Interviewed: David Karoly Honorary Professor, The University of Melbourne; Friederike Otto Senior Lecturer in Climate Science, Imperial College London, Tannecia Stephenson Physics Professor, University of the West Indies, Mona Campus
It showed global temperatures are now 1.1℃ above pre-industrial levels. This warming has driven widespread and rapid global changes, including more frequent and intense weather extremes that are now impacting people and ecosystems all over the world.
But when an extreme weather event hits, how certain can we be that it was made more likely by climate change? How do we know it wasn’t just a rare, naturally-occuring event that might have happened anyway?
Fear & Wonder is a new podcast from The Conversation that takes you inside the UN’s era-defining climate report via the hearts and minds of the scientists who wrote it.
The show is hosted by Dr Joëlle Gergis – a climate scientist and IPCC lead author – and award-winning journalist Michael Green.
In this episode, we’re delving into one of the major shifts in the public communication of climate change – the attribution of extreme weather events to climate change.
Although in the past we knew climate change was making extreme weather more likely, advances in climate modelling now allow scientists to pinpoint the influence of natural and human-caused factors on individual weather extremes.
We speak to climatologist Dr Friederike Otto about a rapid attribution study of a heatwave in Toulouse, France, as it unfolded in 2019. We also hear from climatologist Professor David Karoly to help us understand how climate models actually work, while Professor Tannecia Stephenson explains how global models are then used to develop regional climate change projections over the Caribbean island of Jamaica.
To listen and subscribe, click here, or click the icon for your favourite podcast app in the graphic above.
Fear and Wonder is sponsored by the Climate Council, an independent, evidence-based organisation working on climate science, impacts and solutions.
By: Matthew England, Scientia Professor and Deputy Director of the ARC Australian Centre for Excellence in Antarctic Science (ACEAS), UNSW Sydney; Adele Morrison Research Fellow, Australian National University; Andy Hogg Professor, Australian National University; Qian Li Massachusetts Institute of Technology (MIT); Steve Rintoul CSIRO Fellow, CSIRO.
Off the coast of Antarctica, trillions of tonnes of cold salty water sink to great depths. As the water sinks, it drives the deepest flows of the “overturning” circulation – a network of strong currents spanning the world’s oceans. The overturning circulation carries heat, carbon, oxygen and nutrients around the globe, and fundamentally influences climate, sea level and the productivity of marine ecosystems.
But there are worrying signs these currents are slowing down. They may even collapse. If this happens, it would deprive the deep ocean of oxygen, limit the return of nutrients back to the sea surface, and potentially cause further melt back of ice as water near the ice shelves warms in response. There would be major global ramifications for ocean ecosystems, climate, and sea-level rise.
Conveyer overturning schematic showing the pathways of flow in the upper, deep and bottom layers of the ocean.
Our new research, published today in the journal Nature, uses new ocean model projections to look at changes in the deep ocean out to the year 2050. Our projections show a slowing of the Antarctic overturning circulation and deep ocean warming over the next few decades. Physical measurements confirm these changes are already well underway.
Climate change is to blame. As Antarctica melts, more freshwater flows into the oceans. This disrupts the sinking of cold, salty, oxygen-rich water to the bottom of the ocean. From there this water normally spreads northwards to ventilate the far reaches of the deep Indian, Pacific and Atlantic Oceans. But that could all come to an end soon. In our lifetimes.
The authors explain the results of their landmark paper: Is the Southern Ocean about to have its own ‘Day After Tomorrow’ moment? Fact-checked by experts, the video explains how these changes would profoundly alter the ocean’s overturning of heat, freshwater, oxygen, carbon and nutrients, with impacts felt throughout the global ocean for centuries to come.
Why does this matter?
As part of this overturning, about 250 trillion tonnes of icy cold Antarctic surface water sinks to the ocean abyss each year. The sinking near Antarctica is balanced by upwelling at other latitudes. The resulting overturning circulation carries oxygen to the deep ocean and eventually returns nutrients to the sea surface, where they are available to support marine life.
If the Antarctic overturning slows down, nutrient-rich seawater will build up on the seafloor, five kilometres below the surface. These nutrients will be lost to marine ecosystems at or near the surface, damaging fisheries.
Changes in the overturning circulation could also mean more heat gets to the ice, particularly around West Antarctica, the area with the greatest rate of ice mass loss over the past few decades. This would accelerate global sea-level rise.
An overturning slowdown would also reduce the ocean’s ability to take up carbon dioxide, leaving more greenhouse gas emissions in the atmosphere. And more greenhouse gases means more warming, making matters worse.
Meltwater-induced weakening of the Antarctic overturning circulation could also shift tropical rainfall bands around a thousand kilometres to the north.
Put simply, a slowing or collapse of the overturning circulation would change our climate and marine environment in profound and potentially irreversible ways.
Signs of worrying change
The remote reaches of the oceans that surround Antarctica are some of the toughest regions to plan and undertake field campaigns. Voyages are long, weather can be brutal, and sea ice limits access for much of the year.
This means there are few measurements to track how the Antarctic margin is changing. But where sufficient data exist, we can see clear signs of increased transport of warm waters toward Antarctica, which in turn causes ice melt at key locations.
Indeed, the signs of melting around the edges of Antarctica are very clear, with increasingly large volumes of freshwater flowing into the ocean and making nearby waters less salty and therefore less dense. And that’s all that’s needed to slow the overturning circulation. Denser water sinks, lighter water does not.
How did we find this out?
Apart from sparse measurements, incomplete models have limited our understanding of ocean circulation around Antarctica.
For example, the latest set of global coupled model projections analysed by the Intergovernmental Panel on Climate Change exhibit biases in the region. This limits the ability of these models in projecting the future fate of the Antarctic overturning circulation.
To explore future changes, we took a high resolution global ocean model that realistically represents the formation and sinking of dense water near Antarctica.
We ran three different experiments, one where conditions remained unchanged from the 1990s; a second forced by projected changes in temperature and wind; and a third run also including projected changes in meltwater from Antarctica and Greenland.
In this way we could separate the effects of changes in winds and warming, from changes due to ice melt.
The findings were striking. The model projects the overturning circulation around Antarctica will slow by more than 40% over the next three decades, driven almost entirely by pulses of meltwater.
Abyssal ocean warming driven by Antarctic overturning slowdown, Credit: Matthew England and Qian Li.
Over the same period, our modelling also predicts a 20% weakening of the famous North Atlantic overturning circulation which keeps Europe’s climate mild. Both changes would dramatically reduce the renewal and overturning of the ocean interior.
We’ve long known the North Atlantic overturning currents are vulnerable, with observations suggesting a slowdown is already well underway, and projections of a tipping point coming soon. Our results suggest Antarctica looks poised to match its northern hemisphere counterpart – and then some.
What next?
Much of the abyssal ocean has warmed in recent decades, with the most rapid trends detected near Antarctica, in a pattern very similar to our model simulations.
Our projections extend out only to 2050. Beyond 2050, in the absence of strong emissions reductions, the climate will continue to warm and the ice sheets will continue to melt. If so, we anticipate the Southern Ocean overturning will continue to slow to the end of the century and beyond.
The projected slowdown of Antarctic overturning is a direct response to input of freshwater from melting ice. Meltwater flows are directly linked to how much the planet warms, which in turn depends on the greenhouse gases we emit.
Our study shows continuing ice melt will not only raise sea-levels, but also change the massive overturning circulation currents which can drive further ice melt and hence more sea level rise, and damage climate and ecosystems worldwide. It’s yet another reason to address the
climate crisis – and fast.
The Intergovernmental Panel on Climate Change’s (IPCC) synthesis report recently landed with an authoritative thump, giving voice to hundreds of scientists endeavouring to understand the unfolding calamity of global heating. What’s changed since the last one in 2014? Well, we’ve dumped an additional third of a trillion tonnes of CO₂ into the atmosphere, primarily from burning fossil fuels. While world leaders promised to cut global emissions, they have presided over a 5% rise.
The new report evokes a mild sense of urgency, calling on governments to mobilise finance to accelerate the uptake of green technology. But its conclusions are far removed from a direct interpretation of the IPCC’s own carbon budgets (the total amount of CO₂ scientists estimate can be put into the atmosphere for a given temperature rise).
The report claims that, to maintain a 50:50 chance of warming not exceeding 1.5°C above pre-industrial levels, CO₂ emissions must be cut to “net-zero” by the “early 2050s”. Yet, updating the IPCC’s estimate of the 1.5°C carbon budget, from 2020 to 2023, and then drawing a straight line down from today’s total emissions to the point where all carbon emissions must cease, and without exceeding this budget, gives a zero CO₂ date of 2040.
A full description of the above chart is available here.
If emissions stay at their current levels, we will exhaust the 50% chance of 1.5°C in 9 years. If we begin to immediately cut emissions following the blue line, then to stay within the carbon budget for 50:50 chance of not exceeding 1.5°C we need zero global emissions by 2040. The vertical axis represents how much carbon is emitted each year – note the pandemic-related blip in 2020.
Given it will take a few years to organise the necessary political structures and technical deployment, the date for eliminating all CO₂ emissions to remain within 1.5°C of warming comes closer still, to around the mid-2030s. This is a strikingly different level of urgency to that evoked by the IPCC’s “early 2050s”. Similar smoke and mirrors lie behind the “early 2070s” timeline the IPCC conjures for limiting global heating to 2°C.
IPCC science embeds colonial attitudes
For over two decades, the IPCC’s work on cutting emissions (what experts call “mitigation”) has been dominated by a particular group of modellers who use huge computer models to simulate what may happen to emissions under different assumptions, primarily related to price and technology. I’ve raised concerns before about how this select cadre, almost entirely based in wealthy, high-emitting nations, has undermined the necessary scale of emission reductions.
In 2023, I can no longer tiptoe around the sensibilities of those overseeing this bias. In my view, they have been as damaging to the agenda of cutting emissions as Exxon was in misleading the public about climate science. The IPCC’s mitigation report in 2022 did include a chapter on “demand, services and social aspects” as a repository for alternative voices, but these were reduced to an inaudible whisper in the latest report’s influential summary for policymakers.
The specialist modelling groups (referred to as Integrated Assessment Modelling, or IAMs) have successfully crowded out competing voices, reducing the task of mitigation to price-induced shifts in technology – some of the most important of which, like so-called “negative emissions technologies”, are barely out of the laboratory.
The IPCC offers many “scenarios” of future low-carbon energy systems and how we might get there from here. But as the work of academic Tejal Kanitkar and others has made clear, not only do these scenarios prefer speculative technology tomorrow over deeply challenging policies today (effectively a greenwashed business-as-usual), they also systematically embed colonial attitudes towards “developing nations”.
With few if any exceptions, they maintain current levels of inequality between developed and developing nations, with several scenarios actually increasing the levels of inequality. Granted, many IAM modellers strive to work objectively, but they do so within deeply subjective boundaries established and preserved by those leading such groups.
If we step outside the rarefied realm of IAM scenarios that leading climate scientist Johan Rockström describes as “academic gymnastics that have nothing to do with reality”, it’s clear that not exceeding 1.5°C or 2°C will require fundamental changes to most facets of modern life.
Starting now, to not exceed 1.5°C of warming requires 11% year-on-year cuts in emissions, falling to nearer 5% for 2°C. However, these global average rates ignore the core concept of equity, central to all UN climate negotiations, which gives “developing country parties” a little longer to decarbonise.
Include equity and most “developed” nations need to reach zero CO₂ emissions between 2030 and 2035, with developing nations following suit up to a decade later. Any delay will shrink these timelines still further.
Most IAM models ignore and often even exacerbate the obscene inequality in energy use and emissions, both within nations and between individuals. As the International Energy Agency recently reported, the top 10% of emitters accounted for nearly half of global CO₂ emissions from energy use in 2021, compared with 0.2% for the bottom 10%. More disturbingly, the greenhouse gas emissions of the top 1% are 1.5 times those of the bottom half of the world’s population.
So where does this leave us? In wealthier nations, any hope of arresting global heating at 1.5 or 2°C demands a technical revolution on the scale of the post-war Marshall Plan. Rather than relying on technologies such as direct air capture of CO₂ to mature in the near future, countries like the UK must rapidly deploy tried-and-tested technologies.
Retrofit housing stock, shift from mass ownership of combustion-engine cars to expanded zero-carbon public transport, electrify industries, build new homes to Passivhaus standard, roll-out a zero-carbon energy supply and, crucially, phase out fossil fuel production.
Three decades of complacency has meant technology on its own cannot now cut emissions fast enough. A second, accompanying phase, must be the rapid reduction of energy and material consumption.
Given deep inequalities, this, and deploying zero-carbon infrastructure, is only possible by re-allocating society’s productive capacity away from enabling the private luxury of a few and austerity for everyone else, and towards wider public prosperity and private sufficiency.
For most people, tackling climate change will bring multiple benefits, from affordable housing to secure employment. But for those few of us who have disproportionately benefited from the status quo, it means a profound reduction in how much energy we use and stuff we accumulate.
The question now is, will we high-consuming few make (voluntarily or by force) the fundamental changes needed for decarbonisation in a timely and organised manner? Or will we fight to maintain our privileges and let the rapidly changing climate do it, chaotically and brutally, for us?
Since COP26, the ‘Don’t-Look-Up’ mentality, or perhaps the ‘war-in-Ukraine’ and ‘post-Covid-economy’ have become diversionary topics. The latest UN GAP Report begins with a clear admission, and an admonition. Nations have shaved just 1% off their projected greenhouse gas emissions for 2030, at a time when reductions need to be 45% to have even a chance to keep temperatures under 1.5C. In short, there is no credible no credible pathway in which global temperatures under that 2.8C, and “...uncertainties in the climate system mean that warming of up to 4C cannot be fully ruled out.”
If you’re not up to reading the full report, Carbon Brief has an in depth analysis. While the report also offers solutions, the window is closing on fingernails barely clinging to the sill.
Look up.
Please.
“Every year, the negative impacts of climate change become more intense. Every year, they bring more misery and pain to hundreds of millions of people across the globe. Every year, they become more a problem of the here and now, as well as a warning of tougher consequences to come. We are in a climate emergency.
“And still, as UNEP’s Emissions Gap Report 2022 shows, nations procrastinate. Since COP26 in Glasgow in 2021, new and updated nationally determined contributions (NDCs) have barely impacted the temperatures we can expect to see at the end of this century.
“This year’s report tells us that unconditional NDCs point to a 2.6°C increase in temperatures by 2100, far beyond the goals of the Paris Agreement. Existing policies point to a 2.8°C increase, highlighting a gap between national commitments and the efforts to enact those commitments. In the best- case scenario, full implementation of conditional NDCs, plus additional net zero commitments, point to a 1.8°C rise. However, this scenario is currently not credible.
“To get on track to limiting global warming to 1.5°C, we would need to cut 45 per cent off current greenhouse gas emissions by 2030. For 2°C, we would need to cut 30 per cent. A stepwise approach is no longer an option. We need system-wide transformation. This report tells us how to go about such a transformation. It looks in-depth at the changes needed in electricity supply, industry, transport, buildings and food systems. It looks at how to reform financial systems so that these urgent transformations can be adequately financed.
“Is it a tall order to transform our systems in just eight years? Yes. Can we reduce greenhouse gas emissions by so much in that timeframe? Perhaps not. But we must try. Every fraction of a degree matters: to vulnerable communities, to species and ecosystems, and to every one of us. Most importantly, we will still be setting up a carbon-neutral future: one that will allow us to bring down temperature overshoots and deliver other benefits, like clean air.
“The world is facing other crises. We must deal with them. But let us remember that they also offer opportunities to reform our global economy. We have missed the opportunity to invest in a low-carbon recovery from the COVID-19 pandemic. Now, we are in danger of missing the opportunity to boost clean and efficient energy as a response to the energy crisis. Instead of missing such opportunities, we must capitalize on them with confidence.
“I urge every nation and every community to pore over the solutions offered in this report, build them into their NDCs and implement them. I urge everyone in the private sector to start reworking their practices. I urge every investor to put their capital towards a net-zero world. The transformation begins now. ”
But as our research published today in Nature Communications has found, some oceans work harder than others.
We used a computational global ocean circulation model to examine exactly how ocean warming has played out over the last 50 years. And we found the Southern Ocean has dominated the global absorption of heat. In fact, Southern Ocean heat uptake accounts for almost all the planet’s ocean warming, thereby controlling the rate of climate change.
This Southern Ocean warming and its associated impacts are effectively irreversible on human time scales, because it takes millennia for heat trapped deep in the ocean to be released back into the atmosphere.
This means changes happening now will be felt for generations to come – and those changes are only set to get worse, unless we can stop carbon dioxide emissions and achieve net zero.
It’s important yet difficult to measure ocean heating
Ocean warming buffers the worst impacts of climate change, but it’s not without cost. Sea levels are rising because heat causes water to expand and ice to melt. Marine ecosystems are experiencing unprecedented heat stress, and the frequency and intensity of extreme weather events is changing.
Yet, we still don’t know enough about exactly when, where and how ocean warming occurs. This is because of three factors.
First, temperature changes at the ocean surface and in the atmosphere just above track each other closely. This makes it difficult to know exactly where excess heat is entering the ocean.
Second, we don’t have measurements tracking temperatures over all of the ocean. In particular, we have very sparse observations in the deep ocean, in remote locations around Antarctica and under sea ice.
Last, the observations we do have don’t go back very far in time. Reliable data from deeper than 700 metres depth is virtually non-existent prior to the 1990s, apart from observations along specific research cruise tracks.
Earth’s heat inventory since 1960 (ZJ = 10²¹ J). Credit: von Schuckmann et al. (2020).
Our modelling approach
To work out the intricacies of how ocean warming has played out, we first ran an ocean model with atmospheric conditions perpetually stuck in the 1960s, prior to any significant human-caused climate change.
Then, we separately allowed each ocean basin to move forward in time and experience climate change, while all other basins were held back to experience the climate of the 1960s.
We also separated out the effects of atmospheric warming from surface wind-driven changes to see how much each factor contributes to the observed ocean warming.
By taking this modelling approach, we could isolate that the Southern Ocean is the most important absorber of this heat, despite only covering about 15% of the total ocean’s surface area.
In fact, the Southern Ocean alone could account for virtually all global ocean heat uptake, with the Pacific and Atlantic basins losing any heat gained back into the atmosphere.
One significant ecological impact of strong Southern Ocean warming is on Antarctic krill. When ocean warming occurs beyond temperatures they can tolerate, the krill’s habitat contracts and they move even further south to cooler waters.
As krill is a key component of the food web, this will also change the distribution and population of larger predators, such as commercially viable tooth and ice fish. It will also further increase stress for penguins and whales already under threat today.
So why is the Southern Ocean absorbing so much heat?
This largely comes down to the geographic set-up of the region, with strong westerly winds surrounding Antarctica exerting their influence over an ocean that’s uninterrupted by land masses.
This means the Southern Ocean winds blow over a vast distance, continuously bringing masses of cold water to the surface. The cold water is pushed northward, readily absorbing vast quantities of heat from the warmer atmosphere, before the excess heat is pumped into the ocean’s interior around 45-55°S (a latitude band just south of Tasmania, New Zealand, and the southern regions of South America).
This warming uptake is facilitated by both the warmer atmosphere caused by our greenhouse gas emissions, as well as wind-driven circulation which is important for getting heat into the ocean interior.
And when we combine the warming and wind effects only over the Southern Ocean, with the remaining oceans held back to the climate of the 1960s, we can explain almost all of the global ocean heat uptake.
But that’s not to say the other ocean basins aren’t warming. They are, it’s just that the heat they gain locally from the atmosphere cannot account for this warming. Instead, the massive heat uptake in the Southern Ocean is what has driven changes in total ocean heat content worldwide over the past half century.
We have much to learn
While this discovery sheds new light on the Southern Ocean as a key driver of global ocean warming, we still have a lot to learn, particularly about ocean warming beyond the 50 years we highlight in our study. All future projections, including even the most optimistic scenarios, predict an even warmer ocean in future.
And if the Southern Ocean continues to account for the vast majority of ocean heat uptake until 2100, we might see its heat content increase by as much as seven times more than what we have already seen up to today.
To capture all of these changes, it’s vital we continue and expand our observations taken in the Southern Ocean.
One of the most important new data streams will be new ocean floats that can measure deeper ocean temperatures, as well as small temperature sensors on elephant seals, which give us essential data of oceanic conditions in winter under Antarctic sea ice.
Even more important is the recognition that the less carbon dioxide we emit, the less ocean change we will lock in. This will ultimately limit the disruption of livelihoods for the billions of people living near the coast worldwide.
The Environmental Defence Society has filed its submission on the Ministry for the Environment’s regulations on coastal wetlands and says that the Ministry’s approach undermines the original intent of the regulations and leaves coastal wetlands vulnerable to future degradation.
This is a classic case of maladaptation, the exact opposite to adaptation that the Government itself warned against in its National adaptation plan.
“The Resource Management (National Environmental Standards for Freshwater) Regulations 2020 (NES-F) set national direction to protect and improve wetlands and put a stop to further loss of their values”, said EDS COO Shay Schlaepfer.
“The NES-F was clearly intended to apply to both inland and coastal wetlands. The Ministry is now proposing a policy U-turn and wants to exclude coastal wetlands from the regulations.
“This approach is totally unjustified. Coastal wetlands are capable of being mapped so there is no reason why they should not be included. The NES-F is a rules framework that integrates national policy relating to wetlands and provides a consistent approach to wetland management across all domains.
“Removing coastal wetlands from the NES-F will leave a gap in their management and protection at the national level and leave too much discretion with regional councils.
“The Ministry also seeks to exempt certain activities from the consenting pathways set out in the NES-F. These activities have the potential to adversely affect coastal wetlands and should be subject to the regulations.
“Wetlands are one of the country’s most valuable ecosystems. They have undergone extensive loss with over 90% of them destroyed since human occupation. Many of those that remain are in a severely degraded state. The Ministry’s proposed approach will only serve to further continue this decline.
“This cannot be allowed to occur and we urge the Ministry to think again,” Ms Schlaepfer concluded.
The global carbon budget tells us how much more carbon we can emit or ‘spend’ before we risk temperatures passing 1.5°C. On the current trajectory, we have about 316 Gigatonnes left before we run out around May 2029. This is why there is such an urgent push to reduce emissions by 2030.
But this budget is based on emissions from fossil fuels and agriculture. It doesn’t include emissions from ferocious forest fires, or even more concerning, melting permafrost (Fig. 1).
“Permafrost emissions are really hard to capture in global models, so even in the [new climate models] being used to project climate in the future and the behaviour of the planet and the global climate system, these emissions are not included…climate modellers don’t want to include it; permafrost modellers really think they should.” – Video (top) State of the Cryosphere Report, COP26
Fig. 1: Estimated permafrost changes 2003-2017. Images: International Cryosphere Climate Initiative at COP26. See the video at the top of this page for the full presentation.
Presently, emissions from permafrost are about the same as Japan’s; around 1.15 Gigatonnes. Not accounting for these emissions is like knowing that someone is withdrawing money from your bank account, but ignoring it. As temperatures continue to rise, more permafrost melts, so there’s even less available to ‘spend’. To compound the problem, the Arctic is warming as much as four times faster than the rest of the planet.
“Suppose we do reach net zero emissions by 2050, permafrost is going to continue emitting for at least a couple of centuries. So, in addition to the negative emissions that are in the models to keep temperature below 1.5°C, we also have to have negative emissions to offset permafrost. And we’re going to have to continue doing that for a couple of hundred years until the permafrost stabilises,” – Op cit.
The science is unequivocal. The 12-minute video above succinctly outlines this complex issue. The figures at the bottom of this page are eye-watering…and that’s just from processing meat and dairy.
“From production to transportation packaging use and waste management, based on the most detailed meta analysis of life cycle assessments to date, on average it takes 71kg of CO2 to produce 1kg of beef. For lamb, it’s about 40kg; pigs 12kg; and poultry 10kg.
“Some 26% of greenhouse gasses comes from agriculture. By far the largest share is methane and nitrous oxide from cattle. Methane alone has already caused caused around 24-40% of human-made warming.
“The destruction of forests for farmland not only releases the CO2 that was bound in the flora, it sets free carbon that was stored in the soil and destroys its ability to store it in the future. This aspect accounts for much of the range of emissions in beef.”
This loss continues in Aotearoa (13,000 hectares lost in the past 5 years alone). Then there’s the nitrogen and phosphates added to farms that ends up in waterways, which results in, amongst other things, algae blooms that emit methane when they die:
“Between 1991 and 2019, estimates from sales data of nitrogen applied to land in fertiliser increased from 62,000 to 452,000 tonnes (just over a sixfold increase, 629 percent).
“Since our last update of this indicator in April 2019, there was a 5.4 percent increase from 2015 to 2019 in nitrogen applied from fertiliser. In this period, urease inhibitor use increased 48 percent.” – Statistics NZ
And then there’s the palm oil imported to feed our ‘grass fed’ cows:
“A new Greenpeace International report has found evidence of systematic violations by the Indonesian Government regarding plantation and forest release permits in the Papua region. The report also finds that clearing forest for palm plantations in the Papua area could release huge amounts of carbon into the atmosphere, undoing previous climate action.
“New Zealand is the world’s biggest importer of palm kernel expeller–a product of the palm industry used as supplementary feed for New Zealand’s 6.5 million dairy cows.
“In 2018, a Greenpeace investigation found that Fonterra’s key supplier of PKE, Wilmar International, has been linked with the mass destruction of rainforest in Papua, Indonesia. In 2020, Fonterra handed over its half of PKE-importing business Agrifeeds to business partnerWilmar International.
“Greenpeace Aotearoa campaigner Amanda Larsson says the dairy industry’s continued use of PKE is one of myriad ways that intensive dairying is fuelling the climate crisis.
“Right now, dairying is New Zealand’s biggest climate polluter. We’ve got methane from 6.5 million cows, nitrous oxide from cows and synthetic nitrogen fertiliser, and carbon from the coal used to process milk,” says Larsson.” – Greenpeace April, 2021
Finally, there’s the carbon cost of processing all that meat and dairy. Remember, this is in addtion to the methane, nitrous oxide and CO2 emissions from growing this meat on farms. Fonterra is the worst carbon polluter in the country, emitting a staggering 16.3 million tonnes of eCO2 in 2020 alone. Silver Fern farms emitted 8.3 million tonnes(Table 9 below: from the New Zealand Government EPA report ‘ETS Participant Emissions‘, October 2021, pages 27-30).
So yes, meat and dairy really is that bad for the climate.
Some greenhouse gases are many times more powerful than others when it comes to warming the atmosphere. This is called their global warming potential (GWP). Three of these gases, carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) are the main concern.
Of these, CO2 from burning fossil fuels (coal, oil etc) is globally the largest. For this reason, CO2 is used as a benchmark against which the GWP of all other gasses are measured.
Some greenhouse gases stay in the atmosphere longer than others, so time is also included in the equation. Over 100 years, the GWP of methane (CH4) is 25 times that of CO2, so it’s written as 25CO2-e. The GWP of nitrous oxide (N2O) over the same time period is 298 so it’s written as 298CO2-e in New Zealand.
When emissions are added together, the term eCO2 is used.
The carbon budget: a moving target that politicians just moved beyond reach.
Fig. 1. This live feed from the Mercator Institute is, by default, set to show how much time we have left before the CO2 budget to stay under 2°C is no longer possible. The CO2 budget is in tonnes. Currently (18 March 2022), it’s 1,060Gt (Gt = 1 billion tonnes). At the present rate of emissions, this will run out around April 2047.
However, if we want the planet to remain habitable for most (but not all) people, and accept losing entire ecosystems like the Great Barrier Reef, we need to keep the average temperature rise under 1.5°C.
Click the box on the top right ‘1.5°C scenario‘ to see that a 66% chance of succeeding means that (as of 18 March 2022), we can emit no more that 309Gt. At the current rate of emissions, that’s July 2029.
Others tipping points include wildfires in the Arctic and Australia. Together these released around 1Gt of CO2 in 2020. The devastation was so great in places that the conditions that led to the evolution of these ancient ecosystems no longer exist. ‘Zombie’ wildfires in boreal forests in Siberia and Canada and Alaska continue to burn peat underground over winter, re-igniting record-breaking forest fires in the summer of 2021.
These forests, which make up large parts of the biosphere that once absorbed carbon and locked it away, are now releasing carbon to the atmosphere together with human-caused emissions. They have passed a tipping point; a point of no return. The countdown clock in Fig. 1 doesn’t include these emissions because the compound effects are so complex, they have yet to be included in Earth systems models used by the Intergovernmental Panel on Climate Change (IPCC).
But the atmosphere doesn’t care where these emissions originate. Nor how much nations—most notably New Zealand—or businesses cheat on their carbon accounting. The reality is that the carbon budget is a globally shared account. Governments think they know how much we have left to ‘spend’, but the burning forests and melting permafrost and methane clathrates are making CO2 withdrawals over which we have no control. All we know is that somewhere between warming of 1-2°C, some tipping points will be irreversible and warming will accelerate, causing even more tipping points to fall like dominoes.
A race against time
Currently, atmospheric CO2 is around 418ppm and climbing 2-3ppm every year. Global average temperatures are 1.2°C and rising. The last time CO2 in the atmosphere exceeded 400ppm was during the Pliocene Epoch (2.6-5.3 million years ago). Global average temperatures were 2-3°C warmer, Antarctica was 14°C warmer, and melting ice caps added 10-20 metres to sea levels.
So why aren’t we already that hot?
The relationship between the amount of CO2 in the atmosphere and warming is well-understood physics and chemistry. But there is a delay—a lag time of 10-20 years—between adding CO2 to the atmosphere and warming. So even if we switch off all emissions today, things will get hotter over the next two decades. It takes even longer for melting icecaps to raise sea levels, unless there’s an abrupt Meltwater Event (historically, these have raised sea levels as much as 4m/century).
The IPCC is banking our future existence on the lag time to literally buy us time to drawdown enough CO2 from the atmosphere and permanently store it back where it came from, with fingers crossed that will return the planet to a safe operating space of 350ppm.
The Plan: built-in assumptions
The crucial thing about The Plan is that it depends entirely on assumptions. The most important assumption is that carbon capture technologies will draw down and safely store CO2 underground before warming triggers irreversible tipping points. This assumption (otherwise known as magical thinking) is because there isn’t enough land on Earth to plant enough trees to offset emissions while still being able to grow food to feed an exploding global population:
“If we absolutely maximised the amount of vegetation all land on Earth could hold, we’d sequester enough carbon to offset about ten years of greenhouse gas emissions at current rates. After that, there could be no further increase in carbon capture.
“Together, land plants and soils hold about 2,500Gt of carbon – about three times more than is held in the atmosphere.
“In recognition of these fundamental constraints, scientists estimate that the Earth’s land ecosystems can hold enough additional vegetation to absorb between 40 and 100Gt of carbon from the atmosphere. Once this additional growth is achieved (a process which will take a number of decades), there is no capacity for additional carbon storage on land.”
– Bonnie Waring, Senior Lecturer, Grantham Institute, Climate Change and Environment, Imperial College London
In spite of this limitation, deploying natural climate solutions (NCS) to draw down carbon into restored natural ecosystems would help restore critical, life-supporting ecosystem services.
Because we literally cannot live without these services, including their role in climate adaptation and mitigation, every government and council should be treating natural ecosytems as critical natural infrastructure. This is a higher-order priority than critical built infrastructure. Built infrastructure cannot exist without natural infrastructure, whereas natural infrastructure does not need built infrastructure.
So, what does The Plan look like?
The Plan by the numbers: 2019 – 2050
Atmospheric concentration at the start of2019: 408ppm
Emit: no more than 400Gt of CO2 over the next 21 years; this would add around 23ppm to the atmosphere.
Offset emissions: as some emissions are unavoidable, they must be 100% offset by drawing down the same amount of CO2 as emitted and storing it permanently underground or in natural ecosystems. Plantation forestry is by definition not permanent, so it shouldn’t be regarded as a permanent offset because the carbon in it is recycled back into the atmosphere.
Draw down: an average 3.9Gt of CO2 every year (total 81.9Gt between 2019-2050) and store it underground and in natural ecosystems. In total, this would remove around 10.5ppm. Again, plantation forestry shouldn’t be regarded as a permanent drawdown.
Together, The Plan means that atmospheric concentration as of January 2050 will be: 408ppm + 23ppm – 10.5pm = 420.5ppm.
Limitations to offsetting and drawdown:
The world’s terrestrial ecosystems can only hold between 40 and 100Gt, so by 2050, CO2 will need to be permanently stored elsewhere.
Burning forests and melting permafrost and methane clathrates are emitting CO2 and methane. We don’t know how much, we have no control over it, but we do know this is eating into the existing carbon budget.
The Plan by the numbers: 2050 – 2100
The planned atmospheric concentration at the start of 2050: 420.5ppm
Emit: zero CO2
Offset: As some emissions are unavoidable, they must be 100% offset by drawing down the same amount of CO2 as emitted and storing it permanently underground. By now, terrestrial ecosystems will be unable to store any more carbon.
Draw down average 24Gt/year until 2100 (24Gt x 50 years = 1,250Gt or 72ppm) and store it…somewhere.
Planned atmospheric concentration at the start of 2100: 420.5ppm – 72ppm = 348.5ppm.
Limitations to offsetting and draw down:
Burning forests and melting permafrost and methane clathrates will be emitting far more CO2 and methane, so the budget will likely need further revision.
The Plan: how are we doing so far? 2019 – 2021
Atmospheric concentration at the start of 2019: 408ppm
Atmospheric concentration at start of 2022: 418ppm, ie, we’re going to hit 420.5pm before 2024, not 2050.
Emitted: 107Gt of CO2 (26.7% of the 21-year budget ‘spent’ in 3 years)
Offset: A handful of the world’s largest carbon polluters are buying up most of the land available for afforestation/reforestation to offset their emissions, leaving no available land for others to offset theirs. This includes land needed to feed people. Many are investing in low value or ‘ghost’ forests such as palm oil plantations, because plants that grow faster earn far more money from carbon credits. Many corporations have no plans to ever become carbon neutral because they will pass the cost of cheap and often useless offsets onto customers. The New Zealand Government, which is using taxpayer dollars to subside the eye-watering carbon cost of agriculture (giving them a 95% discount on emissions), and Fonterra, our largest carbon polluter, also plan to buy carbon credits offshore because they’re cheaper.
“New Zealand’s proposals to COP-26 were dismaying, seeking to shift the task of seriously tackling climate change to others. Spending five billion dollars on international credits to ‘restore’ forests overseas when our own forests are dying is like investing in someone else’s business when your own is going bankrupt. It’s irresponsible.”
– Dame Anne Salmond, Distinguished Professor in anthropology at the University of Auckland, and 2013 New Zealander of the Year.
Draw down: In spite of all the reforestation and rewilding projects around the globe, terrestrial ecosystem destruction (land use change) exceeded reforestation and offsetting by approximately 10Gt (Fig. 2). A large chunk of these losses are from the Amazon, parts of which have become so dry that they can no longer support re-forestation, so they’re turning in savannahs or being used to grow palm oil, soya, and methane-emitting cows.
Limitations to offsetting and drawdown:
Oddities with emissions trading schemes not accounting for the value of carbon locked in established forests and their soils, has created perverse incentives: old-growth and naturally regenerating forests are being cut down and/or burned so they can be replaced by fast growing monoculture crops like pine forests that earn more from carbon credits (if they survive wildfires and rapidly rising temperatures). And COP26 did nothing to prevent this from happening into the future (scroll down).
The only company extracting CO2 and permanently storing it underground (versus selling it as fuel) is in Iceland. In September 2021, Climeworks’ operations scaled up. It now draws down and stores 4,000 tonnes CO2/year. To scale up to 3.9Gt/year (‘The Plan’) would require building and deploying 9.5 million additional fully operating plants of the same size. To scale up to 24Gt/year from 2050 onward would require 58.5 million additional fully operational plants of the same size. And then there’s this:
“No artificial machines that are even in the design stage will also clean our air, clean our water, provide habitat for wildlife and all the other useful features of trees.” –Sophie Bertazzo, Senior editor, Conservation International
Fig. 2. Sources of carbon emissions 2021 (Image: www.co2.earth/global-co2-emissions)
COP26: bankrupting the carbon budget
“We are on the verge of the abyss, and when you are on the verge of the abyss, you need to be very careful about what the next step is. And the next step is COP26 in Glasgow.”
Video 1: “I apologise for the way this process has unfolded. I am deeply sorry. I also understand the deep disappointment but I also think, as you have noted, that it is vital that we protect this package.”
–Alok Sharma, President COP26 following last minute changes from India and China.
As Sharma pointed out, the final package, as weak as it was, brings agreement to the rules in Paris Agreement. And, while it’s taken 165 years, fossil fuels have now been formally recognised as the primary driver of climate change.
The ‘Reducing Deforestation’ COP26 Article
This looks like a win…except that the same declaration was also made 17 years ago, after which deforestation subsequently increased:
“The Glasgow declaration on forests and land use is a pledge to end or significantly reduce deforestation by 2030… In 2014 the New York declaration on forests promised to cut deforestation by 50% by 2020 and end it completely by 2030. Since then there’s been an increase in global deforestation contributing an estimated 23% to total global CO2 emissions.
“Under the UN rules, man-made plantations count as forests even though they contain none of the rich ecosystems and biodiversity of indigenous forests. Environmental groups worry that a big chunk of the $19.2 billion dollars allocated to the Glasgow declaration will be used to tear down existing forestry land to create more of these plantations for things like palm oil, paper and wood pellets, instead of preserving and protecting the trees and plants and wildlife that are now so critically endangered.
“And how about this doozy: the declaration’s terminology of deforestation refers to ‘permanent loss of forests when land is fully converted to some other use like agriculture or development’. It’s almost completely silent on the role of traditional logging in driving forest degradation from within. Under this agreement loggers can still disappear deep inside a rainforest like the Amazon and destroy forest biodiversity and carbon stocks resulting in almost exactly the same devastating impacts as true deforestation.”
– David Borlace, Video 2 (below)
Between 2012 and 2018, New Zealand indigenous land cover area decreased by 12,869ha. In 2020 alone we lost 8,530ha of native forest. There is no reason to expect that trend or enforcement of current or future policies to reverse that trend.
So where does that leave us?
Carbon Brief has done a full analysis of the outcomes. If every country actually delivers on their promises and statements made at COP26, warming will be around 2.4°C. But that was before India and China insisted in last minute changes. China, India, Australia, and Russia announced plans to open more coal mines. And oil production from OPEC increased.
The most commonly repeated mantra that you’ll hear on the news, is that to stay within 1.5°C target, global emissions need to fall 45% by 2030. But that’s based on The Plan. The countdown clock at the top of the page, which reflects what’s actually happening in the atmosphere, is clear: to have a 66% chance of staying under 1.5°C emissions need to fall to zero by 2027. As we have no control over the growing emissions from wildfires, melting permafrost and methane clathrates, we had also better start drawing down and permanently storing CO2 as fast as possible.
Fig. 3. The most optimistic scenario of 1.8C (pale blue box) requires every single country to meet every single promise and every single target by 2030. This does not include tipping points (Image and linked PDF report: Climate Action Tracker. )
COP26: The oceans
As Bonnie Waring said in the quote above:
“If we absolutely maximised the amount of vegetation all land on Earth could hold…”
The oddity in The Plan is that it largely ignores 70% of the surface of the planet that’s not land: the oceans, or more specifically the blue carbon in them. For the first time, the capability of the oceans to rapidly draw down and permanently store vast quantities of CO2 was finally addressed at COP26.
New Zealand has an exclusive oceanic economic zone 14 times larger than our land area. Why isn’t the government (and heavy carbon polluters) using that incredible capacity to invest far more in locally produced blue carbon? Fed by the sun, with no need for irrigation or agricultural chemicals, some species can grow up to 1m/day, drawing down as much as five times more carbon dioxide from the atmosphere than rainforests, and permanently sequestering if not harvested and instead, cut and dropped into deep ocean.
(ppm = parts per million; Gt = one gigatonne or one billion tonnes)
2.13 Gt of carbon = 1ppm currently in the atmosphere
To convert carbon (C) to carbon dioxide (CO2), first divide the atomic mass of carbon (12) by the atomic mass of CO2 (44) = 3.67.
Then multiply this by 2.13 Gt carbon: 3.67 x 2.13 = 7.8 Gt carbon dioxide = 1ppm of CO2 currently in the atmosphere.
As there is currently around 415ppm* of CO2 in the atmosphere, that’s 415 x 7.8 Gt = 3,373Gt CO2.
* The amount of CO2 in the atmosphere varies seasonally because plants accumulate carbon in the spring and summer and release some back to the air in autumn and winter. As the northern hemisphere has more land and plants, carbon dioxide levels go up in winter because plants become less productive. Annual measurements of carbon dioxide are an average of these ups and downs. On April 11, 2021, CO2 in the atmosphere peaked at 420ppm
Calculations for adding carbon to the atmosphere from emissions
Emissions are NOT the same as concentrations. This is because the ocean and biosphere absorbed* around 55% of emissions while 45% stays in the atmosphere, adding to what’s already there.
To calculate each additional ppm, divide 7.8 Gt / 0.45 = 17.3Gt
So it takes about 17.3Gt of CO2 emissions to add 1ppm to the atmosphere
* Note: That number is not a constant because the oceans and biosphere are no longer able to absorb as much CO2. Moreover, some is now being emitted by ecosystems that once absorbed it:
“Additional ecosystem responses to warming not yet fully included in climate models, such as CO2 and CH4[methane] fluxes from wetlands, permafrost thaw and wildfires, would further increase concentrations of these gases in the atmosphere (high confidence).” – IPCC 2021 p41.
Restoration planting costs about 100 times as much per hectare (sometimes more) as it does to protect pre-existing remnant vegetation, and is less likely to result in the same ecologically desired outcome as protecting existing forests. On-the-ground costs associated with 15 recent examples of remnant vegetation protection in North Canterbury hill-country QEII covenants and strategic restoration plantings came in at about $655/ha:
$595/ha for fencing
$55/ha for initial pest & weed control
$5/ha for strategic restoration planting
Likely ongoing maintenance costs were not included
The likely cost of establishing planted stock with a minimum of 1 weed control operation per year for the two years after planting came in at $63,900/ha. If the site required 5 weed control visits per year in the two years after planting, the cost would rise to about $103,900/ha. When closer plant spacing is required (as is often the case for wetlands) then the cost will rise (most likely nearer $150,000/ha).
This does not mean we should not replant natives. Rather, it advocates for protecting every hectare we have, encouraging natural regeneration bordering native forests using eccosystem-based strategies outlined on this page and at Hinewai Reserve on the Banks Peninsula.
A mixed model of planting a small percentage of fast growing exotic species to fund the cost of planting natives is used by EKOS in the Tasman District. See the video for an overview of how this operates within the Emissions Trading Scheme:
We need carbon. We need water, too. But like all good things, there can be too much. Too little water and we die of thirst. Too much, we drown. The same with carbon. Too little in the atmosphere in the form of carbon dioxide (CO2), we go into an Ice Age. Too much, the planet broils. We know this because of the geological evidence and from fundamental laws of physics and chemistry.
How much carbon is there?
There is about 1.85 billion, billion tonnes of carbon on Earth. More than 99% is beneath our feet in soil and rocks including fossil fuels and permafrost. Just 0.2% or 43,500Gt is above the surface. Through natural processes, carbon is constantly in flux. That is, it’s moving between the land, the oceans, and living things (see ‘carbon cycle’ this website). When it’s burned, melted, or respired, it becomes a gas, combining with oxygen to make CO2. Some ends up in the atmosphere*. The rest is absorbed by terrestrial and oceanic ecosystems: forests, grasslands, wetlands, and marine animals and plants that make more than half the oxygen we breathe, and also as carbonic acid (H2CO3) dissolved in ocean and lake waters.
*Calculations at the bottom of this page.
A shift in time
It doesn’t take much CO2 in the atmosphere to warm the planet. Some 18,000 years ago, the concentration of CO2 was 189 ppm (parts per million). Global temperatures were 7-9°C cooler than today, and ice sheets several kilometres thick covered most of Europe and North America.
Over the next 10,000 years, the concentration increased 72ppm, to reach 261ppm. That was enough to warm the planet 6-8°C (Fig 2.).
Fig. 2: The blue line shows globally averaged surface air temperature from 24,000 years ago to the present day, compiled from paleoclimate records with a computer model of the climate system. The horizontal scale has been stretched for the past 1,000 years to show recent changes. Warming begins at the end of the last Glacial around 18,000 years ago, then temperatures stabilize around 9,000 years ago until the last 170 years, when excessive greenhouse gasses triggered rapid warming. (Image: Osman et al /Nature).
By then, some 8,000 year ago, the warming had created a comfortable, and crucially a stable and predictable enough climate to enable humans to plant crops, domesticate livestock, and build civilizations. This land-use change added about 400Gt of CO2 to reach a concentration of 284ppm by the year 1850.
Courtesy of our planet’s eccentric orbit around the sun, the Earth was also entering a gradual cooling cycle that would ultimately lead to another Glacial epoch. This orbital obliquity largely compensated for the gradual warming effect of the extra carbon in the atmosphere. Aside from a few small climatic blips caused by volcanoes and the sun’s activity, the global climate remained stable enough for human civilization to reach a technological watershed moment: the Industrial Revolution.
To power this revolution, we dug carbon out of the ground and burned it to fuel ever-larger machines, fishing fleets, and massive land use changes to feed ever more people, destroying vast natural ecosystems that once locked away millions of tonnes of carbon. Their burned remains entered the atmosphere as CO2. (Slaughtering countless whales may have added quite a bit, too). In the 100 years from 1850 to 1950 we added, either directly or indirectly, another 450Gt of CO2 to the atmosphere, and so concentrations reached 310ppm.
It was about to get worse. Between 1950 and 2000—just 50 years—we added around 1050Gt; more than twice as much as we’d added the previous 7,950 years. Atmospheric CO2 passed 370ppm. Shoveling so much carbon into the atmosphere had postponed the inception of the next Glacial epoch by 100,000 years.
The terrestrial and ocean ecosystems that once supported us continued to being burned and bulldozed. And the pace of destruction kept increasing. The ocean, which had been absorbing more than 90% of the extra heat and as much as half the excess CO2, was becoming dangerously acidic.
Twenty-one years later, on 21 April 2021, atmospheric CO2 passed 420ppm* for the first time in several million years. Our planet is now heating up faster than at any time since the comet wiped out the dinosaurs 65 million years ago. And the oceans are now absorbing only about 25% of it.
*The average for 2021 will be about 417ppm because atmospheric concentrations change between summer (lower) and winter (higher); see the graph below for an explanation.
The carbon budget
When governments signed the 2015 Paris Agreement they did so promising to keep global warming under 1.5°C by staying within a carbon budget. Each nation could choose how they would achieve this by reducing emissions—carbon ‘spending’—and increasing carbon ‘savings’ by planting carbon-absorbing trees. Obviously, to stay within the global budget, every nation had to play its part.
In 2021, the IPCC presented a stark warning. Since the beginning of the Industrial Revolution, we’ve added about 2,400Gt of CO2 the atmosphere, around a third of which we added in just the past 20 years. To have a 66% of staying within 1.5°C, starting from January 2020, the world could emit no more than 400Gt of CO2.
Emissions in 2020 were 38Gt. Emissions in 2021 are projected to be around 39Gt (Fig. 3). That leaves around 323Gt in the budget if we’re prepared to live with a 66% chance of keeping temperatures under 1.5°C. Or we can spend another 421Gt to have a 50% chance.
Scientists had been saying for decades that warming between 1 to 2°C would trigger catastrophic tipping points. At 1.2°C our climate is now already too hot to refreeze the 10,000 cubic metres of ice melting every second from Greenland’s ice sheet. So much freshwater entering the North Atlantic is already changing oceanic currents. This is triggering more tipping points in a cascade effect that will lead to irreversible chain reactions and rapid warming well beyond 3°C. Unless COP26 brings radical and immediate changes, the planet is destined to enter an entirely new ‘hothouse’ state, one we cannot control or reverse. And one hostile to our existence.
“The drama here is that one characteristic of tipping points is that once you press the ‘on’ button you cannot stop it; it takes over. It’s too late. It’s not like you could say, ‘Oops, now I realize I didn’t want to melt the Greenland ice cap. Let’s back off.’ Then it’s too late.” – Johan Rockström, Breaking Boundaries: The Science of Our Planet (Video 1)
Other tipping points are also pushing the carbon budget to the edge of a potential freefall. This includes vast areas of permafrost—frozen soil that contains an estimated 1,600Gt of carbon, almost twice the amount in the atmosphere today—is melting, disgorging CO2 and the far more potent greenhouse gas, methane into the atmosphere. And the Amazon rainforest, which could potentially releasing 200Gt of carbon into the atmosphere over the next 30 years. That is, by 2050. This process has already begun in south-east Amazonia (Video 2).
Earlier this year, the World Meteorological Organization stated that at least one of the next 5 years will be 1.5°C* warmer than pre-Industrial levels. And the chance of this happening is increasing with time.
Would you send your kids to school knowing they had just a 66% chance of coming home alive? Or 50% if we emit an extra 21Gt over the budget? And every day, the odds of their survival are getting increasingly worse because emissions are increasing. That’s what the carbon budget means for their futures.
Kids have done those simple calculations. And that’s why they’re so angry.
*The internal variability in any single year is estimated to be ± 0.25°C, so a single year at 1.5°C could be compensated if the following years are much cooler.
Video 1: in ‘Breaking Boundaries: The Science of Our Planet’, Sir David Attenborough succinctly explains tipping points. This is a short version of the full documentary of the same name, available on Netflix.
(ppm = parts per million; Gt = one gigatonne or one billion tonnes)
2.13 Gt of carbon = 1ppm currently in the atmosphere
To convert carbon (C) to carbon dioxide (CO2), first divide the atomic mass of carbon (12) by the atomic mass of CO2 (44) = 3.67.
Then multiply this by 2.13 Gt carbon: 3.67 x 2.13 = 7.8 Gt carbon dioxide = 1ppm of CO2 currently in the atmosphere.
As there is currently around 415ppm* of CO2 in the atmosphere, that’s 415 x 7.8 Gt = 3,373Gt CO2.
* The amount of CO2 in the atmosphere varies seasonally because plants accumulate carbon in the spring and summer and release some back to the air in autumn and winter. As the northern hemisphere has more land and plants, carbon dioxide levels go up in winter because plants become less productive. Annual measurements of carbon dioxide are an average of these ups and downs. On April 11, 2021, CO2 in the atmosphere peaked at 420ppm
Calculations for adding carbon to the atmosphere from emissions
Emissions are NOT the same as concentrations. This is because the ocean and biosphere absorbed* around 55% of emissions while 45% stays in the atmosphere, adding to what’s already there.
To calculate each additional ppm, divide 7.8 Gt / 0.45 = 17.3Gt
So it takes about 17.3Gt of CO2 emissions to add 1ppm to the atmosphere
* Note: That number is not a constant because the oceans and biosphere are no longer able to absorb as much CO2. Moreover, some is now being emitted by ecosystems that once absorbed it:
“Additional ecosystem responses to warming not yet fully included in climate models, such as CO2 and CH4[methane] fluxes from wetlands, permafrost thaw and wildfires, would further increase concentrations of these gases in the atmosphere (high confidence).” – IPCC 2021 p41.
Instructions for interactive graphs (Credit: The 2°Institute.)
Mouse over anywhere on the graph to see the changes over the last thousand years.
To see time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, then release it.
To see how this compares to the past 800,000 years, click on the ‘time’ icon on the top left.
To return the graphs to their original position, double-click the time icon.
The annual ups and downs in the graph are because plants accumulate carbon in the spring and summer and release some back to the air in autumn and winter. As the northern hemisphere has more land and more plants, carbon dioxide levels go up in winter because plants become less productive. Annual measurements of carbon dioxide are an average of these ups and downs.
