The first 12 years (1974–1985) of continuous atmospheric CO2 measurements from the NOAA GMCC program at the Mauna Loa Observatory in Hawaii are analyzed. Hourly and daily variations in the concentration of CO2 due to local sources and sinks are described, with subsequent selection of data representing background concentrations. A digital filtering technique using the fast Fourier transform and low‐pass filters was used to smooth the selected data and to separate the seasonal cycle from the long‐term increase in CO2. The amplitude of the seasonal cycle was found to be increasing at a rate of 0.05±0.02 ppm yr−1. The average growth rate of CO2 was 1.42±0.02 ppm yr−1, and the fraction of CO2 remaining in the atmosphere from fossil fuel combustion was 59%. A comparison between the Mauna Loa continuous CO2 data and the CO2 flask sample data from the sea level site at Cape Kumukahi, Hawaii, showed that the amplitude of the seasonal cycle at Cape Kumukahi was 23% larger than at Mauna Loa, with the phase of the cycle at Mauna Loa lagging the cycle at Cape Kumukahi by about 1–2 weeks.

The distribution and variations of atmospheric CO2 from 1981 to 1992 were determined by measuring CO2 mixing ratios in samples collected weekly at a cooperative global air sampling network. The results constitute the most geographically extensive, carefully calibrated, internally consistent CO2 data set available. Analysis of the data reveals that the global CO2 growth rate has declined from a peak of ∼2.5 ppm yr−1 in 1987–1988 to ∼0.6 ppm yr−1 in 1992. In 1992 we find no increase in atmospheric CO2 from 30° to 90°N. Variations in fossil fuel CO2 emissions cannot explain this result. The north pole‐south pole CO2 difference increased from ∼3 ppm during 1981–1987 to ∼4 ppm during 1988–1991. In 1992 the difference was again ∼3 ppm. A two‐dimensional model analysis of the data indicates that the low CO2 growth rate in 1992 is mainly due to an increase in the northern hemisphere CO2 sink from 3.9 Gt C yr−1 in 1991 to 5.0 Gt C yr−1 in 1992. The increase in the north pole‐south pole CO2 difference appears to result from an increase in the southern hemisphere CO2 sink from ∼0.5 to ∼1.5 Gt C yr−1.

[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.

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.

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 and Fig. 1(a)). These trends are primarily due to stricter air quality emission controls that candidate species for studying hemispheric gradients and long-term changes. 57We analyzed ten years of NMHC data collected at 44 remote global sampling sites from NOAA's 58 Global Greenhouse Gas Reference Network (GGGRN). We also include data from in-situ moni-59 toring at Summit, Greenland 8 , at Hohenpeissenberg (HPB) in Southern Germany 9 , Jungfraujoch resolved in-situ record from HPB has its minimum in 2009 ( Fig. 1 (e)), in agreement with the JFJ 78 FTIR column observations ( Fig. 1(c)). Focusing on the most recent five years (2009.5 -2014.5) 79 we find variable results in the observed rate of change; however, a consistent picture emerges 80 that shows the largest increases at NH sites (Fig. 3). Of 33 NH sites, 7 exhibit ethane growth 81 rates > 50 pmol mol -1 yr -1 , and 10 sites exhibit growth rates between 25-50 pmol -1 yr -1 (Table S1). one from JFJ ( Fig. 1(c)) 12 , and the other one from Lauder, New Zealand ( Fig. 1(d) emission increases outside of NA that currently cannot be well defined due to the sparsity of 170 observations in those regions (for instance in the middle-East, Africa, and Asia).

Long-term atmospheric CO2 mole fraction and δ13CO2 observations over North America document persistent responses to the El Niño–Southern Oscillation. We estimate these responses corresponded to 0.61 (0.45 to 0.79) PgC year−1 more North American carbon uptake during El Niño than during La Niña between 2007 and 2015, partially offsetting increases of net tropical biosphere-to-atmosphere carbon flux around El Niño. Anomalies in derived North American net ecosystem exchange (NEE) display strong but opposite correlations with surface air temperature between seasons, while their correlation with water availability was more constant throughout the year, such that water availability is the dominant control on annual NEE variability over North America. These results suggest that increased water availability and favorable temperature conditions (warmer spring and cooler summer) caused enhanced carbon uptake over North America near and during El Niño.

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