Carbon is the headline metric for data centre sustainability for an obvious reason. It is reported, it is regulated, it is auditable, it ties directly to a number on a balance sheet. It is also incomplete. The full environmental and social footprint of a server includes several dimensions that carbon does not, on its own, capture.

A proper lifecycle assessment of server hardware needs to account for all of them. Here is what that actually covers.

What LCA measures

Lifecycle assessment (LCA) is a discipline borrowed from broader product sustainability work and adapted for IT hardware. Its basic principle is to compare like for like, functional unit against functional unit, much the way Interact compares servers in terms of compute power delivered per Watt of electrical energy used. Once functionality is defined, the variables get layered in.

On the environmental side, the variables divide into resources consumed and emissions created. The list is longer than it first appears:

  • Carbon: scope 1, 2 and 3, across manufacture, use phase and end of life
  • Water: extraction in mining, processing in fabrication, cooling during operation
  • Toxicity: chemical and heavy-metal exposure across mining, manufacture and disposal
  • Materials depletion: notably Critical Raw Materials (CRMs), a list the EU monitors at 30 substances, several of which face supply constraints within the next decade

On the social side, lifecycle work increasingly draws on the principles of the UN Global Compact: working conditions in the supply chain, human rights exposure across mining and manufacturing regions, the labour standards of subcontractors several tiers below the visible manufacturer.

The discipline's intellectual frame is planetary boundaries: the conditions under which the earth can replenish what it loses, set against the social minimum every individual needs to have. Sustainable, in this framing, means staying inside both at once.

The nine boundaries

The planetary boundaries framework, developed by the Stockholm Resilience Centre, identifies nine biophysical thresholds within which humanity has reliably operated for the last 10,000 years:

  • Climate change
  • Ocean acidification
  • Stratospheric ozone depletion
  • Nitrogen and phosphorous flows
  • Freshwater depletion
  • Land system change
  • Biodiversity loss
  • Atmospheric aerosol loading
  • Chemical pollution and novel entities

The most recent comprehensive assessment (Wang-Erlandsson et al, 2022) found that humanity is now exceeding the safe operating space for six of the nine. Two of the remaining three have not yet been satisfactorily measured. Climate change, the boundary that gets the most attention, is one of the six already breached.

The implication for any sustainability assessment of IT hardware is that carbon, while critical, is one dimension among many. The water cost of fabrication. The chemical and toxicity footprint of disposal. The biodiversity impact of CRM mining. Each of these maps directly to a planetary boundary that is either breached or close to it. Procurement decisions made on carbon alone leave most of the picture unmeasured.

Why this matters for procurement

The practical reason a data centre buyer should care about all of this is that the carbon arithmetic alone increasingly understates the case for circular and refurbished options. A new server's embodied carbon footprint can equal or exceed the carbon saved by running it instead of a refurbished alternative. The carbon comparison alone also misses the water saved, the CRMs not extracted, the toxic exposure avoided, and the supply-chain risk not added.

Account for those, and the case for buying carefully on lifecycle terms rather than narrowly on operational efficiency gets harder to argue against. The procurement decision that looks neutral on carbon often comes out distinctly better on every other dimension.

What this looks like in practice

LCA is not a perfect discipline. The data is harder to come by than carbon data, the assumptions are more contested, and the comparisons are sensitive to scope choices. But it is improving, and tools that aggregate the dimensions into a single accessible comparison are emerging. The Circular Data Centre Compass developed by the CEDaCI project is one of the early examples, comparing new and refurbished servers across the full set of environmental and social variables, using data from partners including Interact.

The direction of travel is clear. Carbon will remain the headline. The dimensions underneath it will increasingly determine whether the headline number is the right one.