This study quantitatively estimates the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial ...datasets, and a high-resolution atmospheric transport model. Results show that current inventories from the US Environmental Protection Agency (EPA) and the Emissions Database for Global Atmospheric Research underestimate methane emissions nationally by a factor of ∼1.5 and ∼1.7, respectively. Our study indicates that emissions due to ruminants and manure are up to twice the magnitude of existing inventories. In addition, the discrepancy in methane source estimates is particularly pronounced in the south-central United States, where we find total emissions are ∼2.7 times greater than in most inventories and account for 24 ± 3% of national emissions. The spatial patterns of our emission fluxes and observed methane–propane correlations indicate that fossil fuel extraction and refining are major contributors (45 ± 13%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be 4.9 ± 2.6 times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on the US EPA’s recent decision to downscale its estimate of national natural gas emissions by 25–30%. Overall, we conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.
Anthropogenic methane emissions from China are likely greater than in any other country in the world. The largest fraction of China's anthropogenic emissions is attributable to coal mining, but these ...emissions may be changing; China enacted a suite of regulations for coal mine methane (CMM) drainage and utilization that came into full effect in 2010. Here, we use methane observations from the GOSAT satellite to evaluate recent trends in total anthropogenic and natural emissions from Asia with a particular focus on China. We find that emissions from China rose by 1.1 ± 0.4 Tg CH
yr
from 2010 to 2015, culminating in total anthropogenic and natural emissions of 61.5 ± 2.7 Tg CH
in 2015. The observed trend is consistent with pre-2010 trends and is largely attributable to coal mining. These results indicate that China's CMM regulations have had no discernible impact on the continued increase in Chinese methane emissions.
High-latitude ecosystems have the capacity to release large amounts of carbon dioxide (CO₂) to the atmosphere in response to increasing temperatures, representing a potentially significant positive ...feedback within the climate system. Here, we combine aircraft and tower observations of atmospheric CO₂ with remote sensing data and meteorological products to derive temporally and spatially resolved year-round CO₂ fluxes across Alaska during 2012–2014. We find that tundra ecosystems were a net source of CO₂ to the atmosphere annually, with especially high rates of respiration during early winter (October through December). Long-term records at Barrow, AK, suggest that CO₂ emission rates from North Slope tundra have increased during the October through December period by 73% ± 11% since 1975, and are correlated with rising summer temperatures. Together, these results imply increasing early winter respiration and net annual emission of CO₂ in Alaska, in response to climate warming. Our results provide evidence that the decadal-scale increase in the amplitude of the CO₂ seasonal cycle may be linked with increasing biogenic emissions in the Arctic, following the growing season. Early winter respiration was not well simulated by the Earth System Models used to forecast future carbon fluxes in recent climate assessments. Therefore, these assessments may underestimate the carbon release from Arctic soils in response to a warming climate.
Emissions-reducing policies include measures that promote energy sources generating fewer emissions and that boost energy efficiency (such as building wind turbines or insulating homes), or those ...that decrease activities that emit greenhouse gases (such as flying or driving). Measures that increase emissions support conventional fossil-fuel industries or encourage greater energy consumption (for example, by reducing petrol taxes). ...our estimates are based on government spending announcements, particularly for long-term spending packages. ...almost all G20 economies provided financial support to domestic airlines, but only France made its support conditional on meeting climate goals by asking Air France to cease domestic flights on routes that compete with high-speed rail.
Abstract
Greenhouse gas emissions from meat and dairy production are often highly uncertain; these emissions are typically estimated using inventory-based, ‘bottom-up’ models, which contain ...uncertainties that are difficult to quantify. Modeled emissions estimates can be corroborated using atmospheric measurements—taken above and downwind of animal production regions—to produce ‘top-down’ emissions estimates. Top-down and bottom-up estimates of animal methane show good agreement when considering global emissions. However, in the US, where animal production is predominantly highly intensified with confined feeding operations, animal methane emissions may be 39%–90% higher than bottom-up models predict (expressed as mean differences across studies). Animal emissions may grow in the future as meat and dairy demand increases in developing countries. We examine East and Southeast Asia as a test case, where emissions from increased meat and dairy production are expected to be offset by improved efficiency from intensive methods. We adjust the share of direct emissions projected to come from intensive systems by the intensities derived from US top-down estimates. We find that region-wide emissions from meat and milk production could reach 1.52 (1.41–1.62) GtCO
2
eq by 2050, an amount 21% (13%–29%) higher than previously predicted. Therefore, intensification may not be as effective in mitigating emissions in developing countries as is commonly assumed.
Uncertainties in supply chain emissions raise questions about the benefits of natural gas as a bridge fuel, but recent efficiency improvements in gas-fired electricity generation remain overlooked. ...Our comprehensive analysis of supply chain infrastructure and electricity generation across the United States informs spatially and temporally resolved estimates of life cycle greenhouse gas emissions. Results show decreasing life cycle emissions over each year examined: 629, 574, and 525 kg CO2 eq MWh–1 in 2005, 2010, and 2015, respectively. Electricity generation contributed 86% of emissions or greater for each year. Despite concerns over uncertain methane leaks, efficiency improvements make it much more likely that natural gas electricity has an unambiguous greenhouse gas benefit relative to coal. Methane leaks would have to be 4.4 times the Environmental Protection Agency (EPA) value in 2015 to reverse these benefits over 20-year time horizons. With retiring coal plants and scrutinized supply chain emissions, our results show that natural gas can provide a lower emissions option to coal in an increasingly decarbonized power sector.
The Orbiting Carbon Observatory 2 (OCO-2) is NASA's first satellite dedicated to monitoring CO2 from space and could provide novel insight into CO2 fluxes across the globe. However, one continuing ...challenge is the development of a robust retrieval algorithm: an estimate of atmospheric CO2 from satellite observations of near-infrared radiation. The OCO-2 retrievals have undergone multiple updates since the satellite's launch, and the retrieval algorithm is now on its ninth version. Some of these retrieval updates, particularly version 8, led to marked changes in the CO2 observations, changes of 0.5 ppm or more. In this study, we evaluate the extent to which current OCO-2 observations can constrain monthly CO2 sources and sinks from the biosphere, and we particularly focus on how this constraint has evolved with improvements to the OCO-2 retrieval algorithm. We find that improvements in the CO2 retrieval are having a potentially transformative effect on satellite-based estimates of the global biospheric carbon balance. The version 7 OCO-2 retrievals formed the basis of early inverse modeling studies using OCO-2 data; these observations are best equipped to constrain the biospheric carbon balance across only continental or hemispheric regions. By contrast, newer versions of the retrieval algorithm yield a far more detailed constraint, and we are able to constrain CO2 budgets for seven global biome-based regions, particularly during the Northern Hemisphere summer when biospheric CO2 uptake is greatest. Improvements to the OCO-2 observations have had the largest impact on glint-mode observations, and we also find the largest improvements in the terrestrial CO2 flux constraint when we include both nadir and glint data.
US natural gas production increased by ∼43% between 2005 and 2015, but there is disagreement among existing studies on whether this growth led to increased methane emissions. We evaluate the likely ...contributions of atmospheric transport to an upward trend in atmospheric methane enhancements during 2007–2015, defined as the contribution of North American emissions to atmospheric observations across the US. We find that interannual variability (IAV) in transport yields an apparent upward trend in enhancements across much of the US during this time and can explain disagreements among existing studies over emissions trends. We further find that enhancements at satellite and in situ monitoring sites are 19% higher during El Niño than La Niña, possibly because air masses spend more time over North America on average during some years. The results show that accurate modeling of IAV in transport is a key prerequisite to quantifying emissions trends.
Plain Language Summary
US natural gas production increased from 18 to 27.1 trillion cubic feet per year between 2005 and 2015 as a result of the shale gas boom and the associated technological breakthrough of combining horizontal drilling and hydraulic fracturing. This increase in natural gas activity has caused concern about methane emissions, since methane is the primary constituent of natural gas and an important greenhouse gas. However, existing studies of US methane emissions trends have reached conflicting conclusions. Furthermore, atmospheric methane levels at many US observation locations have increased faster than the global mean, raising questions about whether increasing US natural gas production has led to increased emissions. In this study, we explore the roles of changing emissions versus meteorology in explaining recent increases in atmospheric methane enhancements across the US and we explore the meteorological factors that may be driving these trends. We find that variability in meteorology can explain this recent atmospheric increase. Overall, the results lend support for the conclusion that there was little upward trend in US methane emissions during this time.
Key Points
Atmospheric transport explains an upward trend in observed atmospheric methane enhancements across the US between years 2008 and 2015
The time modeled air masses spend over North America varies by 15%–20% among years and correlates with variability in methane enhancements
Modeled methane enhancements at satellite and in situ monitoring sites are 19% higher during El Niño than La Niña
China is the world’s largest producer and consumer of coal, but the country has recently set ambitious targets for cleaner energy sources. These include goals to capture and utilize methane from coal ...seams as a source of unconventional natural gas. We investigate the impacts of using coal methane to displace coal power plants and residential coal combustion across northern China. We compare the greenhouse gas emissions, air quality, and public health impacts of several scenarios for coal methane utilization. We find that China’s existing goals would decrease the country’s total carbon emissions by ∼2.3% (284 million tons CO2eq). Furthermore, these reductions are dominated by mitigated methane emissions and therefore confer a much larger climate benefit than would be expected from other forms of natural gas. Our results also indicate that the air quality and health impacts strongly depend on how the methane is utilized. Using the methane to displace coal-fired electricity would reduce annual mean ambient PM2.5 concentrations by up to >2.5 μg/m3 and prevent up to 9290 premature mortalities annually (95% confidence interval: 7862–9992). By contrast, utilizing coal methane in home heating yields smaller changes to ambient air quality (∼0.6 μg/m3), but improvements to indoor air quality could produce comparable reductions in premature mortality.
The daily variation of ground‐level ozone (O3), a harmful pollutant, is positively correlated with air temperature (T) in many midlatitude land regions in the summer. The observed temporal regression ...slope between O3 and T (dO3/dT) is referred to as the “ozone‐climate change penalty” and has been proposed as a way to predict the impact of future climate warming on O3 from observations. Here, we use two chemical transport models to show that the spatial variation of dO3/dT is primarily determined by simultaneous meridional advection of O3 and T. Furthermore, the sign and magnitude of dO3/dT can be approximated by their climatological meridional gradient ratio (O3 gradient divided by T gradient). Consideration of expected changes in the meridional gradients of T and O3 due to climate change indicates that dO3/dT will likely change. Caution is needed when using the observed climate penalty to predict O3 changes.
Plain Language Summary
At Earth's surface, ozone is a harmful pollutant. In the summer, we observe higher ozone concentrations on hotter days over land in the midlatitudes. This leads researchers to expect higher ozone concentrations as a result of global warming, based on chemistry that associates higher ozone concentrations with higher temperatures. Here, we show that the relationship between ozone and temperature is largely controlled by the north‐south movement of air which simultaneously transports ozone and heat. Therefore, the background spatial distributions of ozone and temperature determine how ozone and temperature covary. The ozone‐temperature relationship in the future may look different from today, because global warming is not spatially uniform. We advise caution in using observed ozone‐temperature relationship to estimate future ozone changes.
Key Points
Transport by meridional advection of O3 and T explains the spatial variation in the daily O3‐T relationship
Daily regression slope dO3/dT can be approximated by the ratio of O3 and T mean meridional gradients when temperature gradients are strong
Gradient ratio suggests dO3/dT will change with warming, making it questionable to use observed dO3/dT in O3 projections
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