences) constant.

        So you don’t have to reach mega-densities to start realising energy efficiency gains from density.

        1. Not quite – need to differentiate between average and marginal mix. On average you’re right, our electricity mix is quite renewable (~80%) and trending upwards as geothermal and wind are used to meet baseload growth (although that’s fairly scant these days).

          But at the margin and in peaks our generation is dominated by thermal plant, especially gas. So if we cut just 20% of our energy demand, then we’d probably cut 50% of our Co2 emissions, at a guess.

          1. Stu this argument is so boring. NZ needn’t have any FF generation at all, if we choose to, so to argue that the marginal use is all FF and therefore all electricity offers no alternative to driving (your argument) may make you feel like Mr balanced and reasonable but is in fact just a big fat cop out.

            NZ, like Norway and Canada, is brilliantly placed to be the leaders (note not followers, fast or otherwise) in the shift from FF to electrons. FFS, get with the programme! (Sorry for grumpy tone)

          2. Those new shareholders will be keen on renewables Patrick. Ooops, no they won’t as it often costs a bit more and their dividend payout could be reduced. Why are we selling such a major shareholding again? Ahh, to build schools. Hang about, isn’t that what our taxes do? Where is our tax going then?

          3. You need to read this B, the powerco model is facing terminal disruption:

            We live in more interesting times than most grasp, won’t happen here? Already happening in Aus, where distributed solar is killing the growth models for big generation. Great news of course, except for the Business As Usual rentier crowd.

          4. The price to equip an average family home with grid tied solar is now very affordable and the payback is in years – not tens of years. Most places can be done, so I understand, for around the $10 to$13K mark. Even if you do not receive a cent for any power you send to the grid, most families could save between $1,500 to $2,000 per year. That would make power free after less than 10 years. If the panels last a minimum of 25 years (as they are supposed to), that is 15 years of pretty much free power, apart from line charges. Now, some changes will need to be made to our grid (as has happened in Germany) and the line charges will need to increase, but we will be making an investment in our countries future.

        2. That marginal vs average point is actually a good one that I must admit I hadn’t fully appreciated. I guess that also means what’s really important is trying to curb a bit of power use at the “peak of the peak” (i.e. 6pm on a cold July evening) as chances are the power burned then is probably the most emitting of all. Agree with Patrick that with a bit of clever thinking (i.e. more geothermal and perhaps tidal power as baseload) NZ could easily become 100% clean renewable.

          1. Just the will, there are no end of renewable projects actually consented in NZ but demand is stalling, so how do we get that last 20% to happen? Price carbon properly now.

            Remember there are no subsidies for wind and geo in NZ, they work brilliantly, why, because the fuel is free…. and in NZ there’s plenty of both hot rocks and strong winds. furthermore the intermittency of wind is easily balanced by our existing Hydro. We are lucky, but led by oafs.

          2. “the intermittency of wind is easily balanced by our existing Hydro”

            …thermal stations are used to meet peak demand. They are fired up when all of the other generators (including hydro) are already running. If a significant portion of our electrical demand is met by wind how is hydro “easily” going to meet the shortfall caused by a drop in wind at peak times? Are you proposing to retrofit existing hydro stations with additional penstocks, turbines, generators, turbine halls etc? If so, how can this accurately be described as easy? If not, what is the proposition?

            Wind and PV are non-dispatchable generators. Until they can be converted to dispatchable sources by the addition of storage mechanisms they cannot be treated as equivalent equivalent to thermal or hydro generation. It’s just not an apples to apples comparison.

          3. Hydro is 50% of NZ’s supply, and can be controlled very quickly and precisely, Geo is not intermittent, and the intermittency of individual wind farms is in practice balanced when there is sufficient quantity with a wide enough geographical spread [it’s almost always blowing somewhere in this long exposed country]. I’m sorry but your model is very dated. We do have sunk cost in our 20% thermal plants and they do not have to pay for their true externalities, so are in effect subsidised [in contrast to wind and geo in NZ]. Furthermore we have an industry that is set up to make money with the current model.

            The truth is that renewables are a disruptive technology, especially when installed at the distributed level, and the first thing they are disrupting are the business plans of big power cos and faith in the ‘market’ structures constructed with such effort across the world over the last couple of decades. Why are they disruptive? Because the fuel is free once the initial capex is spent, so what is the marginal cost of the power? Zero or less than zero? And therefore the cost plus and peak demand gaming models of profitability break down. Its certainly already happen in Germany and distributed solar is starting to seriously effect the plans of big generating in Australia too.


            What’s great for the nation as a whole is not the same as what is in the interests of power cos on the current model, and visa versa.

            Might pay to consider the above article carefully that when making investments decisions this year, especially for a medium or long term hold!

          4. You are obfuscating. Explain how “the intermittency of wind is easily balanced by our existing hydro” at times of peak demand. These are the times when thermal stations are fired up and when hydro generators are running at full capacity. In particular, please explain how it is easy.

            Explain how a model where electricity supply and demand need to be in balance to maintain grid frequency and voltage is “very dated”. Explain how a model in which a generator running at 100% capacity cannot produce any more is “very dated”. These are issues of physics and engineering and plain old logic. If that is not the model you are referring to then you are being wildly presumptuous.

            Explain how the url that you gave has any relevance to the above. Smoke and mirrors….

          5. Brilliant! You write exactly like traffic engineers do about traffic demand. You describe the current set up as if it were permanent and unchangeable. Clearly I am describing a situation where the current thermal stations are replaced by new renewable ones. If we had only 60% renewable would you be claiming it is impossible to change that to 80% because that isn’t already the case? Change is not only possible but also in many cases desirable. And also, one way or another; inevitable.

            I’m sorry you can’t or won’t understand the article linked to above and how it describes the dynamic nature of the world’s electricity supply situation, I agree it is subtle and is entirely about disruption of a static pricing and supply environment so perhaps it’s too difficult to imagine…?

          6. No explanation? You have made a statement that you cannot or will not support. Let me spell it out for you:


            You can stamp your feet and rail against the physics of it and claim that it’s a matter of attitude or lack of imagination but guess what?- the physics will just laugh at you.
            You could claim that what you really meant was that peak demand could be met by a geographically-distributed array of wind turbines
            You could claim that, actually, what you really, really meant was that thermal stations would be replaced by some unspecified renewable ones…

            Thus when you state “clearly” you are mistaken. Your claims change so it is not clear what your premise is at all. What exactly is your proposal re replacement of thermal stations that meet peak load with renewables? What type of renewables? What rating and how will they cope with the peak demand? Where will they be located and will the present grid have sufficient capacity to support it? Let’s see some figures and specifics. Don’t spend too long on it because, after all, it’s easy – right?

            Nothing in the URL you provided supports your original claim. Instead it is largely a gripe from a Portugese conspiracy theorist as to why PV subsidies in Europe (and Germany in particular) are being cut. He is wrong on a number of points and I am more than willing to debate those in a separate thread but let’s just deal with the realities of PV-generated electricity in Germany:

            It produces electricity during the day with a peak around midday (depending on orientation and weather). There is a daytime glut of it at certain times of the year and none of it at night. The early morning and evening peak loads have to be met by other generators (of whatever type) who are expected to provide high capacity for short periods of the day and others who are expected to provide the network to support it. The net result is that peak electricity prices rise as fixed costs are covered by lower income. The German government subsidy program drove global growth in PV manufacturing and has achieved economies of scale (with subsequent falls in the price of PV modules) together with meeting a substantial portion of Germany’s electrical demand. It has been very successful in achieving its objectives. The German government has recognised, however, that to make further inroads it must address the prime shortcoming of PV (the lack of dispatchability) and switched its attention to incentivising electrical storage. Given the efficacy of the PV subsidy program I am guessing that they will be successful. The net result is that PV (or wind) can truly substitute for a thermal station and further growth of renewables can take place.

            There is no doubt that NZ could generate 100% of its electricity from renewables. Providing for the daily peaks in demand is NOT going to be easy or cheap since it is plant that is idle for most of the day. We have benefitted from the largesse of the German taxpayer in the form of low PV module and inverter prices. I am reasonably confident that we will also benefit in terms of large-scale electrical storage as well. In the meantime it is technically feasible to run a combined-cycle gas turbine generator on renewable fuel, albeit at considerable cost.

            Armchair experts full of bluster, presumption and opinion selectively trawled from the internet harm the cause rather than advancing it.

          7. I am sorry to get you so worked up and shouty but rereading your post it is clear where your confusion lies. I discussed two separate issues that you have conflated. First I said that NZ could become 100% renewable in its electricity generation, and I am delighted to see that you concede this point, which is, after all hardly controversial being an actual stated government aim. And second I linked to a very interesting and detailed article outlining the challenges to the market electricity model caused by renewables in europe. Two different ideas.

            Lets just deal with the first because you clearly aren’t interested/can’t grasp the second:

            You seem to be very upset with the idea that hydro can balance the intermittency of wind generation, well I’m sorry it can and it does now. At no point did I make any claim to the quantities of each required for this to be workable, the term I used was renewables, which is very broad and not all renewable sources are intermittent, this clearly includes the second most significant source of renewable energy in NZ right now; Geothermal, which is not intermittent. As well as other systems that are yet to make much impact on the NZ generation scene such as solar, [or tidal or biomas]. Funny anyway that this idea upsets you so much because you then go on to say that we ‘will also benefit in terms of large-scale electrical storage’. Well what is water behind a dam but stored potential energy? We already have a great deal of energy storage, this is how balancing with intermittent sources is already achieved in NZ. When a powerco’s wind farms are delivering well it provides the opportunity to slow the flow of water through the turbines of their hydro assets. Wind energy is currently a little over 4% of the total and hydro at 50-55%, this is an uncontroversial idea. The recent growth in Geothermal generation in fact assists in this management of generation assets by taking base load work away from the flexible Hydro assets allowing them to be more actively managed. Therefore it is no surprise then that this is exactly what the future looks like. This from MRP’s website:

            “It is our view that geothermal and wind will be the main fuels of choice for new generation development in New Zealand over the next decade. We have already secured future growth opportunities in these renewable fuel types.”


            And no I make no claim to particular expertise in this field but I have stood in the control room of a major power company and discussed the actual practicalities of responding to variations in demand; I was surprised by how flexible their control of generation is with their Hydro assets, and this is even including the legal niceties of how much variation in lake level they are allowed to play with on top of the actual mechanics of the operation.

            Additionally I mentioned that a wide geographic distribution of wind assets is another way that the intermittency issue can be addressed. Another completely uncontroversial claim. Yes this requires the construction of a greater total potential capacity of output than the average output expected, unlike with a traditional thermal plant, but as i didn’t claim otherwise I fail to see how you might imagine this might be what I was claiming.

            So clearly no laws of physics have been ignored, nor even actual operating practicalities.

            Two final points:
            You should be aware that writing in uppercase is not a way of providing evidence, it’s just shouting in text form.
            And I am delighted that you have summed up your own post perfectly at the end: ‘Armchair experts full of bluster, presumption and opinion’ indeed.

            best wishes for a relaxing weekend.

    1. motorbikes are not even counted in the Nz census… it’s specified to exclude motorbikes from the vehicles per household count

    2. You know, although your motorbike may not use all that much fuel they are actually worse for the environment than cars in terms of emissions. Some modern bikes for example put out almost 5000% more of some of the toxic emissions than a modern car.

  2. The other night I couldn’t sleep at 3am so spent an hour trying to figure out how much CO2 I ‘saved’ or not emitted on my recent cycle tour. The tour went from home (Auckland) to Ohiwa (near Opotiki), then to Rotorua, Mangakino, Kawhia, Raglan and back home. Total was 830k cycling, with two short lifts (Katikati to Te Puke, and Rotorua to Mangakino).

    First step, finding out how much CO2 a litre of petrol emits. Result, around 2.3kg. So I calculated that times the number of litres I would have had to use if I was driving. My car does around 400k in open road driving on 30l. So that gave me 60l of fuel. Times that by 2.3kg of CO2 gave me 139kg of CO2 not emitted.

    Interesting fact: what we think of as a tonne is actually called a gigagram, according to Wikipedia.

    Later in March I’ll be cycling to Wellington via Marsterton, and then back up to Feilding, Whangnui, Stratford, Taumaranui, Raglan, home. Will take about three weeks, and I should ‘save’ lots of CO2. 🙂

      1. Correct. A tonne is a megagram.
        It’s been interesting reading about weights. Of course I am assuming that gaseous weights are the same as physical weights i.e. a ‘kilo’ of CO2 means just that, it weighs a kilo. I think I am right, but would be nice to know for sure. More research to do…

        1. We are talking about mass, not weight. Weight is a force created by gravity measured in Newtons, whereas mass is an amount of matter, measured in kilograms (well those are the SI units). A gas has no weight, but its mass is the same in every state of matter. The easiest way to measure the mass of a gas is to condense it to a liquid (or sublime it to a solid in the case of CO2) and measure it’s weight with a force meter, then compare that with the rate of acceleration due to gravity (about 9.81 ms^-2 in Auckland) to find the mass. Of course subliming CO2 is not very practical so using the equation PV=nRT would be easier. (P = pressure (in Pa), V= volume (in m^3), n = ammount of moles, R = the gas constant and T = temperature (in K).) Use that to find the number of moles then multiply the RAM of CO2 (around 44 gmol^-1 or 0.044 kgmol^-1) and you have your mass in kg!

    1. I remember reading a letter in an engineering journal some years ago which purported to show that the respiratory CO2 produced by a hard-pedalling cyclist was actually more than would be produced by a person travelling the same distance in a modern fuel-efficient car. The figures for each were all reliably sourced and believable. For a while this thesis left me wondering, was this guy onto something? Should all cyclists be lumped in with that other allegedly guilty group of carbon emitters, farting farm animals? In fact why stop at cyclists? Runners must be equally bad, as must be rugby players, gym-bunnies and anyone else who breaks a sweat.

      And then I started to see the holes in this chap’s argument. For a start, he had neglected to add in the CO2 which would have been breathed out by the car driver simply through staying alive. True, this would have been less than the sweaty cyclist, but it would nonetheless help to re-balance the argument in favour of the cyclist.

      But the giveaway comment he made was this: “It doesn’t much matter whether that CO2 is produced by burning petrol or last night’s curry. . .”. WRONG! Last night’s curry can be considered as a bio-fuel. Carbon derived from the atmosphere through plant and animal growth is simply returned to the atmosphere for another round. But pumping oil out of the ground and burning it increases the net amount of carbon in the eco-system. There it stays, until we find a way of returning it from whence it came.

      So as a cyclist myself I realised I could breathe easier, untroubled by claims that I am more of a threat to the planet than the gas-guzzling brigade. For such claims are pure hot air.

        1. Agreed. There will be more and more of this nonsense as people knowingly or otherwise get to the deal making phase with their grief over the wind down of our current unsustainable lifestyle. How could anyone let alone an engineer figure that the work of a cyclist to move man and machine (and therefore the emissions) is in anyway equivalent to the work to move a human and a car, no matter how modern!

  3. Don’t forget that according to the graph you’ve used (and figures guessed from that), Agriculture accounts for about 65% of net emissions and Other accounts for about 45% of net emissions, giving us a total of 135% net emissions. That’s the problem with using that term, you are assuming that Forestry only offsets non-transport CO2 sources and while that is OK for the purposes of your argument, it doesn’t change the fact that the same argument then works even better with the (bigger) non-transport sources.

  4. I’d be interested to hear how much CO2 is absorbed by the many trees in NZ as well as how much PM10 and PM2.5 particulates are emitted by each mode of transport.
    PM10 & especially PM2.5 particulates are especially nasty things to breathe in and are emitted in the main by Diesel engines.

    1. Well the absorption is essentially shown on that graph – the green bar for forestry. They absorb about 20 million tonnes. Actually page 173 of New Zealand’s Greenhouse Gas Inventory 1990–2010 reckons forestry absorbs 23 million, but then converting forests to grassland released 3 million.

      PM10 and PM2.5 are certainly pretty yucky things. We don’t measure them at the tailpipe as such (although I think they get checked on cars as they come into the country?), but Niwa measures their concentration in the air, I’m pretty sure. In the US, the EPA has an interesting page:, which shows that the level of these gribblies has dropped over time. This would be due, in large part, to stricter controls on industry and vehicles. Another factor is that there have never been that many diesel vehicles in the US, but the proportion has reduced over time – and as you mention, diesels are worse for these things. Although diesel cars are much cleaner than they used to be.

  5. “Greenhouse gases are another story. In the car engine, petrol or diesel is combusted with oxygen, to produce energy and carbon dioxide (CO2). This chemical reaction is what makes your car move, and CO2 is the inevitable product. This is different from the other nasty stuff above, where the pollutants are byproducts and can be reduced through higher-quality fuels, better filters etc.” says John P.

    Not totally true. You mentioned nitrogen oxides (NOx). There is no nitrogen in vehicle fuel. Vehicles emit NOx because the two main constituents of air are oxygen and nitrogen. Normally these benign compounds keep well away from each other but at high temperatures (in a combustion engine) they combine into toxic NOx. The most toxic NOx is nitrogen dioxide (NO2). Levels of NO2 are measured routinely around the State Highway network by NZTA ( and levels can approach or exceed WHO Guidelines at numerous locations. NO2 is an irritant to asthmatics and chronic exposure amongst children has been linked to stunted lung development in California.

    The point I wanted to make was that, because NO2 isn’t related to the fuel but to the temperature of combustion emission rates have been effectively immune to improvements in fuel, combustion and exhaust technologies. Whereas emission rates of CO2 (and particulate matter, and pretty much every other air pollutant) have improved in recent years in response to technological advancements, emissions of NOx and NO2 specifically have been inexorably rising, as have levels of NO2 in our air at certain locations.

    1. …and combustion temperature is related to compression ratio which is related to Carnot efficiency. Low compression engines operate at lower temperatures and thus produce less NOx but are less fuel efficient. Ultimately I see electric as the way to go but it the meantime reducing vehicle mass would seem to be desirable.

      1. And lowering vehicle mass is critical for EV too, scooters are about right. Except for tethered systems of course, they can be as heavy as you like.

  6. Interesting to see some figures put on this, and to know just how much of the “greenhouse gas” problem can be blamed on unbalanced transport policies which favour mass car-use and discourage alternatives.

    But the graph above shows agriculture as completely dwarfing the emissions picture. Is this largely due to ruminants farting as we are often led to believe? Or does it include things like exhaust emissions from farm machinery, CO2 from equipment and fertiliser manufacture, (road-) transport of agricultural products and livestock, etc?

    With regard to the ruminants, the greenhouse gas methane is considered to be the chief culprit and worse than CO2. However is this really valid, given that ruminants ingest carbon from the ecosystem and then return that same carbon as flatulence. I understand that over time the methane produced progressively reverts to CO2, which is then re-absorbed by more grass thereby completing the “biofuel cycle”. This is in stark contrast to the burning of fossil-fuels, whereby carbon that has been safely buried for millennia is dug up and liberated into the ecosystem as an addition to what was there before?

    I suppose my real question is, are the emissions from NZ’s 3.2 million fossil-fuel burning road vehicles so much less of a problem than from its 10 million cattle, 33 million sheep, 1.1 million deer, etc, or is the above graph not giving us the full story?

      1. @ Patrick: Yes, but is the CO2 produced by agriculture really so much more of a problem than that produced by the motoring brigade? Hard to believe, but that graph suggests that it is. I would love to get to the bottom of this apparent conundrum.

        1. I mean the graph in the original article, not your pie chart. This considers only oil consumption, but the graph in the article appears to show CO2 (or CO2 equivalent) from all sources. I just want to know what is going on here, and whether blaming agriculture is perhaps a red herring.

          1. I have a close relative who has become vegetarian for 2013, partly due to the wastefulness of converting grain or grass into meat.
            Isn’t there a Freakonomics chapter that suggests the person who drives their Hummer to the restaurant and eats a vegetarian meal did less damage than the person who caught the bus or walked but then ate a steak?
            Of course we should do the transport bit, but maybe it’s possible to also do something about agricultural emissions too (admittedly a large percentage of production isn’t consumed in NZ- then you get into a debate about whether it’s the consumer or the producer who should bear the costs of production emissions. I’d suggest both).

          2. NCD beware of clever dicks in other countries who love to calculate the carbon emissions of electricity use as if every election was made burning coal. It is just completely irrelevant here, and in fact is increasingly irrelevant even in the US, not so China.

          3. Humans can’t eat grass. At least in the case of New Zealand the land we use to raise meat animals wouldn’t be productive with food crops we can digest.

            Probably a different story in the US and Australia where they use grain as a feedstock. Then again the Aussies do have huge stations they drove cattle over, having been on one I don’t see how you’d grow anything but the patchy grass and shrubs the animals eat.

          4. “in the case of New Zealand the land we use to raise meat animals wouldn’t be productive with food crops we can digest”

            That’s an overstatement – a significant portion of what is now grassland could be converted to the growing of vegetables, nuts, cereals and fruit. I can think of specific examples local to Auckland where beef cattle graze immediately adjacent to fruit and nut trees. Water resources could be a big issue since grazing animals can be fed with food grown elsewhere or slaughtered in times of low rainfall but less meat and more vegetable matter in our diets would be no bad thing for many of us.

          5. Patrick, the point wasn’t about electricity use and how it’s calculated- it was about emissions from driving vs emissions from eating meat.

            This gained some media currency when a book in the UK (“How to lead a low-Carbon life”) claimed driving to the supermarket might produce less emissions than walking. (Cue media frenzy).

            There’s a good analysis of the issue here:
            Summary: for a 2.4km drive:
            Car: 1000g CO2 (not just tailpipe emissions: they did it right)
            Walking 2.4km takes 123 calories average.
            Getting those cals from eating sirloin produces 2400g of CO2 equivalent,
            Same cals from eating an apple produces 170g CO2 equivalent.
            Of course bicycling there is better still 😉

            There’s a set of cool posters done for world earth day, several of which touch on transport themes, and one on this particular issue:


    1. “With regard to the ruminants, the greenhouse gas methane is considered to be the chief culprit and worse than CO2. However is this really valid, given that ruminants ingest carbon from the ecosystem and then return that same carbon as flatulence”

      Yes, it really is valid. The issue to be addresses is the greenhouse effect of the gas, not the mass of carbon in the atmosphere. A given mass of carbon in the form of methane has a very much greater greenhouse effect than the same mass of carbon in the form of carbon dioxide. Methane emissions are converted to carbon dioxide equivalents by multiplying the emissions by the factor by which methane is “worse” than carbon dioxide at causing a greenhouse effect.

      1. “in the case of New Zealand the land we use to raise meat animals wouldn’t be productive with food crops we can digest”

        That’s an overstatement – a significant portion of what is now grassland could be converted to the growing of vegetables, nuts, cereals and fruit. I can think of specific examples local to Auckland where beef cattle graze immediately adjacent to fruit and nut trees. Water resources could be a big issue since grazing animals can be fed with food grown elsewhere or slaughtered in times of low rainfall but less meat and more vegetable matter in our diets would be no bad thing for many of us.

  7. It’s hard to know what to make of the agriculture numbers.
    If it’s mostly from “breathing” ought not we consider human emissions in the same way?

    1. It’s not mostly from breathing out – it’s methane from bacterial action in the gut of ruminants. It’s belched out by the animals.

    1. To answer my own question, yes, apparently:

      The ETS covers liquid fossil fuels used in New Zealand. It covers petrol, diesel, aviation gasoline, jet kerosene, light fuel oil and heavy fuel oil. Emissions from fuel used for international aviation and marine transport are excluded from the scheme, consistent with our international obligations under the UNFCCC and the Kyoto Protocol.

  8. Ian

    I think although there is motor vehicle engine efficiencies mean motor vehicles produce less CO2 per kilometre the improvemnts are only mild compared to other gases. The actual figures would be good to compare. Also a 30% decrease per kilometre for a car can be lost if people just buy a bigger car (such as a SUV).

  9. Um, according to Phil Jones of the University of east Anglia, there “has been no statistically significant global warming since 1995.” According to the British Met Office, none is expected in the next few years.

    Sorry about that.

  10. You can’t get a better expert than Phil Jones though, nor a better outfit than the British Met Office. Sorry about that.

    1. You do realise that the whole point of the scientific method is that it’s about what we can observe, and about the data, not about how ‘expert’ one person is.. right?

      1. Sorry that may not have come across right. My reply wasn’t a personal remark about your knowledge, just an indication of my surprise at the reason you have given for why 2 results would outweigh 13,926 results.

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