Simple explanation of how net zero CO2 works: right now we add CO2 to the atmosphere - we can shift the balance the other way to sequester CO2 - Earth's natural carbon cycle is close to net zero

This is to explain simple ideas of net zero. I realized today many people don’t thoroughly understand this idea. I realized this after watching a YouTube video that got it completely wrong which I was asked to fact check.

You need to understand the basic idea of the Earth’s natural carbon cycle. That is the key to understanding why we reduce emissions and why net zero is possible.

Before the industrial revolution our carbon cycle was net zero. This video will help you understand how that worked.

Plants turn CO2, nitrogen and water and some other elements into trees, crops, wood, grass etc. Algae also turn CO2, nitrogen, water etc into their bodies. This takes carbon dioxide out of the atmosphere.

When humans eat food or burn wood this returns CO2 to the atmosphere. Similarly also when animals eat food and when plants and animals rot, it returns CO2 to the atmosphere.

We also have yearly cycles.

Every spring the leaves of broadleaf trees in the northern hemisphere take up vast amounts of carbon

Then in the fall as the leaves rot, they return that carbon back to the atmosphere.

We see this cycle every year in the Keeling curve. This measures the CO2 concentration, at the top of a mountain in Hawaii.

It wiggles up and down every year. In the northern spring it falls as the leaves grow. In the fall it rises again as the dead leaves rot. It is delayed a bit because Hawaii is a long way from where the seasonal CO2 is absorbed or emitted.

But right now there is another pattern on top of it, it is going steadily up. This is because of the way we are burning fossil fuels which is returning more CO2 to the atmosphere from ancient plants that were turned into oil, coal, gas etc. millions of years ago.

https://keelingcurve.ucsd.edu/

In the other direction though, some wood, trees, algae, shells etc get buried or fall to the sea floor and turn into rocks like oil, coal shale, limestone, chalk etc.

Most of the carbon is actually buried deep underground or in the sea as various types of rock or fossil fuels.

Then that rock is gradually subducted down as the continents move around and then gets brought up again to the surface where the rock melts and rocks such as limestone and chalk and any shale, coal, oil etc is turned into CO2 and emitted from the volcanoes.

In this way, volcanoes return CO2 to the atmosphere too.

The volcanoes are in balance, they return CO2 to the atmosphere in the very long slow carbon cycle. Actually if we didn't have volcanoes doing that, eventually all the carbon dioxide would be sequestered into chalk, limestones, shale, coal, oil, various rocks and there would be no carbon left for life any more except a small amount falling in from comets.

So the volcanoes are part of the carbon cycle that prevents all the carbon ending up underground or on the sea floor.

However currently humans currently are digging up fossil fuels and returning about 60 times more than volcanoes. This is returning far more CO2 to the atmosphere currently than is lost from it, which is why the planet is warming slightly.

. Which emits more carbon dioxide: volcanoes or human activities?

Then there is another long term burial process - carbon is also buried by weathering of alkaline rock.

Some of this is shown in this diagram (not all of it)

Here is a a page on NASA which will help fill in many more details of the various processes in the carbon cycle, from the fastest (seasonal) to the very slowest (slowly moving rocks getting uplifted into volcanoes).

https://earthobservatory.nasa.gov/features/CarbonCycle

So - before we started to burn down trees, and make steel, and burn charcoal, and especially before we started to burn coal, oil and gas, the carbon was in balance. As much went into the atmosphere as came out of it again. It fluctuated a bit for instance during the ice ages but mainly stayed in a rough balance.

Now because we are burning fossil fuels, more is coming out into the atmospherer than goes back into the ground.

But we can turn that around. For instance if we were to grow lots of wood and just bury it, this would remove CO2 from the atmosphere. We can also slow-burn the wood into biochar and use that to fertilize the soil which sequesters a lot of carbon.

If we mine lots of alkaline rock and crush it and spread it in fields or drop it in the sea this also will remove lots of CO2.

We can use bioreactors to turn plants and other organics into useful products.

There are many other ways to remove CO2 from the atmosphere. I go into those here:

So this is where we could if we want, once we are close to net zero - we could then tip the balance the other way and go net negative. That page looks at variouse ways we could go back to preindustrial levels of CO2 in the atmosphere.

Right now we are going the other way. Every year we add about 40 gigatons of CO2 to the atmosphere mainly by burning fossil fuels.

If we can halve current CO2 emissions by 2030 it will rise by 1 ppm per year instead of the current 2 ppm per year. If we reach zero emissions in 2050 then it stops rising and starts to fall.

Each May the CO₂ level is the highest since the Pleistocene - becuase CO₂ rises by 2 ppm per year.

On low emissions it rises 1 ppm after 2030 then 0 ppm then starts to fall.

This is normal.

The wiggles are for the seasons - in high latitudes northern hemisphere fall, many leaves decay and CO₂ rises. it takes to May to reach Hawaii. As leaves grow, the CO₂ falls again.

See: Guest post: How the Keeling Curve will need to bend to limit global warming to 1.5C - Carbon Brief

Suppose we did no carbon offsetting. We are quickly transitioning to renewables. By doing that we can reduce that 40 gigatons to maybe 2 or 3 gigatons or less a year by the 2040s to 2050s.

A useful rule of thumb is that the temperature rises by about 1 C every 2,222 gigatons.

So at our current 40 gigatons a year or 400 gigatons a decade it is rising by 400/2222 = = 0.18 C per decade.

When we get down to 4 gigatons a year it will be rising at 0.18 C per century, a big difference.

That is an average. It varies by about 0.2 C above and below the average year on year just by year on year variation of the motion of the heat in the system in and out of ocean

That is because we measure the yearly average just in that thin skin of the planet where most humans live - it’s the easiest place for us to measure it

It is easy to measure that figure - but it is very variable year to year because some years a lot of the heat may be buried in the oceans and other time maybe a lot is on the surface making the surface warmer and increasing the global average.

The Earth isn’t fluctuating in temperature year to year. But the average over the entire year over the thin skin where we live varies year to year so we take it and average it again over that longer period of 20 years before and after.

This average fluctuates up and down by a fifth of a degree year to year sometimes more.

That is more than the temperature change over an entire century once we are down to 4 gigatons a year.

You can see that a 0.18 C increase per century will be far far easier for nature and us to adapt to. It is the speed that matters not the end temperature at least for a fair way.

At above 3 C we lose the corals because of ocean acidification and as we approach 3 C we lose some of the more delicate corals. So we want to avoid that. But not that much happens if we stay below 2 C especially well below 2 C.

But we want to avoid even another 0.2 C increase in this century after we reach, say, 1.5 C. So we aim for net zero. Net zero means that we aim to remove as much CO2 from the atmosphere as we add.

This isn't hard through to the middle of this century as there are large areas of degraded ground and cut down forests and we want to restore degraded biodiversity etc. That alone will offset that 0.18 C per century or 4 gigatons per year or maybe less.

But that may “saturate” by 2050 - ,maybe we have done all the restoration and soil improvement we want to do. So then it may start warming again, very slowly, a fifth of a degree, or maybe a tenth of a degree per century.

If we don’t want that to happen, there are many ways we can stop it. That's where the carbon offsetting comes in. We can do it in many ways. Turn agricultural waste into biochar and bury it. Grow giant kelp seaweed farms far out to sea, and then some of the debris from the farming drops to the sea floor. Crushing alkaline rocks and spreading it on sea floors. Some of it pays for itself, enhanced concrete, or the biochar and other ways of making ground more fertile for instance.

And then we can go net negative as I said.

There is nothing impossible about this. It is just about changing the balance so that we are sequestering more CO2 than we are emitting.

It doesn’t violate the law of conservation of energy as some think. It isn’t about an energy balance. It is just about the mass balance of carbon and how much is going into the atmosphere compared to how much is going into the oceans and into deep sediments.

But we might not want to cool down at that point.

A warmer world is much better in many ways. For instance there's a far larger habitable area for corals in a warmer world, It takes them a while to adjust with coral bleaching etc but once they adjust hey can then live in places like Japan in reefs where they never were before. Theres's more agriculture for wheat benefiting countries like Ukraine, Russia, Canada all produce more grains as do countries in Northern Europe because of global warming. More trees in Iceland that never could grow there before and so on.

So - we wouldn't want to go suddenly back to 1.2 C cooler or 1.5 C cooler in just a decade or two, that would be a second shock for ecosystems as bad as the warming.

We could go back more slowly. Or maybe we decide it is better at 1.5 C say. For instance many whales now enjoying almost ice free arctic seas in summer etc.

So we'll have a decision then.

See my:

BLOG: The warming of the Anthropocene has benefited the world in many ways

— the issue is the speed of change and we likely wouldn’t want to go rapidly back to preindustrial from 1.8 C

So but we can certainly achieve net zero. There is no scientific or mathematical problem with doing that.

People raise many issues at this point.

But I want to keep this simple, if you don’t understand net zero then the rest of the discussion is going to be very confusing.

So hopefully now you know if you had confusions about it before.

On some other points, you will often hear people claim that if we raise temperature just a bit then it will suddenly speed up, in a runaway.

They may say this is because of methane in the sea floor, or arctic ice melting, or the permafrost melting, or to do with cloud patterns and can raise many such ideas. But the IPCC in 2021 did a comprehensive look at all of that and found out that it is virtually certain that there is no sudden increase. This is also backed up by paleodata from times in the past when Earth was this warm with this much CO2 in the atmosphere and more.

This chapter seems to be not very well known for some reason.

Many claim that relying on renewable energy is impossible rebutted here

The idea that we can’t do renewables because of the resources we need for them debunked here:

BLOG: Yes we can rise to the resource challenges of mining minerals for renewables for the green revolution
— with climate smart mining

BLOG: When are we going to reach Peak X? Never
— we have enough resources for this century at least for everything

And many more but I’ll stop there for now. You can find many more blog posts in my list.

For my most recent blog post see:

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