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] There were large interannual variations in burned area in the boreal region (ranging between 3.0 and 23.6 Â 10 6 ha yr À1) for the period of 1992 and 1995-2003 which resulted in corresponding variations in total carbon and carbon monoxide emissions. We estimated a range of carbon emissions based on different assumptions on the depth of burning because of uncertainties associated with the burning of surface-layer organic matter commonly found in boreal forest and peatlands, and average total carbon emissions were 106-209 Tg yr À1 and CO emissions were 33-77 Tg CO yr À1 . Burning of ground-layer organic matter contributed between 46 and 72% of all emissions in a given year. CO residuals calculated from surface mixing ratios in the high Northern Hemisphere (HNH) region were correlated to seasonal boreal fire emissions in 8 out of 10 years. On an interannual basis, variations in area burned explained 49% of the variations in HNH CO, while variations in boreal fire emissions explained 85%, supporting the hypotheses that variations in fuels and fire severity are important in estimating emissions. Average annual HNH CO increased by an average of 7.1 ppb yr À1 between 2000 and 2003 during a period when boreal fire emissions were 26 to 68 Tg CO À1 higher than during the early to mid-1990s, indicating that recent increases in boreal fires are influencing atmospheric CO in the Northern Hemisphere.

International audienceClimate change and air pollution are critical environmental issues both in the here and now and for the coming decades. A recent OECD report found that unless action is taken, air pollution will be the largest environmental cause of premature death worldwide by 2050. Already, air pollution levels in Asia are far above acceptable levels for human health, and even in Europe, the vast majority of the urban population was exposed to air pollution concentrations exceeding the EU daily limit values, and especially the stricter WHO air quality guidelines in the past decade. The most recent synthesis of climate change research as presented in the fifth IPCC Assessment Report (AR5) states that the warming of the climate system is unequivocal, recognizing the dominant cause as human influence, and providing evidence for a 43% higher total (from 1750 to the present) anthropogenic radiative forcing (RF) than was reported in 2005 from the previous assessment report

[1] The global boreal forest region experienced some 17.9 million ha of fire in 1998, which could be the highest level of the decade. Through the analysis of fire statistics from North America and satellite data from Russia, semimonthly estimates of area burned for five different regions in the boreal forest were generated and used to estimate total carbon release and CO 2 , CO, and CH 4 emissions. Different levels of biomass, as well as different biomass categories, were considered for each of the five different regions (including peatlands in the Russian Far East and steppes in Siberia), as were different levels of fraction of biomass (carbon) consumed during fires. Finally, two levels of flaming versus smoldering combustion were considered in the model. Boreal forest fire emissions for 1998 were estimated to be 290-383 Tg of total carbon, 828-1103 Tg of CO 2 , 88-128 Tg of CO, and 2.9-4.7 Tg of CH 4 . The higher estimate represents 8.9% of total global carbon emissions from biomass burning, 13.8% of global fire CO emissions, and 12.4% of global fire CH 4 emissions. Russian fires accounted for 71% of the total emissions, with the remainder (29%) from fires in North America. Assumptions regarding the level of smoldering versus flaming generally resulted in small (<4%) variations into the emissions estimates, although in two cases, these variations were higher (6% and 12%). We estimated that peatland fires in the Russian Far East contributed up to 40 Tg of carbon to the atmosphere in the fall of 1998. The combined seasonal CO emissions from forest and peatland fires in Russia are consistent with anomalously high atmospheric CO measurements collected at Point Barrow, Alaska.

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.

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G lobal climate change is visibly and tangibly manifested through the Arctic cryospheric system: sea ice loss, earlier spring snowmelts, thawing permafrost, retreating glaciers, and coastal erosion. While not as visibly manifest, the role of the atmosphere is also a critical component in determining the trajectory of the Arctic system. The atmosphere not only drives change, but is reciprocally being modified through a complex web of feedbacks, and is the fast-track mechanism for the transport of energy and moisture through the global system that links climate and weather. For decades, it has been recognized that fundamental components of the atmospheric system such as clouds, atmospheric trace gases, aerosols, and atmosphere-surface exchange processes compose some of the major uncertainties that limit the diagnostic or predictive skill of coupled atmosphere-ice-ocean-terrestrial models (IPCC 2013, chapter 9). Arctic nations have responded in recent decades by establishing  A micrometeorological tower in Tiksi, Russia is used to determine the atmospheric-surface energy balance. (Photo credit: Vasily Kustov)

Humans have significantly altered the energy balance of the Earth’s climate system mainly not only by extracting and burning fossil fuels but also by altering the biosphere and using halocarbons. The 3rd US National Climate Assessment pointed to a need for a system of indicators of climate and global change based on long-term data that could be used to support assessments and this led to the development of the National Climate Indicators System (NCIS). Here we identify a representative set of key atmospheric indicators of changes in atmospheric radiative forcing due to greenhouse gases (GHGs), and we evaluate atmospheric composition measurements, including non-CO2 GHGs for use as climate change indicators in support of the US National Climate Assessment. GHG abundances and their changes over time can provide valuable information on the success of climate mitigation policies, as well as insights into possible carbon-climate feedback processes that may ultimately affect the success of those policies. To ensure that reliable information for assessing GHG emission changes can be provided on policy-relevant scales, expanded observational efforts are needed. Furthermore, the ability to detect trends resulting from changing emissions requires a commitment to supporting long-term observations. Long-term measurements of greenhouse gases, aerosols, and clouds and related climate indicators used with a dimming/brightening index could provide a foundation for quantifying forcing and its attribution and reducing error in existing indicators that do not account for complicated cloud processes.