Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Twitter Facebook YouTube Mastodon MeWe

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


What does Net Zero emissions actually mean?

Posted on 12 March 2020 by Guest Author

To stop climate change the world needs to reach net zero greenhouse gas emissions. But what does this actually mean? And can we trust the countries and companies who are announcing their net zero carbon targets.

Support ClimateAdam on patreon:

1 0

Printable Version  |  Link to this page


Comments 1 to 17:

  1. the problem with planting trees is:

    1. Plants grow slowly ... and it takes some time until 1 t of wood (consuming abt. 2 t of CO2) grows ...

    2. When temperatures are high there is bigger danger of lightning etc. which destroys the wood just grown.

    3. etc.

    0 0
  2. Trees do grow slow- but in addition to sequestering carbon, they also produce oxygen, protect watersheds, provide wildlife habitat, provide recreational opportunities, etc. Oh, and forests that are well managed (most are not of course) can produce sustainalbe economic wealth for the owner and for "wood products industries". And, wood as a raw material has a lower carbon footprint that cement and steel.

    JZ- forester since Nixon was in the White House

    0 0
  3. So Climate Adam doesn't like the UK giving the burden of other nations to help it get to net zero- but, it's NOT the British Empire forcing its colonies to do this work- other nations will expect to get paid.

    I'm amazed at how some people are never satisfied. Aiming for net zero, however it's going to happen, is a big deal. Why whine about it?

    0 0
  4. JoeZ,

    I agree with Climate Adam's point that a nation that buys credit from someone else who is behaving better rather than personally behaving better "Is Not Being Helpful".

    The ability to buy legitimate credits is limited. Everybody has to actually personally become No-Harm people. And the wealthiest need to lead that effort, and help others. The cult of the theory of the Free Market mistakenly believes that helpful leadership to a sustainable decent future for everybody will naturally be the result if people are freer to believe what they want and do as they please.

    Letting richer higher-status people who are acting harmfully buy the appearance of being less harmful does not make them more helpful leaders.

    0 0
  5. One Planet Only Forever said, "Letting richer higher-status people who are acting harmfully buy the appearance of being less harmful does not make them more helpful leaders." I don't have a problem with that- but rather than just look at what a nation is doing- we need to look at individuals. I too often notice people complaining about climate change who happen to have a huge carbon footprint. If it's imperative to do their work- that's one thing, but often it's not- it's just that they have a lot of money so they like living a rich life style, while complaining about climate change. I happen to have a low carbon footprint- but not specifically because of climate change- but because I've always believed in not wasting resources of the Earth. My favorite author is Henry David Thoreau and I've always appreciated his living in a tiny cabin- not just to prove he can do it but to find out what is essential in life- and I've come to the conclusion that materialism is not the way to satisfaction beyond a certain level. I do happen to be a climate skeptic- but at least I'm not a pig about bragging about a huge pickup truck and eating beef every day and living in a huge house. I've always said if I got rich, I'd still have a small house but it would be artfully designed. I have clients in my work who live in mansions- and they don't impress me at all.

    0 0
  6. Some of the rich folks who complain about climate change and who have large carbon footprints buy forestry credits or similar to compensate. Prince Harry does this to compensate for his flying all around the place. They are not evil, they have been told planting forests compensates and at least they are doing something. Although why anyone needs to live in a massively huge mansion and fly constantly is beyond me, with or without the climate problem.

    The problem is more that 1) this heavy reliance on planting forests delays real emissions reductions and 2) new forests probably barely keep pace with deforestation and 3) the ability of forests to act as an effective long term carbon store is hard to be precise about and 4) there are limits to land available for new forests. Yet emissions trading schemes make forests a dominant mechanism because its just easier to plant a few forests or buy the credits than actually reduce emissions at source. The later option might be better for a corporate economically if carefully analysed it but human nature being what it is people will go for the simplest option, forestry credits. This is the danger of emissions trading schemes.

    It looks to me like we are planting a lot of forests of dubious merit and delaying emissions reductions at source.

    0 0
  7. JoeZ @5,

    I am not sure what to make of your comment. You quoted the end of my comment that is clearly about Individuals (as is the middle part of my comment) and then said "I don't have a problem with that- but rather than just look at what a nation is doing- we need to look at individuals."

    nigelj's comment is more on target.

    I would add that the discussion needs to be about every individual on the planet becoming a Zero-Excess New GHG-Producer (ZENGHGP), not the same as Net-Zero or Carbon-Neutral, soon enough to keep the total impact below 2C along with actions to draw down the harmfully created excess GHGs from the tragic peak level that is reached. That requires every already wealthier person to prove they deserve their higher status by becoming a ZENGHGP well before 2050 and helping others behave better quicker, the wealthier they are the quicker they are expected to be ZENGHGP and more helpful to others.

    Anyone acting better, not just being ZENGHGP, but also taking actions to remove some of the excess GHGs, should be recognised and rewarded for being a Good Helpful Leader. But no one should expect the games of popularity and profit that developed this problem, and developed massive resistance to correction of the problem, to produce the required result. It is clear that the games of popularity and profit will not encourage and reward that correction of what the games of popularity and profit harmfully developed. Good Governance that significantly meddles in the marketplace will be required.

    Also, the last people to be living in ways that produce new excess GHG impacts would be people who are still being helped to develop to a sustainable decent basic living. They can be excused for not being ZENGHGP if they are not living at least a basic decent living. And the people helping them would already have to be ZENGHGP themselves (no game playing by claiming that non-poor people need to benefit from CO2-Emission activity in order to help the poor, because that is not sustainable helping).

    That is why most carbon-offsets or carbon-credits are disingenuous and rather worthless, as nigelj says “…we are planting a lot of forests of dubious merit and delaying emissions reductions at source.” I would say, and did say “The ability to buy legitimate credits is limited. Everybody has to actually personally become No-Harm people. And the wealthiest need to lead that effort, and help others.” Rich people buying the ability to continue being a part of the problem is not a solution, it is a closed loop to nowhere.

    That exposes how absurd it is for a fossil fuel extraction and sales business to claim they plan to become Net-Zero by 2050. As Climate Adam points out, words are easy and can hide massive loopholes. One loophole is that no longer emitting CO2 does not mean that there are no global warming impacts. Operations that are Zero-CO2-Emissions can still be causing harm by CH4 emissions and other negative impacts of their operations, especially the fact that any fossil fuels sold cause CO2-Emissions by the buyer. The Seller being Net-Zero is meaningless. That Seller needs to have no buyers.

    And the need to minimize future negative impacts also means that any development opportunity and corrections that reduce CO2-Emissions or sustainably remove CO2 should be aggressively pursued regardless of popularity or profitability. One example would be Regulations rapidly ending all recreational activity that is fossil fueled, regardless of the ‘negative economic impact and loss of personal enjoyment’.

    0 0
  8. I'm also skeptical of planting forests for carbon credits - but forests are wonderful so the more we have the better as they produce multiple benefits. There will always be a large demand for wood products so we do need a lot of well managed forests. Wood is a fine raw material and it has a lower carbon footprint than cement or steel. If we have less forest rather than more- the price of wood will be higher- and that doesn't help anyone. In the northeast USA we don't plant forests- they plant themselves if the forests are continuously managed- and if farmland is abandoned, the forests will return with no help from humans. So again, I don't see any need to connect forestry with saving the planet with carbon credits- instead, just be aware of the multiple benefits from good forestry - including some carbon sequestration. Currently, many forests worldwide are in poor condition. One way to improve them is through excellent silviculture which requires some tree harvesting. Over the long term, one of our objectives should be to both increase the amount of carbon stored in forests (trees and soils) while producting valuable wood products contributing to the economy.

    0 0
  9. Joez @8, I largely agree. Its indeed important to consider the combined multi facetted benefits of tree planting and remember they are a sustainable regenerating resource if properly managed. And trees do sequester carbon and have a role to play there. I'm just not sure that cap and trade schemes are the best way to go about it. 

    0 0
  10. Planting a forest where there once was a large area we deforested for timber is likely going to have a temporary beneficial effect on the carbon cycle and global warming, and multiple localised beneficial effects on the surrounding ecology including temperature moderation, hydrological and nutrient cycles, wildlife, reduced erosion and many more.

    However, most forests are near net zero once mature, with a few notable exceptions.

    Furthermore, C3 photosynthesis trees are much slower growing and far less efficient at photosynthesis than rapidly growing C4 grasses, or mixed C4/C3 grasslands. In a grassland about 40% of those products of photosynthesis never get locked in plant primary productivity biomass at all, instead bypassing all that on a pathway entering the geological long carbon cycle. For this reason instead of having a moderating effect, grasslands are actually one of the few biological climate forcings for cooling. Their long term effect is strong enough to cause our current ice age and combined with a few other factors are what gave us our cyclical glaciation cycles.

    Cenozoic Expansion of Grasslands and Climatic Cooling

    It would be far more beneficial to climate acre per acre to restore a lost grassland, tallgrass prairie, and/or savanna. But even here the benefit is not in the biomass, and biomass should not be what is sold on any carbon markets. 

    Instead the soil needs sampled to verify what has been sent on that other pathway.

    Why? Because the added carbon in the atmosphere was supplied from geologically old sources, so the only carbon offsets that should be sold are inputs to geologically old sinks.

    Most forests don't qualify. A few are long term sinks like Mangrove forests yes, but otherwise no. 

    PS This also means the soil tests used need to be the A-horizon and lower, and not the top O-horizon, and can't be part of any tillage system.

    0 0
  11. Red Baron @10. You say, "In a grassland about 40% of those products of photosynthesis never get locked in plant primary productivity biomass at all, instead bypassing all that on a pathway entering the geological long carbon cycle." I can appreciate that some carbon will be stored in soils but why do you say it will enter geologic long carbon cycle? I'm not saying your wrong- I'm just surprised at what you say.

    0 0
  12. @11 JoeZ,

    My appologies for not being detailed enough in my answer.

    Initially the carbon leaves the plant without forming any plant biomass at all, instead it follows this biological pathway:

    Liquid carbon pathway


    Biology in the grasslands soils then form it into this:

    Mollic Epipedon

    I gave a link to the geological long cycle, but it is behind a paywall. I found a better link so you can understand it better without the paywall.

    Cenozoic Expansion of Grasslands and Climatic Cooling


    The paper is rather technical, but the short answer is this carbon has a long chain of events and pathways to follow and ultimately becomes sedimentary rock of various types, locking up the carbon for geological time frames even after it leaves the actual living soil. 

    Biomass carbon generally with a few exceptions returns to the atmosphere, while as much as 78% of the liquid carbon pathway carbon when it degrades ends up locked in sedimentary rock of some sort. It may take hundreds or thousands of years to reach this stage, but the important part for climate scientists is that it doesn't return to the atmosphere. (although human disturbance with the bulldozer, plow, agrochemicals, and other agricultural practices can change this dynamic radically)

    0 0
  13. RedBaron,

    Although my background is in Landscape Architecture, and botany was a minor subject from long ago, I have been intrigued by C4 plants; I have always wondered about the conditions that allowed C4 plants to colonize...that ratio of CO2 and O2 was very different than it is today?  When possible, I try to incorporate these types of grasses/plants into my design schemes, but wonder if the concentration of CO2 in the air today is at a 'toxic' threshold for C4 plants?

    This is an entirely unscientific question, apologies!

    0 0
  14. @meb58,

    It's a good question, but the answer is no. This graph will explain it better than words.

    photosynthesis graph

    Instead what has happened, we are reaching the maximum rate for photosynthesis efficiency on C4 plants, and now as CO2 rises, C3 plants slowly catch up and even pass. C4's are gradually losing their competitive advantage. This is one of the factors which has allowed scrub to take advantage and become invasive where previously grasses dominated. (for exaple much cheetah habitat now is so full of thorny scrub, it is making the cats go blind from all the thorns in the eyes)

    This is also worrisome because scrub is much more susceptable to out of control fires and it does not sequester carbon in the soil like grasses do. So that CO2 goes right back into the atmosphere.

    0 0
    Moderator Response:

    [DB]  Please limit image widths to under 500.

  15. Thank you for the graph.  So...for the time beeing, assuming CO2 remained a static condition, C4 plants theoretically still have an advantage?

    I understand the advantage from an observational perspective only...that many grasses die out entirely during winter months, with the previous season's mass decomposing and adding to the soil - storing CO2 - while new grass structures re-grow each warm season to repeat this cycle.  Scrubby plants - assuming we are referring to deciduous plants - become woody and at best add saome mass back to the soil via leaf drop in the winter, but with far less leaf drop where the Cheetah run?  All a question in the form of a soil sciense classes were long ago too.

    Sad to read about the affect this is having on Cheetah!

    0 0
  16. This is a link to an article that I refer to on occasion.

    0 0
  17. meb58 @15,

    In terms of their contribution to the biosphere, I think the C3/C4 thing is a bit more complex than just CO2 levels. The Wikithing page does a pretty good job describing much of it, and complete with references.

    C4 plants have a competitive advantage over plants possessing the more common C3 carbon fixation pathway under conditions of drought, high temperatures, and nitrogen or CO2 limitation. When grown in the same environment, at 30 °C, C3 grasses lose approximately 833 molecules of water per CO2 molecule that is fixed, whereas C4 grasses lose only 277. This increased water use efficiency of C4 grasses means that soil moisture is conserved, allowing them to grow for longer in arid environments.

    C4 plants arose around 35 million years ago during the Oligocene (precisely when is difficult to determine) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene. C4 metabolism in grasses originated when their habitat migrated from the shady forest undercanopy to more open environments, where the high sunlight gave it an advantage over the C3 pathway. Drought was not necessary for its innovation; rather, the increased resistance to water stress was a byproduct of the pathway and allowed C4 plants to more readily colonize arid environments

    Today, C4 plants represent about 5% of Earth's plant biomass and 3% of its known plant species. Despite this scarcity, they account for about 23% of terrestrial carbon fixation. Increasing the proportion of C4 plants on earth could assist biosequestration of CO2 and represent an important climate change avoidance strategy.

    Of course with C4 plants becoming "ecologically significant " sometime between 35My bp and 6-7My bp, this was also a time of falling CO2 levels with (probably roughly 13My bp) CO2 levels seen dropping below 400ppm(v), until modern times.

    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2023 John Cook
Home | Translations | About Us | Privacy | Contact Us