Abstract
There are major concerns about the sustainability of large-scale deployment of carbon dioxide removal (CDR) technologies. It is therefore an urgent question to what extent CDR will be needed to implement the long term ambition of the Paris Agreement. Here we show that ambitious near term mitigation significantly decreases CDR requirements to keep the Paris climate targets within reach. Following the nationally determined contributions (NDCs) until 2030 makes 2 °C unachievable without CDR. Reducing 2030 emissions by 20% below NDC levels alleviates the trade-off between high transitional challenges and high CDR deployment. Nevertheless, transitional challenges increase significantly if CDR is constrained to less than 5 Gt CO2 a−1 in any year. At least 8 Gt CO2 a−1 CDR are necessary in the long term to achieve 1.5 °C and more than 15 Gt CO2 a−1 to keep transitional challenges in bounds.
Highlights
The Paris Agreement adopted by the member states of the United Nations Framework Convention on Climate Change (UNFCCC) in 2015 was a milestone in international climate policy negotiations
We find that very ambitious near-term mitigation action can keep the well-below 2 ◦C target within reach without carbon dioxide removal (CDR), albeit at significant near-term and transitional challenges
These results indicate that short-term mitigation would need to be increased at least to the level of the costeffective 2◦ CDR 20 scenario, corresponding to about 31 Gt CO2 from fossil fuel use and industry in 2030, in order to attenuate the trade-off between transitional challenges in the period 2030-50 and required CDR availability
Summary
The Paris Agreement adopted by the member states of the United Nations Framework Convention on Climate Change (UNFCCC) in 2015 was a milestone in international climate policy negotiations. A large number of nation states laid out concrete plans for their short-term contributions until 2030 towards the goal to stay well below 2 ◦C and pursue efforts to limit warming to 1.5 ◦C. These nationally determined contributions (NDCs) have to be ratcheted up in the coming years to become more consistent with the long-term goals. Plausible internally consistent pathways are laid out by scenarios that were assessed in the 5th Assessment Report (AR5) of the IPCC (Clarke et al 2014) Almost all of these scenarios rely heavily on large-scale carbon dioxide removal (CDR) on the order of several to several tens of Gt CO2 a−1 (Clarke et al 2014). This may cause risks of climate change irreversibility due to temperature overshoot and higher intergenerational imbalance (Obersteiner et al 2018)
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