How can a US county achieve net-zero in 7 years without CDR?

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E Durbrow

May 13, 2023, 4:29:05 PM5/13/23
Hi. Apologies if this question is too local for the list. A task force in my county of Sacramento (mainly suburban but some farming) plans to achieve net zero CO2e by 2030 ***without carbon dioxide removal and storage**** We currently emit more than 4.3 million tons of CO2e a year. It has roughly been declining 1.5% per year…

Several counties in California also plan on 2030 for net-zero but plan to use some kind of CDR technology. So does San Fran by 2040. And even London, UK.

My question: is a realistic for any county, province, shire, to achieve net zero in 7 years without CDR?

Thanks for any comments.

Bruce Melton -- Austin, Texas

May 13, 2023, 5:19:59 PM5/13/23
to E Durbrow,

I was chair of a stakeholder group that produced a minority report to Austin's latest climate plan: net zero 2040, 1.5 C. There is absolutely no way this can be done without offsets, anywhere. There are simply too many sources of impossible to decarbonize emissions and natural systems are failing left and right. Austin plans on using natural systems and purchased credits because even with natural systems maxed out, Austin has a 30 percent net zero gap.

The deal with natural systems though is they are significantly in decline to already flipped. An example is the ice storm the Austin Region had this winter. Austin Resource Recovery has picked up enough storm debris to fill Q2 Stadium four times. The Texas A&M Forest Service says 10.5 million trees were damaged in the Austin area by the storm. At just 400 pounds biomass lost per tree, at 50 percent water and 50 percent dry weight carbon, this is 525,000 tons CO2 as carbon, equaling 2 million tons as CO2, or 17 percent of Austin's annual emissions. This is equal to all of the transportation electrification emissions reductions goals of the Austin Climate Equity Plan by 2030, at just 400 pounds per tree.

These emissions do not include future reduction in emissions because of the lost biomass. The also do not include mortality from drought where Texas lost 300 million 8 inch diameter or greater trees in the 2011 drought, and the trees  continue to see elevated morality from long-lived stress where drought impacts can be felt for decades to generations in long-lived species.

Globally, most forests are in decline with mortality increasing by a double to four times normal. A doubling of mortality halves carbon storage and because forest are only modest sequestering systems, a doubling of mortality flips the forest from sink to source. (The citations for this one are many and complicated. See below my signature for more.)

In California, just the fires in 2020 released double the greenhouse gas emissions reductions for the entire state from 2003 to 2019.
Science Direct - Environmental Pollution, October 1, 2022.

Also in California, almost the entire carbon buffer pool for forest credits has now burned, a buffer that was supposed to last 100 years.
Badgley et al., California's forest carbon offsets buffer pool is severely undercapitalized, Frontiers in Forests and Global Change, August 5, 2022.

As go these systems locally, likely go similar systems globally.

Austin Climate Plan Minority Report:
Climate Emergency Response

The Urgent and Immediate Response Needed to Reverse Activated Climate Tipping With a Safe, Sustainable and Equitable Target of Less Than 1.0˚C Warming Above Normal
September 2021   

Steep Trails,



Bauman 2022 analyzed a 49-year record across 24 old-growth tropical forests in Australia and found mortality has doubled because of water stress across all plots in the last 35 years indicating a halving of life expectancy and carbon residence time and suggesting that Australian tropical forests have now flipped from a CO2 sink to a source of CO2 emissions. Further, they suggest Southeast Asian tropical forests are behaving similarly. When I asked Bauman to confirm that Australian tropical forests are analog to Southeast Asian tropical forests,  he suggested what he believed now was that the same water stress is likely affecting all tropical forests globally in a similar way. 

Understanding this relationship with mortality doubling resulting in a halving of carbon storage, I recalled McDowell 2015 discussed mortality rates of forests across Western North America:

Increased forest mortality in Western North America between 1980 and the mid-2000s with much of the increase happening recently… It is also pertinent that warming since the mid-2000s has just about doubled as of 2022, and that much of the recent western US forest mortality from bark beetles and increase in burn area was not captured in McDowell 2015:


Mortality of Western North American forests from McDowell 2015:

-- Sierra Nevada mortality has doubled from 0.75 to 1.5 percent
-- Western Canadian forest mortality has quadrupled from 0.6 percent to 2.5 percent

-- Eastern Canadian forest mortality has nearly doubled from 0.8 to 1.45 percent
-- Western US interior forests mortality has more than doubled from 0.3 percent to 0.65 percent.
-- Pacific Northwest forests mortality has tripled from 0.45 to 1.25 percent

Assuming that western North American high altitude and high latitude forests are also analog to similar ecologies across the globe where a doubling of mortality results in a halving of carbon storage, on average then it is likely that in addition to tropical forests globally, high altitude and high latitude forests globally have also flipped from sink to source.

This interpretation is backed up by flips of the Amazon (1 Gt CO2eq emissions annually - Gatti 2021), Canadian forests (250 Mt CO2eq emissions annually - Canadian Forest Service 2020), and permafrost (2.3 Gt CO2eq emissions annually - Natali 2019, where this is net emissions that include drowned forests). We also need to consider the Amazon and permafrost emissions are averages, and both were likely stable at the beginning of the averaging period, therefor emissions at the end of the averaging period could be interpreted as being double the average, assuming a linear increase. This would put emissions from just the Amazon, Canadian forests and permafrost regions at about 7 Gt CO2 annually.

Bauman et al., Tropical tree mortality has increased with rising atmospheric water stress, Nature, May 17, 2022.
(Researchgate, free account required)

McDowell et al., Multi-scale predictions of massive conifer mortality due to chronic temperature rise, Los Alamos National lab, nature Climate Change, December 21, 2015.

Gatti et al., Amazonia as a carbon source linked to deforestation and climate change, Nature, July 14, 2021.

The State of Canada's Forests, Adapting to Change, Canadian Forest Service, 2020.

Natali et al., Large loss of CO2 in winter observed across the northern permafrost region, Nature Climate Change, October 21, 2019.

Globally, Forests mortality more than doubled… "The impacts of global change on forest demographic rates may already be materializing. In mature ecosystems, tree mortality rates have doubled throughout much of the Americas and in Europe over the last four decades (7-9)…  Beyond changing vegetation dynamics within “intact” or relatively undisturbed forests, episodic disturbances are tending to be larger, more severe and, in some regions, more frequent  under global change(17-20).  Similarly, the rates and types of land-use change (LUC) vary widely (21) but have, on average, increased globally in the past few centuries (2,22,23)… Thus, at the global scale, disturbances [climate change related] and LUC [land use change] have likely amplified tree mortality beyond that suggested by the doubling of background mortality rates in undisturbed forests (7-9)."

McDowell et al, Pervasive shifts in forest dynamics in a changing world, Science, May 29, 2020

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
The Band Climate Change
Twitter - BruceCMelton1

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