An Analysis of the Optimal Mix of Global Energy Resources and the Potential Need for Geoengineering Using the CEAGOM Model.

Humanity faces tremendous challenges as a result of anthropogenic climate change caused by greenhouse gas emissions. The mix of resources deployed in order to meet the energy needs of a growing global population is key to addressing the climate change issue. The goal of this research is to examine the optimal mix of energy resources that should be deployed to meet a forecast global energy demand while still meeting desired climate targets. The research includes the unique feature of examining the role that geoengineering can play in this optimization. The results show that some form of geoengineering is likely to be needed by the middle of the 21st century as part of the optimal energy strategy in order to meet a specified climate goal of 580 ppm CO2-eq greenhouse gas concentration (or ≈2 °C average global temperature rise). The optimal energy mix would need to rely on energy efficiency, nuclear, geothermal, hydro, and wind energy for over 50% of global energy needs. In addition, the overall cost of the optimal energy mix is sensitive to the assumed amount of achievable energy efficiency, carbon taxes, deployment of electric vehicles, and the assumed discount rate.

Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase.

Observations of atmospheric methane (CH4) since the late 1970s and measurements of CH4 trapped in ice and snow reveal a meteoric rise in concentration during much of the twentieth century. Since 1750, levels of atmospheric CH4 have more than doubled to current globally averaged concentration near 1,800 ppb. During the late 1980s and 1990s, the CH4 growth rate slowed substantially and was near or at zero between 1999 and 2006. There is no scientific consensus on the drivers of this slowdown. Here, we report measurements of the stable isotopic composition of atmospheric CH4 ((13)C/(12)C and D/H) from a rare air archive dating from 1977 to 1998. Together with more modern records of isotopic atmospheric CH4, we performed a time-dependent retrieval of methane fluxes spanning 25 y (1984-2009) using a 3D chemical transport model. This inversion results in a 24 [18, 27] Tg y(-1) CH4 increase in fugitive fossil fuel emissions since 1984 with most of this growth occurring after year 2000. This result is consistent with some bottom-up emissions inventories but not with recent estimates based on atmospheric ethane. In fact, when forced with decreasing emissions from fossil fuel sources our inversion estimates unreasonably high emissions in other sources. Further, the inversion estimates a decrease in biomass-burning emissions that could explain falling ethane abundance. A range of sensitivity tests suggests that these results are robust.

Air quality in Yanbu, Saudi Arabia.

UNLABELLED: Yanbu, on the Red Sea, is an affluent Saudi Arabian industrial city of modest size. Substantial effort has been spent to balance environmental quality, especially air pollution, and industrial development. We have analyzed six years of observations of criteria pollutants O3, SO2, particles (PM2.5 and PM10) and the known ozone precursors-volatile organic compounds (VOCs) and nitrogen oxides (NOx). The results suggest frequent VOC-limited conditions in which ozone concentrations increase with decreasing NOx and with increasing VOCs when NOx is plentiful. For the remaining circumstances ozone has a complex non-linear relationship with the VOCs. The interactions between these factors at Yanbu cause measurable impacts on air pollution including the weekend effect in which ozone concentrations stay the same or even increase despite significantly lower emissions of the precursors on the weekends. Air pollution was lower during the Eids (al-Fitr and al-Adha), Ramadan and the Hajj periods. During Ramadan, there were substantial night time emissions as the cycle everyday living is almost reversed between night and day. The exceedances of air pollution standards were evaluated using criteria from the U.S. Environmental Protection Agency (EPA), World Health Organization (WHO), the Saudi Presidency of Meteorology and Environment (PME) and the Royal Commission Environmental Regulations (RCER). The latter are stricter standards set just for Yanbu and Jubail. For the fine particles (PM2.5), an analysis of the winds showed a major impact from desert dust. This effect had to be taken into account but still left many occasions when standards were exceeded. Fewer exceedances were found for SO2, and fewer still for ozone. The paper presents a comprehensive view of air quality at this isolated desert urban environment. IMPLICATIONS: Frequent VOC-limited conditions are found at Yanbu in Saudi Arabia that increase ozone pollution if NOx is are reduced. In this desert environment, increased nightlife produces the highest levels of VOCs and NOx at night rather than the day. The effects increase during Ramadan. Fine particles peak twice a day-the morning peak is caused by traffic and increases with decreasing wind, potentially representing health concerns, but the larger afternoon peak is caused by the wind, and it increases with increasing wind speeds. These features suggest that exposure to pollutants must be redefined for such an environment.

Evaluation of ozone, nitrogen dioxide, and carbon monoxide at nine sites in Saudi Arabia during 2007.

UNLABELLED: This paper presents a one-year record of in situ air-quality data from nine sites throughout Saudi Arabia. The data set is composed of hourly measurements of ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO) at six of the largest cities in Saudi Arabia (Riyadh, Jeddah, Makkah, Yanbu, Dammam, Hafouf) and two remote locations in the mountainous southwestern region of Alsodah for the year 2007. The authors found that international O3 and CO standards were routinely exceeded throughout the year at many sites, and that exceedances increased during Ramadan (Sep. 12-Oct. 13), the Islamic month of fasting when much of normal daily activity is shifted to nighttime hours. In general NO2 and CO levels were higher in Saudi cities compared to U.S. cities of comparable population, while O3 levels were lower. There was a general trend for O3 and NO2 to be negatively correlated in Saudi cities in contrast to U.S. cities where the correlation is positive, suggesting that ozone chemistry in Saudi Arabia is limited by volatile organic compound emissions. This may be caused by low biogenic emissions from vegetation. Pollutant levels were lower at most Saudi sites during the four day Hajj period (Dec. 18-21) but higher in Makkah which receives millions of visitors during Hajj. The authors also found that ozone levels were elevated during the weekend (Thursday & Friday) relative to weekday levels despite lower NO2, a phenomenon known as the "weekend effect." As little air quality data is available from Saudi Arabia in the English-language literature, this data set fills a knowledge gap and improves understanding of air quality in an important but under-reported region of the world. IMPLICATIONS: Air quality measurements at nine sites in Saudi Arabia provide a detailed look at spatial and temporal patterns of ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO). NO2 and CO levels increased in most cities during the fasting month of Ramadan, whereas O3 levels decreased. This led to an increased frequency of CO exceedances based on international standards. NO2 and CO also increased in Makkah during the Hajj pilgrimage. In general, NO2 and O3 levels were anticorrelated at most sites, suggesting that O3 chemistry is limited by volatile organic compound emissions throughout much of Saudi Arabia.

Annual and weekly patterns of ozone and particulate matter in Jeddah, Saudi Arabia.

Air pollution has been an increasing concern within the Kingdom of Saudi Arabia and other Middle Eastern countries. In this work the authors present an analysis of daily ozone (O3), nitrogen oxide (NO(x)), and particulate matter (< 10 miccrom aerodynamic diameter; PM10) concentrations for two years (2010 and 2011) at sites in and around the coastal city of Jeddah, as well as a remote background site for comparison. Monthly and weekly variations, along with their implications and consequences, were also examined. O3 within Jeddah was remarkably low, and exhibited the so-called weekend effect--elevated O3 levels on the weekends, despite reduced emissions of O3 precursors on those days. Weekend O3 increases averaged between 12% and 14% in the city, suggesting that NO(x)/volatile organic compound (VOC) ratios within cities such as Jeddah may be exceptionally high. Sites upwind or far removed from Jeddah did not display this weekend effect. Based on these results, emission control strategies in and around Jeddah must carefully address NO(x)/VOC ratios so as to reduce O3 at downwind locations without increasing it within urban locations themselves. PM10 concentrations within Jeddah were elevated compared with North American cites of similar climatology though comparable to other large cities within the Middle East. Implications: Daily concentrations of O3, PM10, and NO(x) in and around the city of Jeddah, Saudi Arabia, are analyzed and compared with those of other reference cities. Extremely low O3 levels, along with a significant urban weekend effect (higher weekend O3, despite reduced NO(x) concentrations), is apparent, along with high levels of PM10 within the city. Urban O3 in Jeddah was found to be lower than that of other comparable cities, but the strong weekend effect suggests that care must be taken to reduce downwind O3 levels without increasing them within the city itself. Further research into the emissions and chemistry contributing to the reduced O3 levels within the city is warranted.

Global methane emissions from terrestrial plants.

Recent measurements suggest that the terrestrial plant community may be an important source of methane with global contributions between 62 and 236 Tg CH4 y(-1). If true, terrestrial plants could rival wetlands as being the largest global source of methane forcing us to rethink the methane budget. While further measurements are needed to confirm the methane release rates from this source and their dependencies, in this work we use the preliminary measurements to assess the potential impact of the methane release from this source globally. Using novel techniques we extrapolate the initially reported chamber measurements to the global scale and calculate the global methane emissions from the terrestrial plant community to be in the range 20 to 69 Tg CH4 y(-1). The spread in emissions is largely due to the sensitivity of the global flux to the prescribed temperature dependence of the plant emission rate, which is largely unknown. The spread of calculated emissions is in good agreement with the upper limit imposed on the source during the late pre-industrial period, which we estimate to range from 25 to 54 Tg CH4 y(-1) during the years 0 to 1700 A.D. using the published atmospheric delta13CH4 record. In addition, if we assume that plant emissions have been constant at the mean value of 45 Tg CH4 y(-1), we find that the methane release from wildfires and biomass burning during the pre-industrial span 0-1000 A.D. must be near 12 Tg CH4 y(-1), which would be in better agreement with previous estimates of the pyrogenic source during this time than a methane budget missing the plant source. We conclude that methane release from the terrestrial plant community as presently understood does not require major innovations to the global methane budget.

Atmospheric methane: trends and cycles of sources and sinks.

For more than 20 years the global emissions and the lifetime of methane have probably been constant, so the buildup of methane in the atmosphere has been slowing down for as long. During this time, there have been periodic events occurring every seven to eight years, when global methane concentrations increased by some 10 ppb and later fell back, in some cases due to temporary increases of emissions from the northern tropics that spread to the global scale. These conclusions are derived from the accumulated global observations that now span 23 years and define the role of human activities in the recent cycle of atmospheric methane.