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Why Is Everybody Getting So Upset About Soil?

Once again, Australia is getting criticized at Copenhagen, only this time it’s not for its weak climate targets—it’s about how the country hopes to achieve those targets. The latest rumor is that Australia will only commit to a 25 percent reduction in greenhouse gases by 2020 if it wins a controversial rule change that would exclude "extraordinary events or circumstances," such as fires or droughts, when measuring the country's emissions.

This change may seem arcane, but questions about land use and its ability to affect the amount of carbon in the atmosphere are becoming increasingly fraught. Politicians in countries like the United States and Australia have long argued that farmers should get credit for using their land in ways that store carbon—say, through better soil management. But critics point out that the evidence about the effectiveness of these practices is ambiguous, and may even lead to some questionable carbon accounting. What's more, these critics argue, if countries get credit for soil sequestration, they should be penalized when their trees go up in smoke.

So who's right? Jason Hill, an expert on bioenergy at the University of Minnesota's Institute on the Environment, told me that it's too simplistic to vilify Australia for not wanting to be held accountable for the carbon that's released during fires. After all, scorched land, if left alone, will start sequestering carbon again once the trees or vegetation grow back. But, on the flip side, there are also serious questions about how much farmers are actually accomplishing when they sequester carbon through conservation tillage:

A big paper came out around 2000 that looked at all the studies that had sampled soil carbon and found that under reduced tillage, there was [carbon] storage. But the samples were shallow, and deeper samples have shown no soil sequestration. In other words, a lot of studies show a sampling artifact, the result of soil compaction from driving over the fields with farm equipment.

Granted, there are a number of steps farmers can take to reduce emissions—using less synthetic fertilizer, capturing methane, planting trees, or shifting to perennial crops. But when farmers convert land for crops, it tends to release carbon into the air, and soil conservation techniques don't appear able to make up the difference. Agricultural science continues to evolve and there's reason to think that, with the proper incentives in place, farmers will adopt techniques to reduce their emissions. But there doesn't seem to be a strong case for counting natural processes—be it forest fires or soil sequestration—when tallying up countries' carbon ledgers.

(Flickr photo credit: onnufry)