Methane: signs of progress along the road.

Analyses of air bubbles within ice cores suggest that the concentration of atmospheric methane remained fairly steady from 1500 BC to 1700 AD. However, with the dawn of the Industrial Revolution atmospheric methane concentrations began to increase. Recent findings of Simpson et al. (2006) have shown that the growth in the concentration of tropospheric methane has leveled off based on air sampling conducted throughout the Pacific basin (71 N–47 S) over the last seven years. Methane is second only to carbon dioxide in terms of importance in climatic greenhouse warming scenarios. This plateau is in stark contrast to the increasing atmospheric methane concentrations during the 1980s, where the concentration grew by an average of 15 ppbv yr 1 (Blake and Rowland, 1988). This slow-down in the growth of methane is positive news in terms of human interaction in reducing greenhouse gas emissions. In my view, there are two important thoughts related to these recent findings that I would like to share: (1) the reduction in the sources of methane, and (2) the importance of actual measurements versus modeled data. One portion of the reduced burden of methane in the atmosphere is a direct result of the increasing number of landfill gas recovery and utilization projects. There has been exceptional growth in the number of landfill gas utilization projects worldwide. The first landfill gas utilization project came to life in 1975. There are currently over 1100 active utilization projects globally, with several additional projects in varying stages of construction or planning (Willumsen, 2003). In the US, the number of projects has more than doubled since 1990, increasing from 130 projects to over 395 in 2006 (http://www.epa. gov/landfill/index.htm). In the US alone, an estimated 600 additional sites have economically-feasible options for utilization. In addition to the new projects, there is rarely a modern landfill built without an active landfill gas recovery system. This recovered methane is subsequently utilized or flared. In developed countries, the decision to install a gas recovery system is largely controlled