Combining policies to remove carbon dioxide (CO2) from the atmosphere with policies to reduce emissions can potentially decrease CO2 concentrations to earlier levels. We model the optimal selection of a dynamic portfolio of abatement, research and development (R&D), and negative emission policies under an exogenous CO2 constraint and with stochastic technological change. We find that near-term abatement is not sensitive to the availability of R&D policies, but the anticipated availability of negative emission strategies can reduce near-term abatement if CO2 targets are sufficiently ambitious. Further, planning to develop and deploy negative emission technologies can shift optimal R&D funding from breakthrough carbon-free technologies into incremental lower-carbon technologies. Importantly, when the goal is to maintain the present CO2 concentration in the year 2100, an optimized portfolio with negative emission strategies can be 80% cheaper than an optimized portfolio lacking such strategies. However, the cost is not reduced by as much if concerns about tipping points rule out using late-century negative emission strategies to temporarily overshoot the CO2 target earlier in the century.