Carbon dioxide and energy flux measurements in four northern-boreal ecosystems at Pallas

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Carbon dioxide and energy fluxes over a northern boreal lake

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Metsäbiomassan energiakäytön ilmastovaikutukset Suomessa

Metsäbiomassan energiakäyttöä suunnitellaan lisättävän merkittävästi Suomessa. Tämän tutkimushankkeen tavoitteena oli arvioida hakkutähteiden, kantojen ja harvennusten tähdepuun energiakäytön aiheuttamat kasvihuonekaasupäästöt ilmakehään ja näiden päästöjen aiheuttama ilmastoa lämmittävä vaikutus. Hankkeessa huomioitiin metsäbiomassan korjuu- ja käyttöketjusta sekä metsän hiilivarastojen muutoksista johtuvat kasvihuonekaasupäästöt. Lisäksi hankkeessa arvioitiin metsäbiomassan energiakäytön aiheuttamat pienhiukkasvaikutukset. Metsäbiomassan energiakäytön aiheuttamat kasvihuonekaasupäästöt ja ilmastovaikutukset arvioitiin sekä metsikkötasolla että koko Suomen tasolla. Metsikkötason tarkastelujen avulla haarukoitiin päästöjen ja ilmastovaikutusten vaihteluväli Suomessa. Koko Suomen tason laskelmien avulla arvioitiin tähän asti toteutuneen metsäbiomassan energiakäytön sekä suunnitellun käytön lisäyksen vaikutukset Suomen metsien hiilitaseeseen ja Suomen kasvihuonekaasupäästöihin. Pienhiukkasvaikutukset arvioitiin metsäbioenergian korjuu- ja käyttöketjun tasolla Etelä- ja Pohjois-Suomessa. Metsäbiomassan energiakäytön aiheuttamia kasvihuonekaasupäästöjä ja ilmastovaikutuksia verrattiin fossiilisten polttoaineiden käytön päästöihin ja vaikutuksiin sadan vuoden aikana. Suomen tason laskelmissa tarkasteltiin jo toteutuneen ja suunnitellun metsäbiomassan energiakäytön lisäämisen vaikutuksia Suomen kasvihuonekaasutaseeseen ja metsien hiilinieluun vuosina 2000-2025. Tuloksista tehtiin johtopäätöksiä, jotka koskivat 1) metsäbiomassan energiakäytön tehokkuutta energiantuotannon päästöjen vähentämisessä ja ilmastonmuutoksen hillinnässä, 2) metsäbiomassan energiakäytön ilmastovaikutusten vähentämismahdollisuuksia sekä 3) metsäbiomassan energiakäytön päästöjen ja ilmastovaikutusten huomioimista ilmastopolitiikan taustalla olevissa laskentajärjestelmissä ja -säännöissä

Spatiotemporal lagging of predictors improves machine learning estimates of atmosphere–forest CO2 exchange

Accurate estimates of net ecosystem CO2 exchange (NEE) would improve the understanding of natural carbon sources and sinks and their role in the regulation of global atmospheric carbon. In this work, we use and compare the random forest (RF) and the gradient boosting (GB) machine learning (ML) methods for predicting year-round 6 h NEE over 1996-2018 in a pine-dominated boreal forest in southern Finland and analyze the predictability of NEE. Additionally, aggregation to weekly NEE values was applied to get information about longer term behavior of the method. The meteorological ERA5 reanalysis variables were used as predictors. Spatial and temporal neighborhood (predictor lagging) was used to provide the models more data to learn from, which was found to improve considerably the accuracy of both ML approaches compared to using only the nearest grid cell and time step. Both ML methods can explain temporal variability of NEE in the observational site of this study with meteorological predictors, but the GB method was more accurate. Only minor signs of overfitting could be detected for the GB algorithm when redundant variables were included. The accuracy of the approaches, measured mainly using cross-validated R-2 score between the model result and the observed NEE, was high, reaching a best estimate value of 0.92 for GB and 0.88 for RF. In addition to the standard RF approach, we recommend using GB for modeling the CO2 fluxes of the ecosystems due to its potential for better performance.Peer reviewe

Identifying main uncertainties in estimating past and present radiative forcing of peatlands

ABSTRACT Reconstructions of past climate impact, i.e., radiative forcing (RF), of peatland carbon (C) dynamics show that immediately after peatland initiation the climate warming effect of CH4 emissions exceeds the cooling effect of CO2 uptake, but thereafter the net effect of most peatlands will move towards cooling, when RF switches from positive to negative. Reconstructing peatland C dynamics necessarily involves uncertainties related to basic assumptions on past CO2 flux, CH4 emission, and peatland expansion. We investigated the effect of these uncertainties on the RF of three peatlands, using either apparent C accumulation (aCAR), net C balance (NCB), or NCB plus C loss during fires as basis for CO2 uptake estimate; applying a plausible range for CH4 emission; and assuming linearly interpolated expansion between basal dates, or comparatively early or late expansion. When we factored that some C would only be stored temporarily (NCB and NCB+fire), the estimated past cooling effect of CO2 uptake increased but the present-day RF was affected little. Altering the assumptions behind the reconstructed CO2 flux or expansion patterns, caused the RF to peak earlier and advanced the switch from positive to negative RF by several thousand years. Compared to NCB, including fires had only small additional effect on RF lasting less than 1000 yr. The largest uncertainty in reconstructing peatland RF was associated with CH4 emissions. As shown by the consistently positive RF modelled for one site, and in some cases for the other two, peatlands with high CH4 emissions and low C accumulation rates may have remained climate warming agents since their initiation. Although uncertainties in present-day RF were mainly due to the assumed CH4 emission rates, the uncertainty in lateral expansion still had a significant effect on the present-day RF, highlighting the importance to consider uncertainties in the past peatland C balance in RF reconstructions.Reconstructions of past climate impact, that is, radiative forcing (RF), of peatland carbon (C) dynamics show that immediately after peatland initiation the climate warming effect of CH4 emissions exceeds the cooling effect of CO2 uptake, but thereafter the net effect of most peatlands will move toward cooling, when RF switches from positive to negative. Reconstructing peatland C dynamics necessarily involves uncertainties related to basic assumptions on past CO2 flux, CH4 emission and peatland expansion. We investigated the effect of these uncertainties on the RF of three peatlands, using either apparent C accumulation rates, net C balance (NCB) or NCB plus C loss during fires as basis for CO2 uptake estimate; applying a plausible range for CH4 emission; and assuming linearly interpolated expansion between basal dates or comparatively early or late expansion. When we factored that some C would only be stored temporarily (NCB and NCB+fire), the estimated past cooling effect of CO2 uptake increased, but the present-day RF was affected little. Altering the assumptions behind the reconstructed CO2 flux or expansion patterns caused the RF to peak earlier and advanced the switch from positive to negative RF by several thousand years. Compared with NCB, including fires had only small additional effect on RF lasting less than 1000 year. The largest uncertainty in reconstructing peatland RF was associated with CH4 emissions. As shown by the consistently positive RF modelled for one site, and in some cases for the other two, peatlands with high CH4 emissions and low C accumulation rates may have remained climate warming agents since their initiation. Although uncertainties in present-day RF were mainly due to the assumed CH4 emission rates, the uncertainty in lateral expansion still had a significant effect on the present-day RF, highlighting the importance to consider uncertainties in the past peatland C balance in RF reconstructions.Peer reviewe

Metsäojitettu suo on suuri hiilinielu kasvihuonekaasumittausten perusteella

Peer reviewe