1. Introduction
Since the beginning of observations of atmospheric carbon dioxide (CO2) at the Mauna Loa Observatory in 1958, which established the famous Keeling curve for CO2 increases (see Bacastow et al. 1985), there has emerged an unprecedented scientific concern (and alarm) regarding climate change attributed to fossil fuel emissions by the industrialized world. Preindustrial CO2 values of 295 ppmv have risen to the current global average of 392 ppmv and the more recent trend of CO2 increase is illustrated in Fig. 1 at 1.88 ppmv yr−1. Trenberth (1981) has determined that 1 ppmv of CO2 increase amounts to 2.13 × 1012 kg, and therefore the 1.88 ppmv represents about 4 billion tons of carbon (4 GtC) added per year (based on the 2000–09 decadal average). Global surface observations of air temperature, coupled with climate model simulations, support the conclusion that CO2 is the principal greenhouse gas (GHG) responsible for much of the 1°C rise in temperature during the twentieth century [see numerous scientific references in Solomon et al. (2007)]. Further, climate model simulations through the twenty-first century (through different scenarios of continued CO2 increase) show additional global warming increases from 1° to 5°C, which would result in unprecedented modern-day geophysical and economic disasters.
Global mean value of CO2 (January 1979–March 2010) depicting the greater than linear increase from 1998 to March 2010. The line is fit to the period January 1979–December 1997 and extrapolated forward in time for comparison. The annual increase in CO2 for the 2000–09 decade is 1.88 ppmv. [Data provided by the National Oceanic and Atmospheric Administration (NOAA)/Earth System Research Laboratory, Boulder, Colorado.]
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
To date, several efforts have been made to address this global emergency, from the Kyoto Protocol (1997) to the Copenhagen summit in December 2009 and from national and state and city planning for mitigation (e.g., due to sea level rise) to calls for CO2 sequestration. The social and economic impacts of global warming are too numerous to discuss in this paper, and the reader is referred to the various working group reports prepared by the Intergovernmental Panel on Climate Change. One particular effort that is relevant to this proposal is the Virgin Earth (VE) Challenge (see http://www.virgin.com/subsites/virginearth/), a $25 million prize initiated and financed by Sir Richard Branson. The requirement of this challenge is to remove 1 GtC from the atmosphere per year, for a 10-yr period. The concept presented in this paper was not submitted for competition, since the deadline for submission was 8 January 2010. Nonetheless, the VE prize is a simple illustration of the perceived importance of removing CO2 from the atmosphere (with $5 million awarded at the beginning and $20 million awarded at the end of a successful decade of removal). As of 2 November 2011 there were no winners; however, 11 leading organizations with promising ideas were announced at the Global Clean Energy Conference in Calgary, Alberta, Canada, to establish next steps for the Virgin Earth Challenge. It is noted that 1 GtC yr−1 is ~0.5 ppmv of CO2 removal and thus represents only a 25% decrease in the rate of increase.
2. The idea
The National Aeronautics and Space Administration’s (NASA) Mars Global Surveyor and Odyssey missions have revealed the presence of a CO2 ice cap on Mars’s South Pole (see Fig. 2), which is annually subjected to deposition and sublimation. The presence of this CO2 ice cap triggered the idea to consider the possibility of terrestrial air CO2 deposition at Earth’s South Pole, considering that this is the coldest location on Earth and the energy required to sequester CO2 from the atmosphere (and to maintain insulated storage) might be within the scope of reality. A depositional plant constructed on Antarctica could conceivably pull air into a refrigerated chamber, where sufficient cooling could result in CO2 “snow” deposition. To pursue this idea, it is first noted that N2, O2, and Ar all would remain in the gas phase as terrestrial air CO2 is brought down to its depositional temperature. Since the atmosphere is only 392 ppmv of CO2, the Clausius–Clapeyron equation, in conjunction with the CO2 vapor pressure curve, can be considered to calculate the atmosphere’s depositional temperature for CO2. Appendix A is presented to show that the relevant depositional temperature for terrestrial air CO2 snow is 133 K, an achievable chilled temperature for the deposition plant. Alternatively, one could consider placing the ambient air under 10 bars of pressure, and the depositional temperature would increase to 152 K. It is noteworthy that liquid N2 has a very high efficiency as a cooling agent at this depositional temperature (considering that pure N2 at 10 bars of pressure condenses at 105 K). A more reasonable target for deposition is the use of liquid N2 at T = 120 K (under a pressure of P = 29.61 bars), within a closed-loop vapor-compression refrigeration system. This will be discussed in a later section.
The CO2 ice cap over the South Pole of Mars, as revealed by NASA’s Mars Global Surveyor and Odyssey missions (2005).
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
3. Antarctica
The coldest surface air temperature ever measured on Earth was at the Vostok Station in 1983 (see Fig. 3), a reading of T = −89.2°C (or 184 K), which is reasonably close to CO2 snow deposition temperature of 133 K (1 bar) or 152 K (10 bars). In fact, much of Antarctica has been getting colder (largely attributed to the O3 hole; see Thompson and Solomon 2002), although the Western Antarctic Ice Sheet is warming (also see Stieg et al. 2009; Franzke 2010). The mean annual temperature of the Antarctic interior is approximately 
The international arena of Antarctica. Potentially favorable locations for CO2 sequestration facilities are along the coastal regions, with favorable katabatic winds and supporting research stations that can benefit from the excess thermal waste of the cooling plants.
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
4. Design of the CO2 sequestration facility
The components of the proposed Antarctic facility are illustrated in Fig. 4, which shows environmental air (A) entering the right side of the depositional chamber (B). Refrigeration is powered by wind farms that drive a closed-loop liquid N2 cooling facility (see Fig. 5). CO2 snow deposition, at rates of approximately 40 cm day−1 (falling to the bottom of a 100 m × 100 m × 100 m chamber; see appendix B), is excavated into the insulated dry ice landfill (D). Appendix C shows the appropriate calculations and design criteria that would remove 1 GtC per year, which could be accomplished by approximately sixteen 1200-MW wind farms. Most individual wind turbines in midwestern United States wind farms are 1–3 MW; however, more powerful turbines could be considered but are not necessary. An example of a wind farm that exists in Antarctica can be found at http://www.antarcticanz.govt.nz/scott-base/ross-island-wind-energy. Appendix D shows the calculations for meeting the energy requirements to support the depositional plants.
Proposed scientific–engineering system for global removal of atmospheric CO2 in Antarctica. System components A, B, C, D, and E are labeled.
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
Closed-loop liquid-vapor cooling system, depicted as an adiabatic cycle. The design of this thermodynamic cooling system is based on operational conditions in Antarctica. The CO2 gas in terrestrial air changes to solid CO2 (“snow”) at a temperature of 133°K. Waste heat from the heat exchanger can be used to heat base facilities. Wind farms are designed to supply electrical energy to drive the compressor.
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
5. Engineering design and operations
The refrigeration cycle and energy requirements for CO2 snow deposition are illustrated in Fig. 5, based on a “closed-loop liquid-vapor cooling system.” Liquid nitrogen is the refrigerant of choice and is effective at the required depositional temperature for CO2 in terrestrial air. Engineering details regarding “compressor” size and “expansion valve” size are under consideration, as is the size of the “heat exchanger.” Multiple components of smaller size (e.g., the compressor) might reduce the energy requirements. Current plans for a 45-MW wind farm (fifteen 3-MW towers) will run one prototype deposition plant. The wind farm should be designed to expand to 1200-MW to supply energy to 28 deposition plants. The CO2 snow landfill for this prototype plant will be 380 m × 380 m × 10 m (for each year of CO2 snow deposition).
The schematic diagram for the CO2 snow deposition chamber is given in Fig. 6. This chamber consists of a 100 m × 100 m × 100 m cubical volume on four support pillars with reversible air intake and exhaust fans for the refrigeration process of the ambient air. The front and back sides of this chamber will have embedded coils of liquid nitrogen coolant. The “floor” of the depositional chamber will be allowed to open for excavation into an insulated CO2 landfill. The prototype system will process ambient air at a depositional rate of 0.4 m of snow per 24-h operational day. This amount of solid CO2 can be stored in an insulated CO2 snow landfill that is 380 m × 380 m × 10 m, which amounts to 2.24 × 10−3 GtC. The intake–exhaust fans will allow reversed airflow to permit the chamber to operate with the ambient wind direction (although typically there will be katabatic flow from the ice sheet to the coastal region). It is further noted that five insulated landfills (380 m × 380 m × 10 m for each) will be constructed in a semicircle in close proximity to each deposition plant to accommodate for 5 yr of CO2 sequestration (one landfill filled per year at each deposition plant and maintained at 195 K).
The proposed CO2 deposition plant. The chamber box for terrestrial air intake is 100 m × 100 m × 100 m. The bottom floor opens for solid CO2 excavation to nearby insulated landfills. Liquid nitrogen is the coolant for the front and back side refrigeration coils. The compressor is driven by wind farm energy (0.4 m of CO2 snow per day can be processed).
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
Figure 7 is an illustration of the landfills (per deposition plant), and they will be insulated with polyisocyanurate (effective down to 93 K). Snowcat-type excavators will operate in groups of five to compact the dry ice into the insulated landfills. A partial vacuum or even refrigeration could be some alternative considerations for maintaining solid CO2.
Schematic of insulated landfills, placed in close proximity to the deposition plant.
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
6. Summary and conclusions
A plausible scientific plan has been presented for removing annually 1 GtC from the atmosphere through refrigeration of terrestrial air and 4 Gt of CO2 snow deposition. The CO2 snow will be stored in insulated landfills onsite in the Antarctic, and the energy for deposition plant operations will be provided by wind farms that will be positioned appropriately for both logistics and katabatic wind currents. The basic scientific concepts presented here are viewed as plausible, while additional engineering details can be provided as the project goes forward. Consideration will also need to be given to other related topics, such as modeling of CO2 global diffusion to the Antarctic (once a CO2 “hole” is created by the deposition plants). It is also noted that diffusion of global CO2 to the Antarctic region should increase as the CO2 is depleted. Last, a global partnership is envisioned and required to solve the global problem, and the Antarctic is the perfect location.
APPENDIX A
Depositional Temperature for Terrestrial Air CO2
a. Clausius–Clapeyron equation
b. Solution for CO2 deposition in Earth’s atmosphere ≡ Tdep (P = 1 bar)
Log of CO2 vapor pressure, using the formula 
Citation: Journal of Applied Meteorology and Climatology 52, 2; 10.1175/JAMC-D-12-0110.1
APPENDIX B
Deposition of Snow Layer on Floor of Chamber (Refrigerator)
To calculate the daily CO2 snow deposition depth, the following 12 steps are used:
Chamber volume is (100 m)3 = 10−3 km3 = 106 m3.
Atmospheric CO2 gaseous content in percent by weight is 0.046.
Density of terrestrial air at T = 226 K (the approximate mean temperature for Antarctica) is ρair = 1.534 kg m−3.
Density of CO2 in terrestrial air at 226 K is 1.534kg m−3 × 0.046 × 10−2 = 0.071 × 10−2 kg m−3.
Mass of CO2 in a 100 m × 100 m × 100 m chamber in Antarctica is 0.071 kg m−3 × 10−2 × 106 m3 = 7.1 × 102 kg.
One chamber flush per 10 s → 6 × 60 × 24 flushes day−1 → total flushes per day = 8640.
Total CO2 mass flushed per day is 7.1 × 102 kg × 8640 = 6.13 × 106 kg day−1.
Density of dry ice = 1.561 × 1012 kg km−3.
Surface area of chamber bottom = 104 m2.
CO2 snow depth is found from
Bottom chamber cumulative depth per hour = 0.393 m ÷ 24 = 0.0164 m h−1.
CO2 snow depth per day = 0.393 m.
APPENDIX C
ΔCO2 Mass and Deposition Plant
a. ΔCO2 mass (4 Gt of CO2 = 1 GtC)
According to Trenberth (1981), the total mass of the atmosphere is 5.137 × 1018 kg, and 1 ppmv of CO2 is 2.13 × 1012 kg of carbon mass. On the basis of global atmospheric CO2 values from 2000 to 2009, the ΔCO2 = 1.88 ppmv yr−1. The carbon mass added to the atmosphere per year is 1.88 × 2.13 × 1012 kg = 4.004 × 1012 kg. The Virgin Earth Challenge of 1012 kg yr−1 of carbon = 1 ÷ 2.13 = 0.47 ppmv. To summarize, 4 GtC into the atmosphere annually increases the atmospheric content of CO2 by ~2 ppmv and the VE Challenge would reduce the annual increase by ~25% (~0.5 ppmv).
b. Deposition plant
The calculations for number of deposition plants involve five steps:
Volume = (100 m)3 = 106 m3 = 106 (10−3 km)3 = 106 (10−9) km3 = 10−3 km3.
Mass of CO2 in the depositional chamber is 7.1 × 102 kg.
360 chamber flushes per hour (for sidewall exhaust velocity = 10 m s−1) leads to a mass of CO2 processed in 1 h = 360 × 7.1 × 102 kg = 2.56 × 105 kg.
Depositional plant mass per year = 24 × 365 × (2.56 × 105 kg) = 8.76 × 103 × (2.56 × 105) kg = 2.24 × 109 kg = 2.24 × 10−3 Gt.
Number of plants for ΔCO2 = 4.004 × 1012 kg ÷ 2.24 × 109 kg = 1.787 × 103 = 1787; therefore, N = 1787 for 4 Gt and N = 446 for 1.0 Gt (Virgin Earth goal), where N is the number of 43-MW depositional plants.
APPENDIX D
Energy and Power Plant Requirements
The calculations for energy and power plant requirements involve six steps:
The CO2 deposition at 136.1 K is 617 J g−1.
The ΔCO2 (1.88 ppmv) is 1.88 × 2.13 × 1012 kg = 4.004 × 1012 kg.
Energy = (617 × 103 J kg−1) (4 × 1012 kg) = 2.47 × 103 × 1015 kg= 2.47 × 1018 J.
Time in seconds per year is 60 × 60 × 24 × 365 = 6 × 6 × 2.4 × 3.65 × 105 s = 315.36 × 105 s = 3.1536 × 107 s.
Power plant rating of 1200 MW = 1.2 × 109 J s−1 and 1 year = 3.1536 × 107 s → one plant for one year: (1.2 × 109) × (3.15 × 107) J = 3.78 × 1016 J.
Number of power plants N* needed = 2.47 × 1018 J/3.78 × 1016 J = 0.653 × 102 ≅ 65.3, so N* = 65 for 4 Gt and 16.2 for 1.0 Gt (Virgin Earth goal). Therefore, N* ≡ sixteen 1200-MW wind farms, with 28 deposition plants powered per wind farm.
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