Meanwhile, there are so many disasters occurring - and so many scientific reports warning of even worse disasters - it's just overwhelming. A comment from John in New Zealand on an earlier post included this link about the difference in tropospheric ozone levels between the northern and southern hemispheres, which states:
"Prolonged exposure to ozone concentrations greater than 40 parts per billion by volume (ppbv) is considered detrimental to human health and plants, including crops. Typical surface ozone levels are 50–80 ppbv in the Northern Hemisphere over some polluted regions and 25–35 ppbv in the Southern Hemisphere."
5.1. Meta-Analyses of Vegetation Effects
Recently published meta-analyses have quantitatively compiled peer reviewed studies from the past 40 yr on the effect of current and future O3 exposures on the physiology and growth of forest and crop species (Feng et al., 2008; Wittig et al., 2007; Wittig et al., 2008). In compiling more than 55 studies, Wittig et al. (2007) reported that current O3 concentrations in the northern hemisphere are decreasing photosynthesis (-11%) and stomatal conductance (-13%) across tree species. They also found that younger trees (<4>3 than older trees. Further, the authors also found that damage to photosynthesis is consistent with the cumulative uptake of O3 into the leaf (Wittig et al., 2007). In another meta-analysis, Wittig et al. (2008) reported that current ambient O3 concentrations (~40ppb) significantly decreased annual total biomass growth (-7%) across 263 studies. However, this effect could be greater (-11 to -17%) in areas that have higher O3 concentrations and as background O3 increases in the future (Wittig et al., 2008). In a meta-analysis of 52 studies of wheat, Feng et al. (2008) reported that current ambient O3 concentrations may be decreasing yield by an average of 17.5%. The authors also found that O3-induced decreases in yield were greater in wheat grown in the field than grown in the in pots. Together these meta-analyses demonstrate the coherence of O3 effects across numerous studies and species using a variety of experimental techniques.
5.2. Field Studies of Forest Ecosystems
Two companion papers (McLaughlin et al., 2007a, 2007b) investigated the effects of ambient O3 on tree growth and hydrology at forest sites in the southern Appalachian Mountains. The authors reported the cumulative effects of ambient levels of O3 decreased seasonal stem growth by 30-50% for most trees species in a high O3 year in comparison to a low O3 year (McLaughlin et al., 2007a). The authors also report that high ambient O3 concentrations can disrupt whole tree water use and in turn reduce late-season stream-flow (McLaughlin et al., 2007b). The finding that O3 exposures disrupt tree water use is consistent with several recent studies that report O3 exposure resulting in loss of stomatal control, incomplete stomatal closure at night and a decoupling of photosynthesis and stomatal conductance (Gregg et al., 2006; Grulke et al., 2007a, 2007b).
5.3. Visible Foliar Injury
Several new studies have been published on the incidence of foliar injury in the field due to ambient O3 concentrations (Campbell et al., 2007; Chappelka et al., 2007; Davis, 2007a, 2007b; Davis and Orendovici, 2006; Kohut, 2007). Kohut (2007) presented a foliar injury assessment for 244 National parks over 5 yr. The author reported that risk of foliar injury was high in 65 parks, moderate in 46 parks, and low in 131 parks. Chappelka et al. (2007) reported that the average incidence of O3-induced foliar injury was 73% on milkweed in the Great Smokey Mountain National Park in the years 1992-1996. Three papers (Davis, 2007a, 2007b; Davis and Orendovici, 2006) reported O3-induced foliar injury in several plants species in National Wildlife Refuges in Maine, Michigan and New Jersey. In a study of the west coast of the U.S, Campbell et al. (2007) reported ozone injury in 25-37% of biosites in California forested ecosystems from 2000-2005.
5.4. Agricultural Crops
The effect of O3 on crop health and productivity is an important area of research, and several studies have been published on this topic since the 2006 AQCD. For example, in a study of peanuts in North Carolina, near ambient and elevated exposures of O3 reduced photosynthesis and yield compared to very low O3 conditions (Burkey et al., 2007; Booker et al., 2007). In another study, Grantz and Vu (2009) reported that sugarcane biomass growth significantly declined under O3 exposure. This result is important because sugarcane is being considered as a bioenergy crop to be grown in the San Joaquin Valley of California, an area with high levels of ambient O3.
"New ecological analyses expand the already large body of evidence indicating that O3 exposure causes injury to plants."
Vollenweider et al. (2003), using data collected from continuous forest inventory (CFI) 23 plots across Massachusetts, compared growth rates among either symptomatic or asymptomatic 24 mature black cherry trees. Of the 120 trees sampled in 1996, 47% exhibited visible foliar injury. Using CFI data, growth rates were compared over a 31-year period. The growth rates for 26 symptomatic trees were reduced by 28% compared with the asymptomatic trees.
"...the D.C. Circuit Court directed that EPA should consider the potential beneficial health effects of O3 pollution in shielding the public from the effects of solar ultraviolet (UV) radiation, as well as the adverse health effects."
"Climate changes will also lead to increases in the emission of CO2 and methane from wetlands, nitrous oxides from soils, volatile organic compounds from forests, and trace gases and soot from fires. All these emissions affect atmospheric chemistry, including the amount of in the lower atmosphere, where it acts as a powerful greenhouse gas as well as a pollutant toxic to people and plants.
Although our understanding of other feedbacks associated with climate-induced ecosystem changes is improving, the impact of these changes is not yet accounted for in climate-change modelling.
An international consortium of scientists, led by Almut Arneth from Lund University, has estimated the importance of these unaccounted "biogeochemical feedbacks" in an article that appears as Advance Online Publication on Nature website.
They estimate a total additional radiative forcing by the end of the 21st century that is large enough to offset a significant proportion of the cooling due to carbon uptake by the biosphere as a result of fertilization of plant growth."