scholarly journals Emulation of long-term changes in global climate: application to the late Pliocene and future

2017 ◽  
Vol 13 (11) ◽  
pp. 1539-1571 ◽  
Author(s):  
Natalie S. Lord ◽  
Michel Crucifix ◽  
Dan J. Lunt ◽  
Mike C. Thorne ◽  
Nabila Bounceur ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
General Circulation ◽  
Spatial Scales ◽  
Atmospheric Co2 ◽  
Proxy Data ◽  
Late Pliocene ◽  
Co2 Concentrations ◽  
Climate Evolution ◽  
Atmospheric Co2 Concentrations

Abstract. Multi-millennial transient simulations of climate changes have a range of important applications, such as for investigating key geologic events and transitions for which high-resolution palaeoenvironmental proxy data are available, or for projecting the long-term impacts of future climate evolution on the performance of geological repositories for the disposal of radioactive wastes. However, due to the high computational requirements of current fully coupled general circulation models (GCMs), long-term simulations can generally only be performed with less complex models and/or at lower spatial resolution. In this study, we present novel long-term continuous projections of climate evolution based on the output from GCMs, via the use of a statistical emulator. The emulator is calibrated using ensembles of GCM simulations, which have varying orbital configurations and atmospheric CO2 concentrations and enables a variety of investigations of long-term climate change to be conducted, which would not be possible with other modelling techniques on the same temporal and spatial scales. To illustrate the potential applications, we apply the emulator to the late Pliocene (by modelling surface air temperature – SAT), comparing its results with palaeo-proxy data for a number of global sites, and to the next 200 kyr (thousand years) (by modelling SAT and precipitation). A range of CO2 scenarios are prescribed for each period. During the late Pliocene, we find that emulated SAT varies on an approximately precessional timescale, with evidence of increased obliquity response at times. A comparison of atmospheric CO2 concentration for this period, estimated using the proxy sea surface temperature (SST) data from different sites and emulator results, finds that relatively similar CO2 concentrations are estimated based on sites at lower latitudes, whereas higher-latitude sites show larger discrepancies. In our second illustrative application, spanning the next 200 kyr into the future, we find that SAT oscillations appear to be primarily influenced by obliquity for the first ∼ 120 kyr, whilst eccentricity is relatively low, after which precession plays a more dominant role. Conversely, variations in precipitation over the entire period demonstrate a strong precessional signal. Overall, we find that the emulator provides a useful and powerful tool for rapidly simulating the long-term evolution of climate, both past and future, due to its relatively high spatial resolution and relatively low computational cost. However, there are uncertainties associated with the approach used, including the inability of the emulator to capture deviations from a quasi-stationary response to the forcing, such as transient adjustments of the deep-ocean temperature and circulation, in addition to its limited range of fixed ice sheet configurations and its requirement for prescribed atmospheric CO2 concentrations.

scholarly journals Emulation of long-term changes in global climate: Application to the late Pliocene and future

2017 ◽  
Author(s):  
Natalie S. Lord ◽  
Michel Crucifix ◽  
Dan J. Lunt ◽  
Mike C. Thorne ◽  
Nabila Bounceur ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
General Circulation ◽  
Spatial Scales ◽  
Computational Cost ◽  
General Circulation Models ◽  
Atmospheric Co2 ◽  
Proxy Data ◽  
Late Pliocene ◽  
Climate Evolution

Abstract. Multi-millennial transient simulations of climate changes have a range of important applications, such as for investigating key geologic events and transitions for which high resolution palaeoenvironmental proxy data are available, or for projecting the long-term impacts of future climate evolution on the performance of geological repositories for the disposal of radioactive wastes. However, due to the high computational requirements of current fully coupled General Circulation Models (GCMs), long-term simulations can generally only be performed with less complex models and/or at lower spatial resolution. In this study, we present novel long-term “continuous” projections of climate evolution based on the output from GCMs, via the use of a statistical emulator. The emulator is calibrated using ensembles of GCM simulations which have varying orbital configurations and atmospheric CO2 concentrations and enables a variety of investigations of long-term climate change to be conducted which would not be possible with other modelling techniques at the same temporal and spatial scales. To illustrate the potential applications, we apply the emulator to the late Pliocene (by modelling SAT), comparing its results with palaeo-proxy data for a number of global sites, and to the next 200 thousand years (kyr) (by modelling SAT and precipitation). A range of CO2 scenarios are modelled for each period. During the late Pliocene, we find that emulated SAT varies on an approximately precessional timescale, with evidence of increased obliquity response at times. A comparison of atmospheric CO2 concentration for this period, estimated using the proxy data and emulator results and using proxy CO2 records, finds that relatively similar concentrations are produced at lower latitudes, although higher latitude sites show larger discrepancies. In our second illustrative application, spanning the next 200 kyr into the future, we find that SAT oscillations appear to be primarily influenced by obliquity for the first ~ 120 kyr, whilst eccentricity is relatively low, after which precession plays a more dominant role. Conversely, variations in precipitation over the entire period demonstrate a strong precessional signal. Overall, we find that the emulator provides a useful and powerful tool for rapidly simulating the long-term evolution of climate, both past and future, due to its relatively high spatial resolution and relatively low computational cost.

Hemispheric TOA SW radiation budgets under changed atmospheric radiation conditions

2020 ◽  
Author(s):  
Traute Crueger ◽  
Hauke Schmidt ◽  
Bjorn Stevens
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
General Circulation Models ◽  
Stratospheric Aerosol ◽  
Atmospheric Co2 ◽  
Atmospheric Radiation ◽  
Co2 Concentrations ◽  
Atmospheric Co2 Concentrations ◽  
Radiation Conditions ◽  
Tropical Clouds

<p>Under present day conditions the observations approximately show a hemispheric symmetry of the top of atmosphere (TOA)  short wave (SW) reflection despite the asymmetry of surface SW reflection. This has been confirmed by climate models. With models in an aqua planet setup, Voigt et al. (2014) found that tropical clouds largely compensate surface SW hemispheric asymmetries, however to a different degree in dependence on the convection scheme.</p><p>In this study, we question, whether there is also a hemispheric symmetry of TOA SW radiation under changed atmospheric radiation conditions. For that reason, we analyze experiments performed with a set of fully coupled general circulation models. The experiments were performed with either a) hemispheric asymmetric incoming radiation, b) increased atmospheric CO2 concentrations, c) increased atmospheric CO2 concentrations combined with increased stratospheric aerosol burden, or d) increased atmospheric CO2 concentration in conjunction with increased ocean albedo.</p><p>We show that generally, a hemispheric symmetry of TOA SW radiation does not occur. Overall, among the group of models, the hemispheric TOA SW radiation budgets are roughly similar for the distinct experiments, although the models utilyze different convection schemes.  We discuss the role of surface and atmospheric feedbacks in the different experiments, especially of tropical and extratropical clouds.</p><p>Reference:<br>Voigt, A., B. Stevens, J. Bader, and T. Mauritsen, 2014: Compensation of Hemispheric Albedo Asymmetries by Shifts of the ITCZ and Tropical Clouds. J. Climate, 27, 1029–1045, https://doi.org/10.1175/JCLI-D-13-00205.1.</p>

scholarly journals The hot and the cold: unravelling the variable response of plant respiration to temperature

2005 ◽  
Vol 32 (2) ◽  
pp. 87 ◽  
Author(s):  
Owen K. Atkin ◽  
Dan Bruhn ◽  
Vaughan M. Hurry ◽  
Mark G. Tjoelker
Keyword(s):  
Water Availability ◽  
Thermal Acclimation ◽  
Atmospheric Co2 ◽  
Co2 Efflux ◽  
Co2 Concentrations ◽  
Long Term Changes ◽  
Q10 Values ◽  
Atmospheric Co2 Concentrations ◽  
Plant Respiration

When predicting the effects of climate change, global carbon circulation models that include a positive feedback effect of climate warming on the carbon cycle often assume that (1) plant respiration increases exponentially with temperature (with a constant Q10) and (2) that there is no acclimation of respiration to long-term changes in temperature. In this review, we show that these two assumptions are incorrect. While Q10 does not respond systematically to elevated atmospheric CO2 concentrations, other factors such as temperature, light, and water availability all have the potential to influence the temperature sensitivity of respiratory CO2 efflux. Roots and leaves can also differ in their Q10 values, as can upper and lower canopy leaves. The consequences of such variable Q10 values need to be fully explored in carbon modelling. Here, we consider the extent of variability in the degree of thermal acclimation of respiration, and discuss in detail the biochemical mechanisms underpinning this variability; the response of respiration to long-term changes in temperature is highly dependent on the effect of temperature on plant development, and on interactive effects of temperature and other abiotic factors (e.g. irradiance, drought and nutrient availability). Rather than acclimating to the daily mean temperature, recent studies suggest that other components of the daily temperature regime can be important (e.g. daily minimum and / or night temperature). In some cases, acclimation may simply reflect a passive response to changes in respiratory substrate availability, whereas in others acclimation may be critical in helping plants grow and survive at contrasting temperatures. We also consider the impact of acclimation on the balance between respiration and photosynthesis; although environmental factors such as water availability can alter the balance between these two processes, the available data suggests that temperature-mediated differences in dark leaf respiration are closely linked to concomitant differences in leaf photosynthesis. We conclude by highlighting the need for a greater process-based understanding of thermal acclimation of respiration if we are to successfully predict future ecosystem CO2 fluxes and potential feedbacks on atmospheric CO2 concentrations.

scholarly journals Comparing Lagrangian and Eulerian models for CO<sub>2</sub> transport – a step towards Bayesian inverse modeling using WRF/STILT-VPRM

2012 ◽  
Vol 12 (19) ◽  
pp. 8979-8991 ◽  
Author(s):  
D. Pillai ◽  
C. Gerbig ◽  
R. Kretschmer ◽  
V. Beck ◽  
U. Karstens ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Wrf Model ◽  
Extreme Case ◽  
Atmospheric Co2 ◽  
Lagrangian Transport ◽  
Airborne Measurements ◽  
Co2 Concentrations ◽  
Lagrangian Time Scale ◽  
Atmospheric Co2 Concentrations

Abstract. We present simulations of atmospheric CO2 concentrations provided by two modeling systems, run at high spatial resolution: the Eulerian-based Weather Research Forecasting (WRF) model and the Lagrangian-based Stochastic Time-Inverted Lagrangian Transport (STILT) model, both of which are coupled to a diagnostic biospheric model, the Vegetation Photosynthesis and Respiration Model (VPRM). The consistency of the simulations is assessed with special attention paid to the details of horizontal as well as vertical transport and mixing of CO2 concentrations in the atmosphere. The dependence of model mismatch (Eulerian vs. Lagrangian) on models' spatial resolution is further investigated. A case study using airborne measurements during which two models showed large deviations from each other is analyzed in detail as an extreme case. Using aircraft observations and pulse release simulations, we identified differences in the representation of details in the interaction between turbulent mixing and advection through wind shear as the main cause of discrepancies between WRF and STILT transport at a spatial resolution such as 2 and 6 km. Based on observations and inter-model comparisons of atmospheric CO2 concentrations, we show that a refinement of the parameterization of turbulent velocity variance and Lagrangian time-scale in STILT is needed to achieve a better match between the Eulerian and the Lagrangian transport at such a high spatial resolution (e.g. 2 and 6 km). Nevertheless, the inter-model differences in simulated CO2 time series for a tall tower observatory at Ochsenkopf in Germany are about a factor of two smaller than the model-data mismatch and about a factor of three smaller than the mismatch between the current global model simulations and the data.

scholarly journals Impacts of Global Warming on the Radial Growth and Long-Term Intrinsic Water-Use Efficiency (iWUE) of Schrenk Spruce (Picea schrenkiana Fisch. et Mey) in the Sayram Lake Basin, Northwest China

Forests ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 380
Author(s):  
Li Qin ◽  
Yujiang Yuan ◽  
Huaming Shang ◽  
Shulong Yu ◽  
Weiping Liu ◽  
...  
Keyword(s):  
Global Warming ◽  
Radial Growth ◽  
Atmospheric Co2 ◽  
Lake Basin ◽  
Picea Schrenkiana ◽  
Co2 Concentrations ◽  
Intrinsic Water Use Efficiency ◽  
Use Efficiency ◽  
Atmospheric Co2 Concentrations

Global warming and the sharp rise in atmospheric CO2 concentrations have a profound impact on forest ecosystems. To better manage these changes, a comprehensive understanding of forest ecosystem responses to global change is essential. There is a lack of knowledge about the growth response of Schrenk spruce (Picea schrenkiana Fisch. et Mey)—an endemic tree species found in the arid Central Asian region—to climate change and rising atmospheric CO2 concentrations. In this study, core samples of Schrenk spruce were collected in the Sayram Lake Basin, Xinjiang. Tree-ring radial growth and long-term intrinsic water-use efficiency (iWUE) chronologies were established based on standard tree-ring width and stable carbon isotope methods. The relationships between atmospheric CO2 concentrations, climate, radial growth, and iWUE were analyzed. Our results indicate that the iWUE of trees in this region has continued to rise rapidly but that radial growth has not increased over the past 160 years. The main factor affecting iWUE is atmospheric CO2 concentrations (Ca), whereas the radial growth is much more sensitive to water availability. This may explain why the increase Ca has not had a fertilizer effect on the radial growth of trees.

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