Transcript Presentation - IEA Bioenergy Task 38

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Climate impacts of bioenergy: Beyond GHGs
Ryan M. Bright1, Rasmus Astrup2, Anders H. Strømman1, Clara AntónFernández2 , Maria Kvalevåg3, Francesco Cherubini1
1Industrial
Ecology Program, Norwegian University of Science & Technology (NTNU), Trondheim, Norway
2Norwegian Forest and Landscape Institute, Ås, Norway
3Center for International Climate & Environmental Research – Oslo (CICERO), Norway
Bioenergy Australia Conference, November 25-26, 2013, Hunter Valley, Australia
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Climate – Ecosystem Dynamics
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Terrestrial ecosystems
and climate are closely
coupled systems
Land cover – especially
the type of vegetation –
affects climate due to
variation in albedo, soil
water, surface roughness,
the amount of leaf area
from which heat can be
exchanged, and rooting
depth
In addition to GHGs, a
change in land cover will
thus perturb climate by
influencing the fluxes of
energy, water vapor, and
momentum exchanged
with the atmosphere
Source: G. Bonan, Ecological Climatology (2008)
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Land Surface Biogeophysics
 Albedo largely determines the amount of net radiation (Rn , i.e., available
energy) at the surface getting partitioned into latent heat, sensible heat, or a
ground heat
Rn = (1-α)SW↓ + (LW↓ - LW↑) =
H + λE + G
Source: G. Bonan, Ecological Climatology (2008)
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Surface Biogeophysics
 Changes in albedo (i.e., from vegetation change) lead to an external forcing at
the surface and top-of-atmosphere. This can directly affect local and global
climate.
 The net local climate effect (near surface temps.) will be determined by the
efficiency with which the remaining net radiation is partitioned into sensible,
latent, and ground heat fluxes via convective and conductive heat transfer. This
is governed largely by surface roughness, plant physiology, and hydrology.
Source: G. Bonan, Ecological Climatology (2008)
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Land Surface Biogeophysics and Hydrology
 Apart from climate, plant physiology governs hydrological processes like
transpiration (rooting depth, leaf stomata) and evaporation (canopy
interception/LAI) and in turn the partitioning of turbulent heat fluxes into latent
heat and sensible heat.
Source: G. Bonan, Ecological Climatology (2008)
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Land Surface Biogeophysics: Roughness
 Surface roughness is mostly determined by vegetation height which transfers
momentum to the surface facilitating convective sensible heat and water vapor
(latent heat) exchange from the surface to the atmosphere.
Rn = (1-α)SW↓ + (LW↓ - LW↑) = H + λE + G
Source: G. Bonan, Ecological Climatology (2008)
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Mesoscale circulations
 Changes in vegetation
properties can influence
mesoscale circulation
patterns (and regional
climate)
 Example: Cross-section
of a dry patch of grass
(black bar) surrounded by
wet forests on a summer
day
 Hot dry air above the
grass is forced upward;
cool, moist air above the
forests subsides
Source: G. Bonan, Ecological Climatology (2008)
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Selected Case Studies
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 Analysis of observed biogeophysical contributions to local climate
(near-surface temps) due to LUC/LCC (~2 Mha) on the Brazilian
cerrado
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From natural vegetation  crop/pasture
From crop/pasture  sugarcane
 Biogeophysical effects considered:
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Evapotranspiration
Surface albedo
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MODIS Observations
 Nat. veg.  Crop =
+∆T; Crop 
Sugarcane = -∆T
 Nat. veg.  Crop = ∆ET; Crop 
Sugarcane = + ∆ET
 Nat. veg.  Crop =
+∆alb; Crop 
Sugarcane = +∆alb
Source: Loarie et al., Nature Climate Change (2011)
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Study Insights
 Conversion of natural vegetation to crop/pasture warms the
cerrado by an average of ~1.6 C
 Conversion of crop/pasture to sugarcane cools the region by an
average of ~0.9 C
 Both land cover types are warmer than natural vegetation
 Evapotranspiration dominates biogeophysical (direct) drivers of
local climate in the region
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ETNat. Veg. > ETSugarcane > ETCrop/pasture
 Biofuel policy implications?
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Discourage area expansion into natural vegetation areas (deforestation); promote local
crop substitution (crop/pasture  sugarcane) instead
Biophysical factors are important: they can either counter of enhance climate benefits
of bioenergy
Source: Loarie et al., Nature Climate Change (2011)
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 Climate modeling simulation of replacing annual crops with
perennial crops in the U.S. Midwest for bioenergy (~84 Mha)
 Biogeochemical factors:
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Life-cycle GHGs from crop and transportation biofuel (EtOH) production
Displaced fossil fuel emissions in transport sector
 Biogeophysical factors:
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∆ Surface albedo
∆ Evapotranspiration
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 A: Perennials minus
annuals
 B: Same as A, but
albedo of perennials =
annuals
 C: Same as A, but
rooting depth of
perennials increased to
2m
Source: Georgescu et al., PNAS (2011)
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Study Insights
 Local and regional cooling from enhanced evapotranspiration
 Local, regional, and global cooling from higher surface albedo
 Albedo impacts alone are ~ 6 times greater than annual
biogeochemical effects from offsetting fossil fuel use
 Results demonstrate that a thorough evaluation of costs and
benefits of bioenergy-related LUC/LCC must include potential
impacts on the surface energy and H2O balance to
comprehensively address important concerns for local,
regional, and global climate change
Source: Georgescu et al., PNAS (2011)
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 Analysis of biogeophysical climate drivers in managed boreal forests
of Norway (observation-based)
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Clearcut vs. Mature coniferous stands
Clearcut vs. Deciduous stands
Decidous vs. Coniferous stands
 Analysis of direct global climate impacts of alternative forest
management scenarios: carbon cycle + albedo dynamics (empirical
modeling-based)
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Mircoclimate: Biogeophysical
Contributions
 ∆Temperature between a mature coniferous and: (a) a clear-cut stand
(b) a deciduous stand
 Contributions from ∆Albedo (green) dominate 6-yr. mean ∆Temp.
 Clear-cut and deciduous stands are cooler than coniferous stands
Source: Bright et al., Global Change Biology (2013)
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Global climate: Including albedo
2010 climate
RCP 4.5
∆NEE
RCP 8.5
 In a scenario in which:
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 Impacts outside the managed forest
landscape were excluded
Net
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∆Albedo
Harvest intensities are increased (e.g., for bioenergy)
Harvested conifer stands are allowed to naturally
regenerate with native deciduous species
∆Albedo (blue) offsets ∆NEE (CO2, red) = net
medium- & long-term global climate cooling
RCP 8.5
RCP 4.5
But carbon-cycle – climate impacts from fossil fuel
substitution with bioenergy are likely beneficial
 Including albedo changes across the
forested landscape is necessary to
avoid sub-optimal climate policy in
boreal regions
2010 climate
Source: Bright et al., Global Change Biology (2013)
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 Included albedo change dynamics in the evaluation of several
prominent global forest bioenergy value chains
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From land use (forest management), not LUC/LCC
Changes in forest albedo along one rotation cycle
 Life cycle perspective
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Attributional (no land use baseline/counterfactuals, no system expansion/avoided
emission credits)
Metric: Global Warming Potential (GWP), TH = 20, 100, & 500 years
Bioenergy products: Heat & Transportation Fuels
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Characterized global direct climate
impacts (per MJ wood fuel combusted)
 Harvesting forests in
regions with seasonal
snow cover = high
+∆albedo
 +∆albedo effects =
climate cooling (blue
bars), offsets direct
biogenic CO2 and lifecycle fossil GHGs
 Net cooling for all
TH’s for ”CA”
(Canada) case
Source: Cherubini, Bright, et al., Env. Res. Letters (2012)
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How to measure?
 Coupled climate models (land + atmosphere; land + atmosphere +
ocean)
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Georgescu et al. (2011)
 Direct observation (satellite imagery, i.e., MODIS, MERIS, SPOTVEGETATION, Landsat 7)
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Loarie et al. (2011)
 Hybrid approaches (satellite imagery + simple climate
models/metrics)
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Bright et al. (2011; 2012; 2013); Cherubini et al. (2012)
 It is possible to adapt existing climate metrics such as GWP or GTP
for albedo
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Bright et al. (2012, 2013); Cherubini et al. (2012)
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Summary & Conclusions
 Climate impact assessments of bioenergy are often incomplete
without the inclusion of biogeophysical dimensions
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Particularly impacts at the local and regional scale
 Biogeophysical climate considerations are more relevant to consider:
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When there is LUC/LCC (i.e., de-/afforestation, crop-switching)
In managed forest ecosystems (i.e., time after harvest disturbance)
 Standardized methodologies and metrics do not yet exist
 Climate profile of bioenergy? It’s all about land use
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How we manage our land to procure biomass for bioenergy dictates climate
impacts/benefits, overwhelms life-cycle emission impacts
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Carbon sinks  global climate
Biogeophysics and hydrology  local and global climate
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Thank You.
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G. Bonan (2008), Ecological Climatology – Concepts and Applications, 2nd Edition, Cambridge University
Press, Cambridge, U.K. & New York, USA
M. Georgescu et al. (2011), Direct climate effects of perennial bioenergy crops in the United States,
PNAS, doi:10.1073/pnas.1008779108
S. Loarie et al. (2011), Direct impacts on local climate of sugar-cane expansion in Brazil, Nature Climate
Change, doi:10.1038/nclimate1067
R. Bright et al. (2013), Climate change implications of shifting forest management strategy in a boreal
forest ecosystem of Norway, Global Change Biology, doi: 10.1111/gcb.12451
F. Cherubini et al. (2012), Site-specific global warming potentials of biogenic CO2 for bioenergy:
contributions from carbon fluxes and albedo dynamics, Environmental Research Letters, doi:
10.1088/1748-9326/7/4/045902
R. Bright et al. (2011), Radiative forcing impacts of boreal forest biofuels: A scenario study for
Norway in light of albedo, Environmental Science & Technology, doi: 10.1021/es201746b
R. Bright et al. (2012), Climate impacts of bioenergy: Inclusion of carbon cycle and albedo dynamics
in life cycle impact assessment, Environmental Impact Assessment Review, doi: 10.1016/j.eiar.2012.01.002
More info: [email protected]