Between Scylla and Charybdis: Delayed mitigation narrows the passage between large-scale CDR and high costs

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 degrees 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 5Gt CO2 a(-1) in any year. At least 8 Gt CO2 a(-1) CDR are necessary in the long term to achieve 1.5 degrees C andmore than 15GtCO(2) a(-1) to keep transitional challenges in bounds.