The threat of dangerous human-induced climate change is the direct result of the ever-increasingly high levels of greenhouse gases in the atmosphere, especially carbon dioxide. If we want to avoid catastrophe, we need to stop emitting carbon dioxide and remove some of it from the atmosphere.
In 2015, 194 countries signed the Paris Agreement, agreeing to limit global warming to well below 2°C, preferably to 1.5°C, compared to pre-industrial levels. To achieve this target, current emissions of carbon dioxide need to be reduced by about 50% by 2030 and reach net zero by mid-century.
A range of cost-effective and socially acceptable low-carbon technologies are available to reduce emissions by 2030, but will require an enabling policy framework to achieve the required market penetration. Carbon dioxide emissions can be reduced through increased use of renewable energy technologies (e.g. solar and wind), nuclear power, increased energy efficiency in transportation, industry and buildings, and decreased deforestation.
The idea behind net zero emissions by 2050 is that any residual emissions of greenhouse gases are balanced by technologies removing them from the atmosphere. Further technology development to reduce emissions after 2030 would likely be required, coupled with removal techniques including mass tree planting (afforestation and reforestation), direct air capture with facilities that remove carbon dioxide from the air and store it, and energy production from biomass with carbon capture and storage.
Achieving “net zero” is a great idea in principle. In practice, it helps perpetuate a belief that cost-effective and environmentally sustainable technologies will be developed in the future to save us. This reduces the sense of urgency surrounding the need to curb emissions now. The focus on net zero has provided a license for a “burn now, pay later” approach which has seen carbon emissions soar from both energy production and consumption, as well as agriculture and deforestation.
Do we need net zero by 2050? Yes. But the urgent challenge is to reduce emissions now. Today’s politicians cannot be held accountable for promises in 2050, but they can be held accountable for emissions between now and 2030.
If we had acted to reduce emissions 20-30 years ago when alarm bells were sounding from the first IPCC reports, we could have had a measured transition to a low-carbon economy. That failure to act means unprecedented rates of decarbonisation of our global energy system are now needed, plus a reliance on negative emission technologies.
Negative emission technologies such as direct air capture are technically feasible, but are they environmentally sustainable, scale-able, and cost-effective? Enhanced oil recovery schemes have shown that compressed carbon dioxide can be separated from other gases and then injected underground to increase oil recovery. Carbon capture and storage offers the possibility that the CO2 would be left underground in depleted oil and gas wells and saline aquifers, removed from the atmosphere. In addition to its use with negative emissions technologies, carbon capture and storage is seen as a means of allowing the continued use of coal and gas as a source of energy.
One of the biggest barriers to large-scale carbon capture and storage is cost. Retrofitting carbon scrubbers on existing power stations, building the infrastructure to pipe captured carbon, and developing suitable geological storage sites is expensive. This is why, even today, there has been no significant deployment of coal-fired power stations with carbon capture and storage facilities in operation. Other issues, beyond cost, include permanence of storage.
Most climate models require negative emissions of carbon dioxide by mid-century and beyond to meet the Paris target of 1.5oC, hence the promotion of large-scale bioenergy with carbon capture and storage (BECCS). BECCS can produce electricity at the same time as removing carbon dioxide from the atmosphere. One problem is the scale of biomass production that would be needed, which may well lead to the large-scale destruction of natural habitats, threatening biodiversity, encroaching on arable land, and threatening food and water security.
The message is clear. We need to significantly reduce global emissions now using known technologies, and not rely on the large-scale deployment of unproven negative emissions technologies in the future. That said, it is almost certain that carbon removal will be needed to offset residual emissions from sectors where zero emissions are unlikely, such as aviation. Given the lack of political will to significantly reduce emissions in the near-term, investigating the environmental, economic and social viability of negative emissions technologies is crucial.
Robert ‘Bob’ Watson is a physical chemist specialising in atmospheric science issues and a leading authority on the science of climate change. His career includes key science policy advisory roles with NASA, US President Bill Clinton, the World Bank, and the UK government. He was Chair of the Intergovernmental Panel on Climate Change from 1997 to 2002.