ESDD - Latest Articles

On the determination of the global cloud feedback from satellite measurements

Fri, 03 Feb 2012 00:00:00 +0100

On the determination of the global cloud feedback from satellite measurements

Earth System Dynamics Discussions, 3, 73-90, 2012

Author(s): T. Masters

A detailed analysis is presented in order to determine the sensitivity of the estimated short-term cloud feedback to choices of temperature datasets, sources of top-of-atmosphere (TOA) radiative flux data, and temporal averaging. It is shown that the results of a previous analysis, which suggested a likely positive value for the short-term cloud feedback, depended upon combining radiative fluxes from satellite and reanalysis data when determining the cloud radiative forcing (CRF). These results are contradicted when ΔCRF is derived from NASA's Clouds and Earth's Radiant Energy System (CERES) all-sky and clear-sky measurements over the same period, resulting in a likely negative feedback. The differences between the radiative flux data sources are thus explored, along with the potential problems with each method. Overall, there is little correlation between the changes in the CRF and surface temperatures on these timescales, suggesting that the net effect of clouds varies during this time period quite apart from global temperature changes. Attempts to diagnose long-term cloud feedbacks in this manner are unlikely to be robust.

Can a reduction of solar irradiance counteract CO₂-induced climate change? – Results from four Earth system models

Wed, 25 Jan 2012 00:00:00 +0100

Can a reduction of solar irradiance counteract CO₂-induced climate change? – Results from four Earth system models

Earth System Dynamics Discussions, 3, 31-72, 2012

Author(s): H. Schmidt, K. Alterskjær, D. Bou Karam, O. Boucher, A. Jones, J. E. Kristjansson, U. Niemeier, M. Schulz, A. Aaheim, F. Benduhn, M. Lawrence, and C. Timmreck

In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of the GeoMIP and IMPLICC model intercomparison projects. In G1, the radiative forcing from an instantaneous quadrupling of the CO₂ concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged, the meridional temperature gradient is reduced in all models compared to the control simulation. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. It is shown that this reduction is only partly compensated by a reduction in evaporation so that large continental regions are drier in the engineered climate. In comparison to the climate response to a quadrupling of CO₂ alone the temperature responses are small in experiment G1. Precipitation responses are, however, of comparable magnitude but in many regions of opposite sign.

Comparison of physically- and economically-based CO₂-equivalences for methane

Fri, 13 Jan 2012 00:00:00 +0100

Comparison of physically- and economically-based CO₂-equivalences for methane

Earth System Dynamics Discussions, 3, 1-29, 2012

Author(s): O. Boucher

There is a controversy on the role methane (and other short-lived species) should play in climate mitigation policies and no consensus on what an optimal methane CO₂-equivalence should be. We revisit this question by discussing the relative merits of physically-based (i.e. Global Warming Potential or GWP and Global Temperature change Potential or GTP) and socio-economically-based climate metrics. To this effect we use a simplified Global Damage Potential (GDP) that was introduced by earlier authors and investigate the uncertainties in the methane CO₂-equivalence that arise from physical and socio-economic factors. The median value of the methane GDP comes out very close to the widely used methane 100-year GWP because of various compensating effects. However there is a large spread in possible methane CO₂-equivalences (1–99% interval: 10.0–42.5; 5–95% interval: 12.5–38.0) that is essentially due to the choice in some socio-economic parameters (i.e. the damage cost function and the discount rate). The methane 100-year GTP falls outside these ranges. It is legitimate to increase the methane CO₂-equivalence in the future as global warming unfolds. While changes in biogeochemical cycles and radiative efficiencies cause some small changes to physically-based metrics, a systematic increase in the methane CO₂-equivalence can only be achieved by some ad-hoc shortening of the time horizon. In contrast using a convex damage cost function provides a natural increase in the methane CO₂-equivalence for the socio-economically-based metrics. We also show that a methane CO₂-equivalence based on a pulse emission is sufficient to inform multi-year climate policies and emissions reductions as long as there is some degree of visibility on CO₂ prices and CO₂-equivalences.

Rolling stones; fast weathering of olivine in shallow seas for cost-effective CO₂ capture and mitigation of global warming and ocean acidification

Tue, 06 Dec 2011 00:00:00 +0100

Rolling stones; fast weathering of olivine in shallow seas for cost-effective CO₂ capture and mitigation of global warming and ocean acidification

Earth System Dynamics Discussions, 2, 551-568, 2011

Author(s): R. D. Schuiling and P. L. de Boer

Human CO₂ emissions may drive the Earth into a next greenhouse state. They can be mitigated by accelerating weathering of natural rock under the uptake of CO₂. We disprove the paradigm that olivine weathering in nature would be a slow process, and show that it is not needed to mill olivine to very fine, 10 μm-size grains in order to arrive at a complete dissolution within 1–2 year. In high-energy shallow marine environments olivine grains and reaction products on the grain surfaces, that otherwise would greatly retard the reaction, are abraded so that the chemical reaction is much accelerated. When kept in motion even large olivine grains rubbing and bumping against each other quickly produce fine clay- and silt-sized olivine particles that show a fast chemical reaction. Spreading of olivine in the world's 2% most energetic shelf seas can compensate a year's global CO₂ emissions and counteract ocean acidification against a price well below that of carbon credits.

Climate sensitivity in the Anthropocene

Thu, 15 Sep 2011 00:00:00 +0200

Climate sensitivity in the Anthropocene

Earth System Dynamics Discussions, 2, 531-550, 2011

Author(s): M. Previdi, B. G. Liepert, D. T Peteet, J. Hansen, D. J Beerling, A. J. Broccoli, S. Frolking, J. N Galloway, M. Heimann, C. Le Quéré, S. Levitus, and V. Ramaswamy

Understanding the sensitivity of Earth's climate to an imposed external forcing is one of the great challenges in science and a critical component of efforts to avoid dangerous anthropogenic interference with the climate system. Climate sensitivity (or equilibrium global surface warming) to a doubling of atmospheric CO₂ has long been estimated to be about 3 °C, considering only fast climate feedbacks associated with increases in water vapor, decreases in sea ice, and changes in clouds. However, evidence from Earth's history suggests that slower surface albedo feedbacks due to vegetation change and melting of Greenland and Antarctica can come into play on the timescales of interest to humans, which could increase the sensitivity to significantly higher values, as much as 6 °C. Even higher sensitivity may result as present-day land and ocean carbon sinks begin to lose their ability to sequester anthropogenic CO₂ in the coming decades. The evolving view of climate sensitivity in the Anthropocene is therefore one in which a wider array of Earth system feedbacks are recognized as important. Since these feedbacks are overwhelmingly positive, the sensitivity is likely to be higher than has traditionally been assumed.

Downscaling climate change scenarios for apple pest and disease modeling in Switzerland

Thu, 25 Aug 2011 00:00:00 +0200

Downscaling climate change scenarios for apple pest and disease modeling in Switzerland

Earth System Dynamics Discussions, 2, 493-529, 2011

Author(s): M. Hirschi, S. Stoeckli, M. Dubrovsky, C. Spirig, P. Calanca, M. W. Rotach, A. M. Fischer, B. Duffy, and J. Samietz

As a consequence of current and projected climate change in temperate regions of Europe, agricultural pests and diseases are expected to occur more frequently and possibly to extend to previously not affected regions. Given their economic and ecological relevance, detailed forecasting tools for various pests and diseases have been developed, which model their phenology depending on actual weather conditions and suggest management decisions on that basis. Assessing the future risk of pest-related damages requires future weather data at high temporal and spatial resolution. Here, we use a combined stochastic weather generator and re-sampling procedure for producing site-specific hourly weather series representing present and future (1980–2009 and 2045–2074 time periods) climate conditions in Switzerland. The climate change scenarios originate from the ENSEMBLES multi-model projections and provide probabilistic information on future regional changes in temperature and precipitation. Hourly weather series are produced by first generating daily weather data for these climate scenarios and then using a nearest neighbor re-sampling approach for creating realistic diurnal cycles. These hourly weather series are then used for modeling the impact of climate change on important life phases of the codling moth and on the number of predicted infection days of fire blight. Codling moth (Cydia pomonella) and fire blight (Erwinia amylovora) are two major pest and disease threats to apple, one of the most important commercial and rural crops across Europe. Results for the codling moth indicate a shift in the occurrence and duration of life phases relevant for pest control. In southern Switzerland, a 3rd generation per season occurs only very rarely under today's climate conditions but is projected to become normal in the 2045–2074 time period. While the potential risk for a 3rd generation is also significantly increasing in northern Switzerland (for most stations from roughly 1 % on average today to over 60 % in the future for the median climate change signal of the multi-model projections), the actual risk will critically depend on the pace of the adaptation of the codling moth with respect to the critical photoperiod. To control this additional generation, an intensification and prolongation of control measures (e.g., insecticides) will be required, implying an increasing risk of pesticide resistances. For fire blight, the projected changes in infection days are less certain due to uncertainties in the leaf wetness approximation and the simulation of the blooming period. Two compensating effects are projected, warmer temperatures favoring infections are balanced by a temperature-induced advancement of the blooming period, leading to no significant change in the number of infection days under future climate conditions for most stations.

The magnitude-timescale relationship of surface temperature feedbacks in climate models

Fri, 01 Jul 2011 00:00:00 +0200

The magnitude-timescale relationship of surface temperature feedbacks in climate models

Earth System Dynamics Discussions, 2, 467-491, 2011

Author(s): A. Jarvis

Because of the fundamental role feedbacks play in determining the characteristics of climate it is important we are able to specify both the magnitude and response timescale of the feedbacks we are interested in. This paper employs three different climate models driven to equilibrium with a 4 × CO₂ forcing to analyze the magnitude and timescales of surface temperature feedbacks. These models are a global energy balance model, an intermediate complexity climate model and a general circulation model. Rather than split surface temperature feedback into characteristic physical processes, this paper adopts a linear systems approach to split feedback according to their time constants and corresponding feedback amplitudes. The analysis reveals that there is a dominant net negative feedback realised during the first year. However, this is partially attenuated by a spectrum of positive feedbacks for time constants in the range 10 to 1000 years. This attenuation was composed of two discrete phases which are attributed to the effects of ''diffusive – mixed layer'' and ''circulatory – deep ocean'' ocean heat equilibration processes. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 % of the overall ocean heat equilibration feedback, whilst the circulatory feedback operated on a centennial timescale and accounted for the remaining 20 to 25 % of the response. It is important to quantify these decadal and centennial feedback processes to understand the range of climate model projections on these longer timescales.

Jet stream wind power as a renewable energy resource: little power, big impacts

Fri, 17 Jun 2011 00:00:00 +0200

Jet stream wind power as a renewable energy resource: little power, big impacts

Earth System Dynamics Discussions, 2, 435-465, 2011

Author(s): L. M. Miller, F. Gans, and A. Kleidon

Jet streams are regions of sustained high wind speeds in the upper atmosphere and are seen by some as a substantial renewable energy resource. However, jet streams are nearly geostrophic flow, that is, they result from the balance between the pressure gradient and Coriolis force in the near absence of friction. Therefore, jet stream motion is associated with very small generation rates of kinetic energy to maintain the high wind velocities, and it is this generation rate that will ultimately limit the potential use of jet streams as a renewable energy resource. Here we estimate the maximum limit of jet stream wind power by considering extraction of kinetic energy as a term in the free energy balance of kinetic energy that describes the generation, depletion, and extraction of kinetic energy. We use this balance as the basis to quantify the maximum limit of how much kinetic energy can be extracted sustainably from the jet streams of the global atmosphere as well as the potential climatic impacts of its use. We first use a simple thought experiment of geostrophic flow to demonstrate why the high wind velocities of the jet streams are not associated with a high potential for renewable energy generation. We then use an atmospheric general circulation model to estimate that the maximum sustainable extraction from jet streams of the global atmosphere is about 7.5 TW. This estimate is about 200-times less than previous estimates and is due to the fact that the common expression for instantaneous wind power ½ ρ v³ merely characterizes the transport of kinetic energy by the flow, but not the generation rate of kinetic energy. We also find that when maximum wind power is extracted from the jet streams, it results in significant climatic impacts due to a substantial increase of heat transport across the jet streams in the upper atmosphere. This results in upper atmospheric temperature differences of >20 °C, greater atmospheric stability, substantial reduction in synoptic activity, and substantial differences in surface climate. We conclude that jet stream wind power does not have the potential to become a significant source of renewable energy.

MEP solution for a minimal climate model: success and limitation of a variational problem

Mon, 23 May 2011 00:00:00 +0200

MEP solution for a minimal climate model: success and limitation of a variational problem

Earth System Dynamics Discussions, 2, 393-434, 2011

Author(s): S. Pascale, J. M. Gregory, M. H. P. Ambaum, R. Tailleux, and V. Lucarini

Maximum Entropy Production conjecture (MEP) is applied to a minimal four-box model of climate which accounts for both horizontal and vertical material heat fluxes. It is shown that, under condition of fixed insolation, a MEP solution is found with reasonably realistic temperature and heat fluxes, thus generalising results from independent two-box horizontal or vertical models. It is also shown that the meridional and the vertical entropy production terms are independently involved in the maximisation and thus MEP can be applied to each subsystem with fixed boundary conditions. We then extend the four-box model by increasing its number of degrees of freedom, and test its realism by comparing it with a GCM output. An order-of-magnitude evaluation of contributions to the material entropy production (≈50 mW m⁻² K⁻¹) due to horizontal and vertical processes within the climate system is carried out by using ad hoc temperature fields. It turns out that approximately 40 mW m⁻² K⁻¹ is the entropy production due to vertical heat transport and 5–7 mW m⁻² K⁻¹ to horizontal heat transport. A MEP solution is found which is fairly realistic as far as the horizontal large scale organisation of the surface climate is concerned whereas the vertical structure looks to be unrealistic and presents seriously unstable features. Finally a more general problem is investigated in which the longwave transmissivity is varied simultaneously with the temperature. This leads to a MEP solution characterised by a much warmer climate, with very vigorous vertical heat fluxes, in which the atmosphere is opaque to longwave radiation. A critical discussion about how to interpret MEP and how to apply it in a physically correct way concludes the paper.

The energetics response to a warmer climate: relative contributions from the transient and stationary eddies

Fri, 08 Apr 2011 00:00:00 +0200

The energetics response to a warmer climate: relative contributions from the transient and stationary eddies

Earth System Dynamics Discussions, 2, 355-391, 2011

Author(s): D. Hernández-Deckers and J.-S. von Storch

We use the Lorenz Energy Cycle (LEC) to evaluate changes in global energetic activity due to CO₂-doubling in the coupled atmosphere-ocean ECHAM5/MPI-OM model. Globally, the energetic activity – measured as the total conversion rate of available potential energy into kinetic energy – decreases by about 4%. This weakening results from a dual response that consists of a strengthening of the LEC in the upper-troposphere and a weakening in the lower and middle troposphere. This is fully consistent with results from a coarser resolution version of the same coupled model. We further use our experiments to investigate the individual contributions of the transient and stationary eddy components to the main energetics response.

The transient eddy terms have a larger contribution to the total energetic activity than the stationary ones. We find that this is also true in terms of their 2 × CO₂-response. Changes in the transient eddy components determine the main energetics response, whereas the stationary eddy components have very small contributions. Hence, the dual response – strengthening in the upper troposphere and weakening below – concerns mainly the transient eddy terms. We can relate qualitatively this response to the two main features of the 2 × CO₂ warming pattern: (a) the tropical upper-tropospheric warming increases the pole-to-equator temperature gradient – strengthening the energetic activity above – and enhances static stability – weakening the energetic activity below; and (b) the high-latitude surface warming decreases the pole-to-equator temperature gradient in the lower troposphere – weakening the energetic activity below. Despite the small contribution from the stationary eddies to the main energetics response, changes in stationary eddy available potential energy (P_se) reflect some features of the warming pattern: stronger land-sea contrasts at the subtropics and weaker land-sea contrasts at the high northern latitudes affect P_se regionally, but do not affect the global energetics response.

No way out? The double-bind in seeking global prosperity along with mitigated climate change

Wed, 06 Apr 2011 00:00:00 +0200

No way out? The double-bind in seeking global prosperity along with mitigated climate change

Earth System Dynamics Discussions, 2, 315-354, 2011

Author(s): T. J. Garrett

In a prior study (Garrett, 2011), I introduced a simple thermodynamics-based economic growth model. By treating civilization as a whole, it was found that the global economy's current rate of energy consumption can be tied through a constant to its current accumulation of wealth. The value of the constant is λ = 9.7 ± 0.3 milliwatts per 1990 US dollar. Here, this model is coupled to a linear formulation for the evolution of atmospheric CO₂ concentrations. Despite the model's extreme simplicity, multi-decadal hindcasts of trajectories in gross world product (GWP) and CO₂ agree closely with recent observations. Extending the model to the future, the model implies that the well-known IPCC SRES scenarios substantially underestimate how much CO₂ levels will rise for a given level of future economic prosperity. Instead, what is shown is that, like a long-term natural disaster, future greenhouse warming should be expected to retard the real growth of wealth through inflationary pressures. Because wealth is tied to rates of energy consumption through the constant λ, it follows that dangerous climate change should be a negative feedback on CO₂ emission rates, and therefore the ultimate extent of greenhouse warming. Nonetheless, if atmospheric CO₂ concentrations are to remain below a "dangerous" level of 450 ppmv (Hansen et al., 2007), there will have to be some combination of an unrealistically rapid rate of energy decarbonization and a near immediate collapse of civilization wealth. Effectively, civilization is in a double-bind. If civilization does not collapse quickly this century, then CO₂ levels will likely end up exceeding 1000 ppmv; but, if CO₂ levels rise by this much, then the danger is that civilization will gradually tend towards collapse.

A simple metabolic model of glacial-interglacial energy supply to the upper ocean

Tue, 22 Mar 2011 00:00:00 +0100

A simple metabolic model of glacial-interglacial energy supply to the upper ocean

Earth System Dynamics Discussions, 2, 271-313, 2011

Author(s): J. L. Pelegrí, R. Olivella, and A. García-Olivares

We use a simple two-state two-box ocean to simulate the CO₂ signal during the last four glacial-interglacial transitions in the earth system. The model is inspired by the similarity in spatial organization and temporal transition patterns between the earth and other complex systems, such as mammals. The comparison identifies the earth's metabolic rate with net autotrophic primary production in the upper ocean, sustained through new inorganic carbon and nutrients advected from the deep ocean and organic matter remineralized within the upper ocean. We view the glacial-interglacial transition as a switch of the upper ocean from a basal to an enhanced metabolic state, with energy supply initially relying on the remineralization of the local organic sources and the eventual steady state resulting from the increased advective supply of inorganic deep sources. During the interglacial-glacial transition the opposite occurs, with an initial excess of advective supply and primary production that allows the replenishment of the upper-ocean organic storages. We set the relative change in energy supply from the CO₂ signal and use genetic algorithms to explore the sensitivity of the model output to both the basal recirculation rate and the intensity-timing of the maximum recirculation rate. The model is capable of reproducing quite well the long-term oscillations, as shown by correlations with observations typically about 0.8. The dominant time scale for each cycle ranges between about 40 and 45 kyr, close to the 41 kyr average obliquity astronomical period, and the deep-ocean recirculation rate increases between one and two orders of magnitude from glacial to interglacial periods.

Climate change, in the framework of the constructal law

Mon, 07 Mar 2011 00:00:00 +0100

Climate change, in the framework of the constructal law

Earth System Dynamics Discussions, 2, 241-270, 2011

Author(s): M. Clausse, F. Meunier, A. H. Reis, and A. Bejan

Here we present a simple and transparent alternative to the complex models of Earth thermal behavior under time-changing conditions. We show the one-to-one relationship between changes in atmospheric properties and time-dependent changes in temperature and its distribution on Earth. The model accounts for convection and radiation, thermal inertia and changes in albedo (ρ) and greenhouse factor (γ). The constructal law is used as the principle that governs the evolution of flow configuration in time, and provides closure for the equations that describe the model. In the first part of the paper, the predictions are tested against the current thermal state of Earth. Next, the model showed that for two time-dependent scenarios, (δρ = 0.002; δγ = 0.011) and (δρ = 0.002; δγ = 0.005) the predicted equatorial and polar temperature increases and the time scales are (ΔT_H = 1.16 K; ΔT_L = 1.11 K; 104 years) and (0.41 K; 0.41 K; 57 years), respectively. In the second part, a continuous model of temperature variation was used to predict the thermal response of the Earth's surface for changes bounded by δρ = δγ and δρ = −δγ. The results show that the global warming amplitudes and time scales are consistent with those obtained for δρ = 0.002 and δγ = 0.005. The poleward heat current reaches its maximum in the vicinity of 35° latitude, accounting for the position of the Ferrel cell between the Hadley and Polar Cells.

Geologic constraints on earth system sensitivity to CO₂ during the Cretaceous and early Paleogene

Thu, 03 Mar 2011 00:00:00 +0100

Geologic constraints on earth system sensitivity to CO₂ during the Cretaceous and early Paleogene

Earth System Dynamics Discussions, 2, 211-240, 2011

Author(s): D. L. Royer, M. Pagani, and D. J. Beerling

Earth system sensitivity (ESS) is the long-term (>10³ yr) equilibrium temperature response to doubled CO₂. ESS has climate policy implications because global temperatures are not expected to decline appreciably for at least 10³ yr, even if anthropogenic greenhouse-gas emissions drop to zero. We report quantitative ESS estimates of 3 °C or higher for much of the Cretaceous and early Paleogene based on paleo-reconstructions of CO₂ and temperature. These estimates are generally higher than climate sensitivities simulated from global climate models for the same ancient periods (~3 °C). We conclude that climate models do not capture the full suite of positive climate feedbacks during greenhouse worlds. These absent feedbacks are probably related to clouds, trace greenhouse gases, seasonal snow cover, and/or vegetation, especially in polar regions. Continued warming in the coming decades as anthropogenic greenhouse gases accumulate in the atmosphere ensures that characterizing and quantifying these positive climate feedbacks will become a scientific challenge of increasing priority.

Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America

Thu, 17 Feb 2011 00:00:00 +0100

Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America

Earth System Dynamics Discussions, 2, 161-210, 2011

Author(s): D. Wisser, S. Marchenko, J. Talbot, C. Treat, and S. Frolking

Northern peatlands contain a large terrestrial carbon pool that plays an important role in the Earth's carbon cycle. A considerable fraction of this carbon pool is currently in permafrost and is biogeochemically relatively inert; this will change with increasing soil temperatures as a result of climate warming in the 21st century. We use a geospatially explicit representation of peat areas and peat depth from a recently-compiled database and a geothermal model to estimate northern North America soil temperature responses to predicted changes in air temperature. We find that, despite a widespread decline in the areas classified as permafrost, soil temperatures in peatlands respond more slowly to increases in air temperature owing to the insulating properties of peat. We estimate that an additional 670 km³ of peat soils in North America, containing ~33 Pg C, could be seasonally thawed by the end of the century, representing ~20% of the total peat volume in Alaska and Canada. Warming conditions result in a lengthening of the soil thaw period by ~40 days, averaged over the model domain. These changes have potentially important implications for the carbon balance of peat soils.

Role of volcanic forcing on future global carbon cycle

Wed, 16 Feb 2011 00:00:00 +0100

Role of volcanic forcing on future global carbon cycle

Earth System Dynamics Discussions, 2, 133-159, 2011

Author(s): J. F. Tjiputra and O. H. Otterå

Using a fully coupled global climate-carbon cycle model, we assess the potential role of volcanic eruptions on future projection of climate change and its associated carbon cycle feedback. The volcanic-like forcings are applied together with business-as-usual IPCC-A2 carbon emissions scenario. We show that very large volcanic eruptions similar to Tambora lead to short-term substantial global cooling. However, over a long period, smaller but more frequent eruptions, such as Pinatubo, would have a stronger impact on future climate change. In a scenario where the volcanic external forcings are prescribed with a five-year frequency, the induced cooling immediately lower the global temperature by more than one degree before return to the warming trend. Therefore, the climate change is approximately delayed by several decades and by the end of the 21st century, the warming is still below two degrees when compared to the present day period. The cooler climate reduces the terrestrial heterotrophic respiration in the northern high latitude and increases net primary production in the tropics, which contributes to more than 45% increase in accumulated carbon uptake over land. The increased solubility of CO₂ gas in seawater associated with cooler SST is offset by reduced CO₂ partial pressure gradient between ocean and atmosphere, which results in small changes in net ocean carbon uptake. Similarly, there is nearly no change in the seawater buffer capacity simulated between the different volcanic scenarios. Our study shows that even in the relatively extreme scenario where large volcanic eruptions occur every five-years period, the induced cooling only leads to a reduction of 46 ppmv atmospheric CO₂ concentration as compared to the reference projection of 878 ppmv, at the end of the 21st century. With respect to sulphur injection geoengineering method, our study suggest that small scale but frequent mitigation is more efficient than the opposite. Moreover, the longer we delay, the more difficult it would be to counteract climate change.

Entropy production of soil hydrological processes and its maximisation

Fri, 28 Jan 2011 00:00:00 +0100

Entropy production of soil hydrological processes and its maximisation

Earth System Dynamics Discussions, 2, 105-132, 2011

Author(s): P. Porada, A. Kleidon, and S. J. Schymanski

Hydrological processes are irreversible and produce entropy. Hence, the framework of non-equilibrium thermodynamics is used here to describe them mathematically. This means flows of water are written as functions of gradients in the gravitational and chemical potential of water between two parts of the hydrological system. Such a framework facilitates a consistent thermodynamic representation of the hydrological processes in the model. Furthermore, it allows for the calculation of the entropy production associated with a flow of water, which is proportional to the product of gradient and flow. Thus, an entropy budget of the hydrological cycle at the land surface is quantified, illustrating the contribution of different processes to the overall entropy production. Moreover, the proposed Principle of Maximum Entropy Production (MEP) can be applied to the model. This means, unknown parameters can be determined by setting them to values which lead to a maximisation of the entropy production in the model. The model used in this study is parametrised according to MEP and evaluated by means of several observational datasets describing terrestrial fluxes of water and carbon. The model reproduces the data with good accuracy which is a promising result with regard to the application of MEP to hydrological processes at the land surface.

Quantifying the thermodynamic entropy budget of the land surface: is this useful?

Wed, 26 Jan 2011 00:00:00 +0100

Quantifying the thermodynamic entropy budget of the land surface: is this useful?

Earth System Dynamics Discussions, 2, 71-103, 2011

Author(s): N. A. Brunsell, S. J. Schymanski, and A. Kleidon

As a system is moved away from a state of thermodynamic equilibrium, spatial and temporal heterogeneity is induced. A possible methodology to assess these impacts is to examine the thermodynamic entropy budget and assess the role of entropy production and transfer between the surface and the atmosphere. Here, we adopted this thermodynamic framework to examine the implications of changing vegetation fractional cover on land surface energy exchange processes using the NOAH land surface model and eddy covariance observations. Simulations that varied the relative fraction of vegetation were used to calculate the resultant entropy budget as a function of fraction of vegetation. Results showed that increasing vegetation fraction increases entropy production by the land surface while decreasing the overall entropy budget (the rate of change in entropy at the surface). This is accomplished largely via simultaneous increase in the entropy production associated with the absorption of solar radiation and a decline in the Bowen ratio (ratio of sensible to latent heat flux), which leads to increasing the entropy export associated with the latent heat flux during the daylight hours and dominated by entropy transfer associated with sensible heat and soil heat fluxes during the nighttime hours. Eddy covariance observations also show that the entropy production has a consistent sensitivity to land cover, while the overall entropy budget appears most related to the net radiation at the surface. This implies that quantifying the thermodynamic entropy budget and entropy production is a useful metric for assessing biosphere-atmosphere-hydrosphere system interactions.

Spectral solar irradiance and its entropic effect on Earth's climate

Tue, 25 Jan 2011 00:00:00 +0100

Spectral solar irradiance and its entropic effect on Earth's climate

Earth System Dynamics Discussions, 2, 45-70, 2011

Author(s): W. Wu, Y. Liu, and G. Wen

The high-resolution measurements of the spectral solar irradiance at the top of the Earth's atmosphere by the Solar Radiation and Climate Experiment (SORCE) satellite suggest significant deviation of solar radiation from the commonly assumed blackbody radiation. Here, we use these spectral irradiance measurements to estimate the Earth's incident solar radiation entropy flux, and examine the importance of a proper estimation approach. The Earth's incident solar radiation entropy flux estimated by directly applying the observed spectral solar irradiance into the most accurate Planck expression is compared with that estimated with a conventional approach that uses the Sun's brightness temperature under the assumption of a blackbody Sun. The globally averaged non-blackbody incident solar radiation entropy flux at the top of the Earth's atmosphere equals 0.31 W m⁻² K⁻¹. This value is about 4 times larger than that estimated from the conventional blackbody approach, with the difference comparable to the typical value of the entropy production rate associated with atmospheric latent heat process. Further analysis reveals that the decrease of spectral solar radiation entropy flux with radiation traveling distance, unlike the decrease of spectral solar radiation energy flux with radiation traveling distance, is wavelength dependent, and that the difference between the two estimates can be attributed to the fact that the conventional approach ignores the influence of radiation traveling distance on the spectral solar radiation entropy flux. Moreover, sensitivity study further shows that the distribution of top-of-atmosphere spectral solar irradiance could significantly impact the magnitude of the estimated Earth's incident solar radiation entropy flux. These results together suggest that the spectral distribution of incident solar radiation is critical for determining the Earth's incident solar radiation entropy flux, and thus the Earth's climate.

Differences and implications in biogeochemistry from maximizing entropy production locally versus globally

Wed, 19 Jan 2011 00:00:00 +0100

Differences and implications in biogeochemistry from maximizing entropy production locally versus globally

Earth System Dynamics Discussions, 2, 1-44, 2011

Author(s): J. J. Vallino

In this manuscript we investigate the use of the maximum entropy production (MEP) principle for modeling biogeochemical processes that are catalyzed by living systems. Because of novelties introduced by the MEP approach, many questions need to be answered and techniques developed in the application of MEP to describe biological systems that are responsible for energy and mass transformations on a planetary scale. In previous work we introduce the importance of integrating entropy production over time to distinguish abiotic from biotic processes under transient conditions. Here we investigate the ramifications of modeling biological systems involving one or more spatial dimensions. When modeling systems with spatial dimensions, entropy production can be maximized either locally at each point in space asynchronously or globally over the system domain synchronously. We use a simple two-box model inspired by two-layer ocean models to illustrate the differences in local versus global entropy maximization. Synthesis and oxidation of biological structure is modeled using two autocatalytic reactions that account for changes in community kinetics using a single parameter each. Our results show that entropy production can be increased if maximized over the system domain rather than locally, which has important implications regarding how biological systems organize and supports the hypothesis for multiple levels of selection and cooperation in biology for the dissipation of free energy.