What is Zero? San Diego debates its ambition to reduce emissions

Last year, San Diego County pledged to achieve “net zero” emissions by 2035. Since then, it has been studying how it will achieve this lofty goal, and early indications are that local governments in their together will need a new political trajectory. entirely.

San Diego Mayor Todd Gloria is pushing the city to pursue that same goal. The update to the city’s climate action plan he proposed last year would require a series of major policy changes, all to achieve a new goal of reaching net zero emissions by 2035.

But we thought maybe it wasn’t obvious what it is first of all for all those who are not already climate enthusiasts.

“Net zero,” as the name suggests, does not mean eliminating all global warming emissions from human activity. Rather, it means achieving a balance between the level of emissions that human society produces over a given time period and the amount of global warming emissions that the planet absorbs or humans absorb over the same time period.

In the immediate term, this elimination of emissions would come almost entirely from natural means. Wetlands and trees extract carbon dioxide (the most prolific greenhouse gas) from the atmosphere and sequester it as part of their natural processes. By restoring and preserving these natural environments, humans can maximize the amount of carbon sequestered by the planet. A “net zero” policy would then allow humans to continue emitting an equivalent share of carbon by driving cars, running factories, pouring concrete to repair sidewalks, heating homes with non-renewable energy and all our other social and economic activities that contribute to climate change.

That is, if the natural world could track the amount of additional greenhouse gases humans are releasing into the atmosphere, which is precisely what is messing up Earth’s climate in the first place.

So, in the medium term, governments, corporations, nonprofits large and small are trying to bridge the gap by making promises and policies that transform fossil fuel-based resources into renewable ones. Yet, so far at least in San Diego, we know the plans on the books are not capable of reducing greenhouse gas emissions to net zero by 2035.

In the long term, many of these net-zero policies rely on yet-to-be-developed technologies that mechanically remove carbon from the atmosphere, called direct air capture.

But even figuring out how many emissions humans need to reduce to truly reach net zero requires both hard science and rigorous policymaking.

Gordon McCord, a sustainability economist at the University of California, San Diego, who led the county’s regional decarbonization study, said the goal of the analysis was to “map out pathways to achieve as close to zero carbon as possible.

“We consider ‘net zero’ only in the sense that we looked at how natural climate solutions in San Diego County could generate more negative emissions, which would be helpful in offsetting the fact that there are sectors/ hard-to-decarbonize uses. “, he wrote in an e-mail.

Gloria’s proposed update to the climate action plan says it would cut 80% of emissions generated by 2035 – leaving another 20% of ongoing emissions that would need to be removed from the atmosphere by natural processes or other means, if the city plans to achieve net zero commitment in the plan.

“This strategy is broad by design and includes developing more effective regional partnerships, further researching (carbon) sequestration opportunities, and collaborating on pilot projects for new technologies,” wrote Alyssa Muto, director of the City of San Diego’s Department of Sustainability and Mobility in an email. .

Let’s try to break down what that would look like in simple math.

The San Diego area emitted about 26 million metric tons of greenhouse gases in 2016, according to the latest greenhouse gas emissions summary from the San Diego Association of Governments. This includes electricity, natural gas, road transportation, solid waste, agriculture…basically anything that produces emissions that warm the planet.

The region, meanwhile, has 58 million tonnes of greenhouse gases stored in its soils, wetlands, trees, etc., according to the same regional study. As long as this land is not disturbed, this carbon will remain there. This same environment also reduces planet-warming gases that are also in the atmosphere. It sucks about 2 million metric tons of carbon from the atmosphere per year and buries it in nature.

So, unless there are changes to increase the ability of the regional environment to pull carbon out of the atmosphere, for San Diego to reach net zero, San Diegans would theoretically have to reduce emissions to 2 million metric tons per year to balance with nature. This means that we would need to eliminate approximately 93% of our existing emissions.

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