Cities Should Account for Trees in their Greenhouse Gas Inventories. New Guidance Shows How

You walk outside on a sunny day, feeling the gentle breeze brush across your face. As you look around, you notice the trees – their leaves rustling, branches swaying. These urban trees aren’t just nice to look at, they play an important role in fighting climate change.

Trees in cities sequester carbon, removing greenhouse gases like carbon dioxide from the atmosphere. But many cities don’t account for this when calculating their greenhouse gas inventories – meaning they’re underestimating their progress in reducing emissions. Exciting new guidance provides a methodology for cities to fully account for their urban trees and get credit for the climate benefits they provide.

Why Urban Tree Carbon Sequestration Matters

With over 55% of the world’s population living in urban areas, cities have an enormous opportunity to harness natural climate solutions. Urban trees alone capture 25 million tons of carbon dioxide annually in the US, offsetting fossil fuel emissions.

Accounting for urban forests more accurately reflects a city’s net emissions and recognizes the valuable role trees play in climate action. It can also unlock additional funding for tree planting efforts when carbon sequestration is quantified.

Crediting urban trees provides incentives for cities to invest in green infrastructure and prioritize nature-based solutions. Trees planted today will continue removing carbon for decades to come.

Challenges in Quantifying Urban Tree Carbon Sequestration

Despite their climate benefits, trees have been left out of many city inventories due to the difficulties of measuring carbon sequestration.

Traditionally, greenhouse gas inventories follow internationally accepted protocols like the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC). But these methods don’t provide guidance on quantifying urban carbon removal.

Tracking tree growth and estimating carbon sequestration is also complex:

• Factors like tree species, age, and location impact sequestration rates
• Measurements require extensive field data collection and analysis
• Sequestration quantities fluctuate year to year as trees grow

This has left a major gap in our understanding of urban forests’ climate impact.

New Framework Enables Cities to Get Credit for Trees

To address this need, a groundbreaking framework has been developed by a partnership between the World Resources Institute (WRI) and the Nature Conservancy.

The Urban Forest Carbon Accounting Framework provides cities with a standardized, scientifically-rigorous methodology to account for urban tree carbon sequestration in their inventories.

Key elements of the framework include:

• Field measurements and statistical sampling to quantify average carbon storage and sequestration rates across different tree species and land uses.
• A life cycle assessment approach that accounts for carbon sequestered annually as trees grow, minus emissions from maintenance, removal, and disposal.
• Inventory guidance integrating urban tree carbon estimates into the GPC framework.

This aligns urban forestry with best practices for greenhouse gas accounting, enabling cities to showcase the full impact of their climate initiatives.

“Cities have been asking for an accounting framework for urban forests for years,” said Dr. Davin Harris of WRI. “This fills a key gap and provides a practical, evidenced-based tool.”

Early Adopters Demonstrate the Potential

The Urban Forest Carbon Accounting Framework has already been tested in several pioneer cities. Early applications indicate the magnitude of previously uncaptured carbon storage:

• In New York City, urban trees sequester an average of 193,000 metric tons of carbon dioxide per year.
• Mexico City’s urban forest captures over 149,000 tons of CO2 annually.
• Baltimore’s street trees alone sequester 36,000 tons of carbon dioxide per year.

These findings make it clear that trees are a critical component of city climate strategies. By following the new framework, urban areas can fully account for the benefits trees provide.

How Cities Can Apply the Framework

To start leveraging the Urban Forest Carbon Accounting Framework, city governments can take the following steps:

1. Build an interdisciplinary team with urban forestry, sustainability, and emissions inventory expertise.
2. Collect urban tree data through field sampling and spatial analysis of different species, sizes, and planting sites.
3. Quantify annual carbon sequestration using the framework’s standardized methodology and accounting guidance.
4. Integrate tree carbon estimates into emissions inventories following the GPC protocol.
5. Track progress over time by updating tree measurements and carbon storage estimates on a regular basis.
6. Use inventory findings to inform policy and direct resources towards expanding urban forests.
7. Share best practices with other cities to drive broader adoption of the framework globally.

Urban Trees: A Natural Climate Solution

City trees provide immense social, economic, and environmental value. Now, forward-thinking cities have a clear methodology to quantify their climate benefits as well.

Crediting urban forests reflects the totality of a city’s emissions profile and demonstrates the power of natural climate solutions. With urbanization accelerating worldwide, understanding the carbon sequestration potential of trees has never been more important.

“Urban trees are a critical tool in the fight against climate change,” said Karen Firehock, Executive Director of The Green Infrastructure Center. “By accounting for their carbon sequestration, cities can strategically invest in green infrastructure that maximizes community benefits.”

The new Urban Forest Carbon Accounting Framework empowers cities to accurately measure and showcase the value of their urban forests. Unlocking this climate solution will not only reduce greenhouse gas emissions, but create greener, healthier, and more livable cities worldwide.

Frequently Asked Questions About Urban Tree Carbon Accounting

Integrating urban forests into greenhouse gas inventories raises many questions. Here are answers to some key issues cities may encounter:

How is tree carbon sequestration measured?

The framework uses field sampling and statistical analysis to estimate carbon storage. Factors like tree species, diameter, height, and land use are measured across random samples and used to model urban forest carbon sequestration.

What tree planting and management practices maximize carbon benefits?

Native tree species that are suited to local growing conditions sequester carbon most effectively. Proper planting, pruning, and care helps trees thrive. Selecting sites with ample growing space and accounting for future development are also important.

How often do tree carbon estimates need to be updated?

Cities should re-measure samples and update estimates every 5-10 years. Annual snapshots can use modeled growth rates to estimate sequestration between field samples.

Does tree maintenance emit significant greenhouse gases?

Maintenance emissions are generally negligible – less than 5% of total sequestration. They should be subtracted from carbon sequestration estimates however.

How are urban tree inventories integrated with traditional emissions accounting?

Tree sequestration is added under GPC Scope 1 as a new sub-category. Documentation should detail the accounting methodology used.

What policy mechanisms help cities expand urban forests?

Many cities adopt urban forest master plans, tree planting goals, canopy cover targets, and dedicated funding. Engaging community groups and developers expands forests on public and private lands.

How can cities access carbon financing for urban forestry?

Voluntary carbon markets enable cities to sell certified carbon credits generated by tree planting and protection programs. Several registries have protocols for quantified urban forest credits.

Key Takeaways on Urban Tree Carbon Accounting

• Urban trees provide important but overlooked carbon sequestration benefits.
• New methodological guidance enables cities to account for tree carbon storage.
• Early adopters have found trees offset significant greenhouse gas emissions.
• By following the framework, cities can integrate urban forests into inventories.
• Accounting for trees helps cities showcase the full impact of their climate actions.
• Urban forest strategies that maximize climate benefits include native tree planting, optimized management, preserving mature trees, and expanding canopy cover.

How You Can Support Urban Trees in Your Community

You don’t have to be a city sustainability director to help expand your local urban forest. Here are some ways you can advocate for more tree planting in your community:

• Petition your city to adopt an urban forestry master plan that sets tree canopy goals. Offer to volunteer with local tree stewards groups.
• Request a street tree to be planted outside your home. Trees in plantings strips cool neighborhoods and filter air pollution.
• Donate to local non-profits that plant and maintain city trees. Many rely on public support.
• Share research on urban tree benefits with decision makers and local media to demonstrate their value.
• Speak up to protect mature trees from removal due to development. Advocate for preserving existing forests alongside new planting.
• Organize a community tree planting event at a school, park, or another public space lacking canopy cover.
• Talk to your employer about creating a greenspace with trees at offices, warehouses, or facilities.
• Vote for ballot measures and political candidates who make urban forestry a priority in their campaigns and policy.

“I encourage all city residents to become tree stewards,” says Rose Epperson, Portland’s Lead Urban Forester. “Learn about our urban forest, spread the word about the benefits, and take action to grow the canopy.”

Even small personal actions, when multiplied across entire communities, can make cities greener, healthier places to live for generations to come.

Conclusion

Urban forests provide immense value in the fight against climate change. But their carbon sequestration benefits have gone unrecognized for too long.

The new Urban Forest Carbon Accounting Framework offers cities a methodology grounded in scientific research to integrate trees into emissions reporting. Early adopting cities have already showcased significant climate impacts from urban forests.

Crediting urban trees provides incentives for continued investment in protecting and expanding urban canopies. It also helps cities more accurately showcase their emissions profiles and climate leadership.

As more metropolitan areas apply the framework globally, the climate mitigation potential of urban forests will be realized. The strategic planting, preservation, and management of city trees can play a vital role in global efforts to reach net zero emissions and build climate resilience.

With the toolkit now available, cities have an opportunity to demonstrate that nature-based solutions are foundational to sustainable urban development. It’s time to give urban forests the credit they deserve as cost-effective, multifunctional assets that communities rely on.