Fractional CSO vs Big Four Consulting
What's the right sustainability support model for your organisation?
As sustainability and climate disclosure requirements increase, particularly with ASRS compliance, many organisations ask the same question: Do we engage a Big Four consultancy, or do we bring in a Fractional Chief Sustainability Officer?
Both models have value. The right choice depends on what you need, how quickly you need it, and how embedded sustainability needs to be within your business.
The Two Models at a Glance
Best suited to:
- Large, one-off transformation programs
- Highly complex global reporting exercises
- Organisations seeking brand reassurance for external stakeholders
Best suited to:
- Organisations needing ongoing senior sustainability leadership
- Boards and executives navigating ASRS compliance and climate disclosure
- Businesses wanting sustainability embedded into strategy, governance, and decision-making
Leadership vs Project Delivery
Big Four Consulting
- • Operates on a project-based model
- • Senior partners sell the work; delivery is often handled by larger teams
- • Focused on defined scopes, milestones, and handover
Fractional CSO
- • Acts as part of your leadership team
- • Provides hands-on guidance, coaching, and decision support
- • Owns outcomes over time, not just deliverables
- • Proactively builds internal capability
Bottom line: A Fractional CSO leads sustainability; Big Four firms deliver projects.
Cost Structure & Value
Big Four Consulting
- • High daily rates, often justified by brand and scale
- • Leveraged delivery model, where senior partners oversee work delivered by larger teams
- • Commercial incentives aligned to defined scopes and change requests
- • As requirements evolve, additional work is typically managed through formal scope extensions, which can drive costs up
Fractional CSO
- • Fixed or predictable monthly retainer
- • Direct access to senior sustainability leadership
- • No leverage layers and no commercial incentives to create scope creep
- • Flexibility to adapt as priorities evolve without constant re-scoping
$5,000–$8,000
per day
Big Four Consulting
$8,000–$15,000
per month
Fractional CSO
$250,000+
per year
Full-time CSO
This allows organisations to access senior sustainability leadership without the cost or rigidity of a full-time executive or large consulting program.
Bottom line: Fractional CSO support delivers executive-level expertise at a fraction of the cost, with incentives aligned to outcomes rather than expanded scope.
A mid-sized manufacturing business was previously relying on project-based ESG consulting to manage sustainability reporting and climate disclosure.
By shifting to a Fractional CSO model, the organisation:
- Reduced its external ESG consulting spend by approximately 60%
- Gained consistent senior leadership oversight
- Improved internal capability and decision-making
- Used ASRS preparation to inform broader risk and operational improvements
The result was lower cost, better continuity, and stronger business outcomes, not just compliant reporting.
ASRS & Climate Disclosure Readiness
For many organisations, ASRS can feel like another compliance burden. We see it differently, as an opportunity to build a stronger, more resilient, and more competitive business.
Big Four Consulting
- • Strong technical and reporting capability
- • Often focused on interpreting requirements and producing compliant disclosures
- • Sustainability and climate disclosure treated primarily as a compliance task
Fractional CSO
- • Translates ASRS requirements into practical business decisions
- • Uses ESG to strengthen resilience, risk management, and long-term performance
- • Builds governance, accountability, and internal ownership
- • Treats compliance as a platform for competitive advantage, not a box-ticking exercise
Bottom line: A Fractional CSO helps you meet ASRS requirements while using ESG to build a stronger, more resilient, and more competitive business.
Why This Matters for Mid-Sized Businesses
Mid-sized organisations don't have the luxury of treating sustainability as a standalone compliance project.
ASRS, climate risk, and ESG decisions directly affect costs, access to capital, customers, talent, and long-term resilience.
A Fractional CSO approach ensures sustainability is used to improve how the business operates and competes, not just to meet minimum reporting requirements, but to support better decisions and long-term performance.
Business Integration
Big Four Consulting
- • External advisor model
- • Sustainability often sits alongside the business, not within it
- • Limited day-to-day influence once the project ends
Fractional CSO
- • Embedded in leadership rhythms
- • Works across finance, risk, operations, and strategy
- • Ensures sustainability informs real business decisions
Bottom line: Fractional CSO support embeds sustainability into how your business actually runs.
Side-by-Side Comparison
| Area | Fractional CSO (ESG Strategy) | Big Four Consulting |
|---|---|---|
| Model | Embedded leadership | Project-based |
| Cost | Predictable retainer | High daily rates |
| Delivery | Senior-led, hands-on | Leveraged teams |
| ASRS support | Strategic + practical | Technical + reporting |
| Governance | Built internally | Often externalised |
| Flexibility | High | Low once scoped |
| Long-term ownership | Yes | No |
A Fractional CSO model is ideal if you:
- Don't need (or want) a full-time CSO yet
- Want board-level sustainability leadership without Big Four overheads
- Need ongoing ASRS and climate disclosure support, not a one-off report
- Want sustainability embedded into strategy, not treated as a compliance exercise
Big Four firms may be suitable if you:
- Are running a large-scale, global transformation program
- Need a brand-led assurance signal for capital markets
- Have a clearly defined, short-term reporting requirement with limited internal change
A Smarter Hybrid Approach
Common in Practice
Many organisations:
This approach avoids dependency, controls cost, and builds real internal capability.
Why ESG Strategy's Fractional CSO Model Is Different
ESG Strategy's Fractional CSO support is led by Lee Stewart, a senior sustainability practitioner with over 20 years' experience across corporate strategy, ESG, and sustainability leadership.
Lee has:
- Served as Head of Sustainability for multi-billion-dollar organisations
- Worked directly with boards, CEOs, and CFOs
- Advised organisations across Australia, New Zealand, and the Pacific
- Supported governments and businesses on climate strategy, disclosure, and resilience
This ensures advice is commercial, practical, and grounded in real-world decision-making, not theoretical frameworks.
Not sure which model is right for you?
We're happy to provide an objective view, even if that means recommending a hybrid or alternative approach.
We don't treat ESG as a compliance obligation, we use it to help businesses perform better, manage risk, and compete more effectively.