A child runs under sprinklers on July 23 during a heat wave in Vienna. Photo: Lisi Niesner/Reuters.
How hot is Earth going to get? Whether our technological progress can avoid it? These are big questions. There is continued uncertainty in forecasting impact of increase in atmospheric CO2 on global warming. However, recently, a study in Science reported that the Earth’s temperature is more sensitive to carbon dioxide levels than earlier predicted. For more than 40 years, scientists have forecasted that a range of possible temperature increases, between 1.5º and 4.5º C that will result from carbon dioxide levels doubling from preindustrial times. Now, the new study has sharply narrowed the range of temperature increases, tightening it to between 2.6º and 4.1º C. This finding has raised interest in carbon dioxide removal (CDR) technologies.
Global annual mean CO2 concentration has increased by over 50% since the start of the Industrial Revolution, from 275 parts per million (ppm) in 1800 to 410 ppm in 2019. Since the Industrial Revolution, humans have emitted more than 2,000 gigatonnes of carbon dioxide into the atmosphere.
Global carbon emissions from human sources were 11.7 gigatonnes of carbon (GtC)/year in 2019. Of this, fossil fuel emissions accounted for about 91% (mainly coal, oil, gas and cement related sectors) and the remaining 9% came from changes in land use.
Some of these emissions are reabsorbed by terrestrial and oceanic ecosystems. Similar to photosynthesis in trees, oceans take in carbon dioxide and give off oxygen. That the net atmospheric carbon increase after accounting for reabsorption was about 5.25 GtC/year (or equivalent to 2.5 ppm/year) is alarming.
The world is rapidly approaching 1.5º C of warming above pre-industrial levels – the target limit of the Paris Agreement – and is on track for 3º C by the century’s end unless we take action. But what is the best action to take? According to the Intergovernmental Panel on Climate Change (IPCC), global emissions must be cut by half by 2030 if we stand a chance of averting the worst impacts of warming. The world is committed to reach net-zero CO2 emissions by around 2050.
The reducing CO2 emissions is imperative by ramping up renewable energy, boosting energy efficiency, halting deforestation. The latest climate data from IPCC shows that these efforts alone aren’t enough to prevent dangerous global warming. The big tech companies are investing heavily in searching for new technologies to trap and store atmospheric CO2 below ground and also CDR technologies.
The large-scale deployment of CDR technologies to remove CO2 from the atmosphere is likely to be important in achieving the most stringent 1.5º C target of the Paris Agreement. The potential of CDR technologies are not known and their wider adoptability is still in question. However, there are some hopes in deploying CDR technologies as shown by science magazine. There are some naturally occurring processes in trees, ocean and soil to remove CO2 from atmosphere, but given the large scale deforestation and deteriorating soil health, industrialisation, now the capacity of these natural CDR processes are below the required level and we need to accelerate these process artificially.
Several technologies have been identified as capable of delivering CDR at scale: afforestation/reforestation (AR/RE), bioenergy with carbon capture and storage (BECCS), biochar, direct air carbon capture and storage (DACCS) and enhanced weathering of minerals (EW).
A recent study published in Nature shows that the existing artificial CDR technologies are in nascent stage compared to natural CDR technologies like afforestation, crops and charcoal. But the same study mentioned that there is huge potential for artificial CDR technologies as well.
At this point, artificial CDR technologies are costly and most of them in pilot stage. While current cost estimates for artificial CDR are about $300 per tonne of CO2, studies project that costs could drop to $100-200 per tonne by 2050. Trees are still the most elegant and effective tools for pulling carbon dioxide out of the atmosphere, costing only about $50 per ton. Nevertheless, artificial CDR technologies needed especially in carbon-intensive sectors like power plants, where CO2 can be sucked out and stored at source of emission.
Deployment of carbon capture and storage (CCS) technologies that remove the carbon dioxide from the power plants and cement companies needs to be encouraged. But the technology remains costly and energy-intensive. Emission reductions could reduce the role for carbon removal. The transition to net zero needs to be technically feasible and financially viable, but should also be socially acceptable and solve some local problems like unemployment and disposal of waste material simultaneously.
Many CDR technologies also provide co-benefits. For example, seaweed cultivation could remove carbon while also supporting ecosystem restoration. This can also be used for products like food, fuel and fertiliser and provide an economic return to farmers and economy.
Investing in technological development, together with continued progress in the deployment of cheap, clean energy, could advance prospects for direct air capture at a large scale. The bottom line is that direct air capture is still a new technology and need public support to advance.
Overall, natural CDR techniques aimed at trapping atmosphere CO2 in trees, seaweeds and phytoplankton etc and artificial CDR techniques like adding certain minerals to increase storage of dissolved bicarbonate in ocean or running an electric current through seawater to help extract CO2 needs to be scaled up simultaneously depending on local techno-economic feasibility and social acceptability. In many countries, developing and deploying a variety of approaches in tandem is the best way to go to limit global warming.
A. Amarender Reddy is the principal scientist, ICAR-Centre Research Institute for Dryland Agriculture, Hyderabad.