Unraveling the Complex Legacy of Carbon Dioxide Removal on Agroecological Droughts
In the relentless pursuit to curb global warming, carbon dioxide removal (CDR) techniques have emerged as a beacon of hope. However, a groundbreaking new study reveals that the impacts of these interventions on agroecological droughts—particularly in globally vulnerable regions—may be far more complex and potentially problematic than previously anticipated. Unlike the straightforward expectation that reversing atmospheric CO₂ concentrations would symmetrically dampen drought stress, this research uncovers a nonlinear and often irreversible behavior of drought patterns as atmospheric conditions undergo manipulation. The findings underscore a critical need to rethink how climate mitigation strategies are designed, moving beyond simplistic carbon accounting towards a nuanced understanding of ecosystem responses.
Agroecological droughts, which relate to both precipitation deficits and evapotranspiration (ET) surpluses, play a critical role in determining water availability for farmland and natural vegetation. Such droughts threaten food security, forest health, and water resources across many global hotspots, including the Amazon, Mediterranean Basin, and parts of North and South Central America. The recent study applies multi-model simulations from the Climate Carbon Dioxide Removal Model Intercomparison Project (CDRMIP) to evaluate the response of these drought phenomena during scenarios of both sustained CO₂ emissions and subsequent CO₂ removal pathways.
What emerges is a nuanced portrait of hysteresis—a lagged and path-dependent dynamical response—where the progression of drought intensification during emission increases does not simply unwind in reverse as CO₂ is removed. In other words, even if atmospheric CO₂ falls back to prior levels, the severity and frequency of droughts may persist or worsen in some regions. This irreversible behavior challenges the assumption held by many policy frameworks that a net-zero or net-negative carbon budget inherently equates to a restoration of climate conditions to safer baselines.
The physical drivers behind these hysteresis effects are twofold: precipitation deficits and evapotranspiration surpluses. Notably, the spatial pattern of these mechanisms varies significantly by region. Atmospheric circulation changes dominate the precipitation reductions in many areas, such as the southward migration of the Intertropical Convergence Zone (ITCZ), which can suppress rainfall over northern land masses including the Mediterranean region and parts of North and South Central America. Meanwhile, evapotranspiration changes hinge heavily on vegetation state shifts, atmospheric demand, and moisture supply dynamics, coupling biophysical feedbacks with climatic drivers in complex ways.
Intriguingly, Earth’s greening—an observed global vegetation surge largely attributed to elevated CO₂ and extended growing seasons—has been estimated to contribute over half the increase in global ET over recent decades. The studied models reveal that during carbon dioxide removal phases, areas with higher leaf area indices (LAI) experience amplified ET increases, exacerbating drought stress despite reductions in atmospheric CO₂. The nonlinear response of vegetation, particularly tree fraction changes modeled in the UK Earth System Model (UKESM), is believed to underlie the observed nonlinear dynamics in evapotranspiration and thus agroecological drought manifestation.
The implications for both natural ecosystems and human societies are profound. The Amazon rainforest, a crucial global carbon sink, faces exacerbated drought stresses that could trigger widespread tree mortality. This releases stored carbon back into the atmosphere, fostering an alarming positive feedback loop that accelerates warming. Equally severe are the risks in the Mediterranean Basin, home to hundreds of millions of people and a critical agricultural hub yielding cereals, olives, and hosting hydropower infrastructure. The persistence of drought conditions, even after emission reductions, signals the urgent need for proactive, long-term adaptation strategies especially in these drought hotspots.
This research injects critical insight into the heated debate surrounding global warming “overshoot” scenarios, where temperatures temporarily exceed targets before being driven down by aggressive CDR later in the century. Prior discussions had been hampered by a lack of robust model evidence regarding the climate risks of overshoot pathways. By illustrating that drought conditions under overshoot are not only worsened but also exhibit hysteresis and irreversibility, the study provides a strong cautionary note: overshoot is not simply a transient problem easily rectified, but a potential trigger for entrenched climate extremes.
Given the complex feedbacks and spatial heterogeneities, the study warns that models used by Integrated Assessment Models (IAMs)—which guide policy and economic decisions—often underestimate or neglect the persistent, irreversible risks posed by extreme climate events such as drought. The call is clear: IAMs must evolve to integrate these impacts more comprehensively to foster realistic and precautionary pathway designs that reduce reliance on uncertain CDR outcomes.
As the world edges closer to the substantial deployment of large-scale CDR to meet Paris Agreement targets, understanding the climatic and ecological side effects becomes paramount. The research emphasizes that merely balancing CO₂ emissions with equivalent removals may be insufficient to restore previous drought conditions. In many key global regions, additional CDR beyond emission levels may be required to mitigate these irreversible impacts—a nuance currently absent from policy narratives.
The conducted simulations relied on idealized CO₂ emission and removal trajectories to isolate fundamental dynamical responses, thereby limiting direct translation into precise real-world CDR prescriptions. Nonetheless, the findings beckon an urgent reevaluation of CDR strategies, recommending the development of novel scenarios that optimize not only for temperature goals but also for minimizing irreversible climate risks to ecosystems and societies. This holistic approach is essential for fostering truly climate-resilient policies in an increasingly uncertain future.
The researchers stress that rapid, rather than delayed, emission reductions are paramount to avoiding hysteresis and irreversible climate damage. While CDR remains a vital component of the global mitigation arsenal, over-reliance on it could entrench drought stresses and other extreme climate risks in ways that carbon accounting alone cannot remedy. Therefore, the study advocates prioritizing emission cuts alongside cautious and well-monitored CDR deployment.
In conclusion, this pioneering work reveals that agroecological droughts—key determinants of terrestrial ecosystem health and human livelihoods—do not simply rewind as atmospheric CO₂ is drawn down. Their asymmetric, hysteretic, and sometimes irreversible responses demand a shift in how climate strategies are framed and executed. Carbon neutrality, it turns out, does not guarantee drought neutrality. By integrating these insights into climate modelling, policy design, and adaptation planning, humanity can better navigate the perilous path towards a stable and sustainable future.
Subject of Research: The hysteresis and reversibility of agroecological droughts in response to atmospheric carbon dioxide removal.
Article Title: Hysteresis and reversibility of agroecological droughts in response to carbon dioxide removal.
Article References:
Liu, L., Hauser, M., Windisch, M. et al. Hysteresis and reversibility of agroecological droughts in response to carbon dioxide removal. Nat Water (2025). https://doi.org/10.1038/s44221-025-00487-8
Image Credits: AI Generated
