Strand has devised a formula to measure the carbon-sequestration efficiency of this process and others using crop residues, something no one has done before.

Carefully tallying how much carbon would be released during the harvest, transportation and sinking of 30 percent of U.S. crop residues and comparing that to how much carbon could be sequestered, Strand says the process would be 92 percent efficient. That's more efficient than any other use of crop residue he considered, including simply leaving crop residue in the field, which is 14 percent efficient at sequestering carbon, or using crop residue to produce ethanol, which avoids the use fossil fuels, but is only 32 percent efficient.

Worldwide, farming is mankind's largest-scale activity. Thirty percent of the world's crop residue represents 600 megatons of carbon that, if sequestered in the deep ocean with 92 percent efficiency, would mean the amount of carbon dioxide in the atmosphere would be reduced from 4,000 megatons o