Lecture 9: Global Climate Change and Vegetation Response PDF

ENVS3202 Lecture 9: Global climate change and vegetation response Jin Wu November 13, 2024 School of Biological Sciences, The University of Hong Kong Land carbon sink: photosynthesis + respiration Atmosphere 829.0 GtC...

ENVS3202 Lecture 9: Global climate change and vegetation response Jin Wu November 13, 2024 School of Biological Sciences, The University of Hong Kong Land carbon sink: photosynthesis + respiration Atmosphere 829.0 GtC Photosynthesis Respiration 123.0 GtC yr-1 118.7 GtC yr-1 Autotrophic Heterotrophic GtC yr-1: Gigatons of carbon per year Source: Global Carbon Project (2016) 2 Land sink importantly buffers recent climate change ~30% 3 3 2020 Global Carbon Budget 3 The forest role’s in buffering climate change is not unlimited 4 4 The forest role’s in buffering climate change is not unlimited Pathway 1: Pathway 2: Plants’ role in Plants’ role in buffering climate facilitating climate change change Currently: pathway 1 > pathway 2; How about in the near-future? Kaushik et al. (2020). The future of the carbon cycle in a changing climate, Eos, 101. 5  Outline Carbon fluxes beyond GPP - Background and recap - Concepts, monitoring methods, and patterns Decadal vegetation response to climate change - Is there an overreaching trend in vegetation productivity? - What are the normal interannual variabilities? - Future implications 6  Photosynthesis Photosynthesis: CO2 + H2O + light → CH2O + O2 Photosynthesis occurs in both land plants and marine phytoplankton (roughly half by each) Chloroplast Light reactions transform light energy to a temporary form of chemical energy, while releasing O2 Calvin cycle use the products of the light-harvesting reactions to convert CO2 into sugars Photo - Synthesis - Won Nobel Prize in Chemistry 1961 Light reactions Calvin cycle 7 Complexity of nature About 14 order of magnitude variations across the space Credit: Dennis Baldocchi 8 How is photosynthesis estimated? –leaf scale Portable Photosynthesis System Credit: Li-COR Inc. 9  How is photosynthesis estimated? –canopy scale Net Ecosystem Exchange (NEE) = Photosynthesis - Respiration CO2 CO2 Photosynthesis Respiration NEE (night) = Respiration NEE(day) = Photosynthesis - Respiration Source: https://eesa.lbl.gov/projects/ameriflux-management-project/ 10 FLUXNET: a network of eddy covariance towers n=914 sites (as to Feb of 2017) Source: https://fluxnet.org/data/fluxnet2015-dataset/ 11 How is photosynthesis estimated? –global scale Optical remote sensing Solar-induced chlorophyll fluorescence 12 Global map of photosynthesis Mean annual photosynthesis (gC yr-1 m-2) Beer et al. (2010). Science 13  Ecosystem carbon flow and storage Gross primary production (GPP) = gross rate of carbon uptake by photosynthesis (usually in gC m−2 yr−1 or simply gC yr−1) Net primary production (NPP): NPP = GPP – autotrophic respiration (by plants) Net ecosystem production (NEP): NEP = NPP – heterotrophic respiration (by all other organisms) Net biome production (NBP): NBP = NEP – disturbances (e.g. wildfires, harvesting, land use, insect outbreaks) Credit: IPCC Land Use, Land-Use Change, and Forestry 14  Carbon flow budget and dynamics The carbon flow budget shows strong dependency on plant biome type at the global scale. The carbon budget varies with forest successional status, as a forest matures, productivity generally peaks and then declines, probably due to canopy light saturation, resource competition, aging, and increasing Age since last disturbance respiration from non-photosynthetic parts. Bonan. (2016). Ecological Climatology: Concepts and Applications. Slide credit to Amos Tai 15  Carbon budget for terrestrial ecosystems Global forest carbon budget for 1990−2007 estimated from forest inventory data and changes in forest carbon stocks Biome Carbon flux (PgC yr−1) Boreal forest −0.5 ± 0.1 Temperate forest −0.7 ± 0.1 Tropical intact forest −1.2 ± 0.4 Tropical net land use change +1.3 ± 0.7 Net forest sink −1.1 ± 0.8 Tropical forests are more or less carbon neutral because deforestation roughly offsets the enhanced carbon sinks in mature Amazonian and African tropical forests. Regrowth of temperate forests in North America and Europe represents the largest residual terrestrial sink. Pan et al. (2011). Science 16  Outline Carbon fluxes beyond GPP - Background and recap - Concepts, monitoring methods, and patterns Decadal vegetation response to climate change - Is there an overreaching trend in vegetation productivity? - What are the normal interannual variabilities? - Future implications 17  How will climate change affect plant productivity? Time series decomposition Q1: Is there an overarching NDVI: Normalized Difference Vegetation Index trend in vegetation --A measure of “greenness” of tree canopy productivity? Q2: What are the normal interannual variabilities? Year Zhou et al. (2001). Journal of Geophysical Research 18  How will climate change affect plant productivity? Time series decomposition Q1: Is there an overarching NDVI: Normalized Difference Vegetation Index trend in vegetation --A measure of “greenness” of tree canopy productivity? Q2: What are the normal interannual variabilities? Year Zhou et al. (2001). Journal of Geophysical Research 19  Earth’s greening leaf area index (LAI): a measure of leaf quantity of a forest canopy Greening Trends in satellite-observed LAI (10-2 m2m-2 yr-1) Zhu et al. (2016). Nature Climate Change 20  Earth’s greening LAI: Leaf Area Index Zhu et al. (2016). Nature Climate Change 21  What drives Earth’s greening? OBS = Observed (from satellite) CO2 = CO2 fertilisation CLI = Climate change NDE = Nitrogen deposition LCC = Land cover change 70% of greening explained by CO2 fertilisation Zhu et al. (2016). Nature Climate Change 22  Slowdown of Earth’s greening over recent years NDVI: Normalized Difference Vegetation Index Underlying reason: --A measure of “greenness” of tree canopy Global warming  higher 0.56 atmospheric water vapor deficit Greening Brown down  plants suffer more water stress  decelerate vegetative 0.52 NDVI productivity 0.48 Implications: Terrestrial ecosystem are now close to their tipping points, after 0.44 1984 1988 1992 1996 2000 2004 2008 2012 which vegetative buffering on climate change might no longer Year exist Yuan et al. (2019). Science Advances 23  What are the normal interannual variability? Time series decomposition Q1: Is there an overarching NDVI: Normalized Difference Vegetation Index trend in vegetation --A measure of “greenness” of tree canopy productivity? Q2: What are the normal interannual variabilities? Year Zhou et al. (2001). Journal of Geophysical Research 24 El Niño effects on land carbon sink 25 Sellers et al. (2018). PNAS  El Niño-Southern Oscillation (ENSO) El Niño: the large-scale ocean- atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific. Cycles roughly 3 - 7 years El Niño = warm waters La Niña = cool waters El Niño years usually correspond to more and bigger drought events on the land. Sea Surface Temperature anomalies around the world from 1982 to 2017 Source:https://climate.nasa.gov/climate_resources/185/sea-surface-temperature-anomaly-timeline-1982-2017/ 26 Drought effects on the Amazon (2005 & 2010) current year −historical mean Rainfall anomaly = standard deviation (SD) of all observations Negative: drought events; < -2 SD: extremely big drought Lewis et al. (2011). Science 27 The 2005 drought effects on the Amazon Ground observations; green  carbon uptake; red  carbon loss The drought induced biomass loss: 1.2-1.6 GtC, which is around 10-15% of annual total anthropogenic carbon emissions Phillips et al. (2009). Science 28  Drought-associated fires in the Amazon Droughts 2005 2010 2015 Active fires Good correspondence between El Niño droughts and active fires in Amazon. Aragão et al. (2018). Nature Communications 29  Fires in the Artic Conventional hotspots: Hot & dry environment > 5 times larger than before New hotspots: the Artic Circle ≈ 3.5% annual total anthropogenic carbon emissions Descals et al. (2022). Science 30 Record-breaking fires in Canada ≈ India carbon emissions 6 times larger than before ! Byrne et al. (2024). Nature; Jain et al. (2024). Nature Communications 31 Global declined resilience Positive δ TAC values suggest a reduction in recovery rates and thus a decline in resilience, and vice versa for negative δ TAC values. Tropical, arid and temperate forests are experiencing a significant decline in resilience Forzieri et al. (2022). Nature 32 The forest role’s in buffering climate change is not unlimited Pathway 1: Pathway 2: Plants’ role in Plants’ role in buffering climate facilitating climate change change Slow down over Increase with the recent years global warming When will pathway 1 < pathway 2 ? Kaushik et al. (2020). The future of the carbon cycle in a changing climate, Eos, 101. 33  Summary of Lecture 10 GPP is only one component of land carbon sink There is an overall increasing trend in global vegetation productivity as a result of climate change Interannual variability in global vegetation productivity is complex – Multiple factors drive this variation, but the predominant driver is climate, driven by the El Niño-Southern Oscillation (ENSO) The role of plants in climate change could be complex than we thought 34  In-class group presentation 1. Presenters: Yu Chuying and Zeng Xiang Group 2. Paper: Yuan et al. (2019). Increased atmospheric vapour pressure deficit reduces 13 global vegetation growth. Science Advances, 5, eaax1396. 1. Presenters: Wang Xinye and Xia Binbin Group 2. Paper: Forzieri et al. (2022). Emerging signals of declining forest resilience under 14 climate change. Nature, 608, 534-539.