This report has been written to address the climate emergency. 
The scientific community has issued stark  warnings about what could happen if we do not rise to the challenge of reducing global CO2e (carbon dioxide equivalent) emissions (IPCC, 2023). To date, the scale and 
urgency of carbon reduction has not been at the pace needed to prevent catastrophic global heating. We are at risk of passing tipping points, beyond which the planet will not recover (IPCC, 2023).
A step change in our response is needed now.

The aim of all those involved in the planning, design, construction, operation and renewal of infrastructure should be to decarbonise it. This means to reduce the embodied and 
operational carbon produced.
The decarbonisation of infrastructure must be equitable, must be done without damaging the environment in other ways such as biodiversity loss or pollution, and 
using methods that maintain and improve health and safety. Any potential impacts of decarbonisation on the quality, durability or design life of structures must be carefully considered.
Sustainability is a decision-making framework that takes account of all these aspects. Considering social, economic and environmental benefits or impacts 
(the ‘three pillars’ model) is the simplest method, but there are also sustainability indexing methods, such as BREEAM (2023), ENVISION (2015) or IS Ratings (2023), that 
can produce scores that enable performance to be measured and comparisons to be made (Figure 1). 
We must work together to reduce CO2e emissions in tunnelling and we must do it urgently.