Friday, April 16, 2021

"We’ve got carbon capture all wrong"

I don't know if I would use the word wrong but that quibble aside this article, especially deeper into it, presents some very interesting opportunities to complement current approaches.

Just as a personal preference, sequestering CO2 as a mineralized solid seems like a possibly more fruitful path than either tying carbon up in plant material—because the plant dies, the carbon gets released, reforms into CO2, that whole carbon cycle thing—or as a gas buried deep under the earth's crust—the potential disaster scenario of a catastrophic leak.

But maybe that's just me.

 From Wired UK April 6:

Carbon capture is viewed by many as a last resort. But in the race to tackle the climate crisis, intelligently taking advantage of natural processes will be key

We’re transitioning to renewables; we are using the energy we generate with extraordinary efficiency; our industries are innovating with clean, green methods; we’re recycling, reusing and reclaiming. Our greenhouse gas emissions are slowing. But perhaps it’s not enough.

There is another final – some might say ‘last resort’ – set of tools in the decarbonisation toolkit: ‘negative emissions technologies’ – technologies that store or sequester more greenhouse gas emissions than they produce. These come in two main forms: nature-based solutions such as reforestation and afforestation, and more technological solutions such as direct air carbon capture and storage, enhanced weathering, biochar, and soil carbon sequestration.

As a 2020 report from the International Energy Agency argues, carbon capture, utilisation and storage technologies are a critical part of ‘net-zero’ goals because they enable key sectors to reduce their emissions directly, but also help to balance some of the more intractable emissions.

But carbon capture is a twin challenge. First, you have to capture the carbon dioxide, either directly from the atmosphere or from emissions sources. Then you have to put it somewhere that will store it securely for as long as possible.

The good news is this is already happening naturally. Around half of the excess carbon dioxide that is released into the atmosphere by human activity – the combustion of fossil fuels – is ‘drawn down’ again by natural processes: half by land-based processes – mainly plants – and half by the oceans. We can’t – and shouldn’t – seek to control these natural processes. But we can take advantage of them.

Ironically, higher concentrations of carbon dioxide in the atmosphere can actually increase plant growth; a phenomenon called carbon dioxide fertilisation. There is evidence that plants are already putting out more leaves during their growing season in response to increasing carbon dioxide availability. However, plants eventually adapt to the higher concentration of carbon dioxide, so the effect is limited. And as climate change brings warmer temperatures and more rainfall to some parts of the world, that could increase the length of the growing season there. But in others, higher temperatures and decreased rainfall could have the opposite effect.

The fact remains, though, that trees are carbon guzzlers. Around half the mass of a single tree is pure carbon. Given that forests cover 31 per cent of global land area – around 4 billion hectares – that’s a lot of stored carbon.

The problem is scientists don’t know exactly how much. At the moment, forest cover is mapped from space using satellites that can tell the difference between surfaces such as forest, grasslands and desert, for example. But they don’t show whether a tree in a forest is ten metres tall or 100 metres tall, and that is a critical piece of climate information. “If we don’t know how much carbon is even stored in the Earth’s forests, let alone how it’s changing with deforestation and whatnot, that’s a massive uncertainty for those climate models,” says remote sensing scientist Laura Duncanson from the University of Maryland.

This uncertainty has significant implications for how we assess the impact of ongoing deforestation, how we plan reforestation or what’s called avoided deforestation – not chopping down existing forests – and how we calculate the emissions credits associated with that reforestation or avoided deforestation. It’s knowledge that is critical to the concept of reducing emissions from deforestation and forest degradation (also known as REDD+).

Which is where GEDI – Global Ecosystem Dynamics Investigation – comes in. This Nasa project uses a technology called LiDAR, or Light Detection and Ranging: a pulsed laser shot from the International Space Station to measure the height of objects like trees. A beam, with a footprint measuring around 25 metres in diameter, is painted billions of times across the Earth’s surface, and the open-source data from those billions of samples can then be translated into a map of the Earth’s forests that will allow scientists to calculate forest carbon with far greater accuracy than ever before. “Instead of just saying, ‘Yes, we know there’s trees there,’ we actually have measurements of the physical structure of those trees that we can turn into estimates of carbon,” says Duncanson.

There are already numerous initiatives underway around the world to plant trees. For example, the Bonn Challenge aims to reforest 350 million hectares of degraded and deforested landscapes by 2030, and has already achieved 150 million hectares of reforestation in countries such as Brazil, Burkina Faso, India and Cameroon. One study has estimated that 0.9 billion more hectares of forests could be grown on existing viable land that isn’t already occupied by forests, agriculture or urban areas, and that these could store 205 gigatonnes of carbon – the equivalent of around one-quarter of the carbon dioxide currently in the Earth’s atmosphere.

But planting trees isn’t quite the straightforward solution that it appears. “It’s this great concept: you plant a tree, you save the planet from climate change and it’s actionable, it’s super-easy to integrate into economic solutions, and we all love trees,” Duncanson says. “But the reality is that it absolutely cannot solve the entire problem.”

For starters, the magnitude of that carbon draw-down is uncertain: Duncanson says some papers have based their calculations on the maximum theoretical amount rather than an average. Trees can’t be planted just anywhere, and not all those areas earmarked for possible reforestation will prove to be suitable. Regional climate or soil conditions may be unfavourable, with the result that tree planting in a particular place, far from helping the environment, will fail or will have a negative impact on local ecosystems. In practical terms, there’s the question of where the seeds and seedlings for such a massive reforestation effort will come from, whether there is enough genetic diversity, and how many of those seeds can be harvested without compromising the survival of existing forests. Finally, trees take a long time to grow and larger trees, which are also the ones storing the most carbon, can take decades to reach maturity – decades we probably don’t have.

Despite these concerns and limitations, given the incredible number of ecosystem services that trees provide to humanity – clear air, water, soil stability, oxygen, shelter, food and building materials – reforestation can only improve our environmental conundrum, not worsen it.

Traditionally, reforestation and agriculture have not sat well together, both requiring land that has sufficient nutrients, rainfall and temperatures conducive to growth. And agriculture, of course, poses its own environmental challenges, being responsible (along with forestry and other land use) for around 23 per cent of anthropogenic greenhouse gas emissions (particularly methane and nitrous oxide). But the two activities are not mutually exclusive. Agriculture can work with reforestation to play a vital role in climate change mitigation – sequestering carbon – while delivering the added benefit of more nutrient-rich soils, less fertiliser use, less water use, increased production and better food and economic security....



Carbon Capture & Storage: The Current State of Play 

"Carbon Capture and Storage: The Negative Carbon Option?"