Many countries' pledges to get to net zero greenhouse gas emissions rely partly on removing carbon dioxide from the atmosphere, using methods such as planting trees and restoring degraded ecosystems.
But a report out today has revealed they are relying too heavily on these carbon drawdown schemes to fulfil these promises.
The Land Gap Report, which was released today by the University of Melbourne and includes input from more than 20 international researchers, has calculated countries would collectively need 1.2 billion hectares of land to meet their Paris Agreement goals.
The study found that, based on current pledges, countries intended to use 633 million hectares for carbon capture tactics such as tree planting, which was deemed unrealistic and would swallow land desperately needed for food production and ecology.
Conversely, it found only 551 million hectares accounted for in pledges would restore degraded lands and primary forests.
So what is carbon drawdown?
Carbon dioxide removal (CDR) or carbon drawdown is the process of removing carbon dioxide from the atmosphere.
Australia's former chief scientist Ian Chubb said the main way that could be achieved right now was through photosynthesis.
"The only mechanism that we know now that we can implement at scale that has the capacity to draw CO2 out of the atmosphere is photosynthesis," Professor Chubb said.
"And that means that we need more capacity, more plants available, and we need to stop cutting down plants, trees, vegetation."
Researchers are working on ways to use chemical processes to draw down carbon dioxide, but it is still in the early conceptual phase according to the Intergovernmental Panel on Climate Change (IPCC).
How much can trees really do?
A new international report has quantified global climate pledges of land-based drawdown methods and found countries were unrealistic and governments were prioritising planting trees ahead of reducing fossil fuel emissions.
Kate Dooley from the University of Melbourne was the lead researcher on the Land Gap Report and said there was too much emphasis on carbon removal in plans to get to net zero emissions.
"We say that it needs to be 80 to 95 per cent emission reductions by 2050. This is global scale, and then the last 5 to 15 per cent could be sequestered [removed from the atmosphere] into land," Dr Dooley said.
"What the focus on net zero has done is it's shifted the focus away from that sort of 95 per cent emission reduction onto the very small amount of removals."
In other words, although carbon drawdown could play an important role, it has deflected away from the main game.
Dr Dooley also said the amount of land required was unrealistic and had major implications for land use practices.
"Almost 1.2 billion hectares of land are in countries' net zero pledges or … 2030 pledges," she said.
"That is almost the equivalent to the area of current global crop land. It's a huge amount of land — it's larger than the size of Australia.
"Removals are just a very small extra thing, but they have huge implications for the land sector, for how we do agriculture, for Indigenous peoples."
She believed Australia was among those over-reliant on forest regrowth and tree planting.
How can you measure how much carbon is removed from the atmosphere?
It is a good question and one of the most contested and controversial ones.
Dr Dooley said the carbon dioxide released from burning fossil fuels was not the equivalent to what was reabsorbed in the land.
"We've added to the carbon cycle in aggregate; moving it into trees doesn't permanently move it back out of the active carbon cycle," she said.
"From the perspective of reducing atmospheric emissions and reducing radiative forcing, which is what's causing climate change and temperatures to warm, sequestering carbon into trees is not the answer and is not equivalent to releasing fossil fuel emissions."
Dr Dooley's research raised problems with carbon accounting methods, which the report found failed to recognise the variation in different kinds of carbon storage.
"All carbon stocks are in effect assumed to have the same stability, longevity, and resilience," the report found.
"Current carbon accounting practices fail to recognise that carbon lost from primary forests is not offset by planting trees — with lower ecosystem integrity in monoculture systems the risk of carbon loss is higher."
She admitted that land could still play an important role in climate mitigation, but that would require better rules for carbon accounting.
What about carbon credits and carbon markets?
Carbon markets have emerged as a way of financing and giving value to carbon abatement projects.
Ben Stuart, chief commercial officer of carbon market trading platform Xpansiv, said carbon markets were a mechanism by which projects could be funded.
"A lot of independent entities and consultants are forecasting [carbon markets] to grow anywhere from 15 to 50 times over the next sort of 20 to 30 years," he said.
"The two main types [of carbon credits] relate to technology so, in some places, renewable energy and other technology advancements can produce carbon credits but then also nature-based solutions like forestry projects or permanent plantations."
Mr Stuart said he believed the way carbon credits were measured was sound.
"There's a lot of science behind it that allows us to actually understand exactly what the measurements equate to in terms of carbon offsets," he said.
"Whether that's either sequestered or avoided, those metrics are robust."
But it's a point of contention.
Australian Carbon Credit Units (ACCUs) are a financial product that represent the removal or avoidance of carbon dioxide.
The federal government has initiated a review of ACCUs, which is being led by Professor Chubb.
"There were complaints about the integrity of the system that led to credits being awarded allegedly to projects that did not lead to genuine abatement," he said.
"One argument is that there is limited integrity and there's the other side of the argument that, when you look at all the data, there is substantial integrity.
"Our job as a review committee is to find where the weight of evidence lies and make recommendations to the government as to how they can improve it."
But he would not say which way the weight of that evidence was pointing.
A scientific analysis has been conducted as part of the review with the final report expected to be released by the end of the year.
Can we offset our way to net zero?
Essentially, no.
An offset is not exactly the same thing as a carbon credit. Businesses can purchase credits to compensate for emissions.
As well as the review into ACCUs the federal government has also initiated a review into the Safeguard Mechanism, which will put requirements on the big polluters to shrink their emissions.
If successful, the two mechanisms combined are designed to both reduce emissions and draw down carbon.
Professor Chubb said carbon credits should not be used as a way to avoid reducing emissions in other ways.
"I think we've got to be realistic and say that we should do more than simply balance any continuing emissions with offsets.
"We've got to get to negative emissions. It is actually more than just an offset scheme; it's actually a drawdown scheme and we do need to draw down CO2 from the atmosphere."
In a statement, the federal government said "offsets from the land and agriculture sectors will play a major role in achieving net zero".
"It is important that Australia's carbon crediting system is operating at the highest level of integrity and standards. This is why the government initiated an independent review of Australian Carbon Credit Units."
Ben Stuart agreed that carbon credits were just one part of the solution.
"I don't think it's a get-out-out-of-jail-free card by any stretch of the imagination," he said.
"I think it's a very useful tool to help move into that transition."
Dr Dooley agreed that how finance was channelled to carbon drawdown projects was important, but said she did not believe offsetting was the answer.
"This is why offsetting has persisted for so long and it's not just in Australia, it's globally, getting finance to tropical forested countries to protect their forests," she said.
"I think that there are better ways to think about financing projects other than allowing the fossil fuel industry to continue burning fossil fuels and releasing emissions.
"We need to reduce those so quickly, so we need to look into other options for project finance."
