Interactions between land use change and carbon cycle feedbacks

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 31 (2017): 96–113, doi:10.1002/2016GB005374.Using the Community Earth System Model, we explore the role of human land use and land cover change (LULCC) in modifying the terrestrial carbon budget in simulations forced by Representative Concentration Pathway 8.5, extended to year 2300. Overall, conversion of land (e.g., from forest to croplands via deforestation) results in a model-estimated, cumulative carbon loss of 490 Pg C between 1850 and 2300, larger than the 230 Pg C loss of carbon caused by climate change over this same interval. The LULCC carbon loss is a combination of a direct loss at the time of conversion and an indirect loss from the reduction of potential terrestrial carbon sinks. Approximately 40% of the carbon loss associated with LULCC in the simulations arises from direct human modification of the land surface; the remaining 60% is an indirect consequence of the loss of potential natural carbon sinks. Because of the multicentury carbon cycle legacy of current land use decisions, a globally averaged amplification factor of 2.6 must be applied to 2015 land use carbon losses to adjust for indirect effects. This estimate is 30% higher when considering the carbon cycle evolution after 2100. Most of the terrestrial uptake of anthropogenic carbon in the model occurs from the influence of rising atmospheric CO2 on photosynthesis in trees, and thus, model-projected carbon feedbacks are especially sensitive to deforestation.National Science Foundation Grant Numbers: AGS 1049033, CCF-15220542017-07-2

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Natural Variability in a Changing Ocean: Emergence and Impacts

Anthropogenically-forced changes in the ocean are underway and critical for the ocean’s role as a carbon sink and marine habitat. Detecting such changes will require quantification of not only the magnitude of the change (anthropogenic signal) but also the natural variability inherent to the climate system (noise). This work uses Earth System Models (ESMs) to (1) evaluate timescales over which anthropogenic signals in the contemporary ocean emerge from natural climate variability and (2) interpret observed variability in the Pacific Basin. We apply time-of-emergence (ToE) diagnostics to a Large Ensemble experiment of an ESM, providing both a conceptual framework for interpreting the detectability of anthropogenic impacts on the ocean carbon cycle and observational sampling strategies required to achieve detection. We find ToEs for different components of the ocean carbon cycle range from under a decade to over a century, a consequence of the time-lag between chemical and radiative impacts of rising atmospheric CO2 on the ocean. Processes sensitive to chemical changes emerge rapidly, such as impacts of acidification on the calcium-carbonate pump (10-20 years), and the invasion of anthropogenic CO2 into the ocean (20-30 years). Processes sensitive to the ocean’s physical state, such as the soft-tissue pump, which depends on nutrients supplied through circulation, emerge decades later (20-80+ years). Next, we evaluate the model- and scenario-sensitivity of ToEs through comparing Large Ensembles from four ESMs. We find ToEs are robust across models for variables that are tied directly with the rise in atmospheric CO2 namely rising sea surface temperature and the invasion of anthropogenic CO2 into the ocean (ToE 20-30 years). For the soft-tissue pump, ocean color, and sea surface salinity, ToEs are longer (50+ years), less robust across the ESMs, and more sensitive to the forcing scenario considered. Finally, we investigate potential mechanisms responsible for recent variability in the Pacific Ocean. We conduct wind-substitution simulations with GFDL-ESM2M in which decadal trends in the trade-winds are nudged toward observed values. These simulations provide better agreement between simulated and observed variability in ocean temperature, circulation, sea-level and air-sea CO2 exchange, indicating this variability could be attributed to strengthening trade winds

Changes in precipitation variability across time scales in multiple global climate model large ensembles

Anthropogenic changes in the variability of precipitation stand to impact both natural and human systems in profound ways. Precipitation variability encompasses not only extremes like droughts and floods, but also the spectrum of precipitation which populates the times between these extremes. Understanding the changes in precipitation variability alongside changes in mean and extreme precipitation is essential in unraveling the hydrological cycle's response to warming. We use a suite of state-of-the-art climate models, with each model consisting of a single-model initial-condition large ensemble (SMILE), yielding at least 15 individual realizations of equally likely evolutions of future climate state for each climate model. The SMILE framework allows for increased precision in estimating the evolving distribution of precipitation, allowing for forced changes in precipitation variability to be compared across climate models. We show that the scaling rates of precipitation variability, the relation between the rise in global temperature and changes in precipitation variability, are markedly robust across timescales from interannual to decadal. Over mid- and high latitudes, it is very likely that precipitation is increasing across the entire spectrum from means to extremes, as is precipitation variability across all timescales, and seasonally these changes can be amplified. Model or structural uncertainty is a prevailing uncertainty especially over the Tropics and Subtropics. We uncover that model-based estimates of historical interannual precipitation variability are sensitive to the number of ensemble members used, with 'small' initial-condition ensembles (of less than 30 members) systematically underestimating precipitation variability, highlighting the utility of the SMILE framework for the representation of the full precipitation distribution.ISSN:1748-9326ISSN:1748-931

Quantifying the Role of Seasonality in the Marine Carbon Cycle Feedback: An ESM2M Case Study

Observations and climate models indicate that changes in the seasonal amplitude of sea surface carbon dioxide partial pressure (A-pCO(2)) are underway and driven primarily by anthropogenic carbon (C-ant) accumulation in the ocean. This occurs because pCO(2) is more responsive to seasonal changes in physics (including warming) and biology in an ocean that contains more C-ant. A-pCO(2) changes have the potential to alter annual ocean carbon uptake and contribute to the overall marine carbon cycle feedback. Using the GFDL ESM2M Large Ensemble and a novel analysis framework, we quantify the influence of C-ant accumulation on pCO(2) seasonal cycles and sea-air CO2 fluxes. Specifically, we reconstruct alternative evolutions of the contemporary ocean state in which the sensitivity of pCO(2) to seasonal thermal and biophysical variation is fixed at preindustrial levels, however the background, mean-state pCO(2) fully responds to anthropogenic forcing. We find near-global A-pCO(2) increases of >100% by 2100, under RCP8.5 forcing, with rising C-ant accounting for similar to 100% of thermal and similar to 50% of nonthermal pCO(2) component amplitude changes. The other similar to 50% of nonthermal pCO(2) component changes are attributed to modeled changes in ocean physics and biology caused by climate change. C-ant-induced A-pCO(2) changes cause an 8.1 +/- 0.4% (ensemble mean +/- 1 sigma) increase in ocean carbon uptake by 2100. The is because greater wintertime wind speeds enhance the impact of wintertime pCO(2) changes, which work to increase the ocean carbon sink. Thus, the seasonal ocean carbon cycle feedback works in opposition to the larger, mean-state feedback that reduces ocean carbon uptake by similar to 60%.11Nsciescopu

Emergence of anthropogenic signals in the ocean carbon cycle

The attribution of anthropogenically forced trends in the climate system requires an understanding of when and how such signals emerge from natural variability. We applied time-of-emergence diagnostics to a large ensemble of an Earth system model, which provides both a conceptual framework for interpreting the detectability of anthropogenic impacts in the ocean carbon cycle and observational sampling strategies required to achieve detection. We found emergence timescales that ranged from less than a decade to more than a century, a consequence of the time lag between the chemical and radiative impacts of rising atmospheric CO2 on the ocean. Processes sensitive to carbonate chemical changes emerge rapidly, such as the impacts of acidification on the calcium carbonate pump (10 years for the globally integrated signal and 9–18 years for regionally integrated signals) and the invasion flux of anthropogenic CO2 into the ocean (14 years globally and 13–26 years regionally). Processes sensitive to the ocean’s physical state, such as the soft-tissue pump, which depends on nutrients supplied through circulation, emerge decades later (23 years globally and 27–85 years regionally)

Trophic level decoupling drives future changes in phytoplankton bloom phenology

© 2022, The Author(s), under exclusive licence to Springer Nature Limited.Climate change can drive shifts in the seasonality of marine productivity, with consequences for the marine food web. However, these alterations in phytoplankton bloom phenology (initiation and peak timing), and the underlying drivers, are not well understood. Here, using a 30-member Large Ensemble of climate change projections, we show earlier bloom initiation in most ocean regions, yet changes in bloom peak timing vary widely by region. Shifts in both initiation and peak timing are induced by a subtle decoupling between altered phytoplankton growth and zooplankton predation, with increased zooplankton predation (top-down control) playing an important role in altered bloom peak timing over much of the global ocean. Only in limited regions is light limitation a primary control for bloom initiation changes. In the extratropics, climate-change-induced phenological shifts will exceed background natural variability by the end of the twenty-first century, which may impact energy flow in the marine food webs.11Nsciessciscopu

Anthropogenic carbon and heat uptake by the ocean: Will the Southern Ocean remain a major sink?

The global ocean has taken up more than a quarter of the carbon emitted fromhuman activities (since 1750; e.g., Sabine et al. 2004) and more than 90% of theexcess heat that has accumulated in the Earth system as a result of these emissions(since 1971; e.g., Church et al. 2011). Hence, the ocean is greatly mitigating the riseof global mean surface temperatures. Among all the oceanic basins, the SouthernOcean, which we define here as the vast area south of 30°S that surroundsAntarctica, is thought to play a dominant role in the uptake of anthropogenic carbonand heat (e.g., Frölicher et al. 2015, Roemmich et al. 2015). Over recent decades,the Southern Ocean has experienced significant changes such as increases in airtemperature, precipitation, glacial melting and westerly winds. These changes areexpected to intensify over the 21st century and have the potential to greatly impactthe uptake of carbon and heat. Careful monitoring of key properties and processesin the Southern Ocean and an improved understanding of their effects on heat andcarbon uptake are thus needed to assess the present and project the future of theclimate system