RAWLS: Scoping the Drawdown Challenge

RAWLS and DAC;  Scoping the Drawdown Challenge

I like acronyms:  Read heading above as regenerative agriculture with livestock (RAWLS) and direct air capture (DAC).  DAC has been around for awhile.  I just invented RAWLS.

We all know that the earth is warming because it receives more energy from the sun than it radiates back into space.  Fundamental physics says that this warming will continue until what comes in equals what goes out.  We are contributing to this imbalance by burning fossil fuels and producing CO2, some of which goes into the atmosphere where it functions as a GHG.

We sometimes forget that, if we stopped adding CO2 to the atmosphere tomorrow, warming would continue because of the CO2 that is already there.    We need to capture some CO2 from the air (DAC) and store it.  This can be done, but proposals so far are either very expensive, very risky, or both.  Except one.

Nature has invented a very safe and reliable way to do this.  It’s called photosynthesis.  All green plants do it for free every sunny hour of a day.  Regenerative agriculture with livestock (RAWLS) can use this natural process to pull CO2 out of the air and store some of the carbon in the soil, with less cost and risk than any other system proposed so far.  There are many important collateral benefits, that we can discuss another day.

Let’s look at some rough numbers:  The CO2 concentration in the atmosphere is now 412 ppm (parts per million).  Climatologist James Hansen has written that we need to bring this back down to 350 ppm, a reduction of 15%.

Wikipedia estimates earth’s atmosphere to weigh 5.1 quadrillion tons.  With this we can calculate the total weight of CO2, then the weight of CO2 per acre, then the weight of carbon per acre, and finally the weight of carbon to draw down per acre.  I show this analysis in the spreadsheet that is attached.  I use an estimate for world farm land area that is the sum of world crop land and world pasture land.

The spreadsheet is here.

The analysis indicates that we need to draw down an average of 12 tons of carbon per acre of farm land. 

Note that this weight estimate is for the carbon in the CO2 that must be drawn down, not for the weight of the CO2 itself, which is heavier by a factor of 3.7.

Note also that this is the amount of carbon that must be drawn down if all additions of CO2 to the atmosphere stop tomorrow.  This, of course, won’t happen, and the amount we must draw down in the future will grow until we stop adding CO2.  Many people have set 2050 as the target year to achieve “net zero” emissions.

There is great variation in the carbon in soils:  A report with a massive amount of data was published by NRCS (National Resources Conservation Service) in 2006.  It shows that soil carbon density varied greatly across the US.  One table divides the country into seven regions and shows 33 tons of carbon per acre of farmland in the southern great plains, 71 tons per acre in the upper mid west, and a national average of 58 tons per acre.

The 12 tons of carbon that we need to draw down and store in soil equals 21% of what was in US soils in 2006.  There is evidence that soil carbon density can be raised substantially with better agriculture practice.

My intent above is to scope the challenge.  I believe RAWLS has the potential to meet it, and in future I plan to explain how.  One more thought now: