The magnitude of future climate change could be moderated by immediately reducing the amount of CO entering the atmosphere as a result of energy generation and by adopting strategies that actively remove CO from it. Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure. Managed croplands worldwide are already equipped for frequent rock dust additions to soils, making rapid adoption at scale feasible, and the potential benefits could generate financial incentives for widespread adoption in the agricultural sector. However, there are still obstacles to be surmounted. Audited field-scale assessments of the efficacy of CO capture are urgently required together with detailed environmental monitoring. A cost-effective way to meet the rock requirements for CO removal must be found, possibly involving the recycling of silicate waste materials. Finally, issues of public perception, trust and acceptance must also be addressed.

Increasing atmospheric methane (CH 4 ) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH 4 as a greenhouse gas, its atmospheric growth rate and dynamics over the past two decades, which include a stabilization period (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), followed by renewed growth starting in 2007, remain poorly understood. We provide an updated estimate of CH 4 emissions from wetlands, the largest natural global CH 4 source, for 2000-2012 using an ensemble of biogeochemical models constrained with remote sensing surface inundation and inventory-based wetland area data. Between 2000-2012, boreal wetland CH 4 emissions increased by 1.2 Tg yr −1 (−0.2-3.5 Tg yr −1 ), tropical emissions decreased by 0.9 Tg yr −1 (−3.2−1.1 Tg yr −1 ), yet globally, emissions remained unchanged at 184 ± 22 Tg yr −1 . Changing air temperature was responsible for increasing high-latitude emissions whereas declines in low-latitude wetland area decreased tropical emissions; both dynamics are consistent with features of predicted centennial-scale climate change impacts on wetland CH 4 emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH 4 emissions have not contributed significantly to the period of renewed atmospheric CH 4 growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH 4 emissions, and a decrease in the atmospheric oxidative sink.

The dramatic decline in atmospheric CO2 evidenced by proxy data during the Devonian (416.0-359.2 Ma) and the gradual decline from the Cretaceous (145.5-65.5 Ma) onwards have been linked to the spread of deeply rooted trees and the rise of angiosperms, respectively. But this paradigm overlooks the coevolution of roots with the major groups of symbiotic fungal partners that have dominated terrestrial ecosystems throughout Earth history. The colonization of land by plants was coincident with the rise of arbuscular mycorrhizal fungi (AMF),while the Cenozoic (c. 65.5-0 Ma) witnessed the rise of ectomycorrhizal fungi (EMF) that associate with both gymnosperm and angiosperm tree roots. Here, we critically review evidence for the influence of AMF and EMF on mineral weathering processes. We show that the key weathering processes underpinning the current paradigm and ascribed to plants are actually driven by the combined activities of roots and mycorrhizal fungi. Fuelled by substantial amounts of recent photosynthate transported from shoots to roots, these fungi form extensive mycelial networks which extend into soil actively foraging for nutrients by altering minerals through the acidification of the immediate root environment. EMF aggressively weather minerals through the additional mechanism of releasing low molecular weight organic chelators. Rates of biotic weathering might therefore be more usefully conceptualized as being fundamentally controlled by the biomass, surface area of contact, and capacity of roots and their mycorrhizal fungal partners to interact physically and chemically with minerals. All of these activities are ultimately controlled by rates of carbon-energy supply from photosynthetic organisms. The weathering functions in leading carbon cycle models require experiments and field studies of evolutionary grades of plants with appropriate mycorrhizal associations. Representation of the coevolution of roots and fungi in geochemical carbon cycle models is required to further our understanding of the role of the biota in Earth's CO2 and climate history.

Chemical breakdown of rocks, 'weathering', is an important but very slow part of thebasalt for equivalent application rates (Fig. 1a-c). We present CO 2 consumption curves 71 assuming mixing depths of 10 cm and 30 cm for each application rate; 10 cm is likely the 72 minimum mixing depth given intense precipitation events, the distribution of macropores and whilst still achieving ~80-89% of the effect (Fig. 1a-c in both the RCP4.5 and RCP8.5 climate change scenarios (Fig. 2a, b). Increasing the 110 application rate to 5 kg m -2 yr -1 over the same 20 Mkm 2 'hotspot' areas lowers the 111 atmospheric CO 2 concentration further by 150-180 ppm under both RCPs (Fig. 2c, d (Fig. 2). For the business-as-usual RCP8.5 scenario, however, the lowest 116 simulated CO 2 concentration by year 2100 in the high-end weathering scenario is still ~730 117 ppm (basalt) or 690-560 ppm (harzburgite) (Fig. 2d) weathering is dependent on climate sensitivity and the actual atmospheric CO 2 concentration. 123Calculated end-of-century 'warming averted' figures for the enhanced weathering scenarios 124 using GENIE, which has a low-to-medium climate sensitivity, are summarized in Table 1. 125For high application rates, WA ranges from 0.9-2.2°C for RCP4.5 and 0.7-1.6°C for RCP8.5 126 ( (Fig. 2), tend to counter the negative impacts 136 on ocean carbonate chemistry (Figs. 3 and 4). Our simulations driven by decreased CO 2 (Fig. 137 2) and increased alkalinity fluxes show that additions of 1 kg m -2 yr -1 of harzburgite or basalt 138 across the weathering 'hotspots' can mitigate future ocean acidification by an average of 139 around 0.1 pH units (Fig. 3a, b). A higher silicate application rate (5 kg m -2 yr -1 ) reverses 140 future surface ocean acidification under RCP4.5, restoring global mean surface ocean pH to 141 year 2000 levels or even pre-industrial levels by 2100 (Fig. 3c). Even for RCP8.5, 5 kg m -2 142 yr -1 reduces ocean acidification by approximately two-thirds by year 2100 (Fig. 3d) 143(Supplementary Information). 144Coral reef health is linked to the ocean's aragonite saturation state (Ω a ), which affects the 145 rate at which corals can precipitate this crystalline mineral form of calcium carbonate and RCP8.5, Ω a at reef sites drops to <3.5 by 2100 (Fig. 4), potentially threatening them with 149 extinction 14 . In simulations for RCP4.5 and RCP8.5, enhanced weathering with 1 kg m -2 yr -1 150 of silicates (basalt or harzburgite) and reduced atmospheric CO 2 , generates conditions of Ω a 151 >3.5 across main regions of coral reef occurrence (Fig. 4a-e). Hence, although this low 152 dosage is rather ineffective at reducing global CO 2 (Fig. 2), it has specific regional advantages 153 in terms of helping protect coral reefs. Applications of either rock at high rates (5 kg m -2 yr -1 ) 154 markedly increase Ω a above 3.5 in both RCP4.5 and RCP8.5 scenarios at low latitudes ( Fig. 155 4c,f). Enhanced weathering on land could therefore be more effective at alleviating stressors 196 Methods 197Methods and any associated ref...

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact