Climate Action

Footprints on the path: how routing data could reduce the internet's carbon toll

The internet's environmental cost is rising – but selecting the right data paths could make a difference

The internet's environmental cost is rising – but selecting the right data paths could make a difference Image: Jason Leung/Unsplash

Simon Scherrer
PhD candidate, ETH Zurich
Markus Legner
Postdoctoral Researcher, ETH Zurich
Tobias Schmidt
Professor of Energy Politics, ETH Zurich
Adrian Perrig
Professor of Network Security, ETH Zurich
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• The internet’s carbon footprint and thus its contribution to climate change is likely to grow massively in the near future.

• Carbon emissions from internet usage could be reduced to a fraction if traffic was transported through countries and networks that use low-emission electricity.

• SCION internet architecture allows users to identify and select environmentally superior paths, incentivizing network operators to attract traffic by becoming greener.

The internet consumes electricity in different places: on our devices, in data centres and in communication networks that transfer data. With today’s widespread internet usage, the total electricity consumption of its infrastructure (networks and data centres, but not consumer devices) is significant, namely around 500 TWh per year or 2.5% of worldwide electricity consumption. Moreover, as internet traffic volume is steadily growing, this energy consumption could experience an eight-fold increase by 2030. Since electricity production still emits considerable amounts of greenhouse gases (475g CO2 equivalents per kWh on a global average), the growth of internet traffic presents a serious concern regarding climate change: If the projections are true, the internet would be responsible for an additional 1.7 billion tons of GHG emissions per year by 2030, corresponding to Russia’s 2019 CO2 emissions.

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On the right path to reduce emissions

Different ways of providing internet service affect the climate to massively different extents: For example, when communicating between Zurich and London, over seven times less carbon emissions are produced if the communication bits travel via France, instead of via Germany and the Netherlands. The reason: Electricity is produced with much lower carbon emissions in France than in the other two countries, and even imports do not eliminate this difference. However, this country-specific carbon intensity varies considerably over time: Because of variable renewable energy plants (solar and wind), German electricity consumption can sometimes be fully satisfied with these low-emission sources, making communication via Germany environmentally more attractive during these periods. It is also possible that the network operators along the paths do not simply consume the local electricity mix, but commit to an exclusive use of low-emission electricity and thereby operate with a small carbon footprint.

The emissions toll of sending data by a particular route shifts according to certain conditions
The emissions toll of sending data by a particular route shifts according to certain conditions Image: Simon Scherrer

Now imagine that communication paths could be dynamically selected based on their current carbon footprint. Such a system has the potential to conserve vast amounts of carbon emissions and thus to significantly reduce the internet’s climate impact. These savings would be even more pronounced if not only the path, but also the other end-point of the communication, could be chosen based on carbon intensity. Thanks to geographical replication, the same content is usually available from different data centres, allowing such optimizations.

A more versatile internet architecture

If users were offered cleaner communication paths and destinations, we expect a substantial share of them to take up such an offer. Estimates of the willingness to pay for CO2 avoidance suggests that demand for environmentally friendly communication would hold up even if such communication was more expensive (low-emission electricity might be more expensive at times) or slower (low-emission paths may not be the fastest paths).

Unfortunately, today’s internet architecture is ill-equipped to accommodate such user preferences. The path-discovery mechanism that is used nowadays (a protocol called BGP) provides only a single path between any two points in the internet, offering neither transparency nor choice to users.

To resolve these drawbacks, researchers have been working for over a decade to create a viable alternative. This alternative, the SCION next-generation internet architecture, allows service providers (ISPs) to offer multiple paths to their customers, to augment these paths with valuable information (such as the carbon footprint of the path), and to forward traffic based on their customers’ path choice.

To introduce SCION, no abrupt replacements regarding the core operations of the Internet are required; instead, SCION can coexist with the present paradigm and enable path selection within the gradually expanding sub-network of entities that adopt SCION. Several ISPs are already running SCION, with Anapaya Systems offering SCION connectivity at over 60 data centres globally.

Internet path selection will economically incentivize ISPs to go green
Internet path selection will economically incentivize ISPs to go green Image: Simon Scherrer/Shancong Yu

A virtuous internet cycle

Given its path-selection features, SCION creates an internet where end users can shift electricity consumption to low-emission network operators. Fascinatingly, such environmentally oriented routing thus creates a reward for providers that invest in energy-efficient equipment and low-emission electricity. This reward mechanism could give rise to a virtuous cycle: If environmentally friendly providers could attract additional traffic, the more polluting providers would conversely lose traffic and, as a result, a share of their revenue.

As internet traffic transportation is a business with high fixed costs and low margins, any reduction in traffic strongly affects a network operator’s profit. Confronted with the danger of deficits, polluting ISPs may hence reduce their carbon footprint by becoming more energy-efficient or subscribing to green electricity, to win back environmentally conscientious users. As a result, path selection in the internet not only reallocates traffic to low-emission members of the networks, but incentivizes all members of the network to reduce their carbon footprint.

There is reason to believe that such environmentally friendly service could be provided profitably. Costs of low-emission electricity have become competitive with standard electricity prices in recent years, though it is still debated how to quantify the costs stemming from the variability of sources such as solar and wind; in any case, electricity costs make up only 5% of the operation costs of telecommunication firms, considerably watering down any increases. On the revenue side, behavioural studies suggest consumers will pay on average 6% more for an internet service offer if that service becomes fully carbon-neutral.


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Therefore, CO2 reduction, at least in partial form, constitutes a plausible business opportunity for ISPs. Environmentally aware routing, as enabled by SCION, might thus not only be good for the planet – it may also be good for business.

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