adjust/update C sink statistics

fixes incorrect Pugh statistic (#92), although I'm still not sure we want to cite the 300 Tg C/yr statistic at all.

update from Pan to Harris citation

cites in-review 2021 global C budget

doc/manuscript/Dow_manuscript_Nature.Rmd

@@ -152,8 +152,8 @@ n_chronologies_HF <- 4
 
 <!--BODY-->
 
-In recent decades, Earth's forests have sequestered ~20% of anthropogenic CO~2~ emissions, thereby slowing the pace of atmospheric CO~2~ accumulation and climate change[@pan_large_2011; @friedlingstein_global_2020].
-A large portion of this CO~2~ sink occurs in temperate deciduous forests, which sequester >300 Tg C yr^-1^ (>30% of the total forest C sink)[@pugh_role_2019]. <!-- The temperate deciduous sink is >300 Tg C yr-1, but Pugh et al. 2019 estimate that ~200 Tg C yr-1 is attributable to demography (forest regrowth), while >100 Tg C yr-1 is controlled by environmental drivers. The latter portion seems more likely to be sensitive to spring temperatures, and I originally cited this number, but upon further thought it's probably complex enough that that's a false distinction. --> 
+In recent decades, Earth's forests have sequestered ~20% of anthropogenic CO~2~ emissions, thereby slowing the pace of atmospheric CO~2~ accumulation and climate change[@friedlingstein_global_2021; @harris_global_2021].
+A substantive portion of this CO~2~ sink occurs in temperate deciduous forests, which sequester >300 Tg C yr^-1^ [@pugh_role_2019]. <!-- See issue # 92: https://github.com/EcoClimLab/growth_phenology/issues/92. ALSO: The temperate deciduous sink is >300 Tg C yr-1, but Pugh et al. 2019 estimate that ~200 Tg C yr-1 is attributable to demography (forest regrowth), while >100 Tg C yr-1 is controlled by environmental drivers. The latter portion seems more likely to be sensitive to spring temperatures, and I originally cited this number, but upon further thought it's probably complex enough that that's a false distinction. --> 
 The future behavior of this CO~2~ sink will play an important yet uncertain role in influencing atmospheric CO~2~ and climate change[@arora_carbon_2020; @friedlingstein_global_2020]. 
 
 In temperate deciduous forests, spring warming generally lengthens the period over which trees have photosynthetically active leaves[@jeong_phenology_2011;@ibanez_forecasting_2010;@menzel_european_2006;@menzel_growing_1999] and that over which the ecosystem is a net CO~2~ sink[@keenan_net_2014].

doc/manuscript/references.bib

@@ -742,6 +742,21 @@ @article{friedlingstein_global_2020
   file = {/Users/kteixeira/Zotero/storage/QW3NKJUJ/Friedlingstein et al. - 2020 - Global Carbon Budget 2020.pdf;/Users/kteixeira/Zotero/storage/TAD5NLLF/2020.html}
 }
 
+@article{friedlingstein_global_2021,
+  title = {Global {{Carbon Budget}} 2021},
+  author = {Friedlingstein, Pierre and Jones, Matthew W. and O'Sullivan, Michael and Andrew, Robbie M. and Bakker, Dorothee C. E. and Hauck, Judith and Le Qu{\'e}r{\'e}, Corinne and Peters, Glen P. and Peters, Wouter and Pongratz, Julia and Sitch, Stephen and Canadell, Josep G. and Ciais, Philippe and Jackson, Rob B. and Alin, Simone R. and Anthoni, Peter and Bates, Nicholas R. and Becker, Meike and Bellouin, Nicolas and Bopp, Laurent and Chau, Thi T. T. and Chevallier, Fr{\'e}d{\'e}ric and Chini, Louise P. and Cronin, Margot and Currie, Kim I. and Decharme, Bertrand and Djeutchouang, Laique and Dou, Xinyu and Evans, Wiley and Feely, Richard A. and Feng, Liang and Gasser, Thomas and Gilfillan, Dennis and Gkritzalis, Thanos and Grassi, Giacomo and Gregor, Luke and Gruber, Nicolas and G{\"u}rses, {\"O}zg{\"u}r and Harris, Ian and Houghton, Richard A. and Hurtt, George C. and Iida, Yosuke and Ilyina, Tatiana and Luijkx, Ingrid T. and Jain, Atul K. and Jones, Steve D. and Kato, Etsushi and Kennedy, Daniel and Klein Goldewijk, Kees and Knauer, J{\"u}rgen and Korsbakken, Jan Ivar and K{\"o}rtzinger, Arne and Landsch{\"u}tzer, Peter and Lauvset, Siv K. and Lef{\`e}vre, Nathalie and Lienert, Sebastian and Liu, Junjie and Marland, Gregg and McGuire, Patrick C. and Melton, Joe R. and Munro, David R. and Nabel, Julia E. M. S. and Nakaoka, Shin-Ichiro and Niwa, Yosuke and Ono, Tsuneo and Pierrot, Denis and Poulter, Benjamin and Rehder, Gregor and Resplandy, Laure and Robertson, Eddy and R{\"o}denbeck, Christian and Rosan, Thais M. and Schwinger, J{\"o}rg and Schwingshackl, Clemens and S{\'e}f{\'e}rian, Roland and Sutton, Adrienne J. and Sweeney, Colm and Tanhua, Toste and Tans, Pieter P. and Tian, Hanqin and Tilbrook, Bronte and Tubiello, Francesco and {van der Werf}, Guido and Vuichard, Nicolas and Wada, Chisato and Wanninkhof, Rik and Watson, Andrew and Willis, David and Wiltshire, Andrew J. and Yuan, Wenping and Yue, Chao and Yue, Xu and Zaehle, S{\"o}nke and Zeng, Jiye},
+  year = {2021},
+  month = nov,
+  journal = {Earth System Science Data Discussions},
+  pages = {1--191},
+  publisher = {{Copernicus GmbH}},
+  issn = {1866-3508},
+  doi = {10.5194/essd-2021-386},
+  abstract = {{$<$}p{$><$}strong class="journal-contentHeaderColor"{$>$}Abstract.{$<$}/strong{$>$} Accurate assessment of anthropogenic carbon dioxide (CO\textsubscript{2}) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO\textsubscript{2} emissions (E\textsubscript{FOS}) are based on energy statistics and cement production data, while emissions from land-use change (E\textsubscript{LUC}), mainly deforestation, are based on land-use and land-use change data and bookkeeping models. Atmospheric CO\textsubscript{2} concentration is measured directly, and its growth rate (G\textsubscript{ATM}) is computed from the annual changes in concentration. The ocean CO\textsubscript{2} sink (S\textsubscript{OCEAN}) is estimated with global ocean biogeochemistry models and observation-based data-products. The terrestrial CO\textsubscript{2} sink (S\textsubscript{LAND}) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (B\textsubscript{IM}), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as \&plusmn;1\&sigma;. For the first time, an approach is shown to reconcile the difference in our E\textsubscript{LUC} estimate with the one from national greenhouse gases inventories, supporting the assessment of collective countries\&rsquo; climate progress.{$<$}/p{$>$} {$<$}p{$>$}For the year 2020, E\textsubscript{FOS} declined by 5.4\&thinsp;\% relative to 2019, with fossil emissions at 9.5\&thinsp;\&plusmn;\&thinsp;0.5\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} (9.3\&thinsp;\&plusmn;\&thinsp;0.5\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} when the cement carbonation sink is included), E\textsubscript{LUC} was 0.9\&thinsp;\&plusmn;\&thinsp;0.7\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1}, for a total anthropogenic CO\textsubscript{2} emission of 10.2\&thinsp;\&plusmn;\&thinsp;0.8\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} (37.4\&thinsp;\&plusmn;\&thinsp;2.9\&thinsp;GtCO\textsubscript{2}). Also, for 2020, G\textsubscript{ATM} was 5.0\&thinsp;\&plusmn;\&thinsp;0.2\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} (2.4\&thinsp;\&plusmn;\&thinsp;0.1\&thinsp;ppm\&thinsp;yr\textsuperscript{\&minus;1}), S\textsubscript{OCEAN} was 3.0\&thinsp;\&plusmn;\&thinsp;0.4\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} and S\textsubscript{LAND} was 2.9\&thinsp;\&plusmn;\&thinsp;1\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1}, with a B\textsubscript{IM} of \&minus;0.8\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1}. The global atmospheric CO\textsubscript{2} concentration averaged over 2020 reached 412.45\&thinsp;\&plusmn;\&thinsp;0.1\&thinsp;ppm. Preliminary data for 2021, suggest a rebound in E\textsubscript{FOS} relative to 2020 of +4.9\&thinsp;\% (4.1\&thinsp;\% to 5.7\&thinsp;\%) globally.{$<$}/p{$>$} {$<$}p{$>$}Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959\&ndash;2020, but discrepancies of up to 1\&thinsp;GtC\&thinsp;yr\textsuperscript{\&minus;1} persist for the representation of annual to semi-decadal variability in CO\textsubscript{2} fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO\textsubscript{2} flux in the northern extra- tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set (Friedlingstein et al., 2020; Friedlingstein et al., 2019; Le Qu\&eacute;r\&eacute; et al., 2018b, 2018a, 2016, 2015b, 2015a, 2014, 2013). The data presented in this work are available at {$<$}a href="https://doi.org/10.18160/gcp-2021" target="\_blank" rel="noopener"{$>$}https://doi.org/10.18160/gcp-2021{$<$}/a{$>$} (Friedlingstein et al., 2021).{$<$}/p{$>$}},
+  langid = {english},
+  file = {/Users/kteixeira/Zotero/storage/EDYDYXQM/Friedlingstein et al. - 2021 - Global Carbon Budget 2021.pdf;/Users/kteixeira/Zotero/storage/D9NWYCTY/essd-2021-386.html}
+}
+
 @article{fu_maximum_2019,
   title = {Maximum Carbon Uptake Rate Dominates the Interannual Variability of Global Net Ecosystem Exchange},
   author = {Fu, Zheng and Stoy, Paul C. and Poulter, Benjamin and Gerken, Tobias and Zhang, Zhen and Wakbulcho, Guta and Niu, Shuli},
@@ -895,6 +910,22 @@ @article{hacket-pain_drought_2017
   file = {/Users/kteixeira/Zotero/storage/B6DXN6LF/Hacket-Pain et al. - 2017 - Drought and reproductive effort interact to contro.pdf;/Users/kteixeira/Zotero/storage/LXIDFNPX/3073981.html}
 }
 
+@article{harris_global_2021,
+  title = {Global Maps of Twenty-First Century Forest Carbon Fluxes},
+  author = {Harris, Nancy L. and Gibbs, David A. and Baccini, Alessandro and Birdsey, Richard A. and de Bruin, Sytze and Farina, Mary and Fatoyinbo, Lola and Hansen, Matthew C. and Herold, Martin and Houghton, Richard A. and Potapov, Peter V. and Suarez, Daniela Requena and {Roman-Cuesta}, Rosa M. and Saatchi, Sassan S. and Slay, Christy M. and Turubanova, Svetlana A. and Tyukavina, Alexandra},
+  year = {2021},
+  month = jan,
+  journal = {Nature Climate Change},
+  pages = {1--7},
+  publisher = {{Nature Publishing Group}},
+  issn = {1758-6798},
+  doi = {10.1038/s41558-020-00976-6},
+  abstract = {Managing forests for climate change mitigation requires action by diverse stakeholders undertaking different activities with overlapping objectives and spatial impacts. To date, several forest carbon monitoring systems have been developed for different regions using various data, methods and assumptions, making it difficult to evaluate mitigation performance consistently across scales. Here, we integrate ground and Earth observation data to map annual forest-related greenhouse gas emissions and removals globally at a spatial resolution of 30\,m over the years 2001\textendash 2019. We estimate that global forests were a net carbon sink of -7.6\,{$\pm$}\,49\,GtCO2e\,yr-1, reflecting a balance between gross carbon removals (-15.6\,{$\pm$}\,49\,GtCO2e\,yr-1) and gross emissions from deforestation and other disturbances (8.1\,{$\pm$}\,2.5\,GtCO2e\,yr-1). The geospatial monitoring framework introduced here supports climate policy development by promoting alignment and transparency in setting priorities and tracking collective progress towards forest-specific climate mitigation goals with both local detail and global consistency. Forest management for climate mitigation plans requires accurate data on carbon fluxes to monitor policy impacts. Between 2001 and 2019, forests were a net sink of carbon globally, although emissions from disturbances highlight the need to reduce deforestation in tropical countries.},
+  copyright = {2021 The Author(s), under exclusive licence to Springer Nature Limited},
+  langid = {english},
+  file = {/Users/kteixeira/Zotero/storage/UQWISEKW/Harris et al. - 2021 - Global maps of twenty-first century forest carbon .pdf}
+}
+
 @article{harris_version_2020,
   title = {Version 4 of the {{CRU TS}} Monthly High-Resolution Gridded Multivariate Climate Dataset},
   author = {Harris, Ian and Osborn, Timothy J. and Jones, Phil and Lister, David},