Urban trees and the zombie carbon sequestration myth

Last summer, my city passed a tree protection ordinance that fines people for removing trees--even those on private property in side or back yards (where they don't shade public sidewalks or road asphalt). It was sent for legal review and will come back on December 20, 2022 for final passage. 

I'm not a lawyer, but I will say as a scientist that it is claptrap. 

So much nonsense was spewed that would fly under the radar of people not in the trenches of housing policy. I suspect that using the need for street trees to push through a more expansive policy is designed to make infill housing (eg ADUs*enabled by SB 9) harder or more prohibitively expensive to build. 

But, I want to push back on the pernicious myth that carbon sequestration through urban trees is better than building infill housing. 

Let's do the math!

A mature urban tree can absorb about 20 kg of CO2 per year. MIT Climate Issues rounded that to about 50 pounds. (Click through to read how they debunk some of the 'nature-based solutions' talking points.)

The EPA, US Environmental Protection Agency, reports that the Greenhouse Gas Emissions from a Typical Passenger Vehicle is 8,887 grams CO2/gallon or 404 grams CO2/mile using the US passenger car fleet average. 

The largest employers in my city are Northrop Grumman (next to a light rail station) and our local school district (dispersed around the city, not served well by transit).  Since school teachers cannot afford the median house price of $1,587,500 

or even the median condo price of $1,007,000

teachers drive in from elsewhere. The only places in LA County actively building new apartments and condos in substantial numbers is Downtown LA (DTLA) or Old Town Pasadena. 

If they want to buy an older single family home, like this one that sold yesterday in Whittier for $630,000, they also face a long commute. 

The Whittier house is 27-29 miles to Redondo Union High School depending on the route. Old Town Pasadena is 30 miles each way. 

A round-trip commute for just one of the hundreds of teachers in our city that cannot afford to live here is about 60 miles/school day. 

60 mi/day * 404 g/mi = 24,240 g/day = 24.24 kg/day

It would take a mature tree more than a year to sequester the carbon emissions of just one day's commute for a teacher commuting in from where they can find housing that they can afford.  

I looked up more data. 

California requires 180 school days/year. There are a few additional teacher prep and in-service education days, but let's use the lower 180 number. 

I looked up the RBUSD budget and see that there are 463.80 Full-Time Equivalent (FTE) teachers in the district. 

24.24 kg/day * 180 days * 463.8 teachers = 2,023,652 kg/year 

That would require 100,000 trees just for in-bound commuting teachers

That's just a few hundred of the 25,000+ jobs in Redondo Beach according to the research arm of Southern California Association of Governments (our regional housing and transportation governing body). 

I can't ensure that all infill homes will go to teachers in the community. 

I do know that teachers have to live somewhere, so they need homes. It would be great if they could live close enough to participate outside of school in the communities where they teach, and if they didn't need to drive a car to work.

The benefits of workforce housing:

• Planet (fewer climate-wrecking CO2 emission)
• Community (the teacher can be more present)
• Public health (fewer car miles = less air/water pollution)
• Teacher health (long driving commutes have well-documented detrimental health impacts)

Now substitute teacher for any other job in our city. This includes store clerks and caregivers to the elderly or young children that make just above minimum wage. They take care of us. We need to take care of them. We won't be able to build enough ADUs to fill the need. But, we can build enough apartments and condos, in a thoughtful way, to reduce the need for climate-destroying and space-gobbling automobiles. 

Asides: 

ADU = Accessory Dwelling Units or Granny Flats or In-Laws' units. ADUs generate a little extra density in single-family neighborhoods, create homes without generating much external impact. In fact, when used to house caregivers or those needing care, or local essential workers, they reduce car traffic or Vehicle Miles Traveled (VMT) overall.

Keeping low-density existing homes is NOT better than replacing them with higher density housing, even accounting for embodied carbon. But, I'll cover that myth in another post. 

I hear lots of chatter about preserving or increasing urban tree canopy in order to combat the urban heat island effect. That's a good idea. I'm all for trees. In fact, we bid aggressively on both our home purchases because they had more trees compared to other homes in our budget/area. More on that later. 

Redondo Beach has no native trees. It was a coastal prairie according to UCLA's Urban Wildlands Group (Dept of Geography). I'm stuck wondering what proponents are calling "Heritage Trees".