The tiny city cowers in the shadow of an enormous tidal wave labelled “COVID-19”. Looming behind is a series of progressively larger tsunamis: “Recession”, “Climate change” and, finally, filling half the frame, “Biodiversity collapse”. This much-copied image by Canadian cartoonist Graeme MacKay is a potent reminder that however bad our immediate troubles are, there is worse to come. And that even if we do manage to reduce carbon emissions to net zero by 2050 – and therefore hold climate change to 1.5°C – this is not the only crisis we need to avert.

 Fortunately, there are strategies we can use to solve more than one problem at the same time. Decarbonization potentially comes with a whole range of “co-benefits” associated with cleaning up the environment and reducing our reliance on polluting technologies. Switching from fossil fuel to electric-powered vehicles in cities removes a major cause of respiratory disease; decentralized renewables can bring power and connectivity to remote communities; rewilding gives nature more space to flourish. This means that we can use decarbonization to further goals on which less progress has been made – there is not yet any equivalent to the Paris Agreement on biodiversity loss, for example. Alternatively, where political will is lacking on decarbonization itself, we can substantially strengthen the case by factoring in the wider socioeconomic gains.

The bottom line is perhaps that if we don’t fully consider all the consequences, net zero projects are less likely to succeed – and even if they did, would we like the result? As Tom Butterworth, WSP’s UK head of biodiversity, puts it: “If we save the world in terms of climate change, but fail to deliver all of these other benefits, then we will have lost what makes it special. Imagine growing up in a place where the only animals are rats, cockroaches and pigeons – what would it be like to be human in that environment?”

Decarbonization may seem intuitively like a good thing for other aspects of sustainability, but nothing is guaranteed. It will take an integrated design approach to balance overlapping, and sometimes conflicting, goals. Higher levels of fresh air and filtration in “healthy” buildings, for example, will push energy use up. On-site renewables can improve resilience to extreme events and grid outages – but so can adding diesel-powered generators.

“It’s definitely not automatic,” says Joshua Radoff, a senior vice president with WSP in Colorado. “There are some things that are inherently good, like removing combustion, and if you’re doing a really efficient passive design, that should mean more thought about ventilation and fresh air. But it doesn’t necessarily mean better landscaping or public spaces or connectivity. You need to be explicit about these things as it’s pretty easy to leave them by the wayside. If you just focus with blinders around zero-carbon, you might engage in things that check all the boxes but don’t have any alternative benefits.”

This is particularly the case with offsets, which may or may not offer a wide spectrum of benefits over and above carbon reductions. “It might just be a wind farm in Texas that was going to happen anyway,” says Radoff, “That has benefit but it’s certainly not helping your community.” Companies may make a conscious decision to buy offsets that align with their mission and values, suggests Tim Parker, sustainability director at WSP in Sydney. “Indigenous engagement is a big thing in Australia, and gaining biodiversity credits from increasing bush in indigenous communities is a far more tangible and valuable offset than buying a wind farm in another country,” he says. “It’s probably going to cost more, but that’s for organizations to weigh up.”

This is the choice Danish member-owned supermarket Coop has made, with its “People’s Forest” (Folkeskove) programme to plant 1,000ha of new forest across the country by 2030. Coop could more easily meet its offset requirements in countries where land and labour costs are lower – but this way, it demonstrates a connection to consumers and enables them to experience co-benefits such as access to nature and greater local biodiversity. “If Coop’s only interest was to be carbon neutral, it would be much more efficient to create new forests in the tropics,” says Allan Bechsgaard, forest director at DDH, which is managing the land on its behalf. “But they see additional value in doing something local. It provides recreation opportunities for the people who live in the area, and for their own employees, and they can show that they’re giving something to society.” DDH, Denmark’s largest forest manager, is seeing increasing interest in such domestic forestry initiatives, he adds, particularly from membership-owned organizations, like Coop, and those with strong local connections.

On zero-carbon projects, there may be a limit to the additional benefits that can be extracted before the investment becomes unviable. One way to manage this is to rank your priorities, as Radoff’s team helped the City of Boulder do on a zero-carbon social housing project. There, affordability came out on top, but the list might look very different for a corporate headquarters. Another solution is to broaden the scope, perhaps securing finance for additional elements like large-scale solar or wind power, which can generally pay for themselves over the longer term. A third is to involve partners who also stand to benefit, such as utility providers. On a 14 million ft2 project in downtown Denver, WSP analysed whether the buildings could be heated from the waste heat from sewage treatment, potentially saving the need to construct a multimillion-dollar cooling plant. “We found it would be a breakeven for the project because you’re just displacing gas, but if we can loop in the benefit of the government not having to build such an expensive facility down the road, then everyone is winning.” The same could be true of electrifying a bus fleet, he adds, if you could quantify the benefits of lower rates of respiratory illness to the local health system. “If there are partners that can share the co-benefits, that can make it worthwhile.”

One area where all of these goals can often overlap is in the greater use of natural landscaping, or green infrastructure. This can support water treatment, stormwater management and carbon sequestration, reduce the risk of overheating, and boost wellbeing by providing spaces to exercise and commune with nature. It can also be cost-effective over the long-term, says Anna Robak, WSP’s research and innovation manager in Canada. “Sometimes there is an upfront extra cost to using green infrastructure, but often it is lower cost to go with the green solution, particularly when you factor in the wider economic benefits, such as to health, food production and reduced materials extraction and waste.”

There’s a community pride dimension to green infrastructure too: one study in the US found that residents were willing to volunteer 50 hours per year of their time to restore rivers and streams to “swimmable” condition. With more work upstream, there’s also less need to treat our drinking water, so fewer chemicals can be used to dose the raw water, and equipment can be sized smaller or operate less intensively and last longer. That also saves cost and reduces emissions. “The water treatment process is in large part a Band-Aid for something that is not ‘right’ upstream,” says Robak. “Most people are still not considering solutions from a multidisciplinary perspective. For green infrastructure, we need not only engineers, but also specialists in ecology, agriculture and community engagement.”

There is a major caveat here, about the impact of large-scale reforestation on ecosystems already threatened by human activity and climate change. One way to sequester a lot of carbon quickly would be to plant a lot of conifers – but this could be catastrophic if the species are not native to the area. “We need to think about how those environments are functioning, whether those conifer plantations are decreasing or increasing flood risk or changing water flows, or changing the acidity of the water or the soils,” says Butterworth. “If we’re going to deliver a climate-resilient society, we need landscapes to provide carbon sequestration, and flood relief, and biodiversity, and food, and nice places for people. If we deal with just one of those, then we will not only be ignoring the others, we’ll be undermining them and we will fail.”

This is especially important because, as a global challenge requiring coordinated action, biodiversity is proving even more challenging than climate change. Scientists have warned that we are entering the sixth mass extinction, with one million species at risk of extinction, and global wildlife populations declining by 68% between 1970 and 2016. “Historically lots of countries have refused to even engage,” says Butterworth. “There is a real reluctance to agree legally binding targets.”

No matter where carbon is emitted, the impacts of climate change will be felt globally. But while the collapse of ecosystems will also be catastrophic for humanity, it is at a local level where the effects are most apparent. “The loss of the Amazon rainforest will have a direct impact on the people living next to the Amazon, but the impact in the UK will be more expensive chicken, which frankly nobody is going to notice. It may well have impacts on the Great Basin in the US because of shifting weather patterns, but it’s really difficult to tell.”

The next milestone is the COP15 UN biodiversity conference to be held in Kunming, China in May 2021, where Butterworth hopes there will be an equivalent of the 2016 Paris Agreement. Even if that comes to pass, it leaves biodiversity five precious years behind, says Butterworth: “So we absolutely have to use the climate targets to deliver multiple benefits.”

Co-benefits can work the other way too. Climate change’s strength when it comes to agreeing targets becomes a weakness for actually delivering against them – as immediate national interest almost always trumps long-term global problems.

One solution is to quantify the local benefits of the transition to net zero, as the Inter-American Development Bank has done with a detailed cost-benefit analysis of Costa Rica’s national decarbonization plan. This revealed a net benefit to the economy of US$41 billion between 2020 and 2050. Crucially, it disregards the benefit from avoiding the impacts of climate change globally, so it represents what Costa Rica stands to gain even if every other country in the world does nothing. “We’re not saying there are no costs to sustainability, we’re saying that the benefits are more than twice the costs,” says Adrien Vogt-Schilb, senior climate change and sustainability economist at the IADB.

This is intended to not only build political support for the plan internally, but to demonstrate the steps that need to be taken by each part of government and the private sector in order to deliver it, he explains. “We’re trying to transform the lofty net zero emissions goal that’s very mystical for a lot of people into specific sectorial actions – for instance, hectares of reforested areas, share of electric vehicles – so that everyone understands what it means for them and how it can help them achieve their own goals. We don’t even need to talk about reducing emissions. So it’s not a sacrifice that you’re asking people today to make for 2050, it’s about improving their lives, improving the business environment, just making things better.”

The methodology was set in 2019, but this kind of analysis is even more important since COVID-19: “If you want to make any climate action politically realistic, you definitely need to emphasize the social and economic benefits – which means you need to ensure that the plan has social and economic benefits in the first place.”

The greatest share of the benefits for Costa Rica are predicted to be felt in two sectors: agriculture, livestock and forestry; and public and private transport and freight. Improved agricultural yields, ecosystem services and support for tourism are worth US$22bn more than the investments required to achieve them and the foregone value of land dedicated to forests. Meanwhile, the costs of switching to electric vehicles and building public transport infrastructure are outweighed by the economic benefits from energy savings, fewer accidents, reduced congestion and the reduced impact of air pollution on health to the tune of US$19bn. Vogt-Schilb thinks that this pattern would hold for most developing countries, with agriculture and transport always in the top three. “The third big one is the benefit of switching to 100% renewable energy, which we don’t see in Costa Rica because it is already at 95%.”

To account for the uncertainty that besets a 30-year programme, the calculations were repeated for 3,003 plausible futures, reflecting assumptions over 300 variables. Virtually all of them resulted in some net benefit, the only exceptions being when two specific conditions were present together. These were both in the transport sector: high costs for several key technologies simultaneously; and low take-up of shared vehicles and slow development of electric bus lines.

So could we just focus on transport technologies and take-up and the rest will come? It’s not that simple, says Vogt-Schilb: this demonstrates the direction of travel, but it’s not a substitute for the journey itself. “Once you’ve got everybody on board and decided that you want things like buses and plant-based agriculture, you still have to design them so that they are good things – that’s its own project.”