While the headlines out of Madrid’s United Nations’ Climate Change Conference (the 25th Conference of Parties) have focused on reducing greenhouse emissions, a serious complementary effort is underway. This is the use of technologies to remove carbon dioxide from the atmosphere, subtracting it from the greenhouse equation.
“At present, without negative emissions technologies, it’s nearly impossible to reach the globally-agreed target of limiting warming to well below 2 °C,” says Dr Andrew Lenton, a climate scientist with CSIRO’s Climate Science Centre. “So to avoid dangerous climate change we’ll need to both reduce sources of greenhouse gases (the positive emissions) and remove greenhouse gases from the air (the negative emissions).”
“The longer we wait, the faster we need to decarbonise, and the more we need negative emissions. Also, there are some sectors such as agriculture, aviation and shipping, and cement and aluminium production, that are important to the economy and where reducing emissions is more difficult. So we need to take up more carbon dioxide than is being emitted to offset this.”
Dr Lenton says the Intergovernmental Panel on Climate Change low emissions scenarios used in planning assume the widespread uptake and use of negative emissions technologies. “So we’re already banking on these technologies and trusting that science and engineering will provide solutions.”
Dr Paul Feron leads CSIRO’s multi-disciplinary team developing methods to capture carbon dioxide. “We’re looking into direct air capture to remove carbon dioxide from the atmosphere. The original way of doing this was making use of the handy natural process of photosynthesis.”
He says growing plants to capture carbon dioxide, and then using the biomass for energy generation, while capturing the resulting emissions, can enable storage of carbon underground. “So you have the multiple benefits of generating energy, taking carbon dioxide out of the air, and storing it for a long time.”
Dr Feron says there is also an engineering approach to take carbon dioxide out of the air: through chemical processes that capture carbon dioxide directly from the air. Chemicals can scrub the atmosphere and suck carbon dioxide out of air like an artificial tree. There are even new building materials that can absorb carbon dioxide. “It’s an interesting area of research, with different concepts and products in development,” says Dr Feron.
Other chemical methods accelerate natural processes and increase the uptake of carbon dioxide from the air. Fertilising the oceans with iron can stimulate growth of phytoplankton, which take up carbon dioxide and sink to the ocean floor. Similarly, adding lime to the oceans enhances alkalinity and increases carbon uptake. Pipes can bring cool, nutrient-rich water to the surface, encouraging algal blooms that absorb carbon dioxide while also cooling the ocean surface. Farmed seaweed can be sent to the seabed or used for biofuels, or liquified carbon can be pumped beneath the seabed. Removing carbon from the air and storing it creates negative emissions.
Direct air capture is a growing field, with Bill Gates, Richard Branson and others investing in projects. While many of the processes work and can be used now, it’s important to scale up the technologies, and ensure they are cost effective.
“The technology works, there’s no doubt you can capture carbon dioxide from the atmosphere, so there’s no fundamental road block,” says Dr Feron. “It’s just expensive to do it. Carbon dioxide makes up 3 to 15 per cent of flue gas; that is, averaging 100,000 parts per million; technology exists to capture that. But the carbon dioxide concentration in air is just over 400 parts per million. So, negative emissions technologies need to treat much more gas to capture the same amount of carbon dioxide. It’s a challenge to make the process cheap enough.”
The cost varies depending on the technology; the best estimate is between $90 and $230 per tonne of carbon dioxide taken out of the air. Increasingly, people are looking at what saleable products can be made from captured carbon dioxide. “As there is money to earn, interest in these technologies is rapidly growing.”
He compares this with the way solar and wind energy were developed. “Initially, harvesting energy from the sun and wind was considered challenging compared with the more concentrated combustion processes. But improving the technology, scaling it up, mass manufacturing, and further research has provided a fertile environment for development of renewables. Something similar is feasible for direct air capture. If we can mass produce carbon capture units, and deploy them widely and cheaply, we can achieve economic feasibility in the way renewables have done.”
Dr Lenton agrees that decarbonising our economy is expensive, but slowly transitioning away from carbon will have economic benefits. “The success of negative emissions technologies will ultimately determine how fast we will need to decarbonise our society,” he says. “If we must decarbonise quickly, there will be shocks to the system. But if we have negative emissions technologies, then we can move away from traditional energy sources more slowly. It’s like there’s a box of emissions reductions, with a slider between either cutting emissions or offsetting them using negative emissions, and you move the slider to adjust the speed we transition away from carbon.”
Negative emissions will be just one part of how we address climate change – they will add to, not replace, emissions reductions from energy efficiency and renewables. “It’s not likely to be one simple global solution,” says Dr Lenton. “It will be a patchwork of solutions, a portfolio of different forms of geoengineering technologies. We need to rapidly pursue emissions reductions combined with negative emissions technologies.”
Negative implications of negative emissions
There is a tension between use of negative emissions technologies and other land and ocean use. “We could be like kids in a candy store with all these options available to us, but each of our options has risk or potential challenges. For example, if you relied on large scale bioenergy with carbon capture and storage alone to stay below 2 °C, it would mean repurposing between 25 and 80 per cent of the world’s cropland, or an area three times the size of India. In reality, it will be a trade-off between food, ecosystem services, and carbon storage.”
“We don’t fully know the potential negative impacts or large scale implications, so we need to think about the reversibility of some of these approaches and we need a considered approach to implementing them.”
This is something being considered by Dr Justine Lacey, who leads CSIRO’s Responsible Innovation Future Science Platform, which is focused on the interface between science, innovation and the associated ethical, social and legal consequences of new and disruptive technologies.
“CSIRO has done a lot of research on the social licence to operate,” she says. “In different countries, with various operations in mining, agriculture and renewable energy, and at various scales, we found that people around the world care about similar things during change. They want to be treated fairly, have the benefit and risk distributed equally, and have confidence in governance arrangements. If authorities can be trusted to take care of problems, people are more likely to trust a new activity. With more trust comes a greater chance of acceptance.”
Dr Lacey is investigating whether there is a way of considering positive social impact to advise the design and delivery of technologies. “I wanted to flip our focus from downstream to upstream – go to the community with options, find the preferred one, and influence technology development. If opposition forms early, it’s incredibly difficult to shift. With new technologies, opinions can set in early.”
She says to fully evaluate negative emissions technologies, you need a whole system approach. “We do interdisciplinary research all the time in CSIRO, so it’s easy to forget not everyone works this way. In CSIRO, we bring multiple areas of scientific research together to look at the economic, environmental, social and whole earth systems to develop responses.”
Dr Lenton emphasises the need for an interdisciplinary, holistic approach. “Carbon storage reservoirs are dynamic and are linked. If you remove carbon dioxide from the air, other reservoirs in the land and ocean balance that. Planting trees requires lots of water. You could take carbon out of the air and impact food and fibre production, which affects the economy. We can’t just look at these things in isolation.”
He says nobody will do the analysis for Australia other than researchers in Australia. “It’s in the national interest to know about impacts of negative emissions technologies on our emissions, our crops, our economy, and our people. We need to understand how global efforts will affect us.”
Dr Feron says that while it’s early days for this research, there are benefits for Australia. “Australia has a lot of land suited for generation of renewables and for direct air capture. Add the country’s geological storage resources, and there’s an opportunity for Australia to be world leaders.”