Why Green Software Matters for UK Businesses
| Driver | UK Requirement | Who It Affects | Urgency |
|---|---|---|---|
| SECR (legal) | Large UK companies (250+ employees or £36M+ turnover) must report Scope 1/2/3 emissions including cloud | Large UK companies — mandatory | Now — SECR mandatory since 2019 |
| Net Zero commitments | UK government Net Zero 2050 target; many UK companies have made voluntary Net Zero commitments earlier | Companies with Net Zero pledges | Varies — 2030–2050 targets |
| SBTi corporate targets | Science Based Targets initiative: corporate Net Zero commitment includes Scope 3 (cloud emissions are Scope 3) | SBTi-committed companies | Now — ongoing measurement required |
| Investor ESG requirements | ESG reporting frameworks (TCFD mandatory for large UK companies) — Scope 3 cloud emissions material for software companies | Listed and PE-backed UK tech companies | TCFD mandatory for large/listed firms |
| Supply chain requirements | Enterprise procurement: UK enterprises increasingly require suppliers to report carbon emissions | UK tech suppliers to enterprise | Growing — becoming procurement standard |
Carbon-Aware Cloud Architecture
| Principle | Carbon Impact | Implementation | UK SECR Category |
|---|---|---|---|
| Right-size compute | Oversized instances waste energy even when idle | Auto Scaling + Fargate (no idle EC2), instance type right-sizing quarterly | Scope 3 (Category 8 — upstream cloud) |
| Efficient code | Poorly written code uses more CPU → more energy | Algorithm optimisation, database query tuning, unnecessary API calls removed | Scope 3 |
| Data transfer minimisation | Data transfer = network energy | CloudFront CDN (reduce origin requests), image compression, API response caching | Scope 3 |
| Batch processing in off-peak hours | Carbon intensity of UK grid varies by hour (lower overnight) | AWS EventBridge cron: batch jobs scheduled 02:00–06:00 UTC (lowest UK grid carbon intensity) | Scope 3 |
| Efficient storage | S3 data costs energy to store | S3 lifecycle policies (Intelligent-Tiering, Glacier for archival), deletion of unused data | Scope 3 |
| Serverless for idle workloads | Lambda: zero energy when not running (vs EC2/ECS always-on) | Lambda for event-driven, cron, webhooks — ECS for always-on services only | Scope 3 |
Software Carbon Intensity (SCI) — Green Software Foundation
Example: an API processing 1,000 requests/day consuming 0.5 kWh at 200 gCO2eq/kWh = 100g CO2eq/day = 36.5 kg CO2eq/year. SCI: 36.5 kg CO2eq per 365,000 requests = 100 mg CO2eq/request.