Warming soil will release billions of tonnes of carbon dioxide

The headline on this story was going to be “The soil is going to kill us”. Sans exclamation mark. But that would be irresponsible reporting, and only 17% true. Because that’s the percentage by which carbon in the ground will increase carbon in the atmosphere by 2050, warming the planet and ending life as we know it.

Now this isn’t good news for South African soil. Only 14% of the country has good enough soil to farm on, and only a fifth of that gets enough rainfall to allow agriculture. The rest has to be fed through irrigation, which uses 60% of the country’s water.

But soil is susceptible to change. The National Climate Change Response White Paper warns that it is “vulnerable to increasing temperatures that adversely affect soil biology, chemical and physical properties”. With carbon still going into the atmosphere, that warming is a given. The white paper projects that the interior will be up to 3.5°C hotter by 2050, and double that by the end of the century.

To be fair, it isn’t the soil’s fault. We started this by digging into the earth so we could scoop out dead plants and dinosaurs and burn them. That mix drove the creation of what we call civilisation. It also pumped hundreds of billions of tonnes of carbon dioxide into the atmosphere. This traps heat and warms the world — this year is to be the hottest on record, according to the World Meteorological Association.

Most of the heat goes into the oceans, which warm over decades. But a third goes into land, which warms in just a year. That’s a serious problem, according to research just published in the peer-reviewed journal Nature.

The report, Quantifying Global Soil Carbon Losses in Response to Warming, looks at 49 studies across the northern hemisphere (because there is little data on the south) and concludes that plant and animal life in soil will release 200-billion tonnes of carbon into the atmosphere by 2050.

To put that in perspective, the United Nation’s Framework Convention on Climate Change says the world can only emit 1 000-billion tonnes of carbon this century if warming is to be kept below 2°C. That’s the target about 200 countries signed up for at the Paris Agreement last year. Any warming above that unravels all the ecosystems that life has come to rely on.

But this goal didn’t include the effect soil would have on climate change. This data gives countries less wiggle room in how much they can emit — and they’ve built a lot of wiggle room into the Paris Agreement, which means South Africa’s commitment could see it release anywhere between 200-million and 600-million tonnes of carbon a year by 2030.

The research is limited because it looks only at the top 10cm of soil; it doesn’t look at the carbon trapped further down.

That also leaves out the effect of permafrost melting and releasing methane. But let’s not think about that. Permafrost melt is one of those climate events, called feedback loops, that dramatically accelerate warming, causing Europe to freeze and flooding in Cape Town.

So, what’s up with our soil? It boils down to the worms and micro-organisms that make a living underground. Their search for food from dead plant matter opens up spaces in the soil for air to move about, which helps plants to grow and creates more food for the creatures. A warming planet also, momentarily, means plants photosynthesise more and grow bigger. The creatures of the soil become more active. This process means more carbon is released by the soil. Much more carbon.

That extra 200-billion tonnes of carbon could ensure dangerous global warming or, in the restrained language of researchers: “This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land-carbon climate feedback that could accelerate climate change.”

Warming will do the following to South Africa’s already scarce good soil: make it more acidic; burn off the nutrients in the soil; boil living organisms in the soil; dry it out so it becomes weaker and more brittle; lower its water-holding capacity; increase runoff so less water soaks into the ground. In other words, degradation of the soil — and that’s not good when you’re a species that needs food to survive.

The drought has given glimpses into this near future. Farmers in the Free State say seeds from last year’s maize crop were cooked in the soil. When it did rain this year, the soil had been baked so hard that the water ran off.

Maybe the soil will kill us.

Sipho Kings
Sipho is the Mail & Guardian's News Editor. He also does investigative environment journalism.

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