Young demonstrators hold placards as they attend a climate change protest organised by "Youth Strike ... [+] 4 Climate", opposite the Houses of Parliament in central London on February 15, 2019. (Photo by BEN STANSALL/AFP via Getty Images)

We are living in a climate crisis, and the time for action is now. That was the rather sobering headline that accompanied the publication of the latest report from the Intergovernmental Panel on Climate Change (IPCC). Written by 278 experts, supported by contributions from another 354, the report runs to 3000 pages and includes 18,000 references. It is a remarkable achievement of science and collaboration. The language in the document – and its associated summaries – doesn’t pull any punches. While reporting on the many achievements to date (e.g. the ever-decreasing costs of solar and wind energy), it tells us that such incremental change will not be enough, “Without immediate and deep emissions reductions across all sectors, limiting global warming to 1.5°C is beyond reach.”

There is some light in this report, though, because it specifically focuses on solutions: the practical steps that need to be taken if we are to stand any chance of keeping the predicted temperature rise to a minimum.

Across its 17 chapters, it examines climate change mitigation efforts in use (or pledged for use) in everything from agriculture and transport, to energy supply and manufacturing. The huge range of approaches reflects the fact that the causes of climate change are numerous – though, it should be said, we humans are to blame for all of them – and tackling it will take a multi-pronged approach. As excited as you might be about specific technologies, there is no magical ‘silver bullet’ solution to climate change.

Chapter 8 of the report looks solely at urban areas. More than half of the global human population now live in these areas, and that proportion is forecasted to increase to nearly 70% by 2050. As a result, those areas are the source of a large proportion – 67-72% – of the world’s greenhouse gas (GHG) emissions as of 2020. “About 100 of the highest emitting urban areas [currently] account for approximately 18% of the global carbon footprint.” Per capita, urbanites in ‘Developed Countries’ produce nearly seven times more emissions than those living in low-emitting regions.

The only upside to this is that cities and towns offer significant opportunities for emissions reductions. Mitigation efforts adopted in urban areas can cascade into other areas and have positive effects across transport, energy, buildings, land use, and behavior. And because urban areas tend to be connected locally, regionally and globally, those mitigation efforts can often roll outward to its surrounding areas and even to other urban regions further afield.

According to this report chapter, urban climate change mitigation fits within three broad strategies: (1) Reducing urban energy consumption across all sectors; (2) Electrification and switching to net zero emissions resources; (3) Enhancing carbon stocks (and managing flows) through green and blue infrastructure. There is arguably a fourth strategy too – behavioral change – though, this often follows on from the successful implementation of the other three.

But what does that really mean? What practical steps can city planners and managers take?

Aerial view of vehicles being driven along the Yan'an Elevated Road on August 20, 2020 in Shanghai, ... [+] China. (Photo by VCG/VCG via Getty Images)

The way we design and build our cities has a huge impact on their emissions footprints. The lowest-impact cities share four key characteristics: they have medium to high density housing close to centers of employment and commerce; they have a rich mix of land uses, a highly connected street network; and they are accessible and offer relatively low travel distances and times, enabled by multiple modes of transport. Amongst many other benefits to this type of city, a ‘walkable’ urban form strongly correlates with low greenhouse gas emissions. It is also less likely to experience the phenomenon of carbon lock-in; when “long-lived, energy and carbon-intensive assets persist, often for decades, and lock out more efficient, lower-carbon alternatives.”

A particularly good example of this is the dominance of private cars seen in many urban areas. This is not a fact of nature – people rely on cars because the infrastructure that cars require (e.g. highways, car parks) have has been repeatedly prioritized and invested in over many decades. And it has been further reinforced by zoning decisions and urban development patterns – if a city is allowed to grow through low-density urban sprawl, where homes are far from places of employment, education and entertainment, it locks people into using cars. Low-density development is also a major obstacle to the creation of alternative mass mobility options.

Established cities that are dispersed and auto-centric are likely to have higher per capita emissions than compact, walkable cities. Breaking out of this is not easy, but it is possible. It requires systematic transformation and decision-making, heavy investment in public transit systems, as well as developments that create new (and improve existing) mixed-use neighborhoods.

The report authors write that, “New and emerging cities have unparalleled potential to become low or net zero emissions urban areas while achieving high quality of life.” This is because, rather than have to undo or replace existing infrastructure, new cities are still assembling those core building blocks. They have the opportunities to make better, lower-emission choices in everything from their construction techniques, through to their planning priorities.

An electricity sub station on the outskirts of Manchester, UK. (Photo by Ashley Cooper/Construction ... [+] Photography/Avalon/Getty Images)

In many urban areas, replacing fossil fuel-based technologies with electrified ones is already making a difference. Electric rail, trams and buses and vehicles are now commonplace in most regions, and are increasingly being adopted elsewhere too. But in order to be truly impactful, decarbonization needs to system-wide. The use of waste heat or renewable energy can help to avoid carbon lock-in to fossil fuels. As can replacing gas-based heating and cooling with electrified district heating and cooling networks, plus heat pumps in homes and businesses. District-wide systems are particularly effective in high-density areas – in some cases, the switch can reduce an area’s carbon footprint by 65%.

Smart (and distributed) electric grids are also enabling a more sustainable approach to electricity supply and demand. Rather than simply generating electricity in one place and sending it to consumer, these grids “are characterized by bi-directional flows of electricity and information between generators and consumers.” Citizen-managed utilities, community batteries, and a peer-to-peer trading infrastructure can support this development.

Of course, in order to be truly ‘green’, a grid must generate its electricity from renewable resources. Several studies (e.g.1, e.g.2) have suggested that integrated systems of roof-top photovoltaics (PVs) and all-electric vehicles alone could reduce CO2 emissions by 54%–95%.

Rapidly growing cities can avoid higher future emissions (and avoid carbon lock-in) by prioritizing a compact urban form over sprawl, and preserving existing green and blue assets. They could also leapfrog fossil fuels and go straight to electrification for all transportation, cooling and heating, water extraction and recycling, cooking, etc., needs. And rather than clear informal settlements at huge financial and environmental cost, they could be regenerated and improved through investment in district-level energy management, water supply and wastewater treatment.

A man works at a construction site of a residential skyscraper in Shanghai on November 29, 2016. ... [+] (Photo by JOHANNES EISELE/AFP via Getty Images)

In the past two decades, demand for construction materials has skyrocketed. Though this has largely been driven by rapid urbanization across China, it is a global phenomenon. As cities grow in size and density, there is an increased demand for buildings and infrastructure. The materials most associated with mid- and high-rise urban construction – namely, concrete, steel, aluminum, and glass – all come with significant carbon (and environmental) cost, despite steady improvements in their production efficiency. According to the OECD, the world’s consumption of materials resources “grew from 27 billion tonnes (Gt) in 1970 to 89 billion tonnes in 2017”. They predict it to double further by 2060.

This has prompted many to begin a drastic rethink of the materials supply chain, and of the construction, operation, and demolition cycle. Researchers at ETH’s Future Cities Laboratory believe that part of the answer to this is to enable a circular loop within the urban landscape. Rather than continue the relentless flow of materials from the Earth into infrastructure, we should instead learn how to use our current cities as a material bank for the construction of future cities. Prof Daniel Hall told me that one way to do this is adopt a materials passport for construction projects: “In the same way that I get a stamp in my passport each time that I stop somewhere on my journey, materials can also receive a record of where they've been, how they've been processed, and other information attached to them; like their warranty, chemical data, etc.……when the building is harvested [later], you’d have a clear record of the different components.”

An additional approach is to replace the most energy-intensive materials stocks with lower impact alternatives. A specific example mentioned in the IPCC report is the use of engineered timber (rather than steel) in mid-rise urban buildings – something I first wrote about several years ago. The authors say that it could “transform cityscapes from their current status as net sources of GHG emissions into large-scale, human-made carbon sinks.” A paper referenced in the report suggests that constructing timber buildings for 2.3 billion urban dwellers (between 2020 and 2050) could store between 0.01 and 0.68 Gt CO2 per year, depending on a number of factors, including the average floor area per capita.

Of course, transitioning to such biomass-based building materials will be a successful mitigation strategy only if working forests are managed and harvested sustainably. This will require more robust forest and urban land governance and management policies. It will also require something that is in discussion more broadly in the construction sector – internationally standardized carbon accounting methods. The hope is that applying a monetary value to natural resources in this way will incentivize forest restoration, afforestation, and sustainable forestry practices.

Green infrastructure takes many forms

We’ve talked about both green and blue infrastructure numerous times in this column, so you may not be surprised to see them mentioned again here. In short, these can include everything from parks, street trees, garden roofs, living facades, greenways, nature reserves, wetlands, sustainable urban drainage systems. As well as providing flood protection and improving water management processes, such systems store carbon and help to reduce temperatures in cities, which in turn reduces building energy use. The co-benefits of green-blue infrastructure are numerous – they promote biodiversity, improve air quality, and provide accessible public spaces for city-dwellers, which can often lead to improvements in human health.

Trees get a special mention in the IPCC chapter, because as the authors say, “On a per-tree basis, urban trees offer the most potential to mitigate climate change through both carbon sequestration and GHG emissions reduction from reduced energy use in buildings.” The world’s urban trees already store approximately 7.4 billion tonnes of carbon, but if all of the plantable (non-tree and non-impervious) space in our cities were converted to tree cover, that carbon storage value could almost triple.

A man and his son ride along a street in San Francisco, California, in a configurated Yuba brand ... [+] cargo bicycle. (Photo by Robert Alexander/Getty Images)

We’re so often told that our individual behavior has no impact on mitigating the effects of climate change. And while it’s true that corporations and governments must shoulder much of the responsibility for large-scale changes, we can – and do – make a difference. Reducing your transport emissions are one way to do that. Can you work from home part of the time? Could you use mass transit, take to your feet or travel by bicycle? Maybe you could carpool with a neighbor. Taking fewer flights helps too. What about your home energy use – could you install better insulation, use more efficient appliances, or reduce your thermostat? They might seem small steps, but a study highlighted in the chapter suggests that changes in behavior across all areas (e.g., transport, buildings, food, etc.) could reduce an individual’s emissions by 5.6–16.2% relative to an accumulated GHG emissions baseline.

Making behavior change easy and convenient is the job of policy makers. So get involved in lobbying your local representatives, and vote for those who prioritize the climate. Tell them you want more walkable neighborhoods, financial support for renovations and energy-saving retrofits, and easier access to sustainable modes of transport.

There’s no easy answer to all this, but one thing is for sure – we can’t afford to wait any longer to take action. Climate change is a direct result of more than a century of ignored warnings and and unsustainable approaches to using precious resources. The next few years are absolutely critical in changing that. As IPCC Chair Hoesung Lee said, “The decisions we make now can secure a liveable future. We have the tools and know-how required to limit warming.”