Updated October 21 with timeline of events

The ART Secretariat welcomes third-party review of publicly available information as an important aspect of maintaining transparency and confidence in carbon markets. Recently, this transparency led to the identification by a third-party of a calculation error involving an incorrect spreadsheet cell reference used to calculate the volume of 2023 credits issued to Guyana. The error was in the number used in the calculation, not the underlying forest monitoring data or the program’s activities.

The error was brought to ART’s attention initially by Climate Focus and was addressed through an internal review by the ART Secretariat followed by the implementation of ART’s procedure for verification and remedy of the error as outlined in the TREES Validation and Verification Standard (Section 3.13) and the ART Registry Terms of Use (Section 8.h.i).

The Government of Guyana was immediately informed and has been fully cooperative and acted promptly to facilitate the correction including transferring 4 million unsold 2023 credits into an ART Registry Administrator account, securing the credits required for the correction. No transacted or contracted volumes have been impacted by this process. While not applicable in this instance, the Terms of Use does include options for remedy of an error where volumes issued in error have already been transacted as transacted volumes would not be invalidated.

The final adjustment to the 2023 credit issuance volume is being independently verified as part of the ongoing verification of Guyana’s 2024 results. Once verified, ART will cancel the appropriate number of 2023 credits to remedy the over-issuance and return the balance to Guyana.

Timeline of Events

In early 2026, ART was contacted by Climate Focus with questions about some of the numbers used to calculate the 2023 TREES Credit volume issued to Guyana. ART did an internal review of the numbers in question and did not find any errors in those figures. In the spring, Climate Focus asked ART about the inputs and results of the Monte Carlo analysis, a standard statistical technique used to account for uncertainty in emissions estimates, helping ensure that carbon credits are issued on a conservative basis. In line with ART’s practice of referring requests for additional detailed program information to Participants, ART provided Climate Focus with an introduction to the Government of Guyana to answer questions.

On August 26th, Climate Focus raised to ART a concern about the specific cell-reference issue as a possible source of an error in the credits issued to Guyana. ART immediately launched an internal review, and once the existence of the error was confirmed, ART notified the Government of Guyana and AENOR, the independent Validation and Verification Body (VVB), initiating the published corrective action process in TREES and the Terms of Use. Guyana re-ran the Monte Carlo analysis, calculating the estimated over-issuance volume to be 3.7 million tons, and transferred a conservative volume of 4 million unsold 2023 credits into an ART Registry Administrator account to remove those credits from circulation.

It was while these required corrective actions were in process that BeZero contacted ART about the crediting error. ART informed BeZero that the error had been identified, that the remedy was being implemented and that the calculation of the over-issuance will be verified as part of the Guyana 2024 verification process, resulting in ART cancelling the verified volume of over-issued 2023 credits to remedy the error.

ART Actions to Prevent Future Errors

ART continually reviews its processes to assess opportunities for improvement. In August 2026, ART published the revised TREES Validation and Verification Standard v.3.0, which codifies new and more detailed competency and procedural requirements for VVBs and outlines additional oversight elements conducted by the ART Secretariat.

These changes resulted from ART’s experience with the initial validations and verifications under TREES as well as feedback from stakeholders. While these changes were not in response to any specific error detected, they were designed to strengthen the validation and verification process by making the process more prescriptive with greater oversight from the ART Secretariat.