Fossil fuels in a net-zero world

Achieving international climate targets sets a tight carbon budget which requires most fossil fuels to remain in the ground.?

Climate change caused by anthropogenic greenhouse gas (GHG) emissions has already increased the average global surface temperature by 1°C since pre-industrial times. Limiting further increases and reducing damage to society and the environment requires the rapid decarbonisation of all parts of the global economy. The Intergovernmental Panel on Climate Change’s (IPCCs) Special Report on Global Warming of 1.5°C (based on 6,000 peer reviewed publications) concluded that limiting warming to 1.5°C is possible but requires an unprecedented transition of our energy and infrastructure systems and our approaches to land-use. Furthermore, the IPCC concluded that reducing emissions alone is not sufficient. The removal of GHG already present in the atmosphere is also required to achieve an overall balance of ‘net-zero’ emissions.

According to the International Energy Agency global fossil fuel use and CO2 emissions from the energy sector are currently at an all-time high (with short-term reduction in 2020 due to the COVID-19 pandemic). For all the progress in recent years scaling up and deploying renewables technologies, natural gas, oil and coal are by far still the world’s biggest sources of energy, providing over 80% of total global primary energy supply. Fossil fuels are also the biggest contributors to climate change, responsible for around 75% of global GHG emissions with the rest coming primarily from agriculture and land-use change.

Given the scale and impact of fossil fuel use, it is evident that addressing climate change and achieving net-zero emissions will require reductions in fossil fuel use. But by how much?

The net-zero target date of 2050 or 2070 is based on the recommendation in the Paris Agreement which commits to limiting the rise in global temperature to “well below 2°C” above pre-industrial levels with “efforts to limit” this increase to 1.5°C above pre-industrial levels. It is worth noting that the target date of net-zero emissions is potentially a distraction as the level of warming is dependent on the cumulative emissions released into the atmosphere – known as the carbon budget. The Intergovernmental Panel on Climate Change (IPCC) estimate the remaining carbon budget from the beginning of 2018 to be around 500GtCO2 for limiting warming to 1.5°C (or 1,300GtCO2 for limiting warming to 2°C). Considering that our current annual emissions are around 43GtCO2, this estimated remaining budget will be consumed in under 12 years with business as usual.

The potential emissions associated with burning all the fossil fuel reserves and resources ?are estimated to be around 2900GtCO2 if burned unabated. These emissions are about six times greater than the remaining carbon budget for 1.5°C and three times greater than 2°C. Moreover, recent studies suggest that committed emissions from existing and proposed fossil fuel infrastructure already exceeds these budgets.

However, could carbon capture and storage (CCS) or other “negative” emissions approaches allow us to continue using greater amounts of fossil fuels whilst still keeping “net” emissions within the carbon budget?

To address this question, we can look at energy system pathways developed by academia and industry that assume high levels of CCS and carbon dioxide removal (such as afforestation and bioenergy with CCS [called BECCS]). In these pathways, fossil fuel use is unsurprisingly higher than in pathways with low CCS and CDR; but strikingly still requires a dramatic reduction (~60%) in fossil fuel use in absolute terms compared to today.

In addition, the required capacity of CCS and CDR deployment assumed in these pathways poses a massive delivery challenge. The Shell Sky scenario which achieves net-zero emissions in 2070 assumes construction of around 10,000 large scale CCS plants in that period. The Global CCS Institute suggests that as of 2019, there were only 19 CCS plants in operation. Assuming a linear trend of CCS plant deployment, this scenario would require commissioning 2,000 plants every decade or 200 plants every year from 2020 onwards!

Another challenge to address in scenarios with a high reliance on BECCS in particular is whether planetary boundaries of land use may be exceeded. Some estimates suggest a land mass five times the size of India would be required solely for growing biomass for BECCS. Securing this staggering amount of land is likely to be infeasible and could set BECCS against food production and natural habitats.

Whilst CCS and CDR technologies are in my view critical in our journey towards net-zero, they don’t fundamentally change the requirement for most fossil fuels to remain the ground in order to achieve a net-zero economy.