What does carbon neutral mean?

I'm glad that AOC and her allies are serious about combatting climate change and willing to commit the necessary focus and urgency to one of the biggest challenges we face.  But, I hear people use terms interchangeably that mean very different things to different people.  Here's an explainer to translate.

Let's backtrack to look at the CO2 measurements at the Mauna Loa Observatory. The trend is upward, which is what is the main cause of global warming.  Do you see the jagged sawtooth edge?

Full record of CO2 measurements at the Mauna Loa Observatory

Let's look at a close-up for the last year.  See the scatter of the real data?  Real data is messy.  They take weekly and monthly averages of the measurements and add them to the long-term plot above.

Mauna Loa CO2 measurements for the last year

The jagged nature of the data means that, for part of the year, roughly May through September, raw CO2 counts are going *down* (net negative).  It's going down because the earth is taking up more CO2 than we are spewing out.  There is more land, vegetation and human activity in the northern hemisphere (NH) than in the southern hemisphere (SH).  During the NH (Boreal) summer, trees and crops are growing and we spew less CO2 because we don't need as much heating and lighting.

September to May, the cycle reverses and the planetary CO2 becomes net positive.  While there are forests and cropland in the SH, there are much fewer.  The trees in the NH slow down or go dormant, NH farms lie fallow,  and carbon sequestration decreases on a global basis. Overall, the trend is up and net positive.

When scientists say that we need to be net zero (aka carbon neutral) and that it is possible to do so, we are not saying we will stop producing CO2 altogether.  We mean we can slow down our generation of CO2 to a sustainable rate that the earth can take up (sequester) in ways that are not harmful.

Carbon neutral and net zero is not zero CO2 emissions.

This is an estimate of the amount of CO2 emitted to generate one million British thermal units (Btu) of energy.  (This is an average of all the plants in operation.  Different plant designs have different efficiencies.)  eia.gov, the Energy Information Administration, publishes more detailed statistics by state.

Carbon efficiencies for different types of fuels.

According to an IPCC report in 2018, we can contain the warming to 1.5 degrees Celsius if we halve our CO2 emissions by 2030 and go net zero by 2050.

Pathways to save our skins

We already have the technology to hit our 2030 target.  We just need to quit arguing and do it.  Let me explain.

If we switch off coal to natural gas, we produce half our CO2 emissions right there.  Coal-fueled power plants are closing across the US.  We should replace them with wind and solar power plants wherever it is appropriate.  Some places do not get the right type of winds (too weak or turbulent) or enough sunshine.

We make up the difference with new, highly-efficient natural gas power plants as a bridge to the net zero future in 2050.

Simple cycle gas plants produce electricity by burning natural gas to turn a turbine.  They also send up a lot of waste heat into the environment which has its own problems.

Combined cycle gas plants combine the simple system with a second steam engine that uses the waste heat to generate steam that turns another turbine that also produces electricity.  Combined cycle plants produce roughly 1.5 times as much energy per unit of CO2 as simple ones.  This sounds like another slam dunk, right?

There are a couple of gotchas. "The EIA estimated that for a simple cycle plant the cost is about US$389/kW, whereas combined cycle plants are US$500 – 550/kW."  Would you pay an extra 34% for 50% more CO2 efficiency?  It doesn't make economic sense if we are looking at it purely from the point of cost of energy.  But weigh it against a livable planet, and I think combined cycle is the better choice.

The second gotcha is time.  The wind stops blowing or the sun doesn't shine?  A simple cycle plant can be pulled into production in minutes.  A combined cycle plant takes 30 minutes or more to spin up to full production.

As we deploy more renewables in the form of solar and wind, the greater the instability of our power supply.  That instability can cause major fluctuations of voltage and damage equipment, leading to blackouts.  Ironically, the more we reply on renewables, the more we need power than can be brought on and off-line quickly.  Simple gas plants are being used that way for now.

The real payoff for batteries is to bridge that 30 minutes between when we need the power and when the combined plants are running at full efficiency.  Alternatively, combined plants are run continuously and we can pay someone to take the excess power away in the form of negative costs per kilowatt.  (This actually happens on sunny days in California, to Arizona's delight.)

Take a look at CA renewable electricity production on March 20, 2019.  This is all CA-only info from California ISO.

March 20, 2019 CA renewables

Notice the dips in peaks in the solar PV and wind curves.  That's when the sun didn't shine or the wind didn't blow.  This is averaged over the entire state of California, a large area with a diversified portfolio.  Think what the curves would be like for smaller countries.

Production is only one side.  What about demand?

March 20, 2019 CA electricity demand - renewables

There is a big gap between our current demand and renewable energy supply (the green curve above.) We should be doing much more to reduce our demand and to shift it to times when renewables are available.  We also need to keep developing energy sources that don't spew CO2.

Let's take a look at how CA got its energy on March 20, 2019.

• Hydro is larger scale hydroelectric not covered under small hydro in the renewables portfolio
• Imports is electricity imported from out of state and can be generated by any method.  There are some regions in the state, particularly near the boarders that primarily draw electricity from neighboring states.  We also export energy to neighboring states.  Northern (rural) CA imports power from as far away as Utah and Wyoming, which is largely generated with coal (but rapidly changing over to natural gas.)  Norcal also gets power from WA and OR, often hydroelectric.  Southern CA imports electricity from several coal powered plants in Arizona, which are slated to close really soon.  SoCal also imports electricity from a nuclear power plant in AZ.
• Thermal can be coal or natural gas.  CA has shut down all of our coal power plants so this slice is entirely natural gas from power plants of different designs and efficiencies.  Efficiency can be improved, which can reduce our dependence on imported energy.
• Nuclear used to supply 20% of California's annual electricity demand just a few years ago.  Now it supplies 8%.  If we don't invest in nuclear, it will soon be 0.  Shutting down nuclear, our primary source of night-time electricity (along with large hydro) is a large reason why we need natural gas plants.
• Renewables cover solar thermal (currently one plant, which is offline,) solar PV, wind, small hydro, biogas (our collective poop,) biomass and geothermal.

March 20, 2019 CA electricity sources.  Imports are electricity generated outside CA and can be from any source.  Thermal is from natural gas.

The slices that produce CO2 emissions are the light blue natural gas and a portion of the imported energy sources.  Nuclear and hydro also do not spew CO2.

Large hydro has fallen out of favor and is not counted as renewable.  Hydro is the original grid-scale battery.  Water can be released when power is needed.  Since the era when the US built most of our large hydro projects, we have learned a great deal about the harm that it can do.  We have also learned how to mitigate some of the harm.

Climate change is a threat to all river systems, dammed or not.  We should definitely invest in small hydro and also move forward with new large hydro if the environmental and social costs are less than costs of climate change.

Right now, there is simply no way to store enough energy to get us through the night without using natural gas.  There are also environmental problems with batteries.  What happens if lead acid batteries leak?  Lithium batteries are more energy dense, but can spontaneously combust.  Hydrogen is explosive.

We should continue to invest in batteries and battery research but understand that they are not going to solve our night-time energy problem.  We should also invest in making our natural gas plants as efficient as possible and use them as little as possible.

If we demand that there be no new investment in fossil fuel-powered electrical plants, we cannot put scrubbers on coal power plants to remove black carbon (which is extremely warming), replace coal with gas, or upgrade simple gas plants to combined gas plants--all things that would greatly reduce climate change at low cost.

If we stop using nuclear, as Japan and Germany have done, then we can actually increase our CO2 emissions.  All of Germany's gains in renewable energy have been offset by the closing of their nuclear power plants.  They are spewing as much CO2 as ever by replacing nuclear energy with coal.  Is that the model we want to follow?

Coal kills more people every year than nuclear energy in its entire history.  Amongst scientists, support for nuclear energy is much higher than amongst the general populace.

Some existing nuclear power plants were certainly poorly designed or sited (on coastlines or in seismically active areas.)  Now that we no longer use ocean or river water to cool nuclear reactors, they can be sited in much safer areas and away from population centers.  Do we have the political will?

Is nuclear bad?  Possibly.  But I'm sure that climate change is a bigger threat to us right now.  I believe that building new nuclear power plants in geographically safe areas are worth the risk, but can understand why some do not agree with me.

We need to be flexible in our thinking and actions while maintaining a sense of urgency.

For comparison, I'd like to show what happens during extraordinary weather events like the long-duration heat wave we experienced in July 2018.

July 25, 2018 CA renewables

It was relentlessly sunny, so we had plenty of solar PV during the day. Ivanpah was in operation so we also had solar thermal power.  Ivanpah was shut down due to economic reasons even though it generates about 10x the energy per unit of CO2 as old simple cycle gas plants.  Should we make our energy decisions purely on economic factors without factoring the harm of CO2 emissions?

July 25, 2018 CA total electrical sources

Take a look at the scale on the left.  California's electricity demand on July 25, 2018 was roughly double our springtime electricity demand this week.  Renewables made a dent, but supplied only about a quarter of our electricity.  There is more work to do.

Just for fun, I checked California's electricity production and use right now. 61% renewables!  During spring time, for wet years where water is available for hydroelectric, California can approach 100% non CO2-producing electricity sources during the day time.

In closing, let's look at the big picture.  Electricity accounts for 16% (and falling) of CA's CO2 emissions.

A large chunk of the industrial slice is due to cement production, largely to build infrastructure for cars and airplanes. Do we need to drive and fly as much as we do? Do we need as much stuff?

Let's look at agriculture.  Eat less meat and almonds. There is a lot of info about how to reduce the carbon intensity of diet and we'll save that for another day.

The largest component is transportation. We can make huge reductions if we reorganize our society so most people don't need to drive.  Invest in transit and pedestrian and bicycle infrastructure.  Helping people live densely and well is the biggest thing we can do to reduce our carbon emissions.  It would also reduce congestion, air pollution and stress.

Why is it easier to imagine batteries made with unicorn poop than living next door to an apartment complex?

In summary:

• Net zero for electricity is possible right now, with existing technology.  
• We just need to deploy more of it, which means investing in more zero CO2 emitting energy sources and modernizing some natural gas plants.  
• It also requires us to reduce/change our energy consumption habits.
• We don't need to stop using all fossil fuels today or even in 10-12.  We just need to use a lot less of them and phase it out gradually.  Do what you can today.  Reduce a little bit more each year.  
• Carbon neutral or net zero is not zero CO2 emissions.  It is only a reduction to the level that the earth can sequester the CO2.  
• Don't fixate on just electricity production.  Look at all the other slices of our carbon budget.  The biggest and most cost-effective reductions will likely come from the biggest CO2 producing sectors e.g. transportation.
• Reducing demand is the fastest and most economical way to reduce CO2 emissions.  It's fair to ask the people who are using the most to reduce the most.
• Market-based solutions are not enough.  We need to add externalities to the equation and ask ourselves moral questions about fairness.

There is much that I like about AOC's GND, but I also have reservations about some of her wording. I worry about getting attacked by zealots.

Let us agree that:

• Climate change is real
• It is the biggest global crisis that we face (but not the only one)
• The time to act is right now
• We should put a big effort into combatting CC commensurate w/ the size of the problem
• Reducing green house gases can lead to a more just & equitable society if we approach it thoughtfully
• Building for climate resilience can lead to a more just & equitable society if we approach it thoughtfully

* This post is part of a series.

1. Energy and bullshit asymmetry: Mark Jacobson is the Andrew Wakefield of green energy, spreading harmful disinformation to divide us and prevent us from making real progress
2. Green New Deal Reading Some thoughts by myself and others on what the GND means