I made some calculations to address two obvious and important questions regarding CO2 sequestration.
To sequester all of the annual atmospheric increase in CO2 with a citrus forest having a 8.3* tons per hectare per year CO2 uptake, an area equivalent with three times that of Australia would need to be in active cultivation. Using a value of 30 tons per hectare, representative of C4 plants like corn, sorghum, sugar cane , one gets 0.8 x Australia. Yet, as those crop products are consumed and the byproducts decompose, the carbon finds its way back to the atmosphere.
Question: What fraction of Earth’s land area would be needed to sequester the 50 ppm CO2 surplus we currently have in our atmosphere, 50 ppm above the upper safe limit of 350 ppm?
It’s not a fraction, per se. No. Seven times Earth’s land area would need to be in cultivation. I earlier had a more optimistic value based on 30 tons per hectare, half the Earth’s land area would need to be in cultivation. Yet, unfortunately, the associated crops are not suited for long term sequestration.
ps. The calculations are on one of the 9 benefits of the massive scale tree planting I believe we need to increase climate stability and peace globally:
humidification of ground and air
wildlife habitat restoration
human habitat creation
employment in forestry and related industry
sustainable timber production
sustainable economic development modeling
* I had earlier taken 30 tons per hectare from an innacurate source. So I reran the calculation using 8.3 tons per hectare after .
Sometime May, 2014 AirZafari (+299 55 28 19) 13 year old guest photographer Ruben Wernberg-Poulsen captured a new perspective on massive Greenland glacier calving. In addition to the massive scale of the event seen clearly from the air, I think we’ve never seen that basal ice so clearly and so graphically from this birds eye perspective.
The video is from none other than the site than that which grabbed headlines as the world’s fastest glacier calved a giant area (12.4 sq km) and retreated (at least temporarily) to a new record minimum between 14 and 16 August, 2015 .
A rough dimension of the 2014 iceberg in the aerial video suggests a volume of ~180 million cubic meters of ice. If spread out over the Washington DC Mall from the Capitol steps to the Washington Monument (1.8 km x 0.4 km), this ice would have a depth (~375 m) more than twice the 169 m height of the Washington Monument.
Sapphire blue basal ice
Extreme pressure from 500-900 m ice overburden plus extreme strain due to friction between the glacier and its bed, strain heating, all seem to compress air bubbles straining the white ice into denser blue ice. Else, likely pressure melting, possible freeze-on of melt water or sea water may also be at play to produce the curious sapphire blue basal ice on display in this extremely large iceberg calving event.
Commentary on the 12 sq km event 14 to 16 August, 2015 
It’s impressive to see the Jakobshavn glacier retreat further, to a new record position upstream.
I wouldn’t say it’s the largest calving event to occur. The glacier lost a larger area between 2002 and 2004, a floating ice shelf. What’s different now: the ice is grounded or near floatation.
There is an interesting interplay to consider; accelerated forward motion of ice given loss of internal flow resistance on calving that will move the ice front forward quickly to replace the void. So, in not many days, the calving front may be back to the position as in the before image.
The calving front position represents the dynamic interplay between calving, producing front migration upstream and forward flow. Hypotherically, that dynamic could be in balance; no net front position change over time. Or the front could be in imbalance with retreat upstream as is the case in point.
This and most other Greenland glaciers are thinning (vertically), having the effect of un-grounding the ice from the bed at the glacier front. As this is a flooded, underwater system, these glaciers have because of buoyancy forces, what is called ‘marine instability’, allowing the glacier to retreat more quickly as they have fronts near or at floatation. Recent West Antarctic Ice Sheet glacier retreat (e.g. Rignot and others, 2014) suffers from the same marine instability.
This is an inherently unstable system given that the bed of the glacier is underwater several 10s of km upstream.
In this Greenland case, there is an upstream reverse bed slope, the bed gets deeper upstream at some point, not far from where the calving front has retreated to now. Further retreat upstream can be to deeper ice. This is unstable, so an even further retreat will occur given likely continued thinning.
A negative feedback here, something to dampen that instability, is an increase of ice flooding into the void from the sides of the flow, re-jamming it up a bit (regaining internal flow resistance), like partially recorking the flow.
There is a titanic struggle here between accelerated flow [due to loss of flow resistance from calving] and ice flooding into the void, partially re-jamming it up. Given likely continued thinning*, the winner is the loser, of more ice.
* from likely increased surface melting, likely increasing ocean temperatures. However, from year to year (the weather of climate), we may have a cold year that reverses this activity, leading to a short term advance, amid a longer term retreat observed at this an other Greenland glaciers in the past decade.
Rignot, E., J. Mouginot, M. Morlighem, H. Seroussi, and B. Scheuchl (2014), Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011, Geophys. Res. Lett., 41, 3502–3509, doi:10.1002/2014GL060140.
Thanks Ruben Wernberg-Poulsen for capturing and sharing the video with World of Greenland. Thanks to Malik Milfeldt for the tip.