Scientists have identified a staggering 5.5 billion ton gap between greenhouse gas emissions acknowledged each year by the world’s nations and the emissions calculated by independent models, an accounting discrepancy that threatens to complicate the already difficult task of resetting the world’s climate trajectory.
“There is a gap of 5.5 gigatons of CO2, which is a huge gap,” said Giacomo Grassi, a forest expert at the European Commission’s Joint Research Centre, and lead author of the study published Monday in Nature Climate Change. “This gap is quite new.”
The discrepancy emerges at a critical moment, as world leaders try to pinpoint how — and how quickly — nations must cut greenhouse gas pollution to prevent catastrophic levels of warming in coming years.
As part of the international Paris climate accord and prior agreements, nations are supposed to report detailed information about their emissions to the United Nations, including those related to their forests and other land use. But between 2005 and 2015, Grassi and fellow scientists found, some countries have claimed to take so much additional carbon out of the air that they have created uncertainty about how to evaluate whether they were meeting their individual climate goals.
“It’s like if the navigation system provides information in miles, and the car dashboard in kilometers,” said Grassi, one of 22 separate authors from countries around the world, including Italy, Japan and the United States.
The new research suggests that the current system could cause a diplomatic standoff as early as next year. That is when, under the Paris agreement, nations are required to gather for a global “stocktake” to determine whether the world is actually on track to cut its emissions enough to stay in line with the agreement’s goals.
If countries are using one accounting method but independent models are using another, the results will make it difficult to determine where the world actually stands in its emissions-cutting goals.
It is not that 5.5 billion tons of emissions per year — or rather their opposite, greenhouse gases absorbed by the Earth — are being missed entirely. Rather, the issue is how they are being categorized, who gets the credit and whether that is altering the goal posts for how aggressively individual nations need to cut their fossil fuel emissions.
Both oceans and the land on Earth are powerful natural tools in muting the effect of human greenhouse gas emissions. They absorb an estimated 9.2 billion tons and 12.5 billion tons of carbon dioxide per year, respectively. Without them, climate change would be much, much worse.
No country appears to have yet found a way to claim the beneficial role of the open oceans on their climate balance sheet. But the land is a different story.
Certain countries have long benefited, at least on paper, from the enormous carbon “sink” provided by forests. Claiming the credit from forests is a practice that can be particularly beneficial in countries with vast wooded areas such as Brazil, Canada, Russia, the United States, and others. The result is that after these countries add up the emissions from the power they generate — the cars on their roads and other sources — they are allowed to then subtract a substantial amount based on the carbon-sucking role of their land.
The United States, for instance, reports 6.6 billion tons of carbon dioxide equivalent emissions for 2019, the most recent year of reporting, from the burning of fossil fuels, human agricultural activity, and other sources. But then it subtracts 789 million tons of emissions to take into account the role of the country’s land surfaces. Ultimately, the “net” emissions reported to the international community are roughly 5.8 billion tons. That is a savings of 12 percent, thanks to land alone.
Christopher Williams, an expert on forests and how they are affected by climate change at Clark University, said Monday’s study “draws attention to something that has concerned many of us for quite a while — that our national greenhouse gas inventory reporting is not designed to measure and monitor true mitigation."
“We are lucky to have those natural carbon sinks,” Williams continued. "However, that carbon uptake is a freebie from nature for which we do not really get to take credit in our battle against climate change.”
What the countries are doing is a product of U.N. rules regarding “managed land,” defined as areas “where human interventions and practices have been applied to perform production, ecological or social function.” This definition could involve areas of intensive forestry, but it may also involve national parks or even places where a country is prepared to deploy to fight a wildfire someday.
The “managed land” reporting system exists because of a thorny scientific problem. Countries are supposed to report human-caused impacts on forests and other vegetation within their borders, but that is a difficult figure to accurately calculate. It is relatively easy to capture the direct human impact of logging or planting a tree. But it is more difficult to measure indirect impacts, such as the role of the additional carbon dioxide humans add to the atmosphere in stoking additional tree growth. These indirect effects are hard to separate from what would naturally happen anyway, as forests grow, and burn, on their own.
Therefore, countries are supposed to identify land that is “managed” and then count everything that is happening there. In practice, different countries have adopted different systems for doing that. In the case of the United States, for instance, almost the entire country is categorized as “managed,” with the main exception being many remote regions of Alaska. Recent research has shown that few countries are providing any detailed information about how they determine which lands within their borders are “managed” and which are not.
The new study estimates that under this system, countries are considering far more land to be managed than other independent methods do. The difference amounts to more than 9 million square miles of living, growing Earth.
Grassi argues that no individual nation is at fault for the 5.5 billion ton discrepancy — rather the issue is two incompatible scientific approaches, with the countries’ individual experts using one technique and independent energy system modelers and carbon bookkeepers using another.
“I don’t think the greenhouse gas inventories in average are wrong. The key point is the measurements are different,” Grassi said.
Still, for large emitting countries like the United States, it is certainly convenient — and good optics — to be able to report smaller “net” emissions.
What’s more, the countries’ approach can credit them with carbon subtractions that they have not directly caused through policy actions such as stopping deforestation, replanting trees, or actively restoring degraded forest.
After all, a significant part of the carbon stored in forests today is there because of human carbon dioxide emissions, which forests soak up and use to fuel growth.
“There will be some policy and management in there, but a lot of it is going to be a free lunch,” said Glen Peters, research director of the Center for International Climate Research in Oslo.
There is an arguably bigger issue going forward, Peters added. As the world begins to reduce its emissions in an effort to stave off more warming, countries with large forests might not have to reduce theirs to zero under the current system. Rather, if they take credit for the subtractions of carbon occurring on their land, then they will only have to reduce emissions to the point where forests and other landscapes are offsetting them.
“This will become more problematic in the future," Peters said.
One smaller developing country is already in this situation: Myanmar. By its own accounting, the country is carbon negative already. It has so many forests sucking up carbon that this effect outweighs its greenhouse gas emissions from the burning of fossil fuels. But as Myanmar itself has noted, those fossil fuel emissions are expected to increase rapidly in the future, something the country is hoping to control to maintain its carbon balance.
Grassi and his co-authors say the problem could be addressed by what they call an “adjustment” to the models that policymakers rely upon to chart the world’s climate and carbon trajectories.
While countries could continue to claim emissions reductions from managed land, the approach would adjust other aspects of carbon accounting accordingly, to ensure consistency. That would affect not only the countries’ individual promises and goals, but the global carbon budget — the remaining carbon they can still emit and stay within the Paris agreement’s goals. The adjustment would cause that budget to shrink, increasing the perception of an urgent need to drastically cut emissions.
“In the absence of these adjustments," the study states, “collective progress would appear to be more on-track than it actually is.”