Nearly 200 nations have pledged specific cuts to their greenhouse gases as part of the Paris climate accord, while Massachusetts is legally required to reach strict emissions caps within two years and Boston has committed to becoming carbon neutral by 2050.
Whether those goals are realized, however, may prove difficult to evaluate.
New research has found that the generally accepted methods of measuring planet-warming emissions could be underestimating them by a substantial amount, potentially creating a false sense of progress.
The research suggests that the existing approach omits so much data that nations, states, and cities are effectively flying blind, unaware of how much greenhouse gases they’re producing.
“Without actual measurements of changes in emissions, we don’t know — and we can’t know — if we’re meeting our goals, and that’s a problem,” said Lucy Hutyra, an associate professor of earth and environment at Boston University, one of the lead authors of a new study on emissions. “We don’t want to ‘greenwash’ the situation. We don’t want nations, states, and cities to make claims that they’re doing something; we want them to really do something.”
Hutyra and colleagues at Harvard University have taken aim at the problem, which could have far-reaching implications for efforts to address climate change. In a study published this week in the Proceedings of the National Academy of Sciences journal, the scientists showed for the first time that it’s possible to make relatively accurate assessments of a region’s greenhouse gas emissions by continually testing the air.
State environmental officials and some environmental groups insist their measurements are accurate, but the study highlights a little known aspect of the carbon emissions debate: the way the gases are counted.
Current methods of quantifying emissions don’t actually measure the carbon dioxide, methane, and other greenhouse gases in the atmosphere. Instead, they rely on complex calculations that estimate emissions by tabulating the pollution from power plants, buildings, transportation, and other sources.
That method often overlooks a range of factors, such as unknown natural gas leaks, traffic from outside the state, or the amount of photosynthesis by trees and other vegetation.
Using sensors set up at Boston University, Copley Square, Martha’s Vineyard, Petersham, and in Southern New Hampshire, the scientists calculated that the Boston metropolitan area produced about 86 million tons of carbon dioxide in 2014, 14 percent more than an estimate generated by traditional methods.
Still, the scientists estimate their measurements have a margin of error of about 18 percent, meaning that the region could have produced as much as 101 million tons of carbon dioxide or as little as 71 million tons in that year.
Although the disparity is significant, existing methods don’t cite a margin of error in their assessment of emissions, because they have no way of knowing it, researchers said.
“Significant uncertainties do remain,” said Donald Wuebbles, a professor of atmospheric studies at the University of Illinois.
While serving as president Barack Obama’s assistant director of the Office of Science and Technology Policy, Wuebbles led a team that looked into how to improve emissions estimates. They concluded that measuring emissions directly in the atmosphere was needed to improve assessments and verify that governments are doing what they promised.
“There can be political incentives to distort the measurements in one direction or the other, and right now we have no way of knowing if that is happening,” said Phil Duffy, president of the Woods Hole Research Center in Falmouth, which specializes in climate change research. “You can’t control what you can’t measure.”
Using sensors to track emissions — as Hutyra and her team did — can be expensive, and Duffy said it was reassuring that just five testing sites made it feasible to measure emissions.
“Perhaps, when the methods become more mature, they will become more affordable,” he said.
In Massachusetts, after being forced to do so by the state’s top court, the Baker administration last year issued sweeping new regulations that set specific limits on sources of greenhouse gases.
At the time, environmental officials said the state had already cut its emissions by 21 percent below 1990 levels, a figure that advocates have disputed. A 2008 emissions law requires the state to cut its greenhouse gases 25 percent below 1990 levels by 2020, and 80 percent below 1990 levels by 2050.
In response to questions about how the state calculates emissions, Massachusetts environmental officials said they use “the highest standards of emissions tracking methodology at the statewide scale,” an approach that is accepted by the United Nations’ International Panel on Climate Change.
“The Commonwealth tracks emissions using an approach consistent with that taken by the US [Environmental Protection Agency] and other states and countries that relies on a variety of data sources that can categorize data by location or origin and consistently compare the data with historical emission levels,” said Peter Lorenz, a spokesman for the state’s Executive Office of Energy and Environmental Affairs.
Some environmental advocates also defended the state’s approach. David Ismay, a senior attorney at the Conservation Law Foundation, whose 2014 lawsuit led to the Supreme Judicial Court ruling, called the new research “interesting science, but not particularly relevant for purposes of implementing regulations.”
Testing the air in a region may improve accuracy, but the state’s method allows it to track trends in the largest sources of pollution, he said.
“This type of work — over a sustained time frame — might be helpful, but is not necessarily needed [or] better for regulating emitters,” he said.
Other advocates said they’re concerned more about the state cutting emissions than counting them more precisely.
“While it is necessary to measure greenhouse gas emissions as accurately as possible, we’re in deep trouble if we have to worry about the margin of error in emissions accounting,” said Jordan Stutt, carbon programs director of the Acadia Center in Boston.
For much of the past decade, those polices have concentrated on reducing pollution from power plants, which have cut emissions by about 60 percent since 1990, according to the New England Power Generators Association.
Over the past year, state officials have turned their focus to transportation pollution, which has surpassed power plants as the state’s largest source of greenhouse gases. Transportation now accounts for an estimated 40 percent of the state’s emissions.
In that area, Boston may also be skewing its carbon accounting, because of the difficulty of tracking the number, speed, and fuel economy of cars on the road.
“Ambitious goals are a key first step in addressing our climate problem,” Hutyra said. “But we don’t currently have the tools to adequately assess progress, and we need them to know that our policies are on the right track.”