IFRS S1 and S2 Explained: ISSB Standards vs ESRS

IFRS S1 and S2 Explained: ISSB Standards vs ESRS

IFRS S1 and IFRS S2 are the first two standards issued by the International Sustainability Standards Board (ISSB). IFRS S1 sets the general requirements for disclosing sustainability-related risks and opportunities that could affect a company's prospects, while IFRS S2 sets specific climate-related disclosure requirements. They take an investor-focused, single (financial) materiality approach, in contrast to the EU's European Sustainability Reporting Standards (ESRS), which use double materiality and serve a broader stakeholder audience.

For UK and Irish finance professionals, both frameworks now matter. The UK has adopted the ISSB standards as the UK Sustainability Reporting Standards (UK SRS), while Irish companies in scope of the EU Corporate Sustainability Reporting Directive (CSRD) report under ESRS. Many groups will touch both regimes, so understanding what each requires, and where they align, is becoming core financial reporting knowledge.

What does IFRS S1 require?

IFRS S1, General Requirements for Disclosure of Sustainability-related Financial Information, is the umbrella standard. It requires an entity to disclose material information about all sustainability-related risks and opportunities that could reasonably be expected to affect its cash flows, access to finance or cost of capital over the short, medium or long term. Key features include:

• Four-pillar architecture: disclosures are organised around governance, strategy, risk management, and metrics and targets, following the familiar TCFD structure.
• Financial materiality: information is material if omitting or misstating it could influence decisions of investors, lenders and other creditors.
• Connectivity: sustainability disclosures must be published at the same time as the financial statements, cover the same reporting entity, and connect to the financial statements where relevant.
• Sources of guidance: in identifying risks and opportunities beyond climate, entities consider SASB standards and other materials as guidance.

What does IFRS S2 require?

IFRS S2, Climate-related Disclosures, applies the same four pillars specifically to climate. It requires disclosure of:

• Governance and strategy: board oversight of climate risk, the effects of climate risks and opportunities on business model and strategy, and the entity's transition plan where one exists.
• Climate resilience: scenario analysis assessing the resilience of the strategy to different climate outcomes.
• Greenhouse gas emissions: Scope 1, Scope 2 and Scope 3 emissions measured in accordance with the GHG Protocol, with Scope 3 covering the full value chain (with reliefs and transition arrangements).
• Metrics and targets: climate targets, the use of carbon credits, internal carbon prices, and the proportion of assets or activities vulnerable to climate risks.
• Industry-based metrics: entities consider SASB-derived industry metrics in deciding what to disclose.

What is the UK SRS and what is its adoption status?

The UK Government, through the Department for Business and Trade, published the final UK Sustainability Reporting Standards, UK SRS S1 and UK SRS S2, on 25 February 2026. The standards are the ISSB standards with a small number of UK-specific amendments, including making the consideration of SASB materials permissive ("may" rather than "shall") and removing the ISSB's fixed effective dates so that timing is set by UK regulation instead.

The current position, as at June 2026, is:

• Voluntary use now: any UK company may report against UK SRS voluntarily from publication, on an all-or-nothing basis requiring full compliance with the standards.
• Listed companies: the Financial Conduct Authority consulted (CP26/5, closed March 2026) on requiring UK-listed companies to report under UK SRS, with climate disclosures under UK SRS S2 expected to become mandatory for financial years beginning on or after 1 January 2027, and broader UK SRS S1 reporting following on a comply-or-explain basis later in the decade. A policy statement is expected in autumn 2026, so final scope and dates should be confirmed against the FCA's published rules.
• Economy-wide application: the Government has indicated it will consult separately on extending requirements to large private companies.

The UK joins more than 30 jurisdictions, including Australia, Canada, Japan, Singapore and Hong Kong, adopting ISSB-aligned standards, which is rapidly making IFRS S1 and S2 the global baseline for investor-focused sustainability reporting.

How do the ISSB standards differ from ESRS?

The headline difference is materiality. ISSB standards use financial materiality only: what matters is the effect of sustainability issues on the company. ESRS uses double materiality: companies must also report their material impacts on people and the environment, regardless of financial effect. From that root difference flow several practical contrasts:

• Audience: ISSB serves investors and creditors; ESRS serves investors plus wider stakeholders, including civil society and regulators.
• Topic coverage: IFRS S2 covers climate in detail, with S1 requiring other material sustainability disclosures by reference to guidance. ESRS provides full topical standards across environment, social and governance matters.
• Volume and prescription: ESRS is more prescriptive and datapoint-heavy, although the EU's Omnibus simplification has substantially reduced mandatory ESRS disclosures, with revised standards expected to apply from 2027 reporting.
• Assurance: CSRD mandates limited assurance over ESRS reporting; assurance under UK SRS is subject to ongoing UK policy development.

Are IFRS S1/S2 and ESRS interoperable?

Largely, yes, for climate. The ISSB and EFRAG have worked deliberately to align the climate-related disclosures, and have published interoperability guidance mapping ESRS E2 climate requirements to IFRS S2. Both frameworks build on TCFD, use the same four-pillar structure, and align definitions for greenhouse gas measurement. In broad terms, a company that complies with the full ESRS climate requirements will produce information substantially consistent with IFRS S2, and vice versa, although each framework has incremental requirements the other does not.

For groups exposed to both regimes, a sensible approach is to:

• Run a double materiality assessment (the financial materiality half largely satisfies the ISSB lens).
• Build one climate dataset, governed once, that feeds both ESRS and IFRS S2/UK SRS disclosures.
• Map residual differences, such as specific ESRS datapoints or ISSB industry metrics, and close them deliberately rather than running parallel processes.

What does this mean for Irish companies?

Ireland sits squarely in the ESRS camp for mandatory reporting: Irish companies in scope of CSRD, as transposed into Irish law, report under ESRS with limited assurance. However, the ISSB standards still matter for Irish finance teams in three situations. First, Irish subsidiaries of UK-listed or other ISSB-jurisdiction parents will be asked to supply IFRS S2-aligned climate data, particularly Scope 1, 2 and 3 emissions and climate risk information, for group reporting. Second, Irish-headquartered groups with international investors increasingly receive requests for ISSB-aligned disclosure even where it is not mandated, because IFRS S1 and S2 are becoming the common language of investor ESG analysis. Third, the EU's Omnibus reforms narrowed CSRD scope considerably, and companies that fell out of scope may choose the voluntary EU standard or an ISSB-aligned approach for the disclosure they still need to make commercially.

The practical takeaway is that the interoperability question is not academic: many Irish and UK finance teams will be running one underlying sustainability data process that has to satisfy two disclosure frameworks, plus bank and customer questionnaires layered on top.

How do the frameworks treat assurance and connectivity?

Both regimes push sustainability information towards financial reporting discipline. CSRD requires limited assurance now, with the possibility of reasonable assurance later. The UK is consulting on its assurance regime, including a voluntary registration framework for sustainability assurance providers. Both frameworks require sustainability disclosures to be consistent with, and published alongside, the financial statements, which means the numbers in the sustainability statement, such as climate-related provisions, impairments and capital expenditure, must reconcile to the accounts. That connectivity requirement is precisely why these standards are landing on the finance function's desk rather than remaining a sustainability team matter.

What should finance professionals do now?

Sustainability reporting is converging on two interoperable baselines, and finance teams are increasingly expected to own the numbers, controls and connectivity to the financial statements. Whether your organisation reports under UK SRS, ESRS or both, the skills are the same: materiality judgement, GHG accounting, scenario analysis and disclosure controls. Structured CPD in ESG and sustainability reporting is the most efficient way to build them before mandatory deadlines arrive.

Study with Learnsignal

Learnsignal's CPD library includes expert-led ESG and sustainability reporting courses covering the ISSB standards, CSRD and the practical skills finance teams need. Stay ahead of UK SRS and ESRS requirements with flexible online learning at Learnsignal CPD.