The new study, published in the journal Earth System Dynamics, is one of the first to examine how ocean alkalinity enhancement, or OAE, would reshape the seasonal rhythm of the carbon cycle rather than just the annual bottom line. Led by Chiara Ciscato of the Euro-Mediterranean Center on Climate Change in Bologna, with colleagues at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, the work used a full Earth system model to simulate a continuous, decades-long dose of alkalinity along the European coastline under two very different futures: a low-emission pathway called SSP1-2.6 and a high-emission pathway called SSP3-7.0. The results reveal a carbon cycle that is stranger, and in some ways more productive, than anyone had mapped before.

OAE is built on a simple piece of chemistry. When alkaline substances such as quicklime or crushed olivine dissolve in seawater, they consume dissolved CO2 and convert it into bicarbonate and carbonate ions, stable forms of inorganic carbon that can persist in the ocean for millennia. This conversion lowers the partial pressure of CO2 at the ocean surface, opening a chemical gap between sea and air. The atmosphere rushes to fill it, and the ocean draws down more CO2. In theory, the approach mimics and accelerates the natural weathering of rocks that has regulated Earth’s climate over geological time, compressed into a human timescale.

In the simulations, the team injected alkalinity continuously into the surface layer of coastal grid cells ringing the European continent, excluding the Mediterranean and the Baltic. Starting in 2025 and ramping up over a decade, the addition reached the equivalent of one gigatonne of fast-reacting calcium hydroxide per year, held constant until 2100. That is an industrial-scale intervention, comparable in ambition to the largest proposed carbon removal schemes, and the model tracked its consequences through every season of the century’s final decades.

The most striking finding concerns summer. Under natural conditions, surface alkalinity in European waters peaks in winter, when deep mixing dredges alkalinity-rich water up from below, and bottoms out in summer, when a warm, stratified cap isolates the surface. But the model showed the opposite happening once alkalinity was added. Because summer stratification traps the added alkalinity in the top layer rather than letting it mix away, surface concentrations climbed highest in the warmest months. Along the coastline itself, the seasonal swing in alkalinity exploded from roughly 19 to 109 micromoles per kilogram under low emissions, and from 24 to 138 under high emissions. The seasonal cycle, in effect, had been turned upside down.

That reversal has cascading consequences. With alkalinity peaking in summer, the partial pressure of CO2 in surface waters falls most sharply precisely when it would naturally be highest, during the months of peak outgassing. Fast gas exchange between ocean and atmosphere then does the rest: the summer release of CO2 flips into summer uptake, and the region becomes a carbon sink all year round. In the broader European domain, the seasonal amplitude of ocean pCO2 shrank by 41 percent under the low-emission scenario, a damping of the natural cycle that the authors attribute to alkalinity addition working hardest against the season of greatest chemical resistance.

Yet the biggest carbon gains did not come in summer. The air-sea CO2 flux remained locked to the rhythm of the mixed layer, deepening in winter as storms and cooling stir the upper ocean and shoaling in summer as the water stratifies. Winter, with its cold water and vigorous mixing, is when CO2 dissolves most readily, and it is winter that saw the largest enhancement of uptake once alkalinity was added. In the European region, the seasonal amplitude of the CO2 flux grew by about 51 percent under low emissions and 52 percent under high emissions. Along the coastline, the effect was more dramatic still: the winter-to-summer swing of the flux nearly tripled under SSP1-2.6 and grew more than two and a half fold under SSP3-7.0.

Perhaps the most counterintuitive result is that the dirtier emissions scenario produced the bigger carbon sink. Under SSP3-7.0, atmospheric CO2 concentrations are far higher, which raises the partial pressure of CO2 in surface waters and weakens the ocean’s buffering capacity, its chemical resistance to absorbing more of the gas. The result is that each unit of added alkalinity pulls down more carbon. The study’s measure of seasonal carbon sequestration potential, the ratio of extra CO2 uptake to the alkalinity added, was consistently higher under high emissions, both along the coast and across the wider European region. A hotter, more carbon-polluted world, in other words, makes this particular removal technology more efficient, even as it makes the underlying climate problem worse.

The findings carry practical weight for the emerging industry of marine carbon removal. Because the excess CO2 uptake extended well beyond the strip of coastline where alkalinity was injected, with some of the additional flux appearing over the open North Atlantic, monitoring schemes confined to national waters or deployment sites could systematically underestimate how much carbon a project actually removes. The authors also flag a caution: summer surface alkalinity along the coast rose by more than 500 micromoles per kilogram in the simulations, levels that could push pH and aragonite saturation past thresholds harmful to local marine life. Choosing the right alkaline feedstock, and tailoring the rate and timing of addition to each site, may be essential to keeping the ecological risks in check.

The study is not without limits. The Earth system model, called FOCI, resolves the ocean at half a degree, which smooths over the fine coastal dynamics where alkalinity is actually added, and the model carries known biases in the North Atlantic, including a cold patch and a low-alkalinity shelf region near Norway. Riverine alkalinity inputs, which follow a strong seasonal cycle, were not represented. The authors argue that because their analysis rests on differences between paired simulations, such systematic errors largely cancel out, but they acknowledge that real-world deployment would demand finer tools. They also note that their continuous injection scheme is idealised; future projects are more likely to use pulsed additions, which earlier work suggests behave differently. Still, as coastal OAE moves from whiteboard to pilot project, the message of this study is clear: the seasons matter. Whoever deploys alkalinity in European waters will be rewriting not just the ocean’s carbon budget, but its calendar.

Subject of Research: Effects of coastal ocean alkalinity enhancement on the seasonal carbon cycle in European waters under low- and high-emission scenarios

Article Title: Impacts of simulated coastal ocean alkalinity enhancement on the seasonal carbon cycle in European waters under a low- and a high-emission scenario

Article References: Impacts of simulated coastal ocean alkalinity enhancement on the seasonal carbon cycle in European waters under a low- and a high-emission scenario. (n.d.). https://doi.org/10.5194/esd-17-1513-2026

Image Credits: AI Generated

DOI: 10.5194/esd-17-1513-2026

Keywords: ocean alkalinity enhancement, carbon dioxide removal, seasonal carbon cycle, European coastal waters, Earth system modelling, ocean pCO2, marine carbon sink, SSP1-2.6, SSP3-7.0, ocean stratification, air-sea CO2 flux, climate mitigation

The research team defined the phenomenon with statistical precision. An energy drought begins when the daily capacity factor of wind or solar generation falls below the tenth percentile of the historical baseline for 1985 through 2014 and stays there for at least three consecutive days. A flash energy drought is then distinguished by its onset speed: the drop in capacity factor from the day before the event to its first day. When that drop exceeds the historical ninetieth percentile of onset speeds, the event is classified as flash. In other words, these are the worst of both worlds, combining an unusually rapid decline with an unusually deep and sustained shortfall in renewable supply. Days when both wind and solar simultaneously fall below their thresholds are treated as compound events, the category that poses the gravest operational challenge.

To project how climate change will alter these events, the team turned to bias-corrected climate model output from the Coupled Model Intercomparison Project Phase 6, the same CMIP6 ensemble underpinning recent assessments of the Intergovernmental Panel on Climate Change. From variables such as wind speed, radiation, temperature and humidity, the researchers calculated hourly wind and solar capacity factors across the globe, then applied their drought detection protocol separately to each technology. For each event they tracked two core metrics: frequency, the count of flash droughts occurring, and duration, the number of days each event persists. They also distinguished between flash wind droughts, flash solar droughts and flash compound droughts, and examined how these metrics shift across seasons and scenarios.

The headline finding concerns duration, and the numbers are stark. Under the SSP1-2.6 scenario, a comparatively ambitious emissions pathway, the duration of flash droughts increases by 25.6 percent for wind resources, 29.8 percent for solar resources, and a remarkable 155.7 percent for compound wind-solar events. That the compound category more than doubles in duration even under moderate climate ambition is perhaps the study’s most alarming signal. Compound flash droughts are precisely the situations in which neither renewable resource can compensate for the other, forcing power systems to lean hardest on dispatchable generation, stored energy and interregional transmission at exactly the moment those reserves are least likely to be ready.

But the authors went beyond cataloguing meteorological extremes. To translate declining capacity factors into consequences for real grids, they built an electricity optimization dispatch model. The model takes technology-specific costs, hourly electricity demand, and hourly wind and solar capacity factors as inputs, and minimizes total annual system cost subject to constraints including the renewable generation share, storage charging and discharging efficiency, ramping limits, reliability requirements and minimum output rules. When flash energy droughts were imposed on this model, the results showed that such events are associated with higher unserved energy, greater flexibility requirements, and higher electricity costs compared with both slow energy droughts and normal operating periods. The abrupt onset is the problem: systems lack the lead time to prepare, so reliability suffers and the cost of emergency balancing climbs.

The global exposure assessment is where the study becomes genuinely sobering for energy planners. By overlaying their drought projections onto the actual geography of wind and solar deployment, the researchers found that approximately 70.8 percent of global wind and solar installed capacity faces rising frequency or duration of flash energy droughts under climate change. The dominant exposure subtype varies by country and grid cell, with some regions driven mainly by flash wind droughts, others by flash solar droughts, and a substantial share by compound events. For the ten countries with the largest existing wind and solar fleets, the study ranked capacity by the magnitude of change it faces, revealing that a large proportion of installed capacity sits in cells where flash drought risk is increasing rather than receding.

Seasonal patterns add another layer of concern. Under the SSP1-2.6 scenario, the team mapped changes in flash wind and solar drought frequency and duration separately for spring, summer, autumn and winter in each hemisphere. Because renewable demand profiles also vary seasonally, a flash drought that coincides with a peak demand season, such as a winter wind drought in the Northern Hemisphere or a summer solar drought during air-conditioning season, carries disproportionate consequences for grid adequacy. The geography of exposure matters just as much as the timing: regions that have bet heavily on a single renewable technology may find that their resource is precisely the one whose flash drought risk is deteriorating fastest.

Crucially, the study does not end in pessimism, because the location of future wind and solar farms is still a matter of choice. Using country-level capacity targets for 2060 drawn from integrated assessment model scenarios compiled by the International Institute for Applied Systems Analysis, the researchers evaluated whether strategically prioritizing deployment, steering new capacity toward grid cells with lower projected flash drought exposure, could mitigate the widespread risk. The answer is yes in principle: siting decisions informed by flash drought projections could substantially reduce the amount of capacity facing rising frequency and duration. But the effectiveness of this strategy depends heavily on two things, the strength of future climate ambitions and the realization of technical potential, including whether the most favorable sites are actually available, connected and buildable at the scale the scenarios assume.

The technical machinery behind these conclusions is worth appreciating, because the reliability of energy drought research depends on it. The team used the ERA5 global reanalysis as a historical foundation and bias-corrected CMIP6 general circulation model output for future projections, steps that guard against known biases in reanalysis wind speeds and irradiance estimates. They converted meteorological variables into capacity factors using standard photovoltaic and wind power conversion approaches, accounting for solar geometry and the power law relationship between wind speeds at different heights. The processed data, along with the custom code implementing the drought detection protocol and the dispatch model, are publicly available through Zenodo, allowing other researchers to reproduce the analysis and extend it to their own regions and scenarios.

The implications ripple outward from grid engineering to climate policy. As decarbonization accelerates, electricity systems will carry far larger shares of weather-dependent generation, and the margin for error shrinks accordingly. Flash energy droughts represent a class of risk that conventional planning, built around seasonal and annual averages, has tended to overlook. The study’s projection that flash compound drought duration could increase by more than 150 percent even under moderate mitigation suggests that energy security in a warming world will require not just more renewable capacity but smarter capacity: diversified technology mixes, long-duration storage, robust transmission interconnection, and siting strategies that treat flash drought exposure as a first-order criterion alongside resource quality and cost. Whether the world’s energy transition absorbs this lesson in time may depend on how quickly these findings move from the pages of a journal into the planning documents of the institutions building the grids of the coming decades.

Subject of Research: Flash energy droughts in solar and wind resources under climate change

Article Title: Flash energy droughts in solar and wind resources under climate change

Article References: Lin, Y., Zheng, D., Tong, D., Davis, S. J., Yin, Z., He, K., & Zhang, Q. (2026). Flash energy droughts in solar and wind resources under climate change. Nature Climate Change. https://doi.org/10.1038/s41558-026-02753-3

Image Credits: AI Generated

DOI: 10.1038/s41558-026-02753-3

Keywords: flash energy droughts, wind power, solar power, climate change, compound events, renewable energy, power system reliability, energy security, CMIP6, SSP1-2.6, grid operation, capacity factors