Carbon Credit Tracking Smart Contract

A comprehensive Clarity smart contract for transparent tracking of carbon credit lifecycle and verification on the Stacks blockchain.

Overview

This smart contract enables organizations to mint, track, and verify carbon credits throughout their entire lifecycle. It provides a transparent and immutable record of carbon credit generation, verification, trading, and retirement phases, ensuring authenticity and preventing double-counting.

Features

• Lifecycle Tracking: Complete tracking of carbon credits from generation to retirement
• Multi-Standard Verification: Support for major verification standards (Verra, Gold Standard, CDM, Climate Action Reserve)
• Immutable Records: Blockchain-based immutable audit trail
• Access Control: Role-based permissions for different operations
• Verification Bodies: Accredited verification body management
• Phase Management: Structured phase transitions with validation

Carbon Credit Phases

The contract tracks four distinct phases in a carbon credit's lifecycle:

1. PHASE_GENERATED (1): Initial creation of the carbon credit
2. PHASE_VERIFIED (2): Credit has been verified by an accredited body
3. PHASE_TRADED (3): Credit has been traded or transferred
4. PHASE_RETIRED (4): Credit has been retired/used to offset emissions

Verification Standards

The contract supports four major carbon verification standards:

1. VERIFICATION_VERRA (1): Verra Verified Carbon Standard (VCS)
2. VERIFICATION_GOLD (2): Gold Standard
3. VERIFICATION_CDM (3): Clean Development Mechanism
4. VERIFICATION_CLIMATE (4): Climate Action Reserve

Contract Functions

Public Functions

mint-credit

(mint-credit (credit-id uint) (initial-phase uint)) -> (response bool uint)

Creates a new carbon credit with the specified ID and initial phase.

Parameters:

• credit-id: Unique identifier for the credit (1-1,000,000)
• initial-phase: Initial phase (typically PHASE_GENERATED)

Authorization: Contract controller or any user (for PHASE_GENERATED only)

update-credit-phase

(update-credit-phase (credit-id uint) (new-phase uint)) -> (response bool uint)

Updates a credit's phase in its lifecycle.

Parameters:

• credit-id: Credit identifier
• new-phase: New phase to transition to

Authorization: Contract controller or credit generator

add-verification-body

(add-verification-body (validator principal) (verification-type uint)) -> (response bool uint)

Adds an accredited verification body for a specific verification standard.

Parameters:

• validator: Principal address of the verification body
• verification-type: Type of verification they're accredited for

Authorization: Contract controller only

add-verification

(add-verification (credit-id uint) (verification-type uint)) -> (response bool uint)

Adds verification to a carbon credit.

Parameters:

• credit-id: Credit to verify
• verification-type: Type of verification being applied

Authorization: Accredited verification bodies only

revoke-verification

(revoke-verification (credit-id uint) (verification-type uint)) -> (response bool uint)

Revokes a verification from a carbon credit.

Parameters:

• credit-id: Credit to revoke verification from
• verification-type: Type of verification to revoke

Authorization: Contract controller or original validator

Read-Only Functions

get-credit-lifecycle

(get-credit-lifecycle (credit-id uint)) -> (response (list 10 {phase: uint, timestamp: uint}) uint)

Returns the complete lifecycle history of a carbon credit.

get-credit-phase

(get-credit-phase (credit-id uint)) -> (response uint uint)

Returns the current phase of a carbon credit.

verify-credit-authenticity

(verify-credit-authenticity (credit-id uint) (verification-type uint)) -> (response bool uint)

Checks if a credit has valid verification for a specific standard.

get-verification-details

(get-verification-details (credit-id uint) (verification-type uint)) -> (response (optional {validator: principal, timestamp: uint, verified: bool}) uint)

Returns detailed verification information for a credit.

Error Codes

• ERR_UNAUTHORIZED (1): Caller not authorized for this operation
• ERR_INVALID_CREDIT (2): Invalid or non-existent credit ID
• ERR_PHASE_UPDATE_FAILED (3): Phase update operation failed
• ERR_INVALID_PHASE (4): Invalid phase specified
• ERR_INVALID_VERIFICATION (5): Invalid verification type or details
• ERR_VERIFICATION_EXISTS (6): Verification already exists for this credit

Usage Examples

Minting a New Carbon Credit

;; Mint a new carbon credit in the generated phase
(contract-call? .carbon-credit mint-credit u12345 u1)

Adding a Verification Body

;; Add Verra as a verification body (contract controller only)
(contract-call? .carbon-credit add-verification-body 'SP1HTBVD3JG9C05J7HBJTHGR0GGW7KX0ET5AJ7B u1)

Verifying a Carbon Credit

;; Verify credit 12345 with Verra standard (must be called by accredited verifier)
(contract-call? .carbon-credit add-verification u12345 u1)

Updating Credit Phase

;; Move credit to verified phase
(contract-call? .carbon-credit update-credit-phase u12345 u2)

Checking Credit Authenticity

;; Check if credit 12345 has Verra verification
(contract-call? .carbon-credit verify-credit-authenticity u12345 u1)

Data Structures

Credit Record

{
  generator: principal,      ;; Original credit generator
  current-phase: uint,       ;; Current lifecycle phase
  lifecycle: (list 10 {...}) ;; Complete phase history
}

Verification Record

{
  validator: principal,  ;; Verification body that validated
  timestamp: uint,       ;; When verification was added
  verified: bool         ;; Current verification status
}

Security Considerations

1. Access Control: Strict role-based access control prevents unauthorized operations
2. Validation: Comprehensive input validation for all parameters
3. Immutable History: Lifecycle events are append-only for audit integrity
4. Double-Spending Prevention: Verification existence checks prevent duplicate verifications
5. Principal Validation: Prevents system principals from being used as validators

Deployment

1. Deploy the contract to your Stacks network
2. The deployer automatically becomes the contract controller
3. Add verification bodies using add-verification-body
4. Begin minting and tracking carbon credits

Integration

This contract can be integrated with:

• Carbon offset marketplaces
• Corporate sustainability platforms
• Compliance and reporting systems
• Environmental monitoring applications

Limitations

• Maximum 10 lifecycle events per credit
• Credit IDs limited to range 1-1,000,000
• Maximum list length constraints apply to lifecycle tracking

Contributing

When contributing to this contract:

1. Ensure all functions include proper validation
2. Maintain backward compatibility
3. Add comprehensive test coverage
4. Update documentation for any new features