Over the past two centuries we’ve added as much carbon dioxide to the atmosphere as it already contained, and the amount should have doubled. However, the concentration has gone from just below 0.03 per cent to just over 0.04 per cent – about half the increase expected!
Much of the carbon dioxide has therefore disappeared, but there’s no surprise or mystery about this. Some went into plants because they breathe in carbon dioxide and turn it into wood, leaves, fruit and so on. Some went into soil because that’s where plants (and plant parts such as leaves) end up when they die. And some dissolved into the ocean because of mixing of air and water as waves break (amongst other things).
Carbon also cycles back into the atmosphere when, for example, animals eat plants and breathe out carbon dioxide. So the carbon cycles around between air, water, plants and soil and gets shared between them.
This suggests a cunning way to reduce the carbon in the atmosphere – can we get the other carbon-reservoirs to keep more than their fair share?
Unfortunately, encouraging extra carbon into the ocean is a bad idea. The ocean becomes more acidic as its carbon-content goes up and ocean acidification is already a concern – it adversely affects many marine organisms and we don’t want to accelerate that problem. But there’s no downside to increasing the carbon held by plants, or sequestered in soil, and techniques for encouraging this are called Natural Climate Solutions (NCS).
The most obvious form of NCS is also the one with the biggest capacity to make a difference -reforestation. I mentioned trees in my last column as a possible contribution towards Wiltshire’s emission reductions and it’s a good solution because planting trees absorbs up to 300 tonnes of carbon dioxide a year for every square kilometre of new forest.
Worldwide, a realistic reforestation programme could soak up 10 billion tonnes a year – that’s a quarter of mankind’s current emissions.
NCS does not stop with trees. Changes in agricultural practices can also play a major role. Farming, and farmers, must be part of any realistic plan to tackle global warming. At the moment agriculture is a net producer of greenhouse gasses – but, with a few tweaks, farming can change from being part of the problem to being part of the solution.
The key is to improve the organic content of soils. This is a good thing anyway – food grows better in well-nourished soils and they also soak up water better, hence reducing the incidence of floods and droughts – but organic matter contains carbon and so having more in the soil means there is less in the air.
There are a number of techniques that can make soil more organic rich – from widespread application of biochar (essentially charcoal made from food and other waste), through reduced ploughing and onto grazing cattle in woodland. Their impact could be enormous, perhaps capturing another five billion tonnes of carbon per year.
So why aren’t we doing this? I’m not a farming expert and I’d love to understand better the financial, regulatory and logistic barriers. Perhaps a cash incentive is needed to make it economically viable. That wouldn’t be a farm-subsidy – we would be paying farmers to provide a vital service.
25 April 2019