In their new paper, Bellanger and coauthors show substantial economic impacts to the EU from neurocognitive impairment associated with methylmercury (MeHg) exposures. The main source of MeHg exposure is seafood consumption, including many marine species harvested from the global oceans. Fish, birds and other wildlife are also susceptible to the impacts of MeHg and already exceed toxicological thresholds in vulnerable regions like the Arctic. Most future emissions scenarios project a growth or stabilization of anthropogenic mercury releases relative to present-day levels. At these emissions levels, inputs of mercury to ecosystems are expected to increase substantially in the future, in part due to growth in the legacy reservoirs of mercury in oceanic and terrestrial ecosystems. Seawater mercury concentration trajectories in areas such as the North Pacific Ocean that supply large quantities of marine fish to the global seafood market are projected to increase by more than 50% by 2050. Fish mercury levels and subsequent human and biological exposures are likely to also increase because production of MeHg in ocean ecosystems is driven by the supply of available inorganic mercury, among other factors. Analyses that only consider changes in primary anthropogenic emissions are likely to underestimate the severity of future deposition and concentration increases associated with growth in mercury reservoirs in the land and ocean. We therefore recommend that future policy analyses consider the fully coupled interactions among short and long-lived reservoirs of mercury in the atmosphere, ocean, and terrestrial ecosystems. Aggressive anthropogenic emission reductions are needed to reduce MeHg exposures and associated health impacts on humans and wildlife and protect the integrity of one of the last wild-food sources globally. In the near-term, public health advice on safe fish consumption choices such as smaller species, younger fish, and harvests from relatively unpolluted ecosystems is needed to minimize exposure risks.<br/><br/>© 2013 the authors

HCFC-22 (CHClF2) is a major greenhouse gas as well as an ozone depleting substance. A low frequency record of HCFC-22 in air since the late 1970s is available through measurements of the Northern Hemisphere Air Samples and the Southern Hemisphere Cape Grim Air Archives. More recently, measurements have been collected using the high-precision high-frequency instruments at the Advanced Global Atmospheric Gases Experiment (AGAGE) stations since the 1990s. NOAA Carbon Cycle Greenhouse Gases Group has also taken measurements from towers since 2006 in addition to the Halocarbon Flask Network measurements since the early 1990s. Using the United Nations Environment Programme data on consumption, as well as an existing bottom-up emissions estimate, we first create gridded a priori HCFC-22 emissions over the 15 years since 1995. We then use the three-dimensional chemical transport model (MOZART v4) and a Bayesian inverse method to estimate global, as well as regional, annual emissions. Our inversion indicates that the global HCFC-22 emissions significantly increased from 1999 to 2001and 2003 to 2006. We further find surge in HCFC-22 emissions in 2009 from Africa and the Middle East. On the other hand, emissions from the Article 5 Asia - the largest emitting region including China and India - show a large decrease in 2008 after the continuous increase from 2005 to 2007, most likely as a result of the Montreal Protocol.

Global emission estimates based on new atmospheric observations are presented for the acylic high molecular weight perfluorocarbons (PFCs): decafluorobutane (C4F10), dodecafluoropentane (C5F12), tetradecafluorohexane (C6F14), hexadecafluoroheptane (C7F16) and octadecafluorooctane (C8F18). Emissions are estimated using a 3-dimensional chemical transport model and an inverse method that includes a growth constraint on emissions. The observations used in the inversion are based on newly measured archived air samples that cover a 39-yr period, from 1973 to 2011, and include 36 Northern Hemispheric and 46 Southern Hemispheric samples. The derived emission estimates show that global emission rates were largest in the 1980s and 1990s for C4F10 and C5F12, and in the 1990s for C6F14, C7F16 and C8F18. After a subsequent decline, emissions have remained relatively stable, within 20 %, for the last 5 yr. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C4F10, C5F12, C6F14 and C7F16, and inventories of C4F10, C5F12 and C6F14 are reported to the United Nations’ Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol. The atmospheric measurement-based emission estimates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude larger for C5F12 (with 2008 EDGARv4.2 estimates for C5F12 at 9.6 kg yr−1, as compared to 67±53 t yr−1 as derived in this study). The derived emission estimates for C6F14 largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the C7F16 emission estimates are comparable to those of EDGARv4.2 at their peak in the 1990s, albeit significant underestimation for the other time periods. There are no bottom-up emission estimates for C8F18, thus the emission rates reported here are the first for C8F18. The reported inventories for C4F10, C5F12 and C6F14 to UNFCCC are five to ten times lower than those estimated in this study.

In addition, we present measured infrared absorption spectra for C7F16 and C8F18, and estimate their radiative efficiencies and global warming potentials (GWPs).We find that C8F18’s radiative efficiency is similar to trifluoromethyl sulfur pentafluoride’s (SF5F3) at 0.57Wm−2 ppb−1, which is the highest radiative efficiency of any measured atmospheric species. Using the 100-yr time horizon GWPs, the total radiative impact of the high molecular weight perfluorocarbons emissions are also estimated; we find the high molecular weight PFCs peak contribution was in 1997 at 24 000 Gg of carbon dioxide (CO2) equivalents and has decreased by a factor of three to 7300 Gg of CO2 equivalents in 2010. This 2010 cumulative emission rate for the high molecular weight PFCs is comparable to: 0.02% of the total CO2 emissions, 0.81% of the total hydrofluorocarbon emissions, or 1.07% of the total chlorofluorocarbon emissions projected for 2010 (Velders et al., 2009). In terms of the total PFC emission budget, including the lower molecular weight PFCs, the high molecular weight PFCs peak contribution was also in 1997 at 15.4% and was 6% of the total PFC emissions in CO2 equivalents in 2009.

© 2012 the authors

Nitrous oxide is an important greenhouse gas and is a major ozone"’depleting substance. To understand and quantify soil nitrous oxide emissions, we expanded the Community Land Model with coupled Carbon and Nitrogen cycles version 3.5 by inserting a module to estimate monthly varying nitrous oxide emissions between 1975 and 2008. We evaluate our soil N2O emission estimates against existing emissions inventories, other process"’based model estimates, and observations from sites in the Amazon, North America, Central America, Asia, Oceania, Africa, and in Europe. The model reproduces precipitation, soil temperature, and observations of N2O emissions well at some but not at all sites and especially not during winter in the higher latitudes. Applying this model to estimate the past 24 years of global soil N2O emissions, we find that there is a significant decrease (increase) in soil N2O emissions associated with El Niño (La Niña) events.

© 2013 American Geophysical Union