Chapter 3 - Chemistry of Global Warming

Global warming potential (GWP): (2)

- a number that represents the relative contribution of a molecule of the atmospheric gas to global warming. - This number takes into account both atmospheric lifetime of greenhouse gases and their effectiveness in absorbing IR light.

Projections of global temps for the year 2100

▪ "projections of global temperature for the year 2100 show that temperatures *will exceed the warmest temperatures during the past 11,000 yr period*- under all plausible greenhouse gas emission scenarios" ▪ the report in Science from 2013 drew much media attention - above is one of their conclusions

Why is CO2 a major player in the debate about global warming?

Carbon dioxide (CO2) is the major player in the global warming since it is known as the prime greenhouse gas

Solar radiation (7)

▪ 46 % of the incoming radiation from the Sun is absorbed by Earth's continents and oceans, warming them. ▪ Earth, in turn, radiates some of its absorbed energy back into the atmosphere in the form of IR radiation (37 %). - It is this IR radiation that greenhouse gases efficiently absorb and reemit. ▪ Therefore, about 80 % [i.e., (37/46)x100] of incoming solar radiation that strikes the earth remains in the atmosphere and does not directly escape into space. - IR radiation is thus trapped in the surface earth (i.e., atmosphere), warming the earth. ▪ This trapping of IR light is known as the greenhouse effect, the process by which atmospheric gases trap and return major portion of the heat (IR radiation) radiated by the earth. - This leads to global warming.

VII. Strategies for removing CO2 and the Kyoto Protocol

▪ Any effort to remove CO2 is called by the term sequestration of CO2 which literally means keeping something apart. ▪ Planting trees would an example of CO2 sequestration as they remove CO2 through photosynthesis. But some researchers concluded that this is not very efficient at sequestering carbon. ▪ An idea of capturing CO2 from a power plant and of subsequent liquefying and pumping it deep into the ocean was proposed. This type of sequestration was implemented off the coast of Norway. ▪ The overarching goal of the Kyoto Protocol is to substantially reduce the amount of greenhouse gases released into the atmosphere. ▪ The Kyoto Protocol has set binding emission targets for the industrialized countries to reduce emissions of greenhouse gases from 1990 levels. ▪ As of 2007, the U.S. has continued to opt out of the Kyoto Protocol because of two reasons: 1) the reductions required by the protocol would cause serious harm to the U.S. economy, and 2) there is the lack of restrictions for developing nations. ▪ With the long delay in ratification and implementation of the Kyoto Protocol, the targets for 2012 most likely cannot be met without further restrictions.

More on GWP values

▪ As the reference value, CO2 has GWP value of 1, and all other greenhouse gases are indexed with respect to it. No GWP values are assigned to water vapor, ozone, aerosols, and other ambient air pollutants, because they have short lifetimes and are distributed unevenly around the world. ▪ Among the three greenhouse gases that have global warming potential, CO2, CH4 and N2O, nitrous oxide has the greatest GWP value. However, an absolute effect of nitrous oxide on global warming should be the least, because it concentration is the lowest among the three gases. ▪ Finally, sulfur hexafluoride (SF6) has the greatest GWP value, 22,000 times more potent as a greenhouse gas than CO2, but its atmospheric concentration is extremely low. SF6 is used for electrical insulation in transformers and a cover gas for smelting operations.

Records of earth's temperature in the past (5)

▪ Earth climate has been fluctuating between ice age (glacial period) and non ice age (interglacial period). ▪ The last glacial period was around 20,000 years ago, and over this period the average temperature was about 9 oC below the 1950-1980 average. ▪ The last major interglacial period was around 130,000 years ago, and over this period the average temperature was about 2 oC above the 1950-1980 average. ▪ A striking correlation exists between earth temperature and CO2 concentration (Fig. 3.4): - when the CO2 concentration was high, the temperature was high. Interglacial atmosphere had high CO2 and glacial atmosphere had low CO2. So it is not difficult to predict that ever increasing CO2 in today's atmosphere will lead to global warming.

VIII. Global warming and ozone depletion

▪ Global warming and ozone depletion both involve the atmosphere. However, effects of ozone on global warming, whether they are positive or negative, are small compared with the observed effects of the major greenhouse gases on global warming. ▪ Table 3.6 on page 142 gives comprehensive summaries comparing the characteristics of global warming and ozone depletion.

stretching of molecules N2 & O2 (6)

▪ If stretching of a molecule occurs (Fig. 3.13 a) in a way that the changes in charge distributions cancel each other due to its symmetrical electron distribution, absorption of IR light into the molecule does not occur. - No absorption of IR light then means no greenhouse effect. ▪ Molecules of N2 and O2 are the typical examples showing this kind of stretching. ▪ Molecules of N2 and O2 do not establish any change in charge distribution during vibration due to their symmetrical electron distributions. - No absorption of IR light occurs in these molecules. Therefore, N2 and O2 are non-greenhouse gases. ▪ CO2, H2O, CH4 (methane), N2O (nitrous oxide), O3 (ozone), CFCs, and others are greenhouse gases because they absorb IR light and do vibrate and remit the light as heat.

What is Albedo?

▪ It is a measure of the reflectivity of a surface. ▪ It is the ratio of the radiation reflected relative to the radiation incident on the surface. ▪ For example, if a snow-covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase further. ▪ Melting ice in the Artic and deforestation in tropical regions all expose darker soil. These exposure make albedo decrease as more sunlight is absorbed in the Earth's surface, which results in the temperature increases.

Molecular geometry and absorption of IR radiation

▪ Molecular vibrations in CO2. ▪ Each spring represents a C=O bond. ▪ (a) = no net change in dipole - no IR absorption. ▪ (b, c, d) = see a net change in dipole (charge distribution), so these account for IR absorption

What are the most important greenhouse gasses? (3) problems (3)

▪ Most important greenhouse gases are CO2 and H2O. - Other greenhouse gases are CH4 (methane), N2O (nitrous oxide), O3 (ozone), CFCs, etc. ▪ Though N2 and O2 are the predominant gases in the atmosphere, they are not greenhouse gases. ▪ Enhancement of the CO2 greenhouse effect by human activities is a problem we are facing now - this is from the increase of CO2 emission from the burning of fossil fuels - this is a major concern bc the effects of anthropogenic CO2 increase on global warming ********************************* ▪ so the greenhouse effect by CO2 is naturally occurring phenomenon the earth as well as Venus ▪ Read thoroughly "Section 3.4 Vibrating Molecules and the Greenhouse Effect" to understand why some are greenhouse gases and others aren't. A summary is also given in the section number III below.

Loss of Polar Ice Cap

▪ NASA Study: The Arctic warming study, appearing in the November 1 2003 issue of the American Meteorological Society's Journal of Climate, showed that compared to the 1980s, most of the Arctic warmed significantly over the last decade, with the biggest temperature increases occurring over North America. - Perennial, or year-round, sea ice in the Arctic is declining at a rate of nine percent per decade.

IV. CO2 contributions from nature and humans (5)

▪ Natural processes adding CO2 to atmosphere: decaying of organic matter (respiration); release from ocean (air-sea interaction); formation of rocks containing carbons (carbonate minerals) in the oceans. ▪ Natural processes removing CO2 from atmosphere: photosynthesis; direct sink to ocean from atmosphere (air-sea interaction). ▪ Human perturbation adding CO2 to atmosphere: burning fossil fuels (coal, petroleum, natural gas); deforestation. ▪ Human perturbation removing CO2 from atmosphere: reforestation. ▪ Natural removal processes do not respond quickly enough to the increased amount of CO2, leading to an accumulation in the atmosphere. (Fig. 3.5)

Nitrous Oxide (3)

▪ Nitrous oxide (N2O, known as laughing gas) is at least 296 time more effective than CO2 in its ability to trap IR energy, and accordingly affecting global warming. ▪ However, CO2 is still considered to be playing more important role in global warming than N2O because (1) CO2 concentration (385 ppm) is much higher than N2O (0.31 ppm). ▪ The majority of N2O molecules in the atmosphere come from the bacterial removal of nitrate ion (NO3-) from soils. Major human-caused sources are automobile catalytic converters, ammonia fertilizers, burning of biomass, etc.

Ozone & CFCs (4)

▪ Ozone also can act like a greenhouse gas. - Since depletion of ozone may have a slight cooling effect, however, ozone is clearly not a principal cause of climate change. ▪ CFCs, HCFC, and halons also absorb IR light and reemit it as heat. - Thus these are greenhouse gases, although their concentrations are still very low.

III. Vibrating molecules and the greenhouse effect (4) Vibrations (4)

▪ Photons in IR light does not have enough energy to break the bonds in chemical species, instead it can cause them to vibrate. ▪ Depending on the molecular structure, only certain vibrations are possible. - Only when a specific IR light energy with a specific wavelength is absorbed by a molecule, a specific vibration can occur within the molecule. - After the vibration the molecule reemits the absorbed energy as heat, causing the surrounding to warm up. ▪ Vibration of molecules means the vibration of the bonds in molecules. ▪ Basically there are two types of molecular vibration: stretching vibration (Fig. 3.13 a & b) and bending vibration (Fig. 3.13 c & d). - Stretching requires more energy than bending. - Thus IR photons with shorter wavelengths cause stretching, and IR photons with longer wavelengths cause bending.

Atmospheric Aerosols

▪ Presence of atmospheric aerosols appears to have a cooling effect, countering the warming effects of greenhouse gases. *Why?* ▪ Many aerosols are smaller than about 4 mm in diameter and are efficient at scattering incoming solar radiation with wavelengths close their size, thus making less solar radiation reaching the surface. ▪ At the same time, these aerosols are not effective in scattering back-radiation (IR light in the range of 4 to 20 mm) coming from the Earth, allowing back-radiation to be absorbed at a reduced level, thus countering the warming effects.

IPCC report

▪ Researchers working on climate models call both natural and man-made causes by the term forcings which are factors that affect the annual global mean surface temperature. ▪ The 2007 IPCC report (intergovernmental panel on climate change report) stated that the scientific evidence for global warming was unequivocal and that human activity is the main driver. The last six years were among the seven hottest years on record since reliable data began being kept in 1861.

V. Methane and other greenhouse gases

▪ Three greenhouse gases that have global warming potential are CO2, CH4, and N2O. ▪ Methane (CH4) is at least 20 times more effective than CO2 in its ability to trap IR light. ▪ However, CO2 is still consider to be playing more important role in global warming than CH4 because (1) CO2 concentration (385 ppm) is much higher than CH4 (1.75 ppm), and (2) CO2 has much longer life time (50 ~ 200 years) in atmosphere than CH4 (12 years). ▪ Globally, methane's effect on temperature will be less pronounced than CO2's effect, adding only perhaps a few tenths of a degree to the average temperature of earth in the next 100 years. This is in sharp contrast to the major effect predicted for CO2, a temperature rise of at least 1.0 ~ 3.5 oC by the end of this century. ▪ Methane in the atmosphere comes from a variety of sources. Methane leaking from the deposits of natural gas during exploration and from the refining of petroleum is considered to be a major source. ▪ Another major source of methane is agriculture such as rice paddies, cattle and sheep. Methane is formed and released through bacterial actions on rice roots and through belching and flatulence of the animals that chew their cud.

VI. Predictions on climate change in the future

▪ To predict climate change various computer modelings are practiced. ▪ The basic assumption of all computer models is that rising concentrations of greenhouse gases will increase the average global temperatures. ▪ An accurate climate model must include many factors such as astronomical, meteorological, geological, and biological factors. However, they are often incompletely understood, very complicated, interrelated, and thus cannot be studied independently. ▪ Important in any model for climate change is the role of the oceans. Increasing the temperature of the oceans will decrease the solubility of CO2, thus releasing more of it into the atmosphere. Just like opening a warm soda container releases CO2 bubbles.

Essential background knowledge (7)

▪ UV light (short wavelength) breaks bonds, causing molecules to come apart (Fig. 3.16). - This is because photons in UV light carry high energies. ▪ IR light (long wavelength) cannot break bonds, instead it causes molecules to vibrate (Fig. 3.16). - This is because photons in IR light carry low energies. ▪ In the atmosphere, molecules absorbing IR light vibrate for a while, and then reemit the light energy as heat. - This is how IR light warms the atmosphere. ▪ Those molecules capable of absorbing and reemitting IR light, causing the atmosphere to warm up, are called greenhouse gases.

CO2 from the jurassic ages

▪ all of those proposals for CO2 sequestration appear not to be working ▪ if we look at this figure one more time and focus on these last 100 million years when we see the natural fall of CO2 from the atmosphere ▪ if we can identify the process/processes responsible for this natural fall over the 100 million year period, and if we can replicate this process/processes at a much faster rate, that will be an idea of CO2 sequestration, although at idea currently looks like a daydream

Average of the surface air temp since 1880 (2)

▪ as you can see overall air temperature keeps increasing, especially if you look at the far right hand side ▪ over the last 40-50 years the rate of increase has been quite significant

Astronomical digression of CO2 as a greenhouse gas (10)

▪ here is the solar system ▪ on the far left hand side you see the sun , and away from the sun you see the planets lining up... ▪ now let's take a look at the surface temperatures of venus and Earth ▪ if the distance from the sun to each one of these two planets is the only determinant factor of each of their surface temperatures, then Venus would be at 212 degrees F and earth's surface temperature would be at 0 degrees F - their actual temperatures are much higher than the predicted temperatures ▪ Venus air is actually 870 F and Earth's air is actually at 60 F ▪ the reason for the difference between those two temperatures is because those two planets contains CO2 in the atmosphere - the CO2 concentration in the venus air is about 97,000 ppm - and earth's CO2 content is 400 ppm which is about .4% ▪ If there was no CO2 in the earth's atmosphere then the ocean would be completely frozen year round

Correlation bw CO2 content & air temp

▪ here we see a nice correlation between the CO2 content in the air (red) and the air temperature (blue) ▪ that higher CO2 content corresponds to higher air temperature, and lower CO2 content corresponds to lower air temperature ▪ these data have been obtained since 150 thousand years - how do we know the older CO2 content in the air, and the older air temperature? ▪ old air CO2 content and temperature are often obtained from ice cores that are retrieved from antarctica ▪ let's take a look at the bottom figure where we see the old air temperature in blue ▪ these temperatures are in nature regional - this means these temperatures represent natural regional antarctic temperatures, they do not represent global average temperatures

CO2 levels appear to be on the rise

▪ here we see the changes in CO2 concentration in our atmosphere since the 1860s ▪ as you can see the increasing CO2 content in our atmosphere is evident - especially if you look at far right hand side over the last 50 years or so, the rate of increase has been dramatic ▪ this data stops at the year 2000 at 370 ppm - we are now at 2013 and the CO2 content is over 380 ppm - by the year 2020 the data should approach close to 400 ppm - Remember 400 ppm as an approximate number for CO2 content in our atmosphere

Ice core

▪ here you see on the left hand side, a thin slice of ice that was cut from an ice core ▪ on the right hand side is the magnified view ▪ those round dark shapes are the air bubbles that were trapped while the snow of this section was accumulating ▪ so we extract these bubbles and measure the CO2 content in these air bubbles ▪ now for the old air temperature, we measure the hydrogen/ice ratio of this ice and convert that ratio to the air temperature

Going further back in history

▪ if we further go back to our earth's history however , we have very interesting data in terms of CO2 content in our atmosphere ▪ x axis is age from 200 million years ago to 50 million years ago, which is called the mesozoic era ▪ in the mesozoic era, the CO2 content was higher than what we have now, especially during the jurassic period within the mesozoic era ▪ Jurassic period CO2 approached 2500 ppm, that is more than 6x greater than what we have now ▪ if this is what it was during the jurassic, then the air temperature at the time must be much higher than what we have now - this is the area where dinosaurs were roaming around extremely tall trees and both antarctica and the arctic were completely free of ice (no ice cap in those two polar regions) ▪ how come jurassic air can have such high CO2 content?

Carbon Budget

▪ in order to explore the possibility of air sea interactions, let's take a look at this carbon budget ▪ this is for the present time ▪ pay attention to atmosphere at the top, surface ocean & deep ocean ▪ Atmosphere - the total carbon content there is 830 Gt (gigaton) ▪ Surface ocean - 900 Gt ▪ Deep ocean - 37100 Gt ▪ deep ocean is the main reservoir that contains the most carbons ▪ if you compare that amount with the amount in the atmosphere , the deep ocean contains more than 400x higher carbon content ▪ obviously these numbers during the jurassic period are totally different, however, the relative abundances among those three reservoirs during the jurassic period were not far different than the relative abundance of those three reservoirs at present time ▪ the only one condition you can think of is ... if there was an efficient upwelling of deep ocean water to the surface, bringing those high CO2 content to the surface ocean, then from the surface ocean, CO2 must have been released to the atmosphere - this is the most plausible explanation for the high CO2 content during the jurassic period

Why are we able to have such a comfortable temperature on earth?

▪ ironically thanks to the CO2 in our atmosphere we are able to have this comfortable temperature

Present day CO2/ocean problems

▪ let's get back to the present day problem of increased CO2 emission into the atmosphere from the burning of fossil fuels ▪ it is estimated that in about 400 years, all fossil fuels will be depleted ▪ Co2 keeps accumulating in the atmosphere ▪ as a result there's a net transfer of Co2 from the atmosphere to the surface ocean at the rate of 3 Gt per year ▪ this net uptake of CO2 by the surface ocean creates a whole new problem called the acidification of the surface ocean water ▪ because CO2 reacts with water, creating carbonic acid, making the surface ocean water more acidic - in consequence, organisms like shellfish/coral become more and more vulnerable because they secrete CaCO3 as their body structures, and CaCO3 is more likely to be dissolved in these corrosive, acidic waters - this is a whole new ecological issue ▪ this net transfer of CO2 from the atmosphere to the surface ocean works as a natural process of removing CO2 ... that runs in the time scale of 100,000 years at the fastest, whereas manmade addition of CO2 works a lot faster (400 years) ▪ natural process of removing CO2 from the atmosphere cannot keep up with the CO2 addition by man made activity ▪ the man made solution to the man made problem: the artificial removal of CO2 from the atmosphere, or what they call CO2 sequestrations

Sequestration of CO2 (4)

▪ many ideas have been proposed for the reduction of atmospheric CO2 these are the main one's ▪ planting trees - this is a good one bc trees obviously naturally take up CO2 through photosynthesis - but as many trees as we planted, we cut down trees as well, especially in the tropical area - the number of trees getting cut down is actually more than the number that we are planting ▪ reduction of fossil fuel use - this has been total failure - we need energy from burning fossil fuels ▪ development of alternative energy - solar energy, electric cars - progress has been slow in this area ▪ Forceful removal by artificial means (CCS)

Ice Cores (2)

▪ these pictures show ice cores ▪ ice core is a time machine that retains old air and any section you can cut from an ice core, can represent a chronological record in terms of old air temperature and old air CO2 content

CO2 smokestacks

▪ this cartoon illustrates the capturing of CO2 from the smokestacks of coal burning power plants and factories, and forcefully bringing it down to deep ocean and burying it there ▪ the entire process would require greater amount of energy that may only be supplied by burning fossil fuels ▪ so this idea would not be as effective as they originally proposed

High CO2 in the Jurassic Atmosphere

▪ this cartoon simplifies the ocean currents into two categories ▪ the ocean currents in yellow and red arrows are much more complicated than the ones in blue ▪ during mesozoic/jurassic period we believe that ocean depths are much shallower than what we have now because ocean basin evolution was still in the early stage ▪ so there must have been effective upwelling of the highly CO2 laden deep ocean water, from there CO2 must have been easily released from the surface ocean to the atmosphere

Global avg. temperatures since 1880

▪ this figure shows the global average temperatures , since 1880 ▪ so these temperatures are global not regional ▪ this figure is from the latest report ▪ they have combined temperature data from 73 stations around the globe, they have expanded the prospective in the global context for the reconstruction of temperature history ▪ overall, even in this global surface air temperature, you see the increasing trend, especially if you look at the far right hand side over the last 40-50 years increasing trend in global surface air temperature is evident

Most plausible reason for high CO2 in jurassic period

▪ was there even more sophisticated civilization, that they burnt even greater amount of fossil fuels than we do now? - Absolutely not ▪ How did it have such high CO2 concentration then? - Well if you remember the fact that more than 70% of the earth's surface is covered by the ocean then the atmosphere must be coming in contact most with the reservoir oceans - if the ocean contains even greater amount of CO2 than the atmosphere, then through air/sea dynamics, the CO2 must have been released from the ocean to the atmosphere - that would be the most plausible region for the high CO2 in the jurassic atmosphere