Boulder has cut greenhouse gas emissions nearly in half since 2005. Here’s what’s driving the decline.

The climate has featured prominently in recent global headlines — COP30 in Brazil, Bill Gates’ climate priorities memo, new coral reef warnings, the EU’s softened 2040 target and the world edging closer to 1.5°C.

Here at home, the Trump administration’s second withdrawal from the Paris Agreement and federal policies favoring fossil fuels have added new uncertainty to national climate action. Colorado’s largest utility, Xcel Energy, still sources more than half its electricity from natural gas and coal, and is seeking to delay the retirement of its Pueblo coal plant, even as it expands renewable generation.

Against this backdrop, Boulder’s progress on climate action becomes even more important and also more complex. Last month, Boulder released its 2024 Greenhouse Gas Inventory, which shows emissions continuing to fall, driven by a mix of local action and broader regional and statewide shifts. Some in Boulder believe the city’s yearslong municipalization effort helped shape Xcel’s clean energy commitments. But after Xcel missed its 2022 and 2024 emissions targets, some residents pursued a new ballot measure to let the city exit the agreement early.

The biggest challenge ahead remains natural gas: Emissions from gas use have only modestly declined, even as electricity and transportation have seen steep drops. Boulder has moved to limit future gas demand, banning natural gas in new construction and major remodels, with some exemptions.

Under targets adopted by city council in 2021, Boulder is pursuing a staged approach:

• Cut emissions 70% by 2030 from 2018 levels.
• Reach net-zero by 2035, meaning Boulder would eliminate most emissions and offset the rest.
• Become carbon-positive by 2040, meaning Boulder would remove more climate pollution than it produces.

These goals build on two decades of climate action, including the city’s early Kyoto work in 2002, the Climate Action Plan Tax in 2006, the Climate Commitment in 2016 and the 2019 Climate Emergency declaration. Voters extended the Climate Tax through 2040.

What the new numbers show, and why they fell

In 2024, Boulder’s community emissions totaled 1,117,543 metric tons, an 8% drop from 2023, a 29% decrease since 2018, and 48% lower than 2005 levels. 

The decline is significant, but most reductions come from factors outside Boulder’s direct control:

• A cleaner electricity grid, as Xcel shifts toward renewables under statewide requirements.
• Lower on-road travel within the city.
• Growing EV adoption supported by state and federal incentives.

Local policies — including energy codes, climate taxes and electrification programs — also play a role. But the inventory suggests that Xcel’s changing electricity mix accounts for roughly 81% of reductions since 2018.

The city notes that meeting Boulder’s 2030 and 2035 targets will require cutting emissions by an average of 10% of current totals per year, about twice the average annual pace since 2018.

Where emissions are coming from

According to the city’s summary report (provided to Boulder Reporting Lab by Boulder’s Climate Initiative Department), the largest individual sources of emissions in 2024 were:

• Building electricity use (38%)
• Building natural gas use (28%)
• Transportation (33%)

Combined, building energy use accounts for about 65% of emissions: 49% from commercial and industrial buildings and 16% from residential buildings. Transportation makes up 33%. Solid waste and wastewater treatment contribute just over 1%.

Taken together, the data show that most of Boulder’s climate footprint comes from how homes and businesses are powered and heated, not just from driving.

For more detail, see the visualization below from the summary report:

Which sectors are shrinking

Two areas saw major declines: 

• On-road transportation emissions have fallen 59% since 2018, driven by fewer miles traveled within city limits and rising EV adoption. Twelve percent of vehicles registered in Boulder are now electric.
• Building electricity emissions have dropped 47% since 2018 because of Xcel’s cleaner energy mix. State law requires the utility to cut power-sector emissions 80% by 2030.

By contrast, building natural gas use, now more than a quarter of Boulder’s emissions, has declined just 8% since 2018.

For a detailed look at city emissions trends (2018, 2023, and 2024) by sector and source see the table below from the summary report:

The harder part starts now

We reached out to Jonathan Koehn, director of Boulder’s Climate Initiatives Department, for his perspective on the latest numbers.

Koehn said he remains optimistic that Boulder will continue making meaningful progress, while acknowledging that “the pace of reductions becomes more challenging over time” and that local programs will need to “scale up significantly to meet the city’s targets.” He noted that Boulder has already cut community-wide emissions roughly 50% since 2005, “an extraordinary accomplishment reflecting our community’s sustained commitment.”

He pointed to electricity-sector progress, noting that “Xcel Energy is targeting up to a 90% reduction in emissions from electricity generation by 2030,” which will continue to drive reductions locally.

A key focus moving forward is reducing natural gas use in buildings.

“Over the next decade, we’ll implement policies, incentives, and partnerships to help residents and businesses transition to electric heating and appliances,” he said. “The roadmap envisions a proactive transition away from natural gas, done thoughtfully and equitably.”

He identified three major shifts that will guide the next decade:

• Building electrification: Expanding programs and incentives that help homes and businesses replace gas furnaces, water heaters and stoves with electric alternatives.
• Strategic decommissioning: Working with Xcel to identify parts of the natural gas system that may no longer be needed as more buildings switch to electric heat.
• Thermal networks and district-scale systems: Exploring neighborhood-level heating and cooling systems that share energy between buildings and reduce the need for individual gas hookups.

Koehn said the city will also continue investing in natural climate solutions “such as soil health, tree canopy expansion and ecosystem restoration,” while monitoring credible carbon removal technologies. Through the Four Corners Carbon Coalition, Boulder and Boulder County are identifying future carbon removal strategies.

Boulder is widely viewed as a leader in local climate action, but city leaders and the new inventory say the hardest work is still ahead, with the 2030, 2035 and 2040 targets requiring faster emissions cuts than ever before, deeper reductions in natural gas use and broad community participation.