1 Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Parks Road, Oxford, UK. myles.allen@physics.ox.ac.uk.
2 Oxford Net Zero, Environmental Change Institute, School of Geog. & the Environment, University of Oxford, S Parks Rd, Oxford, UK. myles.allen@physics.ox.ac.uk.
3 School of Physical and Chemical Sciences, University of Canterbury, PB 4800, Christchurch, New Zealand.
4 Faculty of Environment, Science and Economy, University of Exeter, Exeter, UK.
5 Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, BC, Canada.
6 European Commission, Joint Research Centre (JRC), Ispra, Italy.
7 National Centre for Atmospheric Science, Department of Meteorology, University of Reading, Reading, UK.
8 The Met Office, Fitzroy Road, Exeter, UK.
9 Climate Analytics, Ritterstraße 3, Berlin, Germany.
10 School of Geographical Sciences, University of Bristol, University Road, Clifton, Bristol, UK.
11 UK Centre for Ecology and Hydrology, Wallingford, UK.
12 Oxford Net Zero, Environmental Change Institute, School of Geog. & the Environment, University of Oxford, S Parks Rd, Oxford, UK.
13 Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland.
14 Priestley Centre for Climate Futures, University of Leeds, Priestley Building, Woodhouse, Leeds, UK.
15 Department of Geography, Planning & Environment, Concordia University, Montréal, QC, Canada.
16 School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Melbourne, Victoria, Australia.
17 Seminar for Statistics, Department of Mathematics, ETH Zurich, Zurich, Switzerland.
18 CICERO Center for International Climate Research, Oslo, Norway.
19 Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland.
20 Manchester Metropolitan University, Ormond Building, Lower Ormond Street, Manchester, UK.
21 Centre for Environmental Policy and Grantham Institute, Imperial College London, Exhibition Road, London, UK.
22 Department of Mathematics, University of Exeter, Exeter, UK.
23 Department of Earth, Atmospheric, and Planetary Sciences, MIT, 77 Massachusetts Ave., Cambridge, MA, USA.
24 Oeschger Centre for Climate Change Research, University of Bern, Hochschulstrasse 4, Bern, Switzerland.
25 School of Earth and Ocean Sciences, University of Victoria, PO Box 1700, Victoria, B.C., Canada.
26 Department of Geography, Simon Fraser University, 8888 University Drive, Burnaby, B.C., Canada.

Achieving net zero global emissions of carbon dioxide (CO₂), with declining emissions of other greenhouse gases, is widely expected to halt global warming. CO₂ emissions will continue to drive warming until fully balanced by active anthropogenic CO₂ removals. For practical reasons, however, many greenhouse gas accounting systems allow some "passive" CO₂ uptake, such as enhanced vegetation growth due to CO₂ fertilisation, to be included as removals in the definition of net anthropogenic emissions. By including passive CO₂ uptake, nominal net zero emissions would not halt global warming, undermining the Paris Agreement. Here we discuss measures addressing this problem, to ensure residual fossil fuel use does not cause further global warming: land management categories should be disaggregated in emissions reporting and targets to better separate the role of passive CO₂ uptake; where possible, claimed removals should be additional to passive uptake; and targets should acknowledge the need for Geological Net Zero, meaning one tonne of CO₂ permanently restored to the solid Earth for every tonne still generated from fossil sources. We also argue that scientific understanding of net zero provides a basis for allocating responsibility for the protection of passive carbon sinks during and after the transition to Geological Net Zero.