Data that doesn't cost the Earth: emission definition

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In the last blog, we looked at the progress the data center industry has made towards sustainability over the last decade, and the key areas we will need to focus on to continue this. Now we would like to go into a little more detail on the metrics - the key performance indicators we are working with, and how and where we should use them.

March 7, 20236 mins
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In my last blog I looked at the progress the data center industry has made towards sustainability over the last decade, and the key areas we will need to focus on to continue this. Now I would like to go into a little more detail on the metrics - the key performance indicators we are working with, and how and where we should use them.

Chris Pennington, Director Environmental Sustainability, Iron Mountain Data Centers (IMDC)

At Iron Mountain Data Center we believe that it is vital for our fellow colocation providers and our customers that everyone works together to drive change and show other sectors what can be done. The first step towards this is speaking the same language so that we can set our goals and celebrate our achievements in a way that can be proved to contribute positively to our shared climate goals.


For IT end-users, there are many carbon calculators to choose from. Apps like the Carbonalyser browser extension claim to calculate GHG emissions from web use based on a mix of location and national electrical mix (for instance EU = 0,276 kgCO2e/kWh, USA = 0,493 kgCO2e/kWh) Clearly this is an over-simplification, but that does not mean it is not a worthwhile project. Can corporate IT users do the same thing, but with greater accuracy?

Only five years ago, most companies did not look beyond their walls when assessing environmental impact. That has changed. Now companies recognise that outsourced IT functions count too, and that means equipment and processing in data centers of all types, whether it’s a dedicated colocation facility or an IaaS, PaaS or SaaS one.

As defined by the GHG Protocol and ISO 14064, a colocation provider’s Scope 1 and Scope 2 emissions are part of the customer’s Scope 3 emissions, i.e.

  • Scope 1 = direct emissions
  • Scope 2 = indirect GHG emissions (energy)
  • Scope 3 = other indirect GHG emissions (things like business travel or supplier-related GHG like data processing)

As a step towards more sustainable computing, these emissions should be measured, validated, and published in a meaningful way by both data center providers and users.

This is achievable, but there is a long way to go. While even the larger cloud providers are still in the early stages of providing detailed carbon impact information to customers, IMDC has demonstrated an effective way to address the measurement of customer carbon impact while sharing the benefits of using a renewable-powered provider. The reportable emissions from matching electricity use with renewable power is zero, and we recognized early on that passing through zero carbon energy use to customers was valuable to them. Developed in 2018 in collaboration with the Future of Internet Power initiative, IMDC’s award-winning Green Power Pass was an industry first in helping customers reduce their carbon footprint. It is a transparent solution for customers seeking to report carbon reductions associated with the renewable power they consume at Iron Mountain Data Centers. We have shared the model with the industry, and other providers are now creating similar programs.


At the data center provider level, measurement of environmental impact is still evolving. Stating and sharing clear metrics is the key to shared progress across the industry, but globally, the industry has not been very consistent, and has not fully aligned its measures. As a result, there is always the risk of ‘greenwash’, even if a data center’s actions are well intended. Customers with carbon-reduction targets need to be constantly aware of this risk.

Today there are three core performance indicators for operational sustainability, all of which come from the ISO 30134 standard: Power Usage Effectiveness (PUE), Water Use Efficiency (WUE) and Carbon Usage Effectiveness (CUE). It’s worth defining these, the ways in which they are measured and giving an indication of how that information is being shared.


Most people know PUE, as it is the cornerstone for the industry’s progress to date. It measures the total energy used by a data center versus the energy employed exclusively by customer IT equipment. This metric is attractive due to its simplicity and its versatility – it can be applied either to a whole system or just one section or user area. In 2021, IMDC’s overall PUE was 1.695 which is consistent with the average for the industry. The lower the number the better, with a PUE of 1.0 indicating that 100% of consumed electricity went to the IT equipment and nothing was used for overhead or cooling. Generally, the newer the facility the better the PUE. Newly constructed data centers with the latest systems can achieve PUEs as low as 1.2.

*Metrics from Iron Mountain Data Centers 2021 Sustainability Report


This is the ratio between the use of water in a datacenter system (water loops, adiabatic towers, humidification, etc.) and the energy consumed by IT equipment. This is still a relatively new metric that is rarely reported in the sector and has no standardized reporting site where you can check data per provider. However usage will grow, particularly in areas where water is scarce, and customers are requesting it more often.


For companies aiming at total decarbonization this is the critical measurement. It expresses the relationship between the CO2 emissions the data center is responsible for from daily operations, and the energy consumption of IT equipment. The value can be country-specific or even grid-specific depending on the respective mix of power sources (coal, nuclear, gas, wind, etc.). So, in an environmentally ideal scenario where a data center is designed to work with 100% renewable electricity, CUE values can theoretically equal ‘0’. But factors like diesel generators and possibly refrigerant losses (scope 1) also need to be taken into account. Our Carbon Usage Effectiveness score for 2021 was 9,970,000 KGCO2EQ / 427,985,611 KWH which equals a score of 0.14.

It is important to note that with each of these three metrics the value is in knowing your performance, developing solutions to improve this performance and tracking and publishing progress regularly. Each data center operator has a unique portfolio of facilities, each of which provides unique challenges which will take time to fully optimize. We should all commit now to demonstrating continuous improvement via these three key performance metrics.

In the next blog we will look at renewables, specifically how the industry can transition from annualised VPPAs (virtual power purchase agreements) to hour-by-hour renewable use.

I hope you have found this useful. Please don’t hesitate to get in touch if you have any questions.