In 2016 the ‘new urban agenda’ was introduced by the United Nations and formally adopted by the world’s leaders. It provides a vision and commitment to making cities more inclusive, safe, resilient and sustainable.World Cities Day on 31 October 2019 revolved around how urbanisation can help achieve sustainable development and implement the UN’s new urban agenda.Most industries are implicated in the negative impacts of urbanisation but construction plays a significant role. According to recent research by C40 Cities, Arup and University of Leeds, construction will produce 21% of all consumption-based greenhouse-gas emissions between 2017 and 2050 in nearly 100 of the world’s biggest cities. The use of concrete plays a big part in this given the material accounts for up to 8% of global emissions and 85% of all mining.Although the figures are alarming, they are not without hope. The research concluded that emissions in construction can be cut by 44% if the right action is taken. From building more efficiently to recycling materials, the way structures are designed and built can transform cities’ environmental impact and the lives of people within them. This is where civil and structural engineers come in: they can help achieve the UN’s new urban agenda through the projects they take on and how they are carried out.Creating zero-emissions structuresNet-zero-emissions structures are those where construction and operational emissions are counteracted by offsets or exports of on-site renewable energy. Construction emissions, which are a significant part of this, can be reduced through switching from traditional building materials such as concrete to sustainable carbon stores like cross-laminated timber, which can also help to reduce programme time and conserve resources. In every project, civil and structural engineers should be seeking design solutions which use more sustainable materials.In addition, refurbishing existing structures rather than embarking on new builds is crucial,as well as reusing old building materials. This will not only cut wastage and materials going to landfill but will slash the resources and emissions involved in creating new materials in the first place. Using modular construction techniques can also help with reusing existing stock as they more easily disassembled.Improving urban environmentsUrban structures can address the negative effects of urbanisation as well as not contributing to them. For example, using sustainable drainage systems (Suds) to control surface water flooding is critical as cities grow and climate change intensifies. Ensuring the water table is not disrupted is a crucial consideration for engineers on individual projects, as well as the general need to create sustainable flood protection.The buildings of tomorrow can also play a part in tackling air pollution. This not only involves reducing operational and construction emissions but looking for ways to dissipate or offset it. Milan’s Bosco Verticale (pictured) is a residential tower covered by plants which directly absorb carbon dioxide from the atmosphere.Other practical actions include: embracing digital tools for maximum efficiency; choosing to work on renewable energy projects; designing buildings for longer life-spans; and adhering to environmental assessment standards such as Breeam and Passivhaus.This article is based on the authors’ briefing article in the latest issue (173 CE1) of the ICE Civil Engineering journal.