Direct climate effects of perennial bioenergy crops in the United States

Abstract

Biomass-derived energy offers the potential to increase energy security while mitigating anthropogenic climate change, but a successful path toward increased production requires a thorough accounting of costs and benefits. Until recently, the efficacy of biomass-derived energy has focused primarily on biogeochemical consequences. Here we show that the biogeophysical effects that result from hypothetical conversion of annual to perennial bioenergy crops across the central United States impart a significant local to regional cooling with considerable implications for the reservoir of stored soil water. This cooling effect is related mainly to local increases in transpiration, but also to higher albedo. The reduction in radiative forcing from albedo alone is equivalent to a carbon emissions reduction of 78 t C ha −1 , which is six times larger than the annual biogeochemical effects that arise from offsetting fossil fuel use. Thus, in the near-term, the biogeophysical effects are an important aspect of climate impacts of biofuels, even at the global scale. Locally, the simulated cooling is sufficiently large to partially offset projected warming due to increasing greenhouse gases over the next few decades. These results demonstrate that a thorough evaluation of costs and benefits of bioenergyrelated land-use change must include potential impacts on the surface energy and water balance to comprehensively address important concerns for local, regional, and global climate change.regional climate modeling | agriculture | landscape modification | CO2 S ecuring energy independence and lessening the human fingerprint on climate are two principal motivations behind increased production of bioenergy. Recognition of the full array of costs and benefits of increased production, such as effects on energy and food security, anthropogenic climate change mitigation, and maintenance of biodiversity, will assist in realization of principal objectives (1-8). Prior research gauging the effectiveness of bioenergy has estimated potential impacts based on greenhouse gas (GHG) emission changes through direct or indirect land-use change (LUC) and by means of life cycle analysis (LCA). In addition to impacts on GHGs, LUC also modifies the surface energy and water balance (9), with implications for near-surface temperature and precipitation, and serves as an additional first-order climate forcing on global (10, 11) and regional (9, 12) spatial scales.One of the main proposed strategies for bioenergy production is widespread planting and harvesting of perennial grasses, such as switchgrass (Panicum virgatum L.) or miscanthus (Miscanthus X giganteus). One LCA study suggested that net GHG savings relative to fossil fuels of greater than 200 g CO 2 e-C m −2 yr −1 may be expected for biomass (switchgrass) conversion to ethanol (13) (roughly double for hybrid poplar). Potential mitigation, however, is complicated by variability in inventory components and system boundaries (i.e., LCA methodology) that leads to GHG displacement estimates that diffe...

Climate-regulation services of natural and agricultural ecoregions of the Americas

“…Our results also support recent findings that the net climate impact of bioenergy production may be more positive than previously estimated 14,15 if tropical deforestation is avoided. From a biophysical standpoint, croplands (including bioenergy crops) in temperate regions tend to have climate benefits over natural ecosystems (Fig.…”

“…1b)-a result that is consistent with other studies 16,22 . Although this effect does not rival the warming effect of GHGs on global scales, it somewhat reduces the climate costs of this type of land-use change 14,15 . In addition, dedicated perennial grass bioenergy crops tend to have higher CRVs than their traditional row-crop counterparts (Fig.…”

Afforestation in China cools local land surface temperature

“…Surface cooling will result if this extra energy is dissipated as evapotranspiration (ET) (11) or heat convection (7); otherwise, afforestation will result in surface warming. The biophysical effects of afforestation on local climate can be much larger than the small global cooling effect resulting from uptake of CO 2 by growing forests (8,12,13). However, these biophysical effects are also complex and depend on "background" climate (14).…”

Shaping the multifunctional tree: the use of Salicaceae in environmental restoration

“…Indeed, the success and future development of multipurpose tree plantation is largely dependent upon the selection of appropriate candidate genotypes possessing the most desirable and exploitable growth characteristics, physiology, morphology and adaptability to agronomic practices. Yet, a successful path toward increased production of biomass-derived energy requires a thorough accounting of costs and benefits (Georgescu et al 2011). …”