A 600-acre park in development in Athens, Greece shows the value of prioritizing carbon. The Ellinikon Metropolitan Park is being designed by landscape architects at Sasaki to significantly increase carbon sequestration, avoid emissions, and reuse embodied carbon on a massive scale. Leveraging Sasaki’s Carbon Conscience App, Climate Positive Design’s Pathfinder tool, and Atelier Ten‘s carbon analysis, the project will cut emissions by 45 percent in comparison with a business-as-usual scenario. By designing for the climate first, the project is expected to become carbon neutral in 35 years.

What will be the largest urban coastal park in Europe is taking form on top of the old Athens International Airport, which was decommissioned in 2001.

Over the past twenty years, the city and national government have devised an approach that will keep the majority of the 1,200-acre site public through a combination of the 600-acre park, other spaces, and roadways but also ensure long-term financial sustainability. Through a 99-year lease agreement, Lamda, a Greek developer, will cover the cost of designing, constructing, and operating the park in return for revenues from new residential and commercial developments. “Making this happen required a presidential decree that superseded local regulations and created a unique permitting authority,” explained Michael Grove, FASLA, chair of landscape architecture, civil engineering, and ecology, and principal landscape architect at Sasaki.

The grand new park will be approximately 70 percent of the size of Manhattan’s Central Park and built in three phases. A comprehensive plan and framework by Foster + Partners set the boundaries of the park, which extends to the Saronic Gulf.

Within the existing landscape are layers of history: remnants of prehistoric settlements, agricultural lands, an abandoned airport, and dilapidated Olympics venues, which have inspired novel and sustainable reinterpretations.

“It’s been a joy to be able to plug into this ambitious context — on a site with so much potential to realize what I hope sensitive landscape design can achieve in the 21st century,” said Chris Hardy, ASLA, senior associate at Sasaki and Landscape Architecture Foundation (LAF) Leadership and Innovation Fellow.

According to Sasaki, Athenian society has been changing, and the new park aims to fill a cultural void. “Historically, Athenians returned to family farms in the countryside on weekends. Core to the Athenian identity was a relationship to the Greek landscape. But as the Greek diaspora grew abroad and more multi-generational families stay in Athens, many contemporary Athenians no longer have access to a rural ancestral home, displacing a traditional cultural relationship with nature and resulting in a growing disconnect between urban residents and the landscape.” In addition, the majority of the open spaces in Athens don’t help reforge that connection — they are “either passive landscapes adjacent to ancient ruins, or hyper-urban plazas and streetscapes.”

Much like Central Park, the goal of Ellinikon Metropolitan Park is to bring nature back to the city in a big way. This will occur by creating natively Greek ecological landscapes that will not only resonate on a cultural level but also be designed to store vast amounts of carbon.

The new park will include over 3.3 million Greek-sourced plants; among these are 31,000 new trees, representing 86 species. The team will also collect seeds from the site’s existing ruderal grasses and geophyte species, weaving novel ecosystems back in. More than 70 percent of the park will be designed as a demonstration of Greek landscape restoration.

And all of these landscapes will be nourished by 100 percent reclaimed water, which will be captured from sewage mined from a treatment plant that will be constructed by Lamda. In addition, “a 3.7-acre lake, repurposed from an Olympic kayak and canoe venue, will serve as an emergency stormwater reservoir, filling in the winter and slowly drawing down in the summer. The lake will be refilled with excess reclaimed water and treated through a large-scale flow-through recirculating wetland,” Hardy said.

Working with Atelier Ten and engineering firm LDK, the team also calculated expected future energy use in the giant park, which will include playgrounds, gardens, farms, and event spaces. That enabled the team to determine what size an on-site solar energy facility has to be to meet 100 percent of energy needs.

Hardy explained in detail how early planning and design decisions enabled them to design for carbon while achieving their other goals:

The single most important step to reduce the project’s carbon impact was to “swap out imported soil for amended soil.” Alone, this step is estimated to save approximately 43,000 metric tons of carbon across all phases of the project.

“The second biggest factor is we reduced the need for new concrete,” saving another estimated 41,000 metric tons of carbon across all phases.

Instead of specifying new concrete-based paving, Sasaki designed in stone or salvage concrete slab over aggregate base, so there is no concrete sub-base. In other places, there are just stabilized aggregate surfaces.

The third biggest carbon reduction comes from the reuse of 100 percent of nearly 310,000 cubic feet of concrete from airport runways and tarmac in the new park. The team will bring in concrete mining equipment, which will be operated on-site.

The highest quality concrete will be saved for fountains, retaining walls, custom furnishings, and various hardscapes. “Much of the concrete has marble and quartzite aggregate,” Hardy said, which means it will look appealing once polished and re-used.

Medium quality concrete will either be used as road base or riprap. And the lowest grade salvage will be crushed up to fill in new landscape forms. “Our use of salvage hardscape is saving nearly 12,000 metric tons across all phases.”

The goal was to “upcycle in a conspicuous way,” which will convey a public message of sustainability, Grove added. Ellinikon shows that landscape architects redesigning abandoned infrastructure can find opportunities to reinvent legacy concrete. But he acknowledged there is a cost to mining and crushing concrete on site, which can only be reduced through economies of scale. In projects where this isn’t feasible, “landscape architects can help grow a marketplace for recycled concrete products that can be specified.”

While these strategies outline how Sasaki has reduced or avoided new emissions, the other side of the equation are the approaches for drawing down more carbon from the air.

One core approach is to simply increase the percentage of the project that is covered in plants and soils and only strategically use hardscape in highly trafficked central areas.

Among natural areas, “the highest carbon sequestering land are the wetlands. Those include rain gardens, daylighted culverts, green infrastructure corridor, and a demonstration salt marsh. However, these areas are less than two hectares and will only reasonably sequester approximately 500 metric tons. The highest total individual sequestering landscape is our 11-hectare Dry Mediterranean Mixed Forest, with an estimated 3,300 metric tons sequestered in the study period,” Hardy explained.

“We can expect a total emission global warming potential (GWP) of 40,800 metric tons across all phases, which would reasonably take about 35 years for our softscape to offset. In 80 years, when the project’s landscapes will mostly reach their total ‘carbon carrying capacity,’ we will likely net sequester an additional 37,000 tons.” This means the project will become carbon positive, storing more carbon than it emitted, and then continue to function as a carbon sink far into the future.

Ellinikon Metropolitan Park shows the importance of calculating estimated carbon emissions from the get-go and letting the carbon priorities — the essential need to reduce emissions and increase sequestration — guide the design.

For Hardy, the support of the client has been critical. “Their exceptional commitment to be on cutting edge of sustainability from the beginning of the process and ‘leap frog’ other developments in Greece” enabled Sasaki to establish a climate-responsible framework for the project.

“The important part of the story is that through this process we were able to advocate for big moves towards a climate positive direction. Now we are better prepared to advocate for low-carbon strategies as we move into construction.”

With ETM Associates and LDK Waste Management, Sasaki’s team developed a low-carbon operations and maintenance manual that includes “recommendations for an all electric fleet of maintenance vehicles and landscape maintenance machinery, a large scale compost tea and composting program, and integrated pest management standards.”

Foster + Partners’ master plan also established important guiding principles. The park will integrate with the surrounding new developments, which will include a “waste management facility, enabling a source for our compost and compost tea.” In addition, a large-scale wastewater treatment plant will generate safe, treated water for irrigation.

Light-rail networks along the coast and through the park, along with a new bicycle network, will help get residents and visitors out of their cars, reducing transportation-related emissions.