Specific Climate Impact of Passenger Transport

The ACS journal Environmental Science & Technology just published a paper that's very relevant to my interests.

Borken-Kleefeld J, Berntsen T, Fuglestvedt J. Specific Climate Impact of Passenger and Freight Transport. Environ. Sci. Technol. 2010;44:5700. DOI: 10.1021/es9039693, or direct PDF link here.

This paper is interesting for a few reasons. First is that it doesn't limit its analysis to a simple counting of tons of CO2 per unit travel, as do many simplistic USA Today-article-style fluff pieces: instead it looks at CO2, sulfate aerosols, NOx effects including methane destruction, including the interaction of these elements with cloud formation. It sums up all of these effects in terms of net average global surface temperature change. Furthermore, it extends its analysis beyond the short term, looking at 5, 20, and 50 year time horizons. Due to its unique analysis it comes up with some results that I most definitely did not expect!

Although they graph out all manner of permutations of different possible emissions regulations on ships, planes, motorcycles, etc., most of that is boring even to transportation-and-climate-obsessed me. Instead I think the most pertinent figure is the passenger travel part of Figure 1: "Temperature change per transport work by mode for various years after the emissions". The units are in micro-Kelvin per passenger-kilometer, where passenger-kilometer is the product of number of passengers transported by the distance traveled. Error bars represent +/- 1 std. dev. The figure:



In the short term (5 year time horizon) these results line up with my preconceived notions: airline travel is far, far "dirtier" than driving a car, which is a bit dirtier than driving a motorcycle, which in turn has a greater environmental impact than riding the bus. What's this about riding the train actually leading to net global surface temperature cooling, though? It turns out the sulfur spewed out by all those coal-fired electrical generation plants driving electric trains and diesel generators onboard diesel-electrics leads to cooling through the secondary effect of methane destruction.

The results really get interesting at the 20-year and 50-year time horizons. Note that airline travel at these time horizons has less of an impact on temperatures than driving a car! I would not have anticipated this result at all.

In the authors' words:

Borken-Kleefeld et al. said:

For the passenger travel of the year 2000 [ed: odd grammar theirs, allowing for non-native English writers] the modes with clearly lower specific climate impact than car travel can be readily identified: Rail travel has at least a factor 4 lower specific impact and is cooling on shorter times, bus and coach travel has 2 to 5 times lower specific impact, while travel with two- or three-wheelers has up to a factor 2 lower specific climate impact than car travel. Air travel results in a lower temperature change per passenger-kilometer than car travel on the long run; the integrated radiative forcing of air travel is on short- to medium time horizons much higher than for car travel.

Click to expand...

Also of note for the motorcycle and scooter apologists out there is that adopting stricter emissions controls (ie Euro 3) leads to near-parity of the effect of bus and powered-two-wheelers, whereas with year 2000 emissions the bus comes out strongly in the lead. The moral of this little sub-story: if you're running your motorcycle catless or if it's pre-Euro 3 emissions you're not doing the environment any favors, so go ahead and wipe that smug smile off your face and take off that "one less car" sticker.

I love that the earth is, and has been actively cooling for the last ~800 years or so, yet funding in the right places has managed to sucker many folks in science fields into this.

I guess they forgot the 1970s-1980s climate change fear of CFC's from areosol cans leading to a global cooling fear...

Cool, Toshi. It actually takes into account the half-lives of each emission component and the predicted temperature influence of each particle based on its reflectivity/absorption factors (explored in other papers). That would seem to be a particularly better method for predicting long-term affects. The thing I wonder is if you suddenly introduced a constant greenhouse gas emitting into the world, and left it going, and assuming this greenhouse gas had a "lifespan", would the temperature of the world just keep on increasing or would it just simply converge to a higher equilibrium (Not accounting for fluctuations and influences you'd expect from other sources)? I'm thinking it would converge to a higher equilibrium. Of course, assuming greenhouse emission is constant isn't reasonable - it's been increasing and will keep increasing. Despite the "social goodness" of lowering emissions ("Social goodness" is debatable - I don't necessarily agree that it's good), the sheer economics of co2 sources will ensure its generation increase for at least the next couple of decades. I think there might be a change in the decades after that as resource extraction rates peak and there's a shift to other primary energy sources. And, along with that peak, there'll likely be a peak in the temperature influence of "green-house" gases (Notice I said influence and not simply 'temperature' - the global temperature is the combination/interaction of all possible influences) somewhere near on the timeline.

liveforphysics said:

I love that the earth is, and has been actively cooling for the last ~800 years or so, yet funding in the right places has managed to sucker many folks in science fields into this.

I guess they forgot the 1970s-1980s climate change fear of CFC's from areosol cans leading to a global cooling fear...

Click to expand...

Uh, but it's not cooling. http://www.skepticalscience.com/global-cooling.htm

Toshi said:

liveforphysics said:

I love that the earth is, and has been actively cooling for the last ~800 years or so, yet funding in the right places has managed to sucker many folks in science fields into this.

I guess they forgot the 1970s-1980s climate change fear of CFC's from areosol cans leading to a global cooling fear...

Click to expand...

Uh, but it's not cooling. http://www.skepticalscience.com/global-cooling.htm

Click to expand...

I'm sounding like a fanboy at this point, but sweet source! A source that looks at the total thermal energy content as opposed to simply instantaneous temperatures. I wonder if you were to convert that energy content into temperature (For the ocean, anyways), what the temperature anomaly be? I'm sure they extracted that data from temperature and the ocean's predicted mass, so it'd be a little redundant I'm sure, but it would give some understandable "scope" to the graph.

Toshi said:

liveforphysics said:

I love that the earth is, and has been actively cooling for the last ~800 years or so, yet funding in the right places has managed to sucker many folks in science fields into this.

I guess they forgot the 1970s-1980s climate change fear of CFC's from areosol cans leading to a global cooling fear...

Click to expand...

Uh, but it's not cooling. http://www.skepticalscience.com/global-cooling.htm

Click to expand...

The earth has been cooling for about 4 billion years.
The earth hasn't even gotten hotter in recent decades, the raw data was flawed by measurement issues that skewed the data toward hotter temperatures.
Ice has been melting since the last ice age, and melting ice only means a temperature higher than 0°C.
Climate changes. It always has and always will.
The sun is the over-riding control factor of global temperatures.
The glorified weathermen pushed themselves into the limelight with this crap, and of course it's in their best interest so sell some form of doom and gloom.
The biggest salesman of this scam bought oceanfront property.
Talk of global warming only distracts from real pollution problems that man has created.
Getting off of fossil fuels is inevitable anyway because they are finite.

well stated
the future is coming lol
time to wake up

John in CR said:

The earth has been cooling for about 4 billion years.
The earth hasn't even gotten hotter in recent decades, the raw data was flawed by measurement issues that skewed the data toward hotter temperatures.
Ice has been melting since the last ice age, and melting ice only means a temperature higher than 0°C.
Climate changes. It always has and always will.
The sun is the over-riding control factor of global temperatures.
The glorified weathermen pushed themselves into the limelight with this crap, and of course it's in their best interest so sell some form of doom and gloom.
The biggest salesman of this scam bought oceanfront property.
Talk of global warming only distracts from real pollution problems that man has created.
Getting off of fossil fuels is inevitable anyway because they are finite.

Click to expand...

Just about all of your arguments are addressed here:

http://www.skepticalscience.com/argument.php

England used to have orange and lemon orchards back in the day.

We've definitely been dropping in temp. Didn't the "hockey stick graph" guy that was what they used to kick-start the whole scare finally admit to just fabricating that data anyways? lol

What's really funny about this thing, is in the 1970s, " all the scientists agreed " with all the overwhelming evidence that the climate was cooling at a dangerously high rate, and we would be doomed from global cooling etc. Look back in the Nature, Science, Time, Life, National Geographic, etc magazines archives from the 1970's, and you see all the same NASA and various university professor's charts and graphs showing this 'dooming' temperature dropping trend, and how if we didn't stop using aerosol hair spray, it was going to be the end of us etc etc.

liveforphysics said:

England used to have orange and lemon orchards back in the day.

We've definitely been dropping in temp.

Click to expand...

It was warmer in medieval times, yes. There was a trend of gradual cooling until about 1900.

liveforphysics said:

Didn't the "hockey stick graph" guy that was what they used to kick-start the whole scare finally admit to just fabricating that data anyways? lol

Click to expand...

You might want to check your memory as you are dead wrong on the "hockey stick graph" guy. http://www.skepticalscience.com/broken-hockey-stick.htm .

liveforphysics said:

What's really funny about this thing, is in the 1970s, " all the scientists agreed " with all the overwhelming evidence that the climate was cooling at a dangerously high rate, and we would be doomed from global cooling etc. Look back in the Nature, Science, Time, Life, National Geographic, etc magazines archives from the 1970's, and you see all the same NASA and various university professor's charts and graphs showing this 'dooming' temperature dropping trend, and how if we didn't stop using aerosol hair spray, it was going to be the end of us etc etc.

Click to expand...

Thank you for recycling yet another tired, wrong argument: http://www.skepticalscience.com/ice-age-predictions-in-1970s.htm

skepticalscience.com--read the freakin' articles there before rehashing material from Sen. Inhofe's webpage said:

What was the scientific consensus in the 1970s regarding future climate? The most cited example of 1970s cooling predictions is a 1975 Newsweek article "The Cooling World" that suggested cooling "may portend a drastic decline for food production. ...

A 1974 Time magazine article Another Ice Age? painted a similarly bleak picture: ...

However, these are media articles, not scientific studies. A survey of peer reviewed scientific papers from 1965 to 1979 show that few papers predicted global cooling (7 in total). Significantly more papers (42 in total) predicted global warming (Peterson 2008). The large majority of climate research in the 1970s predicted the Earth would warm as a consequence of CO2. Rather than 1970s scientists predicting cooling, the opposite is the case.


In the 1970s, the most comprehensive study on climate change (and the closest thing to a scientific consensus at the time) was the 1975 US National Academy of Sciences/National Research Council Report. Their basic conclusion was "…we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate…"

This is in strong contrast with the current position of the US National Academy of Sciences: "...there is now strong evidence that significant global warming is occurring... It is likely that most of the warming in recent decades can be attributed to human activities... The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action." This is in a joint statement with the Academies of Science from Brazil, France, Canada, China, Germany, India, Italy, Japan, Russia and the United Kingdom.

In contrast to the 1970s, there are now a number of scientific bodies that have released statements affirming man-made global warming.

Click to expand...

I'm not worried about the earth. Is what I worry about is the air that I must breath in when I'm out on the roads (or even in my yard). Exhaust from ICE has clearly been shown to cause many health problems in congested areas.

I ride a bike, or ebike as much as I can, partly because I know how much I hate it when an ICE pollutes the air I travel into and breath on the roads. I have a pollution mask I wear and pull up whenever a truck or line of cars passes, especially on a hill or if they are accelerating. It makes a big difference in the smell of the air.

Another big benefit of the mask will be when it gets cold out - biking will be much more enjoyable/warmer. It only restricts my breathing if I am pedaling hard.

Luckily, our favorite transportation choice on here is probably the cleanest thing possible. Electric drive converts energy better than humans do... even if the electricity comes from the crappiest coal this planet contains.

Note that there is a subaru-robin 35cc kit out there that gets 200-250mpg on a bicycle. So a motorized bike basically uses 1/10th the power of an average car, if that's a good indicator of how efficient a form of transport this is.

Awesome.. just.. awesome

Well, to be fair, a typical bicycle only has an advantage at low speeds. You see the big motor guys on here, saying they pull 5000watts+ at > 50 mph. That's basically the same as an economy car. If all of us could store 20kw in a 20lb battery, and our motors could sustain 8kw, then our efficiency would nearly as bad as a car since we'd be going high speeds.

Car = horrible horrible at low speeds and in traffic, slightly better at steady speeds from 35-60mph, with a severe drop in efficiency past that
Bike = amazing at low speeds and in traffic, mainly due to weight, but also drivetrain efficiency. efficiency drops like a ROCK after 30mph or so thanks to F'NN exponential wind resistance! grrrr! Although it still drastically beats a car below 45mph.

Streamliner bike = amazing at low and high speeds


My road bike is pretty damn efficient. Yesterday I averaged 9 watt-hours/mile with a LOT of stops, but I averaged only about 13mph too. I just love how I can go 4x faster than someone walking, while using 1/4 of the energy :lol: At 10mph on smooth flat pavement, a road bike is practically energy free transportation. (40watts)

veloman said:

Well, to be fair, a typical bicycle only has an advantage at low speeds. You see the big motor guys on here, saying they pull 5000watts+ at > 50 mph. That's basically the same as an economy car. If all of us could store 20kw in a 20lb battery, and our motors could sustain 8kw, then our efficiency would nearly as bad as a car since we'd be going high speeds.

Click to expand...

Ah, that's true. Which is funny if you think about it.... a person on a bike is aerodynamically disadvantaged compared to someone in a car.. lol.
I bet spandex changes that, but i'm not willing to go there.. lol

neptronix said:

veloman said:

Well, to be fair, a typical bicycle only has an advantage at low speeds. You see the big motor guys on here, saying they pull 5000watts+ at > 50 mph. That's basically the same as an economy car. If all of us could store 20kw in a 20lb battery, and our motors could sustain 8kw, then our efficiency would nearly as bad as a car since we'd be going high speeds.

Click to expand...

Ah, that's true. Which is funny if you think about it.... a person on a bike is aerodynamically disadvantaged compared to someone in a car.. lol.
I bet spandex changes that, but i'm not willing to go there.. lol

Click to expand...

Actually, spandex doesn't change the fundamentals: a (relatively) upright rider on a bicycle has a high Cd and a high frontal area. Barring layback streamliners and the like a car or car-like vehicle (Aptera, anyone?) will beat the pants off of a upright two-wheeled rider at the same speed.

It would take about 6200watts for me, in my road racing spandex on my traditional double diamond road bike, in a typical "brisk riding position", to keep myself at 70mph.

A superb professional time trialist (UCI legal, such as in the Tour de France), would require around 4800watts

A typical casual cyclist in normal clothes on a 'hybrid' would require around 8200watts.

So yeah, 2000watts is nothing to sneeze at, but it goes to show how non-aero even a road cyclist is. But see the big difference between the TT'r and casual hybrid rider?

I got the estimates from plugging in #s at analyticcycling.com

Do these study findings conclude that one person flying on a air plane has a greater environmental impact than one person driving an average car the same distance?

Like, should I feel worse about driving across the country or flying? What if I'm driving a 37mpg car? Bring a friend and the car clearly wins I think. Unless the plane you are boarding has empty seats, you have to assume you being there is having a tangible impact.

According to a couple aero drag calculators I played with, my Honda Insight only requires 3200watts to maintain 70mph on flat ground.

5.1ft^2 frontal area. 0.25Cd.

veloman said:

Do these study findings conclude that one person flying on a air plane has a greater environmental impact than one person driving an average car the same distance?

Like, should I feel worse about driving across the country or flying? What if I'm driving a 37mpg car? Bring a friend and the car clearly wins I think. Unless the plane you are boarding has empty seats, you have to assume you being there is having a tangible impact.

Click to expand...

Check out the first graph again, it's what you're looking for. In text form:

the paper said:

Air travel results in a lower temperature change per passenger-kilometer than car travel on the long run; the integrated radiative forcing of air travel is on short- to medium time horizons much higher than for car travel.

Click to expand...

Here we go again.

liveforphysics said:

We've definitely been dropping in temp. Didn't the "hockey stick graph" guy that was what they used to kick-start the whole scare finally admit to just fabricating that data anyways? lol

Click to expand...

Actually, he was cleared of any wrongdoing by multiple independent panels, and the whole 'climate-gate' e-mail thing was complete BS. No fraud, no scientific malfeasance, no fabricated data, no invalidated conclusions:
http://www.guardian.co.uk/environment/2010/jul/02/michael-mann-cleared

liveforphysics said:

What's really funny about this thing, is in the 1970s, " all the scientists agreed " with all the overwhelming evidence that the climate was cooling at a dangerously high rate, and we would be doomed from global cooling etc. Look back in the Nature, Science, Time, Life, National Geographic, etc magazines archives from the 1970's, and you see all the same NASA and various university professor's charts and graphs showing this 'dooming' temperature dropping trend, and how if we didn't stop using aerosol hair spray, it was going to be the end of us etc etc.

Click to expand...

I think this is probably the third time I've posted this link.
http://www.google.com/url?sa=t&sour...0sSqCw&usg=AFQjCNHFIBo0HnCfeRCddQrQGYB3Y4q8Jg
Here's a synopsis in case you don't want to read the whole thing:
http://www.usatoday.com/tech/science/environment/2008-02-20-global-cooling_N.htm
The supposed "global cooling" consensus among scientists in the 1970s — frequently offered by global-warming skeptics as proof that climatologists can't make up their minds — is a myth, according to a survey of the scientific literature of the era.

Since this is now the "global warming as caused by carbon energy sources" thread du jour, I shall offer my simple worst case evaluation here.

I believe most reserve analyses suggest we've exhausted somewhere around 1/4 of "all possible reserves" and 1/3 of "all extractable reserves"(The kind that's not prohibitively expensive - that is, energy out > energy in.) of coal and oil; we have a ton left of gas, it seems, but it doesn't seem like the production rate can be significantly increased, at least not at present and that's not comparable to CO2 generation from oil and coal. Assuming that CO2 stays in the atmosphere "forever", if we burn off the rest of the reserves, then the difference in heating is about thrice of what it has been (Or close to thrice). Now, since CO2's impact declines with time due to processes that convert it to something else, the longterm impact is less than that number.

So, using that, it appears likely we may only see a heating 2 - 2.5 times greater than the current difference assuming all reserves are used, this number due to supply constraints. Depending on your point of view, that can be bad but I think people have found it's increased by somewhere around 1 degree celsius... what's another degree or two? At least for people in habitable climates, it seems like not a big concern. There *might* be environmental 'catastrophies' due to that warming (ice caps melt, low lying coastal cities flooded, hottest parts of africa become unlivably hot, etc.), but I think the earth has endured warmer temperatures and it's apparently survived.