Critical issues in trace gas biogeochemistry and global change

Abstract

The atmospheric composition of trace gases and aerosols is determined by the emission of compounds from the marine and terrestrial biospheres, anthropogenic sources and their chemistry and deposition processes. Biogenic emissions depend upon physiological processes and climate, and the atmospheric chemistry is governed by climate and feedbacks involving greenhouse gases themselves. Understanding and predicting the biogeochemistry of trace gases in past, present and future climates therefore demands an interdisciplinary approach integrating across physiology, atmospheric chemistry, physics and meteorology. Here, we highlight critical issues raised by recent findings in all of these key areas to provide a framework for better understanding the past and possible future evolution of the atmosphere. Incorporating recent experimental and observational findings, especially the influence of CO 2 on trace gas emissions from marine algae and terrestrial plants, into earth system models remains a major research priority. As we move towards this goal, archives of the concentration and isotopes of N 2 O and CH 4 from polar ice cores extending back over 650 000 years will provide a valuable benchmark for evaluating such models. In the Pre-Quaternary, synthesis of theoretical modelling with geochemical and palaeontological evidence is also uncovering the roles played by trace gases in episodes of abrupt climatic warming and ozone depletion. Finally, observations and palaeorecords across a range of timescales allow assessment of the Earth's climate sensitivity, a metric influencing our ability to decide what constitutes 'dangerous' climate change.

Determination and potential importance of diterpene (kaur-16-ene) emitted from dominant coniferous trees in Japan

“…Studies revealed that there is a significant deviation between the observed modeled (Hallquist et al, 2009;Beerling et al, 2007). These findings suggest the existence of unknown source(s) of reactive VOCs.…”

An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics

“…Similarly, non-CO 2 greenhouse gases, which are usually neglected, may have had a major role. Recent theoretical and experimental studies indicate that, under high p CO 2 , background concentrations of trace gases such as methane and N 2 O should be higher because of greater production under warmer and wetter conditions (that is, more extensive wetlands) and because of lower rates of oxidation in the atmosphere (resulting from lower emissions of volatile organic compounds by plants) 21 . Collectively, such physical and biochemical feedbacks would tend to enhance the sensitivity of climate to changes in CO 2 and might explain the unusual polar warmth of the early Cenozoic.…”

Fossil soils constrain ancient climate sensitivity

“…Thus even for times with little ice, there are important positive feedbacks that are presently not captured adequately in climate models. Processes for warming the high latitudes without a change in CO 2 include more vigorous heat transport (10,11), more widespread stratospheric clouds in the high latitudes (12), and climate feedbacks from polar forests (13).…”