CARBON SEQUESTRATION IN FOREST BASED BUILDING PRODUCTS SUMMARY NOTES

Transcription

1 CARBON SEQUESTRATION IN FOREST BASED BUILDING PRODUCTS SUMMARY NOTES Intrductin Reducing Greenhuse Gas (GHG) emissins assciated with the built envirnment is nw a majr issue in effrts t alleviate the impacts f climate change. Prmting the cnstructin f mre energy efficient and climate resilient buildings has becme a key public plicy fcus in many jurisdictins. Heric effrts have been made in recent years t prmte the greater use f wd building prducts due t their green attributes, mst ntably that lng-lived wd prducts can act as a carbn strage medium. That is, because sme f the carbn initially absrbed by a living tree remains in harvested wd prducts during and fllwing their active service lives. Several cncrete related rganizatins in the Pacific Nrthwest banded tgether t address sme questinable messaging frm ther sectrs abut these assertins. United under the banner f the Pacific Nrthwest Building Resilience Calitin were: Nrthwest Cement Cuncil Washingtn Aggregates and Cncrete Assciatin Cncrete BC Oregn Cncrete and Aggregate Prducers Assciatin Prtland Cement Assciatin The Masnry Institute f Washingtn The Nrthwest Cncrete Masnry Assciatin, and The Cncrete Reinfrcing Steel Institute. We cntracted with Vancuver-based GLOBE Advisrs t undertake an evidence-based analysis f carbn sequestratin and related climate impacts f wd prducts used in building cnstructin. We asked GLOBE t translate the findings f peer-reviewed scientific studies int user friendly messages t help plicy makers, building designers, cntractrs, prperty managers and the public t understand the envirnmental and climate related impacts f wd building materials frm the pint f harvest thrugh t end f life decmpsitin r reuse. As expected, there are many differing perspectives n the carbn impacts f wd use in the built envirnment, and predictably many uncertainties n the jurney frm seedling t landfill PNBRC All Rights Reserved

2 2 Findings frm the Analysis The analysis cnfirmed is that the full stry abut carbn sequestratin in ur frests, the impacts f wd harvesting and manufacturing, and the use f wd in the built envirnment, was nt being accunted fr in the mre cmmnly reprted studies and statistics. Nr was it being reprted n in a balanced way in much f the prmtinal literature supprtive f greater use f wd, particularly fr tall structures incrprating mass timber building prducts. In very brad terms, frest management practices, as well as the impacts f climate change are altering the current an future stck f carbn sequestered in ur frests. S t, the harvesting f wd and the cnversin f that wd int either lnglasting r shrt-term prducts has a climate-related impact that is nt always well described in published statistics r studies. Aside frm the fact that a relatively small amunt f the carbn initially sequestered in a living tree ends up in a lng-lasting wd prduct, the carbn emissins ver the life span f a building far utweigh the initial embedded carbn f building materials. Life cycle analysis cmparisns f building materials types are f questinable value given the multiplicity f factrs in play. Over the lifetime f a building, design and lcatin factrs are mre imprtant than the greenness f the building materials used in its cnstructin. The GLOBE analysis revealed there is cnsiderable uncertainty in the field wrk regarding the carbn-related behavir f wd in landfills. There is a huge disparity between lab mdels in terms f predicted rate and extent f decay and assciated emissins. Simply put, nt enugh is knwn abut the effects f landfilling t make cncrete claims, especially in the wet regins f the Pacific Nrthwest. Accunting fr carbn, either sequestered r released int the atmsphere n a cradle-t-grave basis, is an extremely cmplex, and ften misunderstd endeavur. In brad terms, all surces f emissins are nt always included in carbn accunting mdels, r reprted in fficial statistics. Fr example, in all three jurisdictins, British Clumbia, Washingtn and Oregn, bigenic emissins fr frestry and frest prducts, while measured but are nt included in the fficial prvincial and state greenhuse gases emissins ttals, n the premise f carbn neutrality. The carbn neutrality hypthesis asserts these emissins represent nly the return t the atmsphere f the carbn riginally absrbed by trees while living. As such they can be cnsidered net neutral and need nt be cunted in fficial statistics PNBRC All Rights Reserved

3 3 Frm a climate change perspective, when wd is harvested, transprted, cnverted t building prducts, r burned, it generates carbn emissins with immediate impacts. The simple fact is that carbn emissins are carbn emissins. Separating ut green emissins frm black emissins is an artificial distinctin at best. Full carbn accunting fr wd prducts shuld include all emissins, bth industrial and bigenic, frm cradle-t-grave, alngside net carbn sequestered. That is why it is imprtant t include all emissins in wd prduct carbn accunting frm pint f rigin and manufacture, t use in a building, and eventually t the pint f decmmissining and dispsal. One f the verriding facts that emerged frm the GLOBE analysis was the enrmus cmplexity f the many issues pertaining t carbn sequestratin in wd based building prducts, and the wide diversity f expert pinin n these issues. Key Messages The key messages emerging frm the analysis are as fllws: Carbn in the Frests Pacific Nrthwest frests are the sequestratin champins f Nrth America, accunting fr ten f the natin s tp carbn-string frests. Acreper-acre, the regin s standing trees and sil rganic carbn are amng the mst prductive carbn sinks in the wrld. Old-grwth frests in the Pacific Nrthwest stre mre carbn per unit area than any ther bime n ur planet. Due t their far greater carbn strage, lgging, and cnversin f these frests t managed stands, incurs a carbn debt that culd take up t tw centuries t repay. Old-grwth frests in the Pacific Nrthwest are unequivcally a nn-renewable resurce. Many carbn sequestratin mdels assume that wd is being harvested frm sustainably managed frests. Hwever, many f the studies reviewed fr this reprt suggest that nt all frests in the United States are being sustainably managed frm a carbn perspective. Frest management plicies and practices are critical elements determining the extent f carbn that is sequestered in ur frests. A sustainably managed frest that encurages healthy and rbust grwth may have a higher rate f CO2 absrptin ver the lng term. Rtatin lengths fr certain fast grwing evergreen species in parts f the Pacific Nrthwest can be very shrt, years in sme cases. This can have deleterius effects n lng-term sequestratin prductivity, sil carbn stck, and many ther envirnmental impact areas, such as bidiversity. While sme argue that yung trees grw faster than mature nes, and therefre sequester atmspheric carbn mre prductively, current research shws that the rate f tree grwth, and f carbn strage, increases cntinuusly with size (and age) fr up t 175 years PNBRC All Rights Reserved

4 4 While the rate f carbn absrptin varies with species, simulatins shw that with a 50-year rtatin in varius tree species cmmn in Pacific Nrthwest ecsystems, less than 40% f the carbn initially harvested frm a mature stand is reabsrbed by grwing trees. Harvesting Carbn Frest ecsystem carbn resides in several pls, including the sil, belw grund bimass, live trees, dead trees, and bimass n the frest flr. Sil rganic carbn is the largest pl, making up nearly 50% f ttal ecsystem carbn in many f the Pacific Nrthwest frests. The disruptin t sil carbn pls is nt always accunted fr in sequestratin mdels, despite unambiguus evidence that this pl can be adversely affected by lgging, especially clear cutting. Carbn sequestratin mdels and studies d nt cnsider the effects f cnversin frm ld t yung grwth frests, and the irreversible lss f carbn capital this entails. Because f sil cnditins specific t the Pacific Nrthwest, harvesting residue and waste (slash) is burned r left t decmpse n the frest flr, the latter practice being necessary t return sil nutrients t the ecsystem. Either way, there are large assciated carbn emissins. Manufacturing Wd Prducts It is estimated that f the carbn initially stred in a living tree, nly fifteen t thirty percent is transferred t lng-lived wd prducts. In many mills nly, half f a lg entering a sawmill ends up lumber r veneer, the remainder being burned fr energy r used fr pulp and paper prductin. The wd prduct mills in the Pacific are mstly pwered by burning waste wd residues r bifuels. Based n current carbn prtcls, these bimass emissins are exempt and nt fficially included in the respective jurisdictins fficial greenhuse gas bks. Carbn in the Built Envirnment As much as 90% f the emissins f a building are incurred ver its Use Phase. The initial embdied energy f a building s materials is a relatively small prtin f its verall ftprint. The fcus n carbn sequestratin in wd prducts is centered n initial embdied energy f wd prducts, in ther wrds, n nly 10% f the issue. Mst sequestratin mdels d nt cnsider peratinal (i.e. lifetime Use Phase) energy emissins. Many factrs effect a building s lifetime emissins beynd chice f materials, including lcatin, design, and cnstructin methds. In fact, the building s lcatin may be the key determining factr in the lifetime carbn ftprint f a building. Life Cycle analysis cmparisns f building materials types are f questinable value given the multiplicity f factrs in play PNBRC All Rights Reserved

5 5 End f Life Carbn In landfills, discarded wd is subject t decay which prduces rughly equal parts f carbn dixide and methane gas. Methane has a GHG ptential times that f CO2. Nt all carbn sequestratin accunting is sensitive t the full range f decmpsitin and emissins scenaris fr wd placed in landfills. Brad cnclusins abut the permanent sequestratin benefits f wd prducts stred in landfills may be unfunded fr the wet cnditins f the Pacific Nrthwest, especially as these landfills are nt building and perating misture-free, dry undergrund strage units. There is cnsiderable uncertainty in the field wrk relating t wd in landfills. There is a huge disparity between theretical mdels in terms f predicted rate and extent f decay and the resultant emissins. Simply put, nt enugh is knwn abut practical landfilling effects t make definitive claims. While landfills d huse sme carbn in waste wd in a semi-permanent state, in a brader cntext, this is a pr land-use and land management strategy. Frm an ptimal use perspective wd shuld be never landfilled. Dispsal f wd in landfills shuld be a last resrt. Recycling and cmpsting are mre viable alternatives. Methane and carbn dixide are emitted frm wd dispsed in landfills. Methane (CH4) is a matter f grave cncern as its glbal warming impact is much higher that f carbn dixide. Cautin must be taken in prjecting mdel-based simulatins int real wrld situatins, particularly regarding the lngevity f carbn sequestratin f wd prducts in landfills. Life Cycle Analysis Nt all life cycle mdelling includes all emissins frm the cradle t the grave. Sme mdels examine nly emissins frm the cradle t the factry gate. Others include nly the factry gate t the grave (landfill). The better mdels include cradle t factry gate and factry gate t landfill. The mre cmmnly used carbn sequestratin material tends t fcus nly n the cradle-t-gate prtin f the prducts life cycle, and the Initial Embdied Energy f wd building prducts. It is inapprpriate t draw definitive cnclusins abut different building materials frm cmparative life cycle analyses f individual buildings. Variables such as raw material surces, harvesting methds, supply chain prcesses, transprtatin distances, cnstructin practices, design chices, lcatin, climate, and perating practices, all cmbine t determine the lifetime carbn ftprint f a building. Cmparing building materials types such as cncrete t wd is misleading, as there are far t many ther cmpnents and variables cntributing t a building s embdied emissins PNBRC All Rights Reserved

6 6 Cunting Carbn Despite the variatins in accunting mdels used t analyze the flw f carbn alng the prcessing chain f wd prducts, in their net carbn equivalent emissin figures they typically d nt accunt fr the lss f ld-grwth carbn strage, nr emissins frm disruptins t sil carbn, the single largest carbn pl in the frest. Full carbn accunting fr wd prducts shuld include all emissins, bth industrial and sme bigenic, frm cradle-t-grave, alng with net carbn sequestered. The simple fact is that live trees sequester carbn. Wd prducts are the result f industrial prcesses that emit carbn. Hwever, nt all emissins are always included in many carbn accunting mdels r are reprted in many studies r industry publicatins. Classifying bigenic emissins as carbn neutral is a crucial pint in current carbn accunting mdels. Allwing these emissins t be mitted frm emissins figures gives wd prducts a decided advantage when cmparing the carbn ftprints f varius ther building prducts. In all three jurisdictins, British Clumbia, Washingtn and Oregn, bigenic emissins frm frestry, while cunted, are nt frm part f the fficial prvincial r state carbn emissins ttals, n the premise f the carbn neutrality hypthesis PNBRC All Rights Reserved