Pg CO2 Research Articles

Land and the food–fuel competition: insights from modeling

Ecological–economic model simulations of the world food system have been used to study the impacts of historic and future liquid transport biofuel expansion on agricultural markets and the environment. Almost half of global cropland increase between 2000 and 2008 (about 8 Mha or 0.5% of global cropland) can be attributed to biofuel expansion alone. The central ‘New Policies Scenario’ of the World Energy Outlook 2011 projects an increase of conventional crop‐based biofuel use from 60 Mtoe (2.5 EJ) in 2010 to annually 160 Mtoe (6.7 EJ) in 2035. Until 2020, the projected biofuel consumption provides no or little cumulative net greenhouse gas (GHG) savings as the time period is hardly sufficient to compensate for carbon losses due to over 10 Mha of additional land use conversion. By 2035, cumulative net GHG savings improve up to 2.8 Pg CO2 equivalent in a scenario with assumed higher agricultural productivity growth in developing countries. This scenario increases the developing region's competitive positions and avoids additional people at risk of hunger due to higher commodity prices caused by biofuel use. Available underutilized grassland and woodland may provide land resources suitable for nonfood energy crop production required for the second‐generation biofuel conversion pathways, while causing only limited impacts on food security and biodiversity. We estimate between 246 and 475 Mha of global grassland and woodland to be agronomically suitable for industrial‐scale lignocellulosic energy crop production, with achievable rain‐fed yields of at least 10 tons of dry matter per hectare, with good accessibility and relatively low ruminant livestock density.This article is categorized under: Bioenergy > Economics and Policy Bioenergy > Climate and Environment

Wintertime CO2 efflux from Arctic soils: Implications for annual carbon budgets

Estimates of annual carbon loss from arctic tundra ecosystems are based nearly entirely on measurements taken during the growing season in part because of methodological limitations but also reflecting the assumption that respiration during winter is near zero. Measurements of CO2 flux during winter, however, indicate significant amounts of carbon loss from tundra ecosystems throughout the 240‐day nongrowing season. In our study during the 1996 and 1997 nongrowing seasons, winter carbon losses ranged from 2.0 g CO2 m−2 season−1 in moist dwarf shrub communities to 97 g CO2 m−2 season−1 in natural snowdrift communities, with an average wintertime CO2 efflux of 45 g CO2 m−2 for all Low Arctic tundra communities (0.14 Pg CO2 yr−1 worldwide). These measurements indicate that current estimates of annual carbon loss from tundra ecosystems are low. Inclusion of wintertime losses of CO2 into annual carbon budgets increases the annual carbon efflux of arctic tundra ecosystems by 17% and changes some ecosystems from net annual sinks to net sources of CO2 to the atmosphere.