Carbonate–Silicate Weathering Feedback

• Carbonate–silicate weathering feedback is a planetary-scale geochemical process that regulates atmospheric CO₂ and surface temperature via temperature- and CO₂-sensitive silicate weathering.
• It employs mathematical models that parameterize weathering rates based on temperature, CO₂ levels, land fraction, and fresh mineral supply, distinguishing between kinetic and supply‐limited regimes.
• This feedback is essential for maintaining long-term climate stability on Earth and other planets, and it underpins innovative climate mitigation strategies like enhanced rock weathering.

The carbonate–silicate weathering feedback is a planetary-scale geochemical negative-feedback mechanism that regulates atmospheric CO₂ and surface temperature on timescales of millions to billions of years. Operating through the coupling of silicate mineral weathering, carbonate formation, and volcanic outgassing, this feedback is fundamental to the long-term climatic stability of terrestrial planets and the maintenance of habitable conditions. Its core dynamical principle is that silicate weathering acts as a temperature- and CO₂-sensitive sink for atmospheric CO₂, opposing climate perturbations and extending the habitable zone (HZ) beyond the range set by simple radiative–convective equilibrium.

1. Fundamental Process and Mathematical Framework

The carbonate–silicate cycle is governed by a sequence of geochemical reactions, including the prototypical silicate weathering:

$$\mathrm{CaSiO_3(s) + CO_2(g) \rightleftharpoons CaCO_3(s) + SiO_2(s)}$$

The rate at which atmospheric CO₂ is removed via weathering depends primarily on surface temperature, precipitation/runoff, atmospheric CO₂ partial pressure, and the availability of fresh silicate minerals. Typical parameterizations express the global silicate weathering rate $W$ as:

$$W = W_0 \exp\left(\frac{T - T_0}{T_e}\right) \left( \frac{p_{\mathrm{CO}_2}}{p_{\mathrm{CO}_2,0}} \right)^{\beta}$$

where:

• $W_0$ is a reference rate (modern Earth),
• $T_e$ is an e-folding temperature for weathering kinetics,
• $\beta$ characterizes the CO₂ sensitivity (values from ~0.25 to 1, depending on presence of land plants and lithology),
• $p_{\mathrm{CO}_2,0}$ and $T_0$ are modern reference values.

Negative feedback arises because warmer climates and higher CO₂ both accelerate weathering, drawing down CO₂ and thus cooling the planet; the reverse occurs in colder states.

The total planetary weathering rate may include both continental and seafloor components. For example, a two-component model for total normalized weathering as a function of surface land fraction $\gamma$ is:

$$\begin{aligned} W & = \beta_0 \frac{\gamma}{\gamma_0} (1 + \alpha_p T)^a \phi^b e^T\ & \quad+ (1 - \beta_0) \frac{1 - \gamma}{1 - \gamma_0} \left( \frac{\phi^n + \nu}{1 + \nu} \right) \end{aligned}$$

(Abbot et al., 2012)

where $\phi$ is the normalized CO₂ partial pressure and $\beta_0$, $\gamma_0$, $n$, and $\nu$ are empirical fractions and exponents.

2. Influence of Tectonics, Erosion, and Mineral Supply

The negative feedback strength of silicate weathering is contingent on the continuous resupply of fresh weatherable minerals, strongly linked to tectonic activity and physical erosion. The classic “kinetic” regime, central to robust feedback, is realized when the weathering rate is controlled by surface reaction kinetics, not by supply limits:

$$F_{w_k} = F_w^* \left(\frac{P_{\mathrm{CO}_2}}{P_{\mathrm{CO}_2}^*}\right)^\beta \dots \exp\left[\frac{E_a}{R_g}\left( \frac{1}{T^*}-\frac{1}{T} \right)\right] \left( \frac{f_{land}}{f_{land}^*} \right)$$

(Foley, 2015)

When the physical resupply rate of unweathered minerals (governed by tectonic uplift, mountain building, glacial erosion, or dust supply) is insufficient, weathering becomes “supply limited” and the stabilizing feedback is lost. In this regime, the weathering rate is capped:

$$F_{w_s} = \frac{A_{earth} f_{land} E \rho_r \chi_{cc}}{\bar{m}_{cc}}$$

with $E$ the erosion rate and other parameters reflecting fresh rock properties.

On planets with vigorous plate tectonics, high rates of uplift and erosion maintain the negative feedback over long timescales. In contrast, stagnant-lid planets or worlds with sparse land area may transition to the supply-limited regime, making climates susceptible to pCO₂ buildup, moist greenhouse states, water loss, or snowball transitions (Foley, 2015, Coy et al., 30 Jul 2025).

3. Sensitivity to Land Fraction and Surface Configuration

A key outcome from models with explicit land–ocean partitioning is the surprising insensitivity of the feedback strength to the exact land fraction, provided that some land ($\gamma > 0$) is exposed:

• For $\gamma \gtrsim 0.01$, climate sensitivity to insolation is almost independent of the specific value of $\gamma$.
• This implies robust feedback and habitable conditions across a wide range of planetary land–water fractions, supporting the extension of “Earth-like” habitable zones to worlds with significantly less emergent land than present Earth (Abbot et al., 2012).

Conversely, on “waterworlds” ($\gamma = 0$), if seafloor weathering lacks direct temperature dependence, there is no effective climatic feedback, narrowing the habitable zone (Abbot et al., 2012). This can be alleviated if a waterworld undergoes water loss, eventually exposing land (“waterworld self-arrest”), allowing the rapid onset of stabilizing continental weathering before complete desiccation.

4. Biotic Enhancement and Lithologic Controls

Biological processes exert a profound influence on global weathering rates:

• The biotic enhancement of weathering (BEW) can increase the silicate weathering flux by 10–100× relative to abiotic baselines at constant pCO₂ and temperature, primarily through increased reactive surface area, acidification, and nutrient cycling by plants and soil organisms (Schwartzman, 2015).
• Models and empirical data suggest that during the Phanerozoic, BEW increased pCO₂ drawdown and helped stabilize the Phanerozoic climate with more efficient feedbacks.

Lithology also matters:

• Different rock types exhibit weathering rates (and pCO₂ sensitivity exponents) that vary by orders of magnitude.
• Continental (felsic) rocks weather at rates 1–2 orders of magnitude lower than oceanic (mafic) lithologies, and thermodynamic constraints can reverse the temperature dependence of weathering in equilibrium–limited regimes, potentially leading to a positive feedback if increasing temperature reduces weathering efficiency (Hakim et al., 2020).

5. Extensions: Mars, Venus, Exoplanets, and Limitations

The carbonate–silicate feedback has wide applicability, but its manifestation varies across planetary contexts:

• On early Mars, limited by low insolation and CO₂ outgassing, the cycle produced episodic glaciation–deglaciation, with warm periods punctuated by rapid weathering/CO₂ drawdown and extended glacial intervals (Batalha et al., 2016).
• On Venus, in the absence of plate tectonics, carbonate–silicate cycling proceeded via weathering and burial of basaltic crust, followed by episodic crustal decarbonation and massive CO₂ release after water loss, driving a rapid transition to uninhabitable conditions (Höning et al., 2021).
• On massive terrestrial exoplanets, pressure– and temperature–dependent mantle viscosity controls degassing rates and thus climate stabilization efficacy, but the feedback remains important for a broad range of planetary masses (Kruijver et al., 2021).
• In the outer habitable zone, hydrologic limitations (“warmer but drier” planets) can cause weathering fluxes to decrease with increasing temperature or CO₂—potentially destabilizing the carbon cycle and triggering runaway transitions (Graham et al., 8 May 2024).

Notably, ocean planets lacking subaerial land cannot support a stabilizing negative feedback if weathering is decoupled from temperature; their CO₂ cycle provides a positive (destabilizing) feedback, compressing the habitable zone (Kitzmann et al., 2015).

6. Practical Applications and Modern Extensions

The principles of the carbonate–silicate cycle underpin the concept and engineering of negative emission technologies such as enhanced rock weathering (ERW) for atmospheric CO₂ removal:

• Agricultural deployment of crushed basalt can deliver 0.23–0.38 Gt CO₂ yr⁻¹ sequestration potential in the US alone, scaling costs down to $100–150 t⁻¹ CO₂ by 2050, with ancillary benefits to nutrient delivery and ozone mitigation (Beerling et al., 2023).
• Rigorous monitoring, reporting, and verification (MRV) frameworks, such as the TiCAT soil–mass-balance method, enable empirical quantification of silicate dissolution and thereby robust validation of ERW carbon removal at field scale (Reershemius et al., 2023).

These applications harness the fundamental coupling between mineral dissolution, atmospheric CO₂ drawdown, and secondary carbonate precipitation, integrating natural feedback into anthropogenic climate control.

7. Prospects and Critical Parameters

The sustainability and efficacy of the carbonate–silicate feedback on geologic and planetary timescales depend on:

• The strength of kinetic vs. supply–limited weathering regimes,
• The availability and resupply of weatherable minerals (tectonic, glacial, aeolian, and seafloor-mediated),
• Biospheric productivity and evolutionary history,
• Internal parameters such as lithology, mantle temperature, and redox states,
• External forcings, including insolation, volcanic outgassing variability, and stellar evolution.

Recent models show that for Earth, the future demise of the terrestrial biosphere is controlled not only by the drawdown of CO₂ to levels inhibiting C₃ plant photosynthesis but also by the potential for weathering sensitivity to slow or reverse this decline, possibly extending complex life by ~1.6–1.9 Gyr until extreme heat, rather than CO₂ starvation, imposes the ultimate limit (Graham et al., 16 Sep 2024). On exoplanets, similar coupled models help define the “complex life habitable zone” and guide the remote detection of habitable conditions via predictive relationships between stellar flux, atmospheric pCO₂, and biosignature gases (Lehmer et al., 2020, Höning et al., 16 Dec 2024).

The carbonate–silicate weathering feedback thus remains a central organizing principle in planetary climate dynamics, exoplanet habitability, and climate mitigation efforts, its operation mediated by deep interactions among geochemistry, hydrology, tectonics, and biological evolution.