From its inception, Puro.earth has held a clear and pragmatic vision: to harmonize the climate impact of various carbon removal activities in a way that fosters trust, liquidity, and scalability in the market. This foundational philosophy has guided every step of our standard development, with the ultimate goal of enabling commoditization and fungibility across different carbon removal methods. Why? Because only then can we fully leverage the robust infrastructure and tools that have been developed for other commodities markets—markets that have proven their ability to scale and serve global needs efficiently. 

Moving Beyond Complexity: Durability as a Threshold 

In 2019, when we launched the first version of the Puro Standard, we made a deliberate decision to avoid the complexities of “ton-year” accounting. While ton-year approaches attempt to value temporary storage of carbon, they introduce ambiguity and reduce comparability across methods. Instead, we chose to adopt a minimum threshold for carbon storage durability. 

At the time, we selected 50 years as the initial baseline. However, we quickly recognized that this figure was inconsistent with scientific understandings of carbon dioxide’s atmospheric lifetime and with frameworks such as the GWP100 metric, which reflects the warming impact of CO₂ over a 100-year period. In light of this, in December 2022 Puro Standard Advisory Board made a decisive move: to discontinue all methodologies with a durability below 100 years. 

A Tiered System for Durability: CORC100+, CORC1000+, CORC200+ 

Today, our certification system includes clear and transparent categories of storage durability: 

1. CORC100+: Storage guaranteed to last at least 100 years. 

2. CORC1000+: Storage guaranteed to last at least for millennia. 

3. CORC200+: Storage guaranteed to last at least for several centuries. This newly introduced category is aligned with emerging EU quality criteria for high-durability removals and considered permanent removal in the EU framework. 

All of these categories are relevant removals over policy-relevant timescales to combat climate change. 

Enabling Future Compliance: CORC200+ and the EU ETS 

The CORC200+ category plays a particularly important role in preparing for integration with the EU Emissions Trading System (EU ETS), the world’s largest carbon compliance market. The European Union has introduced the Carbon Removal Certification Framework (CRCF) as a foundational element to define and certify removals that may one day contribute to meeting compliance obligations. 

Puro.earth is committed to supporting this regulatory evolution. By introducing CORC200+, we ensure that projects meeting this higher durability threshold can be eligible for recognition under CRCF-aligned mechanisms in the future. This alignment is essential to unlocking large-scale investment, especially from industries currently regulated under the EU ETS that may eventually be allowed—or required—to use certified removals as part of their decarbonization strategies. 

As the CRCF becomes operational and links to compliance markets are clarified, we believe CORC200+ will provide a bridge between today’s voluntary markets and tomorrow’s compliance-aligned carbon removal economy. 

Durability Is a Guarantee, Not a Limit 

It’s important to underscore that these durability categories express the minimum thresholds, not expiration dates. For example, in biochar projects, we quantify how much carbon remains in the soil after the primary degradation phase. The material continues to degrade slowly, but in all cases, most of it is believed to persist far beyond the threshold. Likewise, mineralisation projects sequester CO₂ for geological timescales, even millions of years, and the category name is 1000+. Our role as a certification standard is to ensure that, at a minimum, the certified tons of CO₂ remain out of atmospheric circulation for the guaranteed duration, based on current scientific consensus and conservatism thresholds suited for carbon markets. 

Building Confidence Through Conservative Claims 
 
Our approach to durability is grounded in scientific rigor—but also in humility. Especially when working with new data or novel carbon removal pathways, Puro.earth applies conservative assumptions to durability estimates. This ensures that climate claims remain credible and withstand scrutiny, even as the science continues to mature. 

Take biochar as a case in point. When we first introduced the methodology in 2019, we applied a CORC100+ classification—aligning it with the Global Warming Potential 100 (GWP100), which is used by the Greenhouse Gas Protocol (GHG Protocol) as a standard way to quantify the climate impact of emissions and removals. Now, as the methodology undergoes its latest update, five years of project data and scientific advances provide a strong basis to consider increasing the durability classification to CORC200+. This proposed change will be reviewed by our Advisory Board following the public consultation. If approved, it would reflect growing confidence in biochar’s long-term stability in soils. 

Importantly, our approach remains measured: despite some studies suggesting a significant proportion of biochar may endure for millennia, we have not adopted such claims as the evidence, while promising, is not yet sufficiently robust or operationalised for use in a carbon market context. 

By applying prudence when the data is still developing—and only increasing durability thresholds once the evidence base is deemed strong enough—we uphold the market’s trust and ensure that every CORC issued reflects a verified, conservative estimate of climate impact. 

What Certification Quality Means 

While durability is foundational to the Puro.earth certification philosophy, it is by no means the only criterion. Additional pillars—such as additionality, environmental and social safety, monitoring, quantification accuracy, risk mitigation, and co-benefits—are equally essential to maintaining high integrity and public trust. These aspects deserve their own in-depth discussion, and we will explore them in a future post. 

For now, we remain committed to maintaining a robust, transparent, and trustworthy carbon removal ecosystem—one that can scale with the urgency of the climate challenge and serve the diverse needs of buyers, suppliers, and regulators alike.