8 JULY 2026
Since 15 June 2026, the European Central Bank has been quietly discounting the corporate bonds banks pledge as collateral, based on how exposed each issuer is to the shock of a low-carbon transition. It is the first time climate risk has been priced directly into the mechanics of Eurosystem lending, and it is already drawing both praise and pointed criticism. Every time a eurozone bank borrows from the European Central Bank, it hands over collateral, typically government bonds, covered bonds or corporate debt, as security for the loan. The ECB has never taken that collateral at face value: it applies “haircuts”, shaving a percentage off the market price to build in a safety margin against the asset losing value before the loan is repaid. Those haircuts have historically been calibrated using decades of historical price data. But climate change does not behave like a normal risk. It is unprecedented, uncertain, and could hit specific sectors hard with very little historical precedent to draw on. That gap is what the ECB’s new “climate factor” is designed to close. Introduced on 15 June 2026 and explained in a blog post published on 7 July by ECB risk experts Dirk Broeders and Daniel Gybas, the climate factor is an additional, forward-looking discount applied specifically to corporate bonds, on top of the ordinary haircut, based on how exposed the issuing company is to climate transition shocks.
Why the ECB felt it needed a new tool
The ECB’s own explanation is candid about the limits of its existing risk controls:
“Climate change introduces unprecedented, uncertain and potentially severe economic and financial consequences for firms that may not be reflected in the historical price data that is used to calibrate asset haircuts.”
A shift in climate policy, a leap in clean technology, or a change in consumer preferences could all suddenly reprice a company’s assets, and standard haircuts, built on historical volatility, would not see it coming. The stakes for the ECB are self-protective rather than purely environmental. If a transition shock hits a bond issuer hard enough, the post-haircut value the ECB assigned to that bond could turn out to be too generous, leaving the Eurosystem exposed to losses if the borrowing bank defaults. The climate factor is framed explicitly as a way to “protect the ECB’s balance sheet against unexpected climate transition shocks,” not as an industrial policy lever, even though its effects ripple outward into the cost of capital for high-carbon issuers.
How the number is actually calculated
The mechanism works in two steps. First, the ECB builds an “uncertainty score” for every corporate bond that a bank could use as collateral. That score is the product of three components. The stressor component estimates how hard a transition shock would hit a given sector, on the logic that utilities, for instance, would take a bigger hit than software firms. Exposure is measured at the level of the individual company, using its greenhouse gas emissions, decarbonisation targets and the quality of its climate disclosures, since two firms in the same sector can be positioned very differently for the transition. Vulnerability is measured at the level of the specific bond, using the square root of its residual maturity, on the reasoning that longer-dated debt has more of its future cash flows exposed to transition developments that haven’t happened yet.
Second, that uncertainty score, which in raw form could run to very large numbers, is rescaled by the Governing Council into a narrow climate factor that functions just like a normal haircut. The ECB’s own worked example makes the mechanics concrete: a bond with a market value of €100, a standard haircut of 10% and a climate factor of 0.978 lets a bank borrow €100 × (1 – 0.10) × 0.978, or €88, instead of the €90 it could have borrowed before the climate factor existed. A €2 difference on a single bond looks trivial, but multiplied across a bank’s entire book of high-carbon collateral, it is a real and growing cost of holding transition-exposed assets. The ECB’s data shows this is not evenly distributed. Bonds from the utility, materials and transportation sectors cluster toward low climate factors, reflecting their capital intensity, regulatory sensitivity and reliance on fossil fuels, while software and consumer services bonds sit toward the high end, largely insulated from transition risk. But the ECB also stresses that the spread within each sector is wide: a utility with a credible transition plan and strong disclosure can still score better than a peer that discloses little and has no roadmap to net zero.
A narrower move than it might sound
The ECB is not alone in making this shift. Just weeks earlier, on 11 June 2026, the Bank of England moved in a related but distinct direction, announcing that bonds from companies active in coal mining would no longer be eligible as collateral at all, with new transition-risk haircut add-ons for other exposed sectors following from 31 October. Where the ECB’s approach discounts risk on a sliding scale, the BoE opted to draw a harder line for the highest-carbon activity, excluding it outright, a distinction that has not gone unnoticed by campaigners.
“It’s particularly significant that the bank will exclude eligibility for sectors particularly exposed to climate-related transition risks, which sets an important precedent. However, the effectiveness of the measures will depend upon their design.” – Ellie McLaughlin, Positive Money
David Barmes of the Centre for Economic Transition Expertise at the London School of Economics framed the BoE’s move as confirmation of a broader shift already under way: the central bank had previously applied climate-related adjustments to the mortgages that make up the bulk of its collateral pool, and this update extends the same precautionary logic to corporate bonds, even though they are only lightly used as collateral for now.
What critics say is still missing
The reaction from climate finance campaigners has been one of qualified welcome rather than celebration. Clarisse Murphy, a central banks campaigner at Reclaim Finance, called the climate factor “a good idea” in an analysis published by Green Central Banking, while identifying three specific gaps she argues the ECB needs to close.
“The climate factor could be a powerful tool to tackle the carbon bias in the collateral framework, potentially restricting indirect support for the worst polluters. But to achieve this, the ECB needs to address some apparent weaknesses in the way the scheme is implemented.” -Clarisse Murphy, Reclaim Finance
The first gap is transparency. The ECB does not plan to publish the climate factor assigned to individual assets, nor the key parameters, such as the minimum permitted value, that determine how harshly an asset can be discounted. Without that data, external researchers and campaigners have no way to independently verify whether the tool is working as intended.
The second is timing. Climate factors are currently recalculated only once a year. An asset that becomes eligible as collateral between those annual updates is assigned a median score by default, which may bear little relation to its actual transition exposure. Murphy argues this is a solvable problem, since the underlying sector and company data needed to score most assets already exists, meaning the ECB could in principle calculate a bond’s climate factor automatically the moment it becomes eligible, rather than waiting for the next scheduled update.
The third, and most structural, critique is scope. As designed, the climate factor applies only to corporate bonds, which make up less than 5% of the assets eurozone banks currently pledge as collateral. The ECB itself frames this as a deliberate first step, focused on the asset class where implementation is most tractable, before extending the approach to others. Reclaim Finance has argued that credit claims, one of the most commonly pledged collateral types, would be a logical next asset class, since a climate factor for credit claims could lean primarily on sector-level data and avoid the company-specific disclosure gaps that make other asset types harder to score.
There is also an open question the ECB has not fully answered: whether the size of the discount is large enough to actually change bank behaviour. All carbon-intensive assets remain eligible as collateral under the climate factor, just at a reduced value, whereas the BoE’s coal exclusion removes eligibility altogether for that one activity. If the climate factor’s discount is too small relative to a bank’s other funding costs, it may register as a compliance formality rather than a genuine disincentive to hold high-carbon debt.
A first step, not a finished framework
The ECB has been explicit that this is not a static rule. Following the 15 June introduction, the Governing Council will review the climate factor’s scope and calibration on an ongoing basis, updating it as climate data improves, regulation evolves and risk assessment methods mature. That review cycle is precisely where the current debate will play out: whether transparency improves, whether the update frequency shortens from annual to automatic, and whether the tool’s reach eventually extends beyond corporate bonds into the rest of the collateral pool. For now, the climate factor stands as a modest but symbolically significant marker: one of the world’s most influential central banks has concluded that climate transition risk is a financial risk, worth pricing into its own operations, not just a topic for its research papers. Whether that number is big enough, transparent enough, or broad enough to change how the financial system treats high-carbon debt is the question campaigners, and rival central banks, will be watching closely over the next annual review cycle.
Sources
Broeders, D. and Gybas, D. (2026) ‘Climate factors: how the ECB tackles climate uncertainty in its collateral framework’, The ECB Blog, 7 July. https://www.ecb.europa.eu/press/blog/date/2026/html/ecb.blog20260707~bb81f1b45e.en.html
Murphy, C. (2026) ‘The ECB’s climate factor: a good idea that deserves better implementation’, Green Central Banking, 6 July. https://greencentralbanking.com/2026/07/06/ecb-climate-factor-good-idea-deserves-better-implementation/
Thomasson, E. (2026) ‘BoE to incorporate climate risks into collateral framework’, Green Central Banking, 17 June. https://greencentralbanking.com/2026/06/17/boe-climate-risks-collateral-framework/
