Doctor of Philosophy, Lunds Universitet (2013)
Robert Jackson, Postdoctoral Faculty Sponsor
- Weakening temperature control on the interannual variations of spring carbon uptake across northern lands NATURE CLIMATE CHANGE 2017; 7 (5): 359-?
- Impacts of land use on climate and ecosystem productivity over the Amazon and the South American continent ENVIRONMENTAL RESEARCH LETTERS 2017; 12 (5)
Carbon cycle responses of semi-arid ecosystems to positive asymmetry in rainfall.
Global change biology
2017; 23 (2): 793-800
Recent evidence shows that warm semi-arid ecosystems are playing a disproportionate role in the interannual variability and greening trend of the global carbon cycle given their mean lower productivity when compared with other biomes (Ahlström et al. 2015 Science, 348, 895). Using multiple observations (land-atmosphere fluxes, biomass, streamflow and remotely sensed vegetation cover) and two state-of-the-art biospheric models, we show that climate variability and extremes lead to positive or negative responses in the biosphere, depending on vegetation type. We find Australia to be a global hot spot for variability, with semi-arid ecosystems in that country exhibiting increased carbon uptake due to both asymmetry in the interannual distribution of rainfall (extrinsic forcing), and asymmetry in the response of gross primary production (GPP) to rainfall change (intrinsic response). The latter is attributable to the pulse-response behaviour of the drought-adapted biota of these systems, a response that is estimated to be as much as half of that from the CO2 fertilization effect during 1990-2013. Mesic ecosystems, lacking drought-adapted species, did not show an intrinsic asymmetric response. Our findings suggest that a future more variable climate will induce large but contrasting ecosystem responses, differing among biomes globally, independent of changes in mean precipitation alone. The most significant changes are occurring in the extensive arid and semi-arid regions, and we suggest that the reported increased carbon uptake in response to asymmetric responses might be contributing to the observed greening trends there.
View details for DOI 10.1111/gcb.13412
View details for PubMedID 27392297
- Compensatory water effects link yearly global land CO2 sink changes to temperature NATURE 2017; 541 (7638)
- Transient dynamics of terrestrial carbon storage: mathematical foundation and its applications BIOGEOSCIENCES 2017; 14 (1): 145-161
- The large influence of climate model bias on terrestrial carbon cycle simulations ENVIRONMENTAL RESEARCH LETTERS 2017; 12 (1)
- Toward more realistic projections of soil carbon dynamics by Earth system models GLOBAL BIOGEOCHEMICAL CYCLES 2016; 30 (1): 40-56
- Simulated carbon emissions from land-use change are substantially enhanced by accounting for agricultural management ENVIRONMENTAL RESEARCH LETTERS 2015; 10 (12)
- Multicriteria evaluation of discharge simulation in Dynamic Global Vegetation Models JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2015; 120 (15): 7488-7505
Water-use efficiency and transpiration across European forests during the Anthropocene
NATURE CLIMATE CHANGE
2015; 5 (6): 579-?
View details for Web of Science ID 000356814800036
Carbon cycle. The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink.
2015; 348 (6237): 895-899
The growth rate of atmospheric carbon dioxide (CO2) concentrations since industrialization is characterized by large interannual variability, mostly resulting from variability in CO2 uptake by terrestrial ecosystems (typically termed carbon sink). However, the contributions of regional ecosystems to that variability are not well known. Using an ensemble of ecosystem and land-surface models and an empirical observation-based product of global gross primary production, we show that the mean sink, trend, and interannual variability in CO2 uptake by terrestrial ecosystems are dominated by distinct biogeographic regions. Whereas the mean sink is dominated by highly productive lands (mainly tropical forests), the trend and interannual variability of the sink are dominated by semi-arid ecosystems whose carbon balance is strongly associated with circulation-driven variations in both precipitation and temperature.
View details for DOI 10.1126/science.aaa1668
View details for PubMedID 25999504
- The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink SCIENCE 2015; 348 (6237): 895-899
- Importance of vegetation dynamics for future terrestrial carbon cycling ENVIRONMENTAL RESEARCH LETTERS 2015; 10 (5)
- Recent trends and drivers of regional sources and sinks of carbon dioxide BIOGEOSCIENCES 2015; 12 (3): 653-679
- Recent changes in the global and regional carbon cycle: analysis of first-order diagnostics BIOGEOSCIENCES 2015; 12 (3): 835-844
Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity
Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) declined substantially between 1982 and 2011. This decrease in RNDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in RNDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.
View details for DOI 10.1038/ncomms6018
View details for Web of Science ID 000343935000001
View details for PubMedID 25318638
- Carbon cycle uncertainty in the Alaskan Arctic BIOGEOSCIENCES 2014; 11 (15): 4271-4288
- Evaluation of Land Surface Models in Reproducing Satellite-Derived LAI over the High-Latitude Northern Hemisphere. Part I: Uncoupled DGVMs REMOTE SENSING 2013; 5 (10): 4819-4838
African tropical rainforest net carbon dioxide fluxes in the twentieth century
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2013; 368 (1625)
The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO₂ fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (-0.02 kg C m⁻² yr⁻¹ or -0.04 Pg C yr⁻¹, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO₂ flux at the beginning of the century (σ1901 = 0.02 kg C m⁻² yr⁻¹), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m⁻² yr⁻¹). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO₂, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO₂ fluxes with increasing atmospheric CO₂ concentrations and extreme climatic events, as the uncertainties will only amplify in the next century.
View details for DOI 10.1098/rstb.2012.0376
View details for Web of Science ID 000331220500015
View details for PubMedID 23878340
Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends
GLOBAL CHANGE BIOLOGY
2013; 19 (7): 2117-2132
The purpose of this study was to evaluate 10 process-based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux-tower-based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free-Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 ± 15 Pg C yr(-1) ) than JU11 (118 ± 6 Pg C yr(-1) ). In response to rising atmospheric CO2 concentration, modeled NPP increases on average by 16% (5-20%) per 100 ppm, a slightly larger apparent sensitivity of NPP to CO2 than that measured at the FACE experiment locations (13% per 100 ppm). Global NBP differs markedly among individual models, although the mean value of 2.0 ± 0.8 Pg C yr(-1) is remarkably close to the mean value of RLS (2.1 ± 1.2 Pg C yr(-1) ). The interannual variability in modeled NBP is significantly correlated with that of RLS for the period 1980-2009. Both model-to-model and interannual variation in model GPP is larger than that in model NBP due to the strong coupling causing a positive correlation between ecosystem respiration and GPP in the model. The average linear regression slope of global NBP vs. temperature across the 10 models is -3.0 ± 1.5 Pg C yr(-1) °C(-1) , within the uncertainty of what derived from RLS (-3.9 ± 1.1 Pg C yr(-1) °C(-1) ). However, 9 of 10 models overestimate the regression slope of NBP vs. precipitation, compared with the slope of the observed RLS vs. precipitation. With most models lacking processes that control GPP and NBP in addition to CO2 and climate, the agreement between modeled and observation-based GPP and NBP can be fortuitous. Carbon-nitrogen interactions (only separable in one model) significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models.
View details for DOI 10.1111/gcb.12187
View details for Web of Science ID 000319963500012
View details for PubMedID 23504870
- The global carbon budget 1959-2011 EARTH SYSTEM SCIENCE DATA 2013; 5 (1): 165-185
- GCM characteristics explain the majority of uncertainty in projected 21st century terrestrial ecosystem carbon balance BIOGEOSCIENCES 2013; 10 (3): 1517-1528
- Robustness and uncertainty in terrestrial ecosystem carbon response to CMIP5 climate change projections ENVIRONMENTAL RESEARCH LETTERS 2012; 7 (4)
- Too early to infer a global NPP decline since 2000 GEOPHYSICAL RESEARCH LETTERS 2012; 39
- The carbon budget of terrestrial ecosystems in East Asia over the last two decades BIOGEOSCIENCES 2012; 9 (9): 3571-3586
- Improved accessibility modeling and its relation to poverty - A case study in Southern Sri Lanka HABITAT INTERNATIONAL 2011; 35 (2): 316-326