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Charting Historical Levels Of Co2 Environmental Sciences Essay

Evidence from observations of environmental change at the present day, and also from records of ancient episodes of environmental change, indicates that major consequences of increased atmospheric CO2 are not restricted to global warming.

At the air-sea surface interface, there is a concentration gradient in CO2 (pCO2). CO2 diffuses across this boundary until the gradient is removed. There is a constant flux of CO2 across the air-sea surface interface caused by the action of wind.

When CO2 dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species: dissolved free carbon dioxide (CO2(aq)), carbonic acid (H2CO3), bicarbonate ions (HCO3−) and carbonate (CO32-) ions. The ratio of these species depends on a range of factors including seawater temperature and alkalinity.

The acidity of seawater is measured by its pH (short for potential for Hydrogen ion concentration). Pure water has a pH of 7.0 - the prevailing pH level in oceans is slightly alkaline at just over 8.0. Any increase in hydrogen ions (H+) in a solution decreases the pH and thus increases acidity. A 10-fold increase in H+ represents a drop of 0.1 pH unit. The more CO2 drawn down from the atmosphere, the more H+ ions and the more acidic is the ocean.

The inherent balance in the Equation Q1(a).1 means that any decrease in pH will result in less of a tendency to draw down CO2 from the atmosphere, decreasing the flux of carbon into the oceans.

Q1(b) What is the geological evidence for increased seawater acidity at the Paleocene–Eocene thermal maximum (PETM)? (Your answer should be up to 200 words in length.)

The dynamics of oceans are governed biogeochemical cycles, as at the air-sea interface, and biogeophysical process, like biological activity and nutrient distribution. In an equlibriated carbon cycle, CO2 is exchanged at the air-sea surface interface from atmosphere to ocean, used in primary production and either moved back into the atmosphere or into the deep ocean before being incorporated into the lithosphere from where it eventually emerges into the atmosphere as volcanic outgassing. This steady state of, plus any perturbations to, the carbon cycle are reflected in the rock record.

For example, black shale is a type of rock commonly deposited in anoxic reducing environment. Black shales are especially rich in unoxidised carbon and thus when laid down on an ocean floor, are an indicator of acidification, and its extreme, anoxia. Further evidence comes from the fact that the organisms preferentially use the lighter of the carbon isotopes, 12C, in their metabolic pathway. If primary productivity changes, this will be reflected in changes in the isotopic signature, δ13C , a measure of the ratio of stable isotopes 13C:12C. At the PETM, there is a negative carbon isotope excursion (CIE) of 2‰–6‰ implying a drop in oceanic primary production at that time. Lastly, evidence from marine floral and faunal turnovers at the PETM, where calcareous shelled plankton suffered crisis not experienced by siliceous plankton species strongly suggest a change in seawater acidity.

(230 words)

Q1(c) Describe how the mass of CO2 that was thought to have been released at the PETM has been estimated. Briefly state two reasons why the estimate is an approximate one. (Your answer should be up to 270 words in length.)

The total mass of carbon calculated to have been released at the PETM is between 1,100 and 2,100 Gt [10]. There are two main ways in which such a large mass of CO2 could have been injected into the atmosphere at the PETM. Seafloor methane hydrates could have dissociated due to oceanic temperature changes – the resultant flux of CH4 into the atmosphere would have quickly oxidised into CO2 (see equation Q1(c ).1)

CH4 + 2O2 CO2 + 2H2O

Another reason could have been flood basalt volcanism, causing wildfires and heating up sediments it overlays.

Mechanisms (B2.1 p1099)

PETM

early Toarcian

methane hydrate dissociation

Yes

Yes

thermogenic methane release

Yes

Yes

widespread burning of terrestrial biomass

Yes

Yes

seawater stratification and overturn

No

Yes

cometary impact

Yes

No

oxidation of marine organic carbon

Yes

No

Kemp, D.B., Coe, A.L., Cohen, A.S. and Schwark, L. (2005) ‘Astronomical pacing of methane release in the Early Jurassic period’, Nature, vol. 437, pp. 396–9.

Dickens, G. R., O’Neil, J. R., Rea, D. K. & Owen, R. M. Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene. Paleoceanography 10, 965–-971 (1995).

Q1(d) Which marine organisms are particularly susceptible to seawater acidification, and why is this? Once again, illustrate your answer with a chemical equation. (Your answer should be up to 200 words in length.)

Seawater acidification eventually affects all marine organisms, independent of size, species or preferred habitat (e.g. benthic, pelagic, photic zones). However, the most immediate impact of seawater acidification is in surface waters at the base of the food chain.

Chemical weathering occurs when a slightly acidic solution of CO2 in raindrops reacts with exposed crustal rocks. The two main weathering reactions are shown below in simplified format.

Carbonate weathering

CaCO3

+

H2CO3

Ca2+

+

2HCO3-

Equation Q1(d).1

calcium carbonate

Dissolved

CO2

Silicate weathering

CaSiO3

+

2H2CO3

Ca2+

+

2HCO3-

+

SiO2

+

H2O

Equation Q1(d).2

wollastonite

Dissolved

CO2

When the weathered material is carried by riverine flux into the oceans, it is used by two main groups of plankton, calcareous and siliceous, examples species of which are given in table 1.

Table 1 – Main skeletal plankton species

Calcareous

Siliceous

Phytoplankton

coccolithophorid

diatom

Zooplankton

foraminifera

radiolarian

Calcareous planktonic species create calcium carbonate shells and skeletons in a metabolic pathway which is essentially the reverse of chemical weathering (Equation Q1(d).1). By adding carbonic acid to the oceanic reservoir, calcareous plankton reduce pH, tending to make seawater more acidic.

Siliceous species metabolise their shells and skeletons using the reverse of silicate weathering (equation Q1(d).2). Siliceous species produce twice as much dissolved CO2 (in the form of carbonic acid) as equivalent calcareous plankton.

As observed by Racki (1999) [34], when calcareous plankton suffer mass extinctions as a result of acidification, biosiliceous productivity tends to increase, thus further increasing acidification. Therefore, seawater acidification causes stress on the calcareous-based food web to the advantage of the biosiliceous species.

(218 words excluding equations and table 1)

References

Charney, J., Stone, P. H., Quirk, W. J. (1975) “Drought in the Sahara - A biogeophysical feedback mechanism” Science, vol. 187, Feb. 7, 1975, p. 434, 435.

Kemp, D.B., Coe, A.L., Cohen, A.S. and Schwark, L. (2005) ‘Astronomical pacing of methane release in the Early Jurassic period’, Nature, vol. 437, pp. 396–9.

Bucefalo Palliani, R., Mattioli, E. & Riding, J. B. The response of marine phytoplankton and sedimentary organic matter to the early Toarcian Lower Jurassic) oceanic anoxic event in northern England. Mar. Micropaleontol. 46, 223–-245 (2002).

(14) Kennett, J.P., Stott, L.D., 1991. Abrupt deep-sea warming, palaeoceanographic changes and benthic extinctions at the end of the Paleocene. Nature 353, 225–229.

(15) Kelly, D.C., Bralower, T.J., Zachos, J.C., Silva, I.P., Thomas, E., 1996. Rapid diversification of planktonic foraminifera in the tropical Pacific (ODP Site 865) during the late Paleocene thermal maximum. Geology 24, 423–426.

Q2. Many of the processes that occur within the Earth system are interconnected and they may be represented schematically by feedback diagrams. The material that you have studied in Blocks 1 and 2 illustrates how a range of positive and negative feedbacks may be initiated by a variety of forcing mechanisms, and how the interactions between Earth processes result in various facets of environmental change.

Figure Q2a.1 is a systems feedback diagram (modified after Meyer and Kump, 2008) that illustrates the processes involved in the development of marine anoxia.

Q2(a) Identify the positive and negative feedback loops of the diagram, and mark them on the copy of this diagram that is provided for you on the ‘Assessment’ page of the S808 website. Submit your annotated diagram as part of your eTMA.

Figure Q2a.1 - Systems feedback diagram for the development of marine anoxia. (Figure originally adapted from Meyer & Kump (2008))

References

Meyer, K.M. and Kump, L.R. (2008) ‘Oceanic Euxinia in Earth History: Causes and Consequences’, Annual Review of Earth and Planetary Sciences, vol. 36, pp. 251–88.

Q2(b) Based upon the knowledge that you have gained from your reading of the core references for Block 2 and additional references you might have found, explain the rate of the positive feedbacks in relation to the rate of the negative feedback. What is the approximate time taken (in years) to establish

the positive feedbacks, and

the negative feedback?

(Your answer should be up to 200 words.)

The physical residence time of carbon in the various reservoirs have been approximated from S250 (Ref) in table Q2(b).1; the short, intermediate and long can be assumed to be logarithmically different.

Table Q2(b).1

Acronym

Sphere

Residence time

Residence time

in years

B

Biosphere

Short time-scale

10-1

S

Hydrosphere (Surface)

Short time-scale

100

A

Atmosphere

Intermediate time-scale

102

D

Hydrosphere (Deep)

Intermediate time-scale

103

L

Lithosphere

Long time-scale

106

A summary of components and feedbacks, with most relevant sphere from table Q2(b).1 is given in table Q2(b).2.

Table Q2(b).2

Component

Feedback

Component

Duration (years)

atmospheric CO2

positive

temperature

A

temperature

positive

increased weathering

B

increased weathering

negative

atmospheric CO2

A

increased weathering

positive

nutrient availability

A

temperature

positive

surface ocean temperature

S

surface ocean temperature

negative

higher oxygen solubility

S

higher oxygen solubility

positive

lower deep-water oxygen

D

lower deep-water oxygen

negative

more deep-water sulfide

D

more deep-water sulfide

positive

nutrient availability

D

nutrient availability

positive

higher export productivity

S

higher export productivity

positive

higher oxygen demand

S

higher oxygen demand

negative

lower deep-water oxygen

D

There is a balance of positive and negative feedbacks in the deep-ocean hydrosphere (D) where the timescales are longest. Therefore the rate of positive and negative feedbacks are in the same order of magnitude. Establishing the positive and negative feedbacks will take as long as the longest ones in the deep-ocean hydrosphere, so in the region of 1,000 years.

(276 words)

Q2(c) For the two examples of sudden environmental change that you have studied in Block 2, describe the evidence that has caused researchers to suggest that volcanism and methane hydrate dissociation were two major potential sources of the CO2 that was responsible for the rapid rise in global temperatures and the carbon isotope excursions at those times. State briefly whether you consider these suggestions to be either likely or unlikely, and explain why. (Your answer should be up to 300 words.)

What extraordinary circumstances could trigger an injection of gigatonnes of carbon into the atmosphere? Two such mechanisms exist and have been posited as the cause of the significant slugs of atmospheric CO2 which signal the start of the PETM and T-OAE; they are volcanism and methane hydrate dissolution.

Prolonged pulses of volcanism have been known in Earth’s history as flood basalt events, evidence for which can be found in Large Igneous Provinces (LIPs). During volcanic activity, carbon molecules are released when the lava reacts with the atmosphere and the ocean. Carbon molecules ejected into the atmosphere and oxic oceans quickly oxidise to CO2. The majority of a basaltic LIP's volume is emplaced in less than 1 million years, which means a considerable amount of CO2 injected into the atmosphere over many millenia.

Part of the carbon cycle is the storage of carbon in the hydrosphere reservoir. Seawater chemistry means that at the right pressure and temperature below the Gas Hydrate Stability Zone (GHSZ) (Ref) gaseous methane (CH4) is trapped in cages of water molecules. If the pressure rises or the temperature increases, there exists the possibility of methane being released into the surrounding waters. It is posited that due to a rapid positive feedback process, large amounts of methane could be burped into the atmosphere. This is also possible from methane trapped in permafrost.

The evidence for sudden environmental change comes from geochemical and biotic records; Geochemical signatures of global warming are preserved in marine and terrestrial carbon isotope records, where the ratio of the two main carbon isotopes (12C:13C) can shed light upon the amount of the originating carbon slug and duration of the injection. Negative carbon isotope excursions (CIE) are pronounced at both the PETM and T-OAE. Some workers (Dickens et.el, 1996, cited in B2.1) have suggested that only a sudden dissociation of methane hydrate could produce such a large CIE (approx 1000-2000 gt C). A methane hydrate dissociation is consistent with other major environmental changes observed at the time of the PETM, e.g. extensive biomass burning (ref) and precessional cycles, which are synchronised with CIEs.

The Earth system has an enormous capacity to absorb perturbations – it seem intuitive that such global warming events at the PETM and T-OAE are caused by combinations of circumstances, where the precessional maximum coincides with rare catastrophic events triggering temporary runaway processes, which take time, sometimes millenia to return to a steady state.

(401 words)

Q2(d) There has been an enormous increase in the use of fertilisers over the last 60 years or so, and consequently a much higher riverine flux of nutrients to many coastal and estuarine localities worldwide. Using information obtained from your reading of the core references, and with reference to Figure Q2a.1 and the geological analogues that you have studied, explain how increased fertiliser usage affects oxygen levels in these parts of the oceans. (Your answer should be up to 300 words.)

Analysis of the fossil record shows an equilibrium balance of carbon, nitrogen and phosphorous in the shells of calcareous plankton, in a ratio of 106:16:1. (For siliceous plankton, the ratio includes silica and goes 106:25:16:1). This so-called Redfield ratio reflects the optimal conditions for growth of plankton in surface oceans. An imbalance in the ratio affects primary productivity in the ocean, leading in extremis to either oligotrophic condition (known colloquially as ocean deserts) or eutrophic conditions (e.g. algal blooms).

Although there is a very large mass of nitrogen in the atmosphere, and also in sea-surface waters through mixing, it is in the form of N2 that is unusable by most of the biota. (There are some nitrogen-fixing bacteria, but these have little effect on the nitrogen budget). Of the Redfield ratio elements nitrogen is the most common bio-limiting element. Most of the ocean’s nitrogen occurs in the form of nitrate ions (NO3-) originating from the breakdown (nitrogen-fixing bacteria more widespread in the pedosphere) of terrestrial ammonium (NH4) itself derived from the decomposition of organic matter in the pedosphere and supplied to the oceans via riverine flux.

The increase in the use of nitrate fertilisers over the last 60 years has led to an increase of surface run-off of nitrates directly into rivers, producing a pulse of nitrates into the oceans. This affects the nutrient ratios in the local waters, resulting in the eutrophic conditions that promote excessive growth and decay, favouring simple algae and plankton over other more complicated organisms. In addition, nitrogen-fixing organsism Enhanced growth of phytoplankton and other vegetation (disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen in the water. This creeping anoxia in surface waters creates stress in larger organisms like fish and shellfish.

(284 words)

Reference

Meyer, K.M. and Kump, L.R. (2008) ‘Oceanic Euxinia in Earth History: Causes and Consequences’, Annual Review of Earth and Planetary Sciences, vol. 36, pp. 251–88.

Q3. Read the review article ‘Atmospheric Lifetime of Fossil Fuel Carbon Dioxide’ by David Archer and colleagues (2009). Write an essay of up to 1200 words (excluding references) that summarises the key findings of the article

The carbon cycle is the biogeochemical feedback system which causes carbon atoms to move between reservoirs (figure 1). The movement of carbon is driven by various chemical, physical, geological, and biological processes. Archer and colleagues (2009) address the residence time of carbon dioxide at the atmosphere-ocean interface in order to challenge some popular misunderstandings in the anthropogenic climate change debate. This essay describes what drives the carbon cycle and how things are not as obvious as they seem.

Figure 1 - The carbon cycle describes the exchange of carbon between the atmosphere, the hydrosphere, the biosphere, the pedosphere and the lithosphere. The black numbers indicate how much carbon is stored in various reservoirs, in billions of tons ("GtC" stands for GigaTons of Carbon and figures are circa 2004). The dark blue numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen.

Credit:

Figure 1 shows that the oceans are the largest carbon reservoir, but that there is a difference between surface waters and deep waters. Because of the effectiveness of winds on oceans surfaces, CO2 is exchanged efficiently and rapidly over the sea-air interface, resulting in an approximate equilibrium between the partial pressures of CO2 (pCO2) in the atmosphere and the surface ocean water. Seawater chemistry is crucially sensitive to the exchange of CO2 between the atmosphere and the oceans. The ocean is slightly alkaline, with an average pH just above 8.0 (Ref). At the sea surface, atmospheric CO2 reacts with seawater to create carbonic acid (H2CO3) which further reacts to create bicarbonate (HCO3−) and carbonate (CO32-) ions, along with the dissociated hydrogen ions (H+). The pH of any solution is directly affected by the concentration of H+; the more H+, the lower the pH and the more acidic is the solution. Therefore, the more CO2 absorbed into the ocean system, the more acidic surface waters becomes. Before a point of saturation is reached, the pCO2 causes the general direction of the exchange of gases to be from sea-surface to atmosphere. As a result, CO2 cannot be taken up by surface water without a process that transfers carbon from surface to deeper waters.

Waters are exchanged between the surface and deep ocean by physical processes (upwelling and downwelling) and biological processes (the biological pump - In oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior). Many planktonic organisms have metabolic processes that utilise minerals in the seawater to build shells. Redfield ratios and biolomiting of rare . The shells of dead plankton and the fecal pellets of zooplankton (collectively called marine snow) drift downward under the pressure of gravity from surface to deep water. There are some boundaries in the water column where pressure and temperature changes cause minerals to dissolve – for example, the lysocline, the depth past which calcite is decomposed, and thus not deposited onto the sea floor and eventually incorporated into the lithosphere, becomes shallower in a more acidic ocean. Thus the amount of carbon incorporated into the lithosphere is reduced, leaving more carbon in the ocean, keeping it more acidic for longer. (Zachos et al, 2004 say the opposite, p1612).

Under equilibrium conditions, the ocean acts as a carbon sink, maintaining atmospheric CO2 levels by absorbing excess carbon. However, if an extraordinary event were to happen which caused the atmosphere CO2 to suddenly increase by large amounts (for example, large igneous province or methane hydrate dissociation), then the system would not be able to quickly equilibriate. As the pH reduces and the sea water becomes more acidic, there are other effects. Phytoplankton are very sensitive to pH and a sharply decreasing pH may cause a primary producer crisis with consequent knock-on effects in the marine food web

Signposting – The carbon cycle is described in great detail in the IPCC reports as a prelude to informing decision-makers about climate change policies. CO2 plays a pivotal role in these reports, since it is the most abundant greenhouse gas in the atmosphere plus it is the gas that is at the end of the process of using fossil fuel. The issue Archer and colleagues (2009) are addressing is how long fossil fuel originating CO2 remains in the atmosphere.

The residence time of a molecule of gas in a reservoir is traditionally calculated as reservoir size divided by inflow/outflow rate (inventory over flux). Kump (p154, 2009) recycles this linear approach to residence time by calculating a residence time of 12.7 years, based upon an atmospheric CO2 reservoir size of 760Gt(C) and an annual respiration rate of 60Gt(C). This simplistic view has been taken by the non-scientific community to mean that any increase in atmospheric CO2 will be absorbed within a couple of human generations after which the climate status quo will be restored.

However, the implication underlying this equation is that all participating ‘systems’ are in a steady state. In systems parlance, when a system is perturbed and moves out of steady state, residence time becomes the characteristic response time Kump (p 154, 2009), defined as the time taken to react to imbalances in inputs. The number of years taken to return to a steady state depends upon the interaction of many sub-systems of the Earth system. In addition, the ability of the system to absorb atmospheric CO2 depends critically on the state of the system into which it is released

The additional carbon resulting from the spike interacts with other biogeochemical systems on longer time-scales. (Keeling & Bacastow, Walker & Keeling). The terrestrial atmosphere-biosphere system can absorb some extra carbon, but the other outputs from the biosphere (from biomass to decomposing litter to rivers and oceans and finally into the lithosphere) takes many centuries (Ref). Similarly for the marine atmosphere-biosphere system; the shells of dead phytoplankton and the faecal pellets of zooplankton drift down from surface waters as marine snow, a large proportion of which is consumed or recycled as a result of pressure changes. That which does reach the ocean floor can eventually be incorporated into the lithosphere, a process taken millennia (Ref). The movement of carbon into these reservoirs operates over very long-timescales. Furthermore, as each component becomes more saturated in carbon, its ability to absorb more carbon is restricted, slowing the uptake of CO2 from the atmosphere (the Revelle factor) (Ref), further undermining the linear view of systems.

So the common misconception of atmospheric CO2 residency time of about 100 years or less promotes a dangerous complacency which contributes to the lack of political action on this truly global, ‘system’ issue. This complacency is compounded by the fact that CO2 is used as the reference greenhouse gas called Greenhouse Warming Potential (GWP) against which the relative strength of other greenhouse gases are measured (AR4WG1_Pub_Ch02, table 2.14). It is also known as CO2 equivalent.

GWPs measure the influence greenhouse gases have on the natural greenhouse effect, including the ability of greenhouse gas molecules to absorb or trap heat and the length of time greenhouse gas molecules remain in the atmosphere before being removed or broken down, the atmospheric lifetime. In this way, the contribution that each greenhouse gas has towards global warming can be assessed. GWPs can also be used to define the impact greenhouse gases will have on global warming over different time periods or time horizons. These are usually 20 years, 100 years and 500 years. For most greenhouse gases, the GWP declines as the time horizon increases. This is because the greenhouse gas is gradually removed from the atmosphere through natural removal mechanisms, and its influence on the greenhouse effect declines. By convention, the GWP of carbon dioxide is the standard, because it is the greenhouse gas of highest concentration in the atmosphere, contributing about 60% to the enhancement of the greenhouse effect. In addition it is the greenhouse gas about which most research has been done.

However, the GWP scale has been developed for policy makers based upon physical science calculations, to the exclusion multi-disciplinary aspects, effectively assuming a steady state (Bradford, 2001) and also ignoring the fact that the residence time of the all GWP greenhouse gases is significantly at variance (Godal, 2003). The 1990 IPCC report gave a residence time of between 50 and 200 years (IPCC, 1990) and subsequent IPCC reports have refined that figure using the atmosphere-ocean coupling as a basis. IPCC (2007) acknowledges the longevity of atmospheric CO2 by stating that 20% will remain in the atmosphere for many 1000s of years.

In an attempt to challenge the linear approach to atmospheric CO2 residence time, Archer and colleagues (2009) compared the results of several mature climate models when run with a scenario of an initial pulse of CO2 into the atmosphere, using feedbacks additively from climate (C), sediments (CS), weathering (CSW) and vegetation dynamics (CSWV). There were two initial slugs of CO2; 1000 PgC equivalent to the estimated total mass of carbon calculated to have been released at the PETM and 5000 PgC an analogue for T-OAE.[10] The measurements from the climate models was the residence time of the carbon injected into the atmosphere as CO2.

The graphical representation of model results for both slug amounts are reminiscent of Al Gore’s ubiquitous hockey stick (ref), only laid in the opposite direction. In the case of the PETM simulation, there is a noticeable immediate drop in atmospheric CO2 to about a third higher than the pre-slug concentration after 1000 years. Over the next 10,000 years, the atmospheric CO2 ppm slightly diminishes, but remains at a higher steady state. Unsurprisingly for a factor of 5 greater injection of carbon, the definition of the hockey-stick is less well-defined, in that the initial adjustment to the injection is relatively less pronounced. After 10000 years, the new steady state is between 2 and 5 times higher than the pre-slug atmospheric CO2 concentration.

How does this tally with the evidence for PETM and T-OAE events? For the PETM, a massive sea-floor carbonate dissolution is indicated by a rapid CCD shoaling followed by a gradual recovery lasting 100,000 years (Zachos et.al., 2005). Cohen et al (2009) (B2.1) use other sources to say the CIE associated with the PETM was about 85,000 years. The CIE in the T-OAE was estimated as 300,000 years (B2.1), with estimates of onset as little as 650 years.

So, Archer and colleagues (2009) posited that the residence tome of CO2 in the atmosphere is far more complex than the physical sciences would suggest and that therefore the IPCC reports are misleading. Further, they have demonstrated that past spikes of CO2 into the atmosphere of a similar quantity to that current anthropogenically generated support their hypothesis of a long dispersion tail to an injection of CO2 into the atmosphere. A worrying paper.

Reference

(30) Godal, O., 2003: The IPCC assessment of multidisciplinary issues: The choice of greenhouse gas indices. Clim. Change, 58, 243–249.

(31) Bradford, D.F., 2001: Global change: time, money and tradeoffs. Nature, 410, 649–650, doi:10.1038/35070707.

(http://www.ace.mmu.ac.uk/eae/Global_Warming/Older/GWPs.html)

AR4WG1_Pub_Ch02

Archer, D., Eby, M., Brovkin, V., Ridgwell, A., Cao, L., Mikolajewicz, U., Caldeira, K., Matsumoto, K., Munhoven, G., Montenegro, A. and Tokos, K. (2009) ‘Atmospheric Lifetime of Fossil Fuel Carbon Dioxide’, Annual Review of Earth and Planetary Sciences, vol. 37, pp. 117–34.

Q4. Choose the subject for your ECA from the list of topics you were given in Question 3 of eTMA01. You can opt for the same topic as you wrote about in eTMA01, or can choose a different one from the list of six that you saw there. (Note: you will still be able to change the subject of your ECA to another of the six topics after completing eTMA02 if you wish, but if you do continue to work on the same topic you will be able to collect valuable resources now, ready for the ECA.)

Write an outline plan that details the aspects of the subject that you will be covering in your 3000-word critical review for the ECA, including the main questions and hypotheses you intend to investigate and the sources (core papers, set book, databases, OU Library, internet search) you used to find information about the subject. Provide a list of articles (around 8–10) that you consider will be most relevant to your critical review.

Snowball Earth: extreme Earth system events?

Outline plan, including main questions to address

Section title

Objective of section

Two principal questions addressed by the section

Introduction

Snowball Earth – a definition and variations

Define what they are and the variations documented in the literature. For example, Slushball Earth (Lewis et.al, 2007), Zipper-raft Earth (107) and even Mudball Earth (108)

One extreme is lack of polar and mountain-top ice; the other is global ice cover. Have both occurred in Earth’s history?

How are the cryosphere and its constituent components affected by the Snowball Earth paradigm? Is global ice-cover more precise?

Palaeo-evidence for Snowball Earths

Describe the geological structures and chemical composition of sediments that suggest a fully pole-to-pole glaciation

How does the biota cope with the approaching Snowball Earth?

Is there any evidence for the existence of the biota during a Snowball Earth? [18]

Process for creating a Snowball Earth

Describe the system of feedbacks that prevent a snowball earth, and then describe the runaway glaciations that leads to snowball earth

Draw a feedback diagram: how do the checks and balances of negative feedback prevent a Snowball Earth?

What are the runaway positive feedbacks that cause a Snowball Earth in the models available today?

Process for recovering from a Snowball Earth

Describe the systems of feedbacks that lead to de-glaciation from a Snowball Earth

Draw a feedback diagram: how is the steady state of a Snowball Earth maintained in equilibrium?

What feedback process breaks the steady state and starts the warming process that moves the Earth away from pole-to-pole ice cover?

Extra-terrestrial evidence for Snow-covered planets

Describe the extra-planetary science research that identify snow-covered planets

The solar system contains ice-covered objects (e.g. Titan and Enceladus, the largest and sixth-largest moons of Saturn respectively). Have we anything to learn from its palaeoecology?

Is there any evidence from astronomy of ice-covered planets?

Anthropogenic activity and likelihood of a Snowball Earth in future times

Compare the anthropogenically created climate change with the drivers for Snowball Earth events in the past

Compare the Earth system prior to proposed Snowball Earth events with today’s climate change – what are the similarities and differences?

How do timescales compare with suspected Snowball events of the past and today?

Summary

Sources used to find information about the subject

Despite repeatedly being told in all recent OU course tutors not to use Google Scholar and Wikipedia, these sites are my first port of call when starting on a new research subject. This is mainly because I will not have familiarised myself enough with the subject area to be able to successfully engage with the deeply technical phraseology used in abstracts of research papers. Also, I believe that this approach lends itself to a cross-disciplinary approach to research, rather than limiting oneself to apparently relevant journals. The set book (Kump, et. al., 2009) is an invaluable tool is validating the basics. For Snowball events, I found the core reading set less valuable.

Once I have a feel for the kind of journals that contain relevant articles, I use the Open Library website (http://library.open.ac.uk/) in the browser Firefox with the Zotero add-in. I find this far superior in usability than RefWorks, my citation tool of choice until 2008. (By the way, I think the OU’s Reference Works interface to RefWorks is a great improvement, however the all round immediacy and integration of Zotero with Firefox make it a winner for me)

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