Explore the vast range of titles available.

Climate change, rising atmospheric carbon dioxide, excess nutrient inputs, and pollution in its many forms are fundamentally altering the chemistry of the ocean, often on a global scale and, in some cases, at rates greatly exceeding those in the historical and recent geological record. Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants. Most of these perturbations, tied either directly or indirectly to human fossil fuel combustion, fertilizer use, and industrial activity, are projected to grow in coming decades, resulting in increasing negative impacts on ocean biota and marine resources.

High-quality climate predictions are crucial for understanding the impacts of different greenhouse gas emission scenarios and for mitigating and adapting to the resulting climatic changes. Bonan and Doney review advances in Earth system models that include the terrestrial and marine biosphere. Such models capture interactions between physical and biological aspects of the Earth system. This provides insight into climate impacts of societal importance, such as altered crop yields, wildfire risk, and water availability. Further research is needed to better understand model uncertainties, some of which may be unavoidable, and to better translate observations into abstract model representations. Science , this issue p. eaam8328 Many global change stresses on terrestrial and marine ecosystems affect not only ecosystem services that are essential to humankind, but also the trajectory of future climate by altering energy and mass exchanges with the atmosphere. Earth system models, which simulate terrestrial and marine ecosystems and biogeochemical cycles, offer a common framework for ecological research related to climate processes; analyses of vulnerability, impacts, and adaptation; and climate change mitigation. They provide an opportunity to move beyond physical descriptors of atmospheric and oceanic states to societally relevant quantities such as wildfire risk, habitat loss, water availability, and crop, fishery, and timber yields. To achieve this, the science of climate prediction must be extended to a more multifaceted Earth system prediction that includes the biosphere and its resources.

Scenarios for meeting ambitious climate targets rely on large-scale deployment of negative emissions technologies (NETs), including direct air capture (DAC). However, the tradeoffs between food, water and energy created by deploying different NETs are unclear. Here we show that DAC could provide up to 3 GtCO2 yr−1 of negative emissions by 2035—equivalent to 7% of 2019 global CO2 emissions—based on current-day assumptions regarding price and performance. DAC in particular could exacerbate demand for energy and water, yet it would avoid the most severe market-mediated effects of land-use competition from bioenergy with carbon capture and storage and afforestation. This could result in staple food crop prices rising by approximately fivefold relative to 2010 levels in many parts of the Global South, raising equity concerns about the deployment of NETs. These results highlight that delays in aggressive global mitigation action greatly increase the requirement for DAC to meet climate targets, and correspondingly, energy and water impacts.Negative emissions technologies are essential in scenarios for meeting Paris climate targets. Modelling results show that direct air capture could play an important role with less demand for land yet high energy and water use compared with BECCS and afforestation.

Projected increases in greenhouse gas emissions could suppress marine biological productivity for a thousand years or more. As the climate warms, westerly winds in the Southern Hemisphere will strengthen and shift poleward, surface waters will warm, and sea ice will disappear. Moore et al. suggest that one effect of these changes will be a dramatic decrease in marine biological productivity (see the Perspective by Laufkötter and Gruber). This decrease will result from a global-scale redistribution of nutrients, with a net transfer to the deep ocean. By 2300, this could drive declines in fisheries yields by more than 20% globally and by nearly 60% in the North Atlantic. Science , this issue p. 1139 ; see also p. 1103 Multicentury climate warming could suppress marine biological productivity for a millennium. Climate change projections to the year 2100 may miss physical-biogeochemical feedbacks that emerge later from the cumulative effects of climate warming. In a coupled climate simulation to the year 2300, the westerly winds strengthen and shift poleward, surface waters warm, and sea ice disappears, leading to intense nutrient trapping in the Southern Ocean. The trapping drives a global-scale nutrient redistribution, with net transfer to the deep ocean. Ensuing surface nutrient reductions north of 30°S drive steady declines in primary production and carbon export (decreases of 24 and 41%, respectively, by 2300). Potential fishery yields, constrained by lower–trophic-level productivity, decrease by more than 20% globally and by nearly 60% in the North Atlantic. Continued high levels of greenhouse gas emissions could suppress marine biological productivity for a millennium.

Nutrient fluxes to coastal areas have risen in recent decades, leading to widespread hypoxia and other ecological damage, particularly from nitrogen (N). Several factors make N more limiting in estuaries and coastal waters than in lakes: desorption (release) of phosphorus (P) bound to clay as salinity increases, lack of planktonic N fixation in most coastal ecosystems, and flux of relatively P-rich, N-poor waters from coastal oceans into estuaries. During eutrophication, biogeochemical feedbacks further increase the supply of N and P, but decrease availability of silica -– conditions that can favor the formation and persistence of harmful algal blooms. Given sufficient N inputs, estuaries and coastal marine ecosystems can be driven to P limitation. This switch contributes to greater far-field N pollution; that is, the N moves further and contributes to eutrophication at greater distances. The physical oceanography (extent of stratification, residence time, and so forth) of coastal systems determines their sensitivity to hypoxia, and recent changes in physics have made some ecosystems more sensitive to hypoxia. Coastal hypoxia contributes to ocean acidification, which harms calcifying organisms such as mollusks and some crustaceans.

The development of the shared socioeconomic pathways (SSPs) and associated integrated assessment modeling exercises did not include direct air capture with carbon storage (DACCS) in their scenarios. Recent progress in DACCS commercialization suggests it could be a viable means of removing CO2 from the atmosphere with far lower land intensity than bioenergy with carbon capture or afforestation but with higher energy demands. Several forms of DACCS are in development, with different costs and energy inputs, as well as potential for future cost and performance improvements. Here, we use the Global Change Analysis Model to understand the role of DACCS across all 5 SSPs for the below 2 °C and below 1.5 °C end-of-century warming goals. We assess DACCS deployment relative to other carbon capture methods, and its side effects for global energy, water, land systems. We find that DACCS could play up to a tens of GtCO2 yr−1 role in many of these scenarios, particularly those with delayed climate policy and/or higher challenges to emissions mitigation. Our ‘sustainable development’ scenarios, consistent with SSP1, have smaller deployments of DACCS and other negative emissions owing to immediate climate policy onset, greater ease of emissions abatement, and tighter constraints on future negative emissions.

Climate change is altering oceanic conditions in a complex manner, and the concurrent amendment of multiple properties will modify environmental stress for primary producers. So far, global modelling studies have focused largely on how alteration of individual properties will affect marine life. Here, we use global modelling simulations in conjunction with rotated factor analysis to express model projections in terms of regional trends in concomitant changes to biologically influential multi-stressors. Factor analysis demonstrates that regionally distinct patterns of complex oceanic change are evident globally. Preliminary regional assessments using published evidence of phytoplankton responses to complex change reveal a wide range of future responses to interactive multi-stressors with <20–300% shifts in phytoplankton physiological rates, and many unexplored potential interactions. In a future ocean, provinces will encounter different permutations of change that will probably alter the dominance of key phytoplankton groups and modify regional productivity, ecosystem structure and biogeochemistry. Consideration of regionally distinct multi-stressor patterns can help guide laboratory and field studies as well as the interpretation of interactive multi-stressors in global models. Modelling studies of climate change impacts on phytoplankton typically consider individual properties, which ignores the complex nature of the marine environment. This work undertakes regional assessments using multiple properties, including interactions, and finds shifts of <20–300% in phytoplankton physiological rates.

Ocean carbon uptake and storage simulated by the Community Earth System Model, version 1–Biogeochemistry [CESM1(BGC)], is described and compared to observations. Fully coupled and ocean-ice configurations are examined; both capture many aspects of the spatial structure and seasonality of surface carbon fields. Nearly ubiquitous negative biases in surface alkalinity result from the prescribed carbonate dissolution profile. The modeled sea–air CO₂ fluxes match observationally based estimates over much of the ocean; significant deviations appear in the Southern Ocean. Surface oceanpCO₂ is biased high in the subantarctic and low in the sea ice zone. Formation of the water masses dominating anthropogenic CO₂ (Cant) uptake in the Southern Hemisphere is weak in the model, leading to significant negative biases in Cantand chlorofluorocarbon (CFC) storage at intermediate depths. Column inventories of Cantappear too high, by contrast, in the North Atlantic. In spite of the positive bias, this marks an improvement over prior versions of the model, which underestimated North Atlantic uptake. The change in behavior is attributable to a new parameterization of density-driven overflows. CESM1(BGC) provides a relatively robust representation of the ocean–carbon cycle response to climate variability. Statistical metrics of modeled interannual variability in sea–air CO₂ fluxes compare reasonably well to observationally based estimates. The carbon cycle response to key modes of climate variability is basically similar in the coupled and forced ocean-ice models; however, the two differ in regional detail and in the strength of teleconnections.

Seagrass meadows play an important role in “blue carbon” sequestration and storage, but their dynamic metabolism is not fully understood. In a dense Zostera marina meadow, we measured benthic O₂ fluxes by aquatic eddy covariance, water column concentrations of O₂, and partial pressures of CO₂ (pCO₂) over 21 full days during peak growing season in April and June. Seagrass metabolism, derived from the O₂ flux, varied markedly between the 2 months as biomass accumulated and water temperature increased from 16°C to 28°C, triggering a twofold increase in respiration and a trophic shift of the seagrass meadow from being a carbon sink to a carbon source. Seagrass metabolism was the major driver of diurnal fluctuations in water column O₂ concentration and pCO₂, ranging from 173 to 377 μmol L−1 and 193 to 859 ppmv, respectively. This 4.5-fold variation in pCO₂ was observed despite buffering by the carbonate system. Hysteresis in diurnal water column pCO₂ vs. O₂ concentration was attributed to storage of O₂ and CO₂ in seagrass tissue, air–water exchange of O₂ and CO₂, and CO₂ storage in surface sediment. There was a ~ 1:1 mol-to-mol stoichiometric relationship between diurnal fluctuations in concentrations of O₂ and dissolved inorganic carbon. Our measurements showed no stimulation of photosynthesis at high CO₂ and low O₂ concentrations, even though CO₂ reached levels used in IPCC ocean acidification scenarios. This field study does not support the notion that seagrass meadows may be “winners” in future oceans with elevated CO₂ concentrations and more frequent temperature extremes.

Ocean acidification has the potential to significantly impact both aquaculture and wild-caught mollusk fisheries around the world. In this work, we build upon a previously published integrated assessment model of the US Atlantic Sea Scallop (Placopecten magellanicus) fishery to determine the possible future of the fishery under a suite of climate, economic, biological, and management scenarios. We developed a 4x4x4x4 hypercube scenario framework that resulted in 256 possible combinations of future scenarios. The study highlights the potential impacts of ocean acidification and management for a subset of future climate scenarios, with a high CO2 emissions case (RCP8.5) and lower CO2 emissions and climate mitigation case (RCP4.5). Under RCP4.5 and the highest impact and management scenario, ocean acidification has the potential to reduce sea scallop biomass by approximately 13% by the end of century; however, the lesser impact scenarios cause very little change. Under RCP8.5, sea scallop biomass may decline by more than 50% by the end of century, leading to subsequent declines in industry landings and revenue. Management-set catch limits improve the outcomes of the fishery under both climate scenarios, and the addition of a 10% area closure increases future biomass by more than 25% under the highest ocean acidification impacts. However, increased management still does not stop the projected long-term decline of the fishery under ocean acidification scenarios. Given our incomplete understanding of acidification impacts on P. magellanicus, these declines, along with the high value of the industry, suggest population-level effects of acidification should be a clear research priority. Projections described in this manuscript illustrate both the potential impacts of ocean acidification under a business-as-usual and a moderately strong climate-policy scenario. We also illustrate the importance of fisheries management targets in improving the long-term outcome of the P. magellanicus fishery under potential global change.