Measurements of atmospheric CH4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near‐zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH4 from biomass burning. The most likely drivers of the CH4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near‐zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.

[1] Sixteen mixtures of methane (CH 4 ) in dry air were prepared using a gravimetric technique to define a CH 4 standard gas scale covering the nominal range 300-2600 nmol mol À1 . It is designed to be suitable for measurements of methane in air ranging from those extracted from glacial ice to contemporary background atmospheric conditions. All standards were prepared in passivated, 5.9 L high-pressure aluminum cylinders. Methane dry air mole fractions were determined by gas chromatography with flame ionization detection, where the repeatability of the measurement is typically better than 0.1% ( 1.5 nmol mol À1 ) for ambient CH 4 levels. Once a correction was made for 5 nmol mol À1 CH 4 in the diluent air, the scale was used to verify the linearity of our analytical system over the nominal range 300-2600 nmol mol À1 . The gravimetrically prepared standards were analyzed against CH 4 in air standards that define the Climate Monitoring and Diagnostics Laboratory (CMDL) CMDL83 CH 4 in air scale, showing that CH 4 mole fractions in the new scale are a factor of (1.0124 ± 0.0007) greater than those expressed in the CMDL83 scale. All CMDL measurements of atmospheric CH 4 have been adjusted to this new scale, which has also been accepted as the World Meteorological Organization (WMO) CH 4 standard scale; all laboratories participating in the WMO Global Atmosphere Watch program should report atmospheric CH 4 measurements to the world data center on this scale.

Seasonal spatial and temporal gradients for the CO2 mole fraction over North America are examined by creating a climatology from data collected 2004–2013 by the NOAA/ESRL Global Greenhouse Gas Reference Network Aircraft Program relative to trends observed for CO2 at the Mauna Loa Observatory. The data analyzed are from measurements of air samples collected in specially fabricated flask packages at frequencies of days to months at 22 sites over continental North America and shipped back to Boulder, Colorado, for analysis. These measurements are calibrated relative to the CO2 World Meteorological Organization mole fraction scale. The climatologies of CO2 are compared to climatologies of CO, CH4, SF6, N2O (which are also measured from this sampling program), and winds to understand the dominant transport and chemical and biological processes driving changes in the spatial and temporal mole fractions of CO2 as air passes over continental North America. The measurements show that air masses coming off the Pacific on the west coast of North America are relatively homogeneous with altitude. As air masses flow eastward, the lower section from the surface to 4000 m above sea level (masl) becomes distinctly different from the 4000–8000 masl section of the column. This is due in part to the extent of the planetary boundary layer, which is directly impacted by continental sources and sinks, and to the vertical gradient in west‐to‐east wind speeds. The slowdown and southerly shift in winds at most sites during summer months amplify the summertime drawdown relative to what might be expected from local fluxes. This influence counteracts the dilution of summer time CO2 drawdown (known as the “rectifier effect”) as well as changes the surface influence “footprint” for each site. An early start to the summertime drawdown, a pronounced seasonal cycle in the column mean (500 to 8000 masl), and small vertical gradients in CO2, CO, CH4, SF6, and N2O at high‐latitude western sites such as Poker Flat, Alaska, suggest recent influence of transport from southern latitudes and not local processes. This transport pathway provides a significant contribution to the large seasonal cycle observed in the high latitudes at all altitudes sampled. A sampling analysis of the NOAA/ESRL CarbonTracker model suggests that the average sampling resolution of 22 days is sufficient to get a robust estimate of mean seasonal cycle of CO2 during this 10 year period but insufficient to detect interannual variability in emissions over North America.

[1] Recent results from laboratory, field and remote sensing measurements suggest the presence of large methane emissions from the Amazon basin. Here we present regionally integrative, direct trace gas observations from two sites that confirm the presence of large fluxes of methane in eastern Amazônia. Air samples collected on aircraft near Santarém (2.9°S, 55.

[1] Observations of SF 6 are used to quantify the mean time since air was in ("mean age" from) the Northern Hemisphere (NH) midlatitude surface layer. The mean age is a fundamental property of tropospheric transport that can be used in theoretical studies and used to evaluate transport in comprehensive models. Comparisons of simulated SF 6 and an idealized clock tracer confirm that the time lag between the SF 6 mixing ratio at a given location and the NH midlatitude surface provides an accurate estimate of the mean age. The ages calculated from surface SF 6 measurements show large meridional gradients in the tropics but weak gradients in the extratropics, with near-zero ages at the surface north of 30°N and ages around 1.4 years south of 30°S. Aircraft measurements show weak vertical age gradients in the lower and middle troposphere, with only slight increases of age with height in the NH and slight decreases with height in the Southern Hemisphere. There are large seasonal variations in the age at tropical stations (annual amplitudes around 0.5-1.0 year), with younger ages during northern winter, but only weak seasonal variations at higher latitudes. The seasonality and interannual variations in the tropics and Southern Hemisphere are related to changes in locations of tropical convection. There is qualitative agreement, in both spatial and temporal variations, between the simulated ages and observations. The model ages tend to be older than observed, with differences of~0.2 year in the Northern Hemisphere upper troposphere and throughout the Southern Hemisphere troposphere.

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Continuous measurements of atmospheric methane (CH4) mole fractions measured by NOAA's Global Greenhouse Gas Reference Network in Barrow, AK (BRW), show strong enhancements above background values when winds come from the land sector from July to December from 1986 to 2015, indicating that emissions from arctic tundra continue through autumn and into early winter. Twenty‐nine years of measurements show little change in seasonal mean land sector CH4 enhancements, despite an increase in annual mean temperatures of 1.2 ± 0.8°C/decade (2σ). The record does reveal small increases in CH4 enhancements in November and December after 2010 due to increased late‐season emissions. The lack of significant long‐term trends suggests that more complex biogeochemical processes are counteracting the observed short‐term (monthly) temperature sensitivity of 5.0 ± 3.6 ppb CH4/°C. Our results suggest that even the observed short‐term temperature sensitivity from the Arctic will have little impact on the global atmospheric CH4 budget in the long term if future trajectories evolve with the same temperature sensitivity.

Abstract. N 2 O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 • longitude × 2.5 • latitude) and at monthly time resolution. Over the 11-year period, the global total N 2 O source varied from 17.5 to 20.1 Tg a −1 N. Tropical and subtropical land regions were found to consistently have the highest N 2 O emissions, in particular in South Asia (20 ± 3 % of global total), South America (13 ± 4 %) and Africa (19 ± 3 %), while emissions from temperate regions were smaller: Europe (6 ± 1 %) and North America (7 ± 2 %). A significant multi-annual trend in N 2 O emissions (0.045 Tg a −2 N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N 2 O source was observed (0.8 Tg a −1 N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a −1 N, 1 SD) and Africa (0.3 Tg a −1 N, 1 SD). Notable variability was also found for N 2 O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a −1 N, 1 SD, respectively). Interannual variability in the N 2 O source shows some correlation with the El Niño-Southern Oscillation (ENSO), where El Niño conditions are associated with lower N 2 O fluxes from soils and from the ocean and vice versa for La Niña conditions.