Trees and forests as geo-engineers of past and future global climates David Beerling University of Sheffield ([email protected]) The (bio)geochemical carbon cycle CO2 (g) Return of CO2 to the atmosphere CO2 (aq) Weathering burial of CaCO3 CO2 + CaSiO3 CaCO3 + SiO2 Metamorphism with decarbonation, e.g.: CaCO3+SiO2->CaSiO3+CO2 Fossil forests of Gilboa (385-million-years-old) Winifred Goldring (1888-1971) One of the largest rooting systems Root type 1 ‘Trunk’ diameter = 31cm Minimum lateral extent of rooting = ~7m Archaeopteridalean progymnosperms? (Stein and Berry). ~10m max Close-up of root ‘trace’/ mould Reconstruction of Archaeopteris Images: Jenny Morris (Late Devonian); Beck, 1962 Root type 2 Cladoxylopsids (Stein and Berry) Eospermatopteris ‘root mound’ at Cairo ~8m Reconstruction: Sandstone cast of Eospermatopteris, base of Eospermatopteris base; Gilboa Watteiza; Stein et al., 2007 Drilling campaigns Palaeo-Vertisols with slicken-sided (2012, 2013) summary slip planes. Total 14 cores drilled to depths of >1.5m Climate clues: Sub-tropical, with 6 cores beneath Archaeopterid stumps ( ) seasonal precipitation 7 cores beneath cladoxylopsid stumps ( ) 1 ‘control’ on surface without roots Root trace horizons map to tree size Original map by Stein, Berry et al. (in prep). Images/data: Jenny Morris Functional differences in tree rooting depths and soil mineral interactions Cladoxylopsid Archaeopterid Drab-halo of 385 Myr-old rootlets Max. trunk base diameter (cm) Micro-XRF transect across a drab-haloed root 15 25 35 45 55 4500 trace 250 0.0 4000 3500 200 0.5 3000 150 1.0 2500 2000 100 1.5 1500 Counts (solid lines) Counts(dashed lines) 1000 50 Max. rooting depth (m) depth rooting Max. 2.0 500 Cladoxylopsid trees 0 0 0 5 10 15 20 25 30 Archaeopteridalean trees Transect mm Fe P Ca Al K 3cm Images/data: Jenny Morris Artificially enhanced terrestrial weathering as a geoengineering Carbon Dioxide Removal strategy? Global annual CO2 emissions and the magnitude of the task Puny natural weathering C-sink Enhanced weathering lowers RCP4.5 and RCP8.5 atmospheric CO2 trajectories (Bern Carbon Cycle model) CMIP5 RCP4.5 simulations CMIP5 RCP8.5 simulations (medium-level mitigation) (business-as-usual) 100ppm 260ppm Pre-industrial value Taylor et al. (in prep) Could we save reef-building corals? <ocean pH reduces saturation of today mineral forms of calcium carbonate, including aragonite (a) which corals precipitation to build their skeletons. Today coral reefs exist where a>3.5 RCP8.5 (Ricke et al. (2012) Env. Res. Lett. 8, 034003). Taylor et al. (in prep) Beerling Research Group and (some) University of Sheffield collaborators (2014).