Two Offbeat Questions About Greenhouse Gases

In science, something fruitful can arise from innocent or atypical questions.  One of many examples of this was a recent query in Quora, ” Can chlorine be potentially a greenhouse gas? Why or why not?

Here’s what I wrote, but I’ve since added a little more detail.

Short answer , no.  🙂

Now here’s why….

An infrared spectrum is used to check if specific molecules are good absorbers of infrared energy, which qualifies them as “greenhouse gases”. Some chlorine-containing gases like CFCs fall into that category, but diatomic chlorine(Cl2) or monoatomic chlorine(Cl) do not. How come?

In order for molecular vibrations to absorb IR energy, the vibrational motions along the bond must change the dipole moment CO2IRof the molecule. A dipole occurs when pulling forces within a molecule do not cancel out. Why are there forces in the first place? These exist because of the differences in “greediness” for electrons between different atoms. So Cl by itself has no bonds so it can’t even vibrate. Diatomic chlorine does not meet the criteria either because, like O2 and N2 in air, it has the same atom pulling on each side of the bond, and equally important, any type of stretching or bending will not cause or lead to a change in net force between the bonded atoms.
The neat and thing about CO2 is that it doesn’t have a permanent dipole moment, but it can experience a net force during an asymmetric stretch. This happens when one oxygen gets squished towards the carbon in the middle of the molecule while the other oxygen atom stretches away, leading to a change in dipole. That’s what makes carbon dioxide a greenhouse gas. If the oxygen atoms each pull away from the carbon, the net force will still equal zero. With no net change, the symmetric stretch cannot intensify and cannot absorb infrared energy.

co2 asymm

CO2’s asymmetric stretch, which leads to strong absorption of infrared Source for 3 gifs.

co2 symm

This symmetric stretch cannot intensify with incoming infrared red absorption.

There is also some absorption in another part of the infrared spectrum, although not as intense but still due to a change in dipole. It happens when the CO2 molecule bends.

co2 bend

A bending vibration of the CO2 molecule. The change in dipole occurs, implying that it can intensify by absorbing infrared.

At the rish2o symmk of belaboring the idea, let’s point look at the H2O molecule, a strong and more abundant greenhouse gas than CO2.  The latter has a linear shape. Due to  water’s angular shape, water already has an overall dipole.  Even with a symmetric stretch a change in dipole will result. Specifically, the movement shown increases the net pull of oxygen. As a result such a stretch can also be amplified when it absorbs infrared.

By the way, why don’t we focus any attention on our emissions of water vapor? Simplistically, one might attribute it to relative numbers. Air on average is about 2% H2O gas. (The percentage breakdowns for atmospheric composition that are normally given are for dry air.) So although the combustion of petroleum and natural gas emits H2O, relative to CO2, the water produced causes very little change in the overall percentage of water vapor. Moreover, coal, which produces the most CO2 per kWh, produces little water when burnt because hydrogen only makes up about 5% of coal.  There is a net movement of water from land to ocean of 37 trillion tons of water per year. Of this total, about 12 trillion tons of water is in the air at any one time because water vapor only stays in the air for an average of 10 days. That’s 12000 gigatons, of which we add about 3 to 5 gigatons(Gton) annually, a change of 0.03%. In contrast, we add 9 Gtons of carbon dioxide annually. After an increased withdrawal by oceans and land, there is a net annual  input of 4 Gtons to a pool of 840 Gtons, or a 0.5% increase, more than 15 times bigger than that of water.

But far more importantly,  in the real world’s dynamics, CO2 and other non-H2O greenhouse gases, are the major limiting factor in the greenhouse effect.

Without non-condensing greenhouse gases[such as CO2], water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect.


Other references for the above research:

Andrew Lacis. NASA Goddard Institute Space Studies. CO2: The Thermostat that Controls Earth’s Temperature 2010

Lacis, Hansen and al. NASA GISS  The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change 2013


I encountered the second question on a NASA blog. It’s based on a common misconception, but again it shows how even someone without the erroneous idea can still benefit from reading a thorough answer, such as the one given below by Rebecca Lindsey. The ozone hole and global warming are separate problems, but some of the minor connections between the two are rarely discussed in big media.

Are the ozone hole and global warming related ?

 By Rebecca LindseySeptember 14, 2010

The ozone hole and global warming are not the same thing, and neither is the main cause of the other.

The ozone hole is an area in the stratosphere above Antarctica where chlorine and bromine gases from human-produced chlorofluorocarbons (CFCs) and halons have destroyed ozone molecules.

Global warming is the rise in average global surface temperature caused primarily by the build-up of human-produced greenhouses gases, mostly carbon dioxide and methane, which trap heat in the lower levels of the atmosphere.

There are some connections between the two phenomena.

For example, the CFCs that destroy ozone are also potent greenhouse gases, though they are present in such small concentrations in the atmosphere (several hundred parts per trillion, compared to several hundred parts per million for carbon dioxide) that they are considered a minor player in greenhouse warming. CFCs account for about 13% of the total energy absorbed by human-produced greenhouse gases.

The ozone hole itself has a minor cooling effect (about 2 percent of the warming effect of greenhouses gases) because ozone in the stratosphere absorbs heat radiated to space by gases in a lower layer of Earth’s atmosphere (the upper troposphere). The loss of ozone means slightly more heat can escape into space from that region.

Global warming is also predicted to have a modest impact on the Antarctic ozone hole. The chlorine gases in the lower stratosphere interact with tiny cloud particles that form at extremely cold temperatures — below -80 degrees Celsius (-112 degrees Fahrenheit). While greenhouse gases absorb heat at a relatively low altitudes and warm the surface, they actually cool the stratosphere. Near the South Pole, this cooling of the stratosphere results in an increase in polar stratospheric clouds, increasing the efficiency of chlorine release into reactive forms that can rapidly deplete ozone.

  1. References:

  2. Allen, Jeannie. (2004, February 10). Tango in the Atmosphere: Ozone and Climate Change. Earth Observatory. Accessed: September 14, 2010.

  3. Baldwin, M.P., Dameris, M., Shepherd, T.G. (2007, June 15). How will the stratosphere affect climate change?Science, 316 (5831), 1576-1577.

  4. Intergovernmental Panel on Climate Change, (2007). Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge, United Kingdom, and New York, New York: Cambridge University Press.

  5. Ozone Hole Watch. Accessed: September 14, 2010.


Daily Car Use: Mimicking a Bad Habit


from the Vancouver Sun

It’s no secret that our imitative nature is both a blessing and a curse. Our lives would be overwhelming if along with reinventing the wheel we had to recreate tables and chairs along with all the tools and techniques presently at our finger tips. Our ability to mimic also plays a role in the acquisition of a mother tongue and in learning languages of a mathematical, artistic or scientific nature. We base our behavior on that of family and peers to form satisfying relationships and to learn other cooperative strategies. These compensate for our relative physical weaknesses in a world where human beings cannot survive without the support of others.

But mimicking new practices on a global scale, those which technology facilitates even though they have not withstood the test of time, can have serious consequences. The average number of light vehicles per household in Canada—vehicles weighing less than 4500 kilograms—was 1.47 in 2009. In Alberta and in the United States the rate was close to 2, more precisely, 1.87 and 1.9, respectively. If it were not for an affordability factor for some families, the ratio would be even higher because car ownership seems so normal. People like the independence of car travel and the fact that despite traffic, it’s sometimes faster than public transit.

In 2010, in the six largest metropolitan areas in Canada, car users took an average of 27 minutes to get to work, while public transit users took 44 minutes. In mid-sized metropolitan areas (areas with between 250,000 and 1 million residents), the difference in average commuting times was larger—23 minutes for car users and 46 minutes for public transit users.   Statistics Canada

Better catalytic converters have eased the conscience of consumers. But these honeycomb-shaped appendages are far from being perfect filters, and how many drivers know about the existence of PM 2.5 pollution? Worse, CO2 emissions pass through the rhodium-palladium-platinum catalysts completely unscathed. No car manufacture or dealer will advertise the fact that the number of vehicle-miles traveled by passenger cars and light-duty trucks increased 35% from 1990 to 2013, and that they accounted for 60% of transportation’s 34% contribution to greenhouse gases in the U.S in 2013.

mallBut there’s more to it. When every household opts for two cars it creates a greater need for roads which are paved with asphalt, mostly a residue of petroleum distillation, fueling a demand for more oil. More roads entail more overpasses, which need more concrete. Almost two thirds of cement is calcium oxide, a compound generated from heating calcium carbonate, which of course releases more carbon dioxide. In cold areas, automobiles often idle, generating more pollution. Icy roads are treated with chloride salts, which eat away at concrete and metal, leading to the disposal of materials,  more cement production and more car manufacturing to replace corroded ones. The interior of cars is largely synthetic and derived from polymerization of cracked petroleum, again cementing the dependency on fossil fuels.

Cars change the landscape by other means. Drivers become more willing to live far from their work. Housing developments arise to accommodate them, often at the expense of good farmland that was close to a city. It implies that more food then has to be grown farther away from a population center. That creates the need for more transportation from distant places by large diesel-burning trucks and ships.


A view of some Bois Franc residences from one of the many walkways: Source:×615/201207/13/521291-on-voit-ici-situation-geographique.jpg

A generation ago, in Montreal, the Bombardier corporation had the foresight to design a pedestrian-friendly neighborhood close to one of their aircraft plants. Known as Bois Franc,  the project won awards and was used as a model to inspire students of urban planning as far as Queen’s University.  In the neighborhood, green spaces abound.  Eventually the city added bike routes and protected a woodland area and even set aside an area for monarch butterflies.  Through contractors, the company offered initially modest and affordable homes to their employees and other citizens, hoping that the former would walk or bicycle to work. But few of their employees bought the homes. And the majority of those who did continued to drive to work.  The community is close to other industries, several schools, stores and many services, but most of its students and employees mimic the norm prevalent in the rest of the city and do not walk or cycle.

Some compensate for their lack of physical activity by driving to gyms whose artificial walkers and lighting consume electricity, something whose generation in most parts of the world depends heavily on burning coal and natural gas. The parking lots built for gyms are often part of large malls with tarred rooftops and huge asphalted parking lots, which absorb and radiate far more heat than grass and trees. Together with hot vehicles, tar accentuates the heat-island effect of urban centers. This increases the use of air conditioning, which is powered again by CO2-releasing combustion. Furthermore, any leaking a.c. fluids are also greenhouse gases. For many other drivers, their sedentary lifestyle increases the likelihood for type 2 diabetes and heart disease. In 2014, worldwide , 9% of adults 18 years and older—about a half a billion people— had diabetes.

Another  important consequence of having so many cars on the road is that over 30 000 people in the United States are killed in motor vehicle accidents, twice the number who are killed by guns. In 2014 global terrorism claimed over 30 000 lives. Worldwide in 2010, there were 1.25 million casualties from traffic accidents. Yet no politician has ever declared war on automobiles.

The irony in all of this is that cars’ time-saving advantage disappears when people prioritize living close to their employment location. According to Statistics Canada, workers who walk or bicycle to work have shorter trips (14 minutes on average), about half of what drivers expend. What has to be undone is our one-dimensional rationalizations, symptomatic of copycatting behaviors that have no rational foundation.


 “What destroys the poetry of a city? Automobiles destroy it, and they destroy more than the poetry. All over America, all over Europe in fact, cities and towns are under assault by the automobile, are being literally destroyed by car culture. But cities are gradually learning that they don’t have to let it happen to them. Witness our beautiful new Embarcadero!  “Embarcadero4_1000x386