Policy incentives for greenhouse gas removal techniques: the risks of premature inclusion in carbon markets and the need for a multi-pronged policy framework

Almost all modelled emissions scenarios consistent with the Paris Agreement's target of limiting global temperature increase to well below two degrees include the use of greenhouse gas removal (GGR) techniques. Despite the prevalence of GGR in Paris-consistent scenarios, and indeed the UK's own net-zero target, there is a paucity of regulatory support for emerging GGR techniques.. However, the role of carbon pricing is one area that has experienced more attention than others, including discussion about the future inclusion of GGR in carbon markets. Here we identify three risks associated with using carbon markets as the sole, or main, policy lever to encourage the deployment of GGR techniques. Our categorisation of risks stems from discussions with policymakers in the UK and a review of the broader literature on carbon markets and GGR. We present a three-pronged risk assessment framework to highlight the dangers in doing so. First, treating emissions removals and emissions reductions as entirely fungible allows for undesirable substitution. Second, carbon markets may provide insufficient demand pull to drive currently more-costly GGR techniques to deployment at commercial scales. Third, opening up a carbon market for potentially lower-cost GGR (such as nature-based solutions) too early could exert downward pressure on the overall market-based price of carbon, in the absence of adjustments to emissions caps or other safeguards. We discuss how these risks could hamper overall efforts to deploy GGR, and instead suggest a multi-pronged and intertemporal policy and governance framework for GGR. This includes considering separate accounting targets for GGR and conventional emissions abatement, removing perfect fungibility between GGR permits and carbon market permits and promoting a a wide range of innovation and technology-specific mechanisms to drive currently expensive, yet highly scalable technological GGR down the cost curve. Such a framework would ensure that policymakers can utilise carbon markets and other incentives appropriately to drive development and deployment of GGR techniques without compromising near-term mitigation, and that the representation of GGR in modelled low-carbon pathways is cognisant of its real-world scale-up potential in light of these incentives

Parameter Estimation from Time-Series Data with Correlated Errors: A Wavelet-Based Method and its Application to Transit Light Curves

We consider the problem of fitting a parametric model to time-series data that are afflicted by correlated noise. The noise is represented by a sum of two stationary Gaussian processes: one that is uncorrelated in time, and another that has a power spectral density varying as $1/f^\gamma$. We present an accurate and fast [O(N)] algorithm for parameter estimation based on computing the likelihood in a wavelet basis. The method is illustrated and tested using simulated time-series photometry of exoplanetary transits, with particular attention to estimating the midtransit time. We compare our method to two other methods that have been used in the literature, the time-averaging method and the residual-permutation method. For noise processes that obey our assumptions, the algorithm presented here gives more accurate results for midtransit times and truer estimates of their uncertainties.Comment: Accepted in ApJ. Illustrative code may be found at http://www.mit.edu/~carterja/code/ . 17 page

Inner-Insulated Turbocharger Technology to Reduce Emissions and Fuel Consumption from Modern Engines

Reducing emissions from light duty vehicles is critical to meet current and future air quality targets. With more focus on real world emissions from light-duty vehicles, the interactions between engine and exhaust gas aftertreatment are critical. For modern engines, most emissions are generated during the warm-up phase following a cold start. For Diesel engines this is exaggerated due to colder exhaust temperatures and larger aftertreatment systems. The De-NOx aftertreatment can be particularly problematic. Engine manufacturers are required to take measures to address these temperature issues which often result in higher fuel consumption (retarding combustion, increasing engine load or reducing the Diesel air-fuel ratio). In this paper we consider an inner-insulated turbocharger as an alternative, passive technology which aims to reduce the exhaust heat losses between the engine and the aftertreatment. Firstly, the concept and design of the inner-insulated turbocharger is presented. A transient 3D CFD/FEM (Computation Fluid Dynamics/Finite Element Modelling) simulation is conducted and predicts that external heat losses will be reduced by 70% compared to a standard turbocharger, i.e. non-insulated turbocharger. A 1D modelling methodology is then presented for capturing the behaviour of the inner-insulated turbocharger. This is important as conventional models based on isentropic efficiency maps cannot accurately predict turbine outlet temperature. The alternative model is essential to demonstrate benefits in system-level simulations. Experimental results are presented from a transient air-path testing facility to validate the 1D model and demonstrate the characteristics of the inner-insulated turbocharger. Finally, the validated 1D model is used within a powertrain optimization simulation to demonstrate an improvement in fuel consumption for iso-NOx emissions over a low load city cycle of up to 3%. The work was conducted under the THOMSON project which has received funding from the European Union's Horizon 2020 Program for research, technological development and demonstration under Agreement no. 724037. The project aims to increase the market penetration of 48V hybrid vehicles.</p

Inner-Insulated Turbocharger Technology to Reduce Emissions and Fuel Consumption from Modern Engines

Reducing emissions from light duty vehicles is critical to meet current and future air quality targets. With more focus on real world emissions from light-duty vehicles, the interactions between engine and exhaust gas aftertreatment are critical. For modern engines, most emissions are generated during the warm-up phase following a cold start. For Diesel engines this is exaggerated due to colder exhaust temperatures and larger aftertreatment systems. The De-NOx aftertreatment can be particularly problematic. Engine manufacturers are required to take measures to address these temperature issues which often result in higher fuel consumption (retarding combustion, increasing engine load or reducing the Diesel air-fuel ratio). In this paper we consider an inner-insulated turbocharger as an alternative, passive technology which aims to reduce the exhaust heat losses between the engine and the aftertreatment. Firstly, the concept and design of the inner-insulated turbocharger is presented. A transient 3D CFD/FEM (Computation Fluid Dynamics/Finite Element Modelling) simulation is conducted and predicts that external heat losses will be reduced by 70% compared to a standard turbocharger, i.e. non-insulated turbocharger. A 1D modelling methodology is then presented for capturing the behaviour of the inner-insulated turbocharger. This is important as conventional models based on isentropic efficiency maps cannot accurately predict turbine outlet temperature. The alternative model is essential to demonstrate benefits in system-level simulations. Experimental results are presented from a transient air-path testing facility to validate the 1D model and demonstrate the characteristics of the inner-insulated turbocharger. Finally, the validated 1D model is used within a powertrain optimization simulation to demonstrate an improvement in fuel consumption for iso-NOx emissions over a low load city cycle of up to 3%. The work was conducted under the THOMSON project which has received funding from the European Union's Horizon 2020 Program for research, technological development and demonstration under Agreement no. 724037. The project aims to increase the market penetration of 48V hybrid vehicles.</p

Survey for Transiting Extrasolar Planets in Stellar Systems IV: Variables in the Field of NGC 1245

The Survey for Transiting Extrasolar Planets in Stellar Systems (STEPSS) project is a search for planetary transits in open clusters. In this paper, we analyze the STEPSS observations of the open cluster NGC 1245 to determine the variable star content of the cluster. Out of 6787 stars observed with V < 22, of which ~870 are cluster members, we find 14 stars with clear intrinsic variability that are potential cluster members, and 29 clear variables that are not cluster members. None of these variables have been previously identified. We present light curves, finding charts, and stellar/photometric data on these variable objects. Several of the interacting binaries have estimated distances consistent with the cluster distance determined from isochrone fits to the color magnitude diagram. Four stars at the main sequence turnoff of the cluster have light curves consistent with gamma Doradus variability. If these gamma Doradus candidates are confirmed, they represent the oldest and coolest members of this class of variable discovered to date.Comment: 20 pages, 15 figures. Submitted to AJ. PDF version with full-resolution figures at http://www.astronomy.ohio-state.edu/~pepper/ms.pd

Empirical Constraints on the Oblateness of an Exoplanet

We show that the gas giant exoplanet HD 189733b is less oblate than Saturn, based on Spitzer Space Telescope photometry of seven transits. The observable manifestations of oblatenesswould have been slight anomalies during the ingress and egress phases, as well as variations in the transit depth due to spin precession. Our nondetection of these effects gives the first empirical constraints on the shape of an exoplanet. The results are consistent with the theoretical expectation that the planetary rotation period and orbital period are synchronized, in which case the oblateness would be an order of magnitude smaller than our upper limits. Conversely, if HD 189733b is assumed to be in a synchronous, zero-obliquity state, then the data give an upper bound on the quadrupole moment of the planet (J2 < 0.068 with 95% confidence) that is too weak to constrain the interior structure of the planet. An Appendix describes a fast algorithm for computing the transit light curve of an oblate planet, which was necessary for our analysis.Comment: 14 pages, accepted for publication in The Astrophysical Journa

Photometric Follow-up Observations of the Transiting Neptune-Mass Planet GJ 436b

This paper presents multi-band photometric follow-up observations of the Neptune-mass transiting planet GJ 436b, consisting of 5 new ground-based transit light curves obtained in May 2007. Together with one already published light curve we have at hand a total of 6 light curves, spanning 29 days. The analysis of the data yields an orbital period P = 2.64386+-0.00003 days, mid-transit time T_c [HJD] =2454235.8355+-0.0001, planet mass M_p = 23.1+-0.9 M_{\earth} = 0.073+-0.003 M_{Jup}, planet radius R_p = 4.2+-0.2 R_{\earth} = 0.37+-0.01 R_{Jup} and stellar radius R_s = 0.45+-0.02 R_{\sun}. Our typical precision for the mid transit timing for each transit is about 30 seconds. We searched the data for a possible signature of a second planet in the system through transit timing variations (TTV) and variation of the impact parameter. The analysis could not rule out a small, of the order of a minute, TTV and a long-term modulation of the impact parameter, of the order of +0.2 year^{-1}.Comment: V2: Replaced with accepted versio

Near-infrared transit photometry of the exoplanet HD 149026b

The transiting exoplanet HD 149026b is an important case for theories of planet formation and planetary structure, because the planet's relatively small size has been interpreted as evidence for a highly metal-enriched composition. We present observations of 4 transits with the Near Infrared Camera and Multi-Object Spectrometer on the Hubble Space Telescope, within a wavelength range of 1.1--2.0 $\mu$m. Analysis of the light curve gives the most precise estimate yet of the stellar mean density, $\rho_\star = 0.497^{+0.042}_{-0.057}$ g cm$^{-3}$. By requiring agreement between the observed stellar properties (including $\rho_\star$) and stellar evolutionary models, we refine the estimate of the stellar radius: $R_\star = 1.541^{+0.046}_{-0.042}$ R_\sun. We also find a deeper transit than has been measured at optical and mid-infrared wavelengths. Taken together, these findings imply a planetary radius of $R_p = 0.813^{+0.027}_{-0.025}$ $R_{\rm Jup}$, which is larger than earlier estimates. Models of the planetary interior still require a metal-enriched composition, although the required degree of metal enrichment is reduced. It is also possible that the deeper NICMOS transit is caused by wavelength-dependent absorption by constituents in the planet's atmosphere, although simple model atmospheres do not predict this effect to be strong enough to account for the discrepancy. We use the 4 newly-measured transit times to compute a refined transit ephemeris.Comment: 18 pages, 13 figures, accepted for publication in Ap