Your lawn plays a key role in absorbing urban carbon emissions

That sea of manicured green grass stretching across parks, backyards, golf courses, and cemeteries may be doing more than just pleasing the eye.

A new study led by scientists at Pennsylvania State University shows that turfgrass – typically overlooked in urban greenhouse gas models – plays a small but crucial role in shaping carbon dioxide levels. And in winter, when most vegetation is thought to go dormant, these lawns are still quietly at work.

The findings stem from research conducted as part of the Indianapolis Flux Experiment (INFLUX). By adding turfgrass-specific data to carbon models, the team has improved how scientists account for the biological activity of vegetation, leading to more accurate estimates of human-caused emissions.

Lawns’ role in carbon emissions

The study could help reduce uncertainty in estimating human-caused emissions and guide more effective greenhouse gas policies.

Jason Horne is the lead author and a doctoral candidate in meteorology and atmospheric science at Penn State. “There has been a push to better understand the processes that are going on in these areas, because it’s really complex,” he said.

Urban greenhouse gas emissions mainly come from fossil fuel combustion – cars, heating systems, industrial activity – but vegetation complicates the picture.

Plants absorb carbon dioxide through photosynthesis and release it through respiration and decay.

Accurately separating these processes is essential when trying to isolate the human fingerprint on emissions. “And for that, we need to have a good idea of what the biology is doing,” Horne added.

Grass is active in winter

To get that biological snapshot, the team placed eddy covariance flux towers – sensors that track gas exchanges between the land and air – above two distinct turfgrass sites in Indianapolis: a golf course and a cemetery.

These measurements ran for a full year before and after grass was added to the simulation models.

The difference was clear. Existing vegetation types in the models couldn’t match the real seasonal behavior observed at these sites. One key moment stood out: winter.

“Our models were not able to capture the carbon dioxide being removed from the atmosphere by photosynthesis in the middle of winter,” Horne said. “The model showed vegetation was a net source of carbon dioxide during the middle of the day.”

But field data showed that even during freezing temperatures, turfgrass was still performing photosynthesis, albeit at lower levels. That quiet activity matters more than it seems, especially in cities where lawn coverage is extensive.

Grass improves city models

Armed with these observations, the researchers created a new turfgrass vegetation type within their simulation. This tweak allowed the model to better reflect actual winter photosynthesis rates and adjust for the role lawns in removing carbon dioxide from the air.

“Turfgrass photosynthesis is not highly active during the winter, but it’s active enough to make a difference in the models – and that could make a difference in how we understand every emission source,” Horne said.

Misrepresenting vegetation as emitting carbon can lead to inaccurate estimates of total human-caused emissions. For cities like Indianapolis, where 20% to 30% of the land area is covered in turfgrass, even subtle changes add up.

“Even if we see a small drawdown of carbon dioxide in the middle of winter, it’s not insignificant,” Horne emphasized. “If you are not considering that, you may be underestimating anthropogenic emissions.”

Lawn care affects emissions

The two study sites revealed additional insights. The golf course’s grass was irrigated, fertilized, and mowed regularly, while the cemetery’s lawn was less intensely managed.

This difference likely affects both carbon uptake and release. It highlights the need for future research on maintenance practices and environmental factors.

“But it’s clear from our work that turfgrass lawns are worthy of dedicated study,” Horne said. “This could help reduce the amount of uncertainty when we’re trying to estimate anthropogenic emissions to guide policy decisions.”

Rethinking urban green spaces

The work highlights the subtle but real influence of managed lawn grass on carbon dynamics. It also strengthens the case for refining urban emission models to include a broader, more accurate picture of vegetation activity.

By incorporating turfgrass into simulations, scientists are improving their grasp on how cities breathe – and how human behavior, through lawn care and landscaping, may shape that process.

As urban areas expand and climate policy sharpens, even the quietest blades of grass could help write the next chapter of emissions accounting.

The study is published in the Journal of Geophysical Research: Biogeosciences.

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