Decarbonisation 101 Part 2: Turning carbon accounting into science-based targets 

“Good carbon data is the bridge between today’s footprint and tomorrow’s science‑based decarbonisation pathway.” 

Why carbon data and targets matter 

Across the world, countries are adopting net zero pledges and translating them into national climate plans under the Paris Agreement. In parallel, more than ten thousand companies have committed to setting targets through the Science Based Targets initiative to show that their climate ambition is grounded in science rather than marketing.  

This wave of commitments has a very practical consequence: organisations now need reliable, auditable information about their emissions. Carbon accounting is no longer a nice‑to‑have report; it is the backbone of credible carbon management and the starting point for any serious decarbonisation roadmap.  

Regulatory drivers: Why robust data is non‑negotiable 

Several major regulatory regimes already require greenhouse gas disclosures, with more on the way. These include:  

• CSRD in the EU, which mandates detailed greenhouse gas reporting for in‑scope companies.  

• CBAM, which requires exporters to the EU to disclose embedded emissions in certain goods.  

• California’s SB 253 and New York bill 3697 mandate greenhouse gas transparency. 

• Climate‑risk rules aligned with TCFD and ISSB, such as emerging requirements in California and other jurisdictions.  

When a carbon footprint assessment follows a recognised standard, a single dataset can support many of these obligations and reduce duplication of effort.  

Carbon accounting as the foundation 

Part 1 of this series explored how carbon accounting measures, analyses and reports emissions across Scopes 1, 2 and 3. That work provides the baseline: a clear, structured view of where emissions come from and how big they are.  

Without that baseline, it is impossible to evaluate trade‑offs, design credible reduction pathways or track the impact of projects over time. With it, carbon management becomes a strategic discipline rather than a periodic reporting exercise.  

The role of science‑based targets 

Science based targets turn a static inventory into a forward‑looking commitment. In essence, they define how quickly and how far an organisation needs to reduce emissions to align with a 1.5°C or well‑below‑2°C trajectory.  

A 1.5°C trajectory is the most ambitious climate goal. It aims to limit warming to 1.5°C above pre-industrial levels. This requires rapid emissions cuts in the next decade, with a focus on reducing both direct and indirect emissions. Companies must move quickly towards net-zero and rely less on carbon offsets. Achieving this target shows climate leadership and meets the highest expectations from regulators and investors. 

A well-below-2°C trajectory still aligns with the Paris Agreement but is less strict. It allows for slower emissions reductions and more reliance on carbon offsets. Companies can transition at a steadier pace, making this option more accessible for those in the early stages of decarbonisation. While still ambitious, it offers more flexibility and focuses on long-term sustainability with a moderate pace of change. 

To be eligible for validation by the Science Based Targets initiative, a company’s inventory must follow the Greenhouse Gas Protocol and apply consistent, transparent methods. This ensures that reductions claimed against those targets are comparable across sectors and regions, and that progress towards net zero can be tracked over time.  

Building a robust carbon footprint 

Data collection: Getting the basics right 

Once the decision is taken to strengthen carbon management, the immediate challenge is data. Organisations first need to understand who holds which information and in what format. Typical sources include:  

• Finance teams for spend data and supplier records 

• Operations for energy use, fuel consumption and process information 

• Procurement for contract volumes and key vendor details 

• HR and travel providers for commuting and business travel data 

The goal at this stage is not perfection, but coverage. Mapping what exists, where the gaps are and how data flows inside the organisation gives a realistic starting point for a carbon footprint assessment.  

Primary vs secondary data 

Not all data is created equal. Primary data comes directly from meters, invoices or suppliers and tends to be closest to reality. Examples include:  

• kWh of electricity from utility bills 

• Litres of fuel dispensed to fleet vehicles 

• Kilograms of material purchased from a key supplier 

Secondary data involves estimates and assumptions, such as industry averages or extrapolating from incomplete records. While secondary data is less precise, it is often essential when primary information is not yet accessible, particularly in complex supply chains. A pragmatic approach is to use secondary data as a bridge while building relationships that will eventually unlock better information.  

How to calculate? Practical insights 

Overview of calculation approaches 

Once activity or spend data is in place, organisations must decide how to turn it into emissions. There are three main approaches, each with its own balance of effort and accuracy.  

• Supplier‑specific method – uses emissions figures provided by a particular supplier for a product or service. This can be highly accurate but depends on the supplier’s own maturity and willingness to share data.  

• Activity‑based method – multiplies physical quantities (such as kWh, kilometres or kilograms) by appropriate emission factors. This is often the preferred method when good operational data exists.  

• Spend‑based method – estimates emissions from the financial value of goods or services, using emission factors per unit of currency. It is quick to apply and depends mainly on finance data, which is why many organisations use it as a starting point.  

• Estimations and proxies – uses sector data to estimate own emissions. 

In practice, most companies use a mix of these methods across different categories. The important thing is to document choices clearly so that future updates and comparisons remain meaningful.  

Emission factors: Translating data into emissions 

Emission factors link real‑world activities to estimated greenhouse gas output. They express emissions per unit of something measurable, for example per kWh of electricity, per tonne‑kilometre of freight or per euro spent.  

Good practice is to: 

• Select factors from recognised sources, such as government inventories, the GHG Protocol or life‑cycle assessment databases.  

• Match units precisely between data and factors, so that kilograms, litres or currency values line up correctly.  

• Update factors periodically, as electricity grids, fuels and supply chains decarbonise over time.  

With the right factors in place, calculation becomes straightforward: multiply activity data by the relevant factor and convert the result into CO2e to create a consistent view across different gases.  

Common errors to watch out for 

Several recurring issues can undermine an otherwise solid carbon footprint assessment:  

• Double counting, for example using the same spend in both “capital goods” and “purchased goods and services”. 

• Unit mismatches, such as combining kWh data with an emission factor expressed per MWh. 

• Manual‑only processes, where spreadsheets and email threads increase the risk of version errors. 

• Poorly documented assumptions, which make it hard to explain year‑on‑year changes to stakeholders or auditors. 

Recognising these pitfalls early makes it easier to design simple checks and controls into the carbon accounting process.  

Improving quality over time 

No organisation will have perfect data in its first year. A realistic plan focuses on improvement over time, for example by:  

• Prioritising the largest emissions categories for better data or improved methods 

• Shifting from spend‑based approaches towards activity‑based or supplier‑specific data where feasible 

• Introducing light‑touch automation, such as standard data templates or integrations with finance systems 

This gradual strengthening of the dataset supports more confident carbon management decisions year after year.  

From footprints to target‑driven action 

Using data to shape science‑based targets 

Once the main emissions sources are quantified, the organisation can see where it has the greatest leverage. Hotspot analysis typically reveals a small number of categories or suppliers that drive most of the footprint. 

These insights are vital when designing science based targets. They help define which scopes and categories to prioritise, what level of reduction is realistic in the short and long term, and where collaboration with partners will be essential. With this information, a company can submit targets to the Science Based Targets initiative that reflect both scientific pathways and operational reality.  

Download our factsheet to get more insights specific to science-based target setting. 

Integrating targets into strategy and governance 

Targets only drive change if they influence day‑to‑day decisions. That means weaving them into:  

• Capital allocation and investment criteria 

• Procurement policies and supplier engagement plans 

• Performance objectives and remuneration frameworks 

When these elements line up, science‑based targets become a compass for the wider organisation rather than a standalone sustainability project. Over time, this alignment supports a credible trajectory towards net zero, guided by clear carbon accounting and robust governance.  

A continuous improvement loop 

Each annual cycle of carbon footprint assessment provides new information about progress, obstacles and emerging opportunities. This feedback can be used to refine calculation methods, improve data quality and update carbon management initiatives.  

In this way, the combination of high‑quality data, thoughtful methodologies and science‑based targets creates a self‑reinforcing loop: better insight leads to better decisions, which in turn lead to deeper emissions reductions and more resilient business models. 

Take action now 

Decarbonisation is a long‑term journey, but the first step can be taken today. Nexio Projects helps organisations move confidently from basic compliance to a clear, purpose‑driven sustainability strategy, combining integrated ESG advisory with deep expertise in climate and emissions reduction.  

Our specialists design and implement science based targets, build practical decarbonisation roadmaps and set up data management systems that fit your organisation’s reality rather than forcing a one‑size‑fits‑all approach. With a track record of delivering SBTi‑aligned targets and robust carbon strategies across sectors, the team is ready to translate your ambition into concrete plans and measurable outcomes. 

Ready to get started? Contact us for a free consultation to explore where you are today and what your next steps could be. 

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