Sustainable irrigation expansion over water limited croplands is an important measure to enhance agricultural yields and increase the resilience of crop production to global warming. While existing global assessments of irrigation expansion mainly illustrate the biophysical potential for irrigation, socioeconomic factors such as weak governance or low income, that demonstrably impede the successful implementation of sustainable irrigation, remain largely underexplored. Here we provide five scenarios of sustainable irrigation deployment in the 21st century integrated into the framework of Shared Socioeconomic Pathways, which account for biophysical irrigation limits and socioeconomic constraints. We find that the potential for sustainable irrigation expansion implied by biophysical limits alone is considerably reduced when socioeconomic factors are considered. Even under an optimistic scenario of socio-economic development, we find that additional calories produced via sustainable irrigation by 2100 might reach only half of the maximum biophysical potential. Regions with currently modest socioeconomic development such as Sub-Saharan Africa are found to have the highest potential for improvements. In a scenario of sustainable development, Sub-Saharan Africa would be able to almost double irrigated food production and feed an additional 70 million people compared to 2020, whereas in a scenario where regional rivalry prevails, this potential would be halved. Increasing sustainable irrigation will be key for countries to meet the projected food demands, tackle malnutrition and rural poverty in the context of increasing impacts of anthropogenic climate change on food systems. Our results suggest that improving governance levels for example through enhancing the effectiveness of institutions will constitute an important leverage to increase adaptive capacity in the agricultural sector.

Bioenergy with carbon capture and storage (BECCS) is a carbon dioxide removal (CDR) solution necessary to achieve net-zero-carbon-emissions goals. While the BECCS potential from large industrial emitters has been quantified, the BECCS potential of small emitters, such as biogas facilities, has not been investigated. Moreover, most BECCS solutions rely on the expected availability of large geological storage capacity for future CDR implementation, although the deployment of CO2 transport and storage supply chains is still a barrier for geological carbon storage ambitions. An alternative opportunity for permanent sequestration of CO2 is concrete, in which captured CO2 can be permanently fixed through carbon dioxide mineralization technologies. We describe and discuss this solution by quantifying the potential of a European bioenergy with carbon capture, utilization, and storage (BECCUS) supply chain, which relies on biogenic CO2 from biogas facilities as a CO2 source, and on carbon dioxide mineralization in concrete as a permanent CO2 sink. This solution is available today, can be adopted seamlessly, and does not need economies of scale for its deployment. We find that European biogas facilities produce 24 Mtons of biogenic CO2 per year, of which 4 Mtons of CO2 per year are emitted from facilities already upgrading biogas into bio-methane. We estimate that carbon dioxide mineralization in recycled concrete aggregates in Europe could permanently store up to 8 Mtons of CO2 per year. Despite the limited storage potential, BECCUS supply chains would reduce CO2 transportation distance and system complexity compared to BECCS supply chains, and would result in a marketable product, namely concrete. Overall, carbon dioxide mineralization in recycled concrete aggregates combines carbon utilization with permanent sequestration, hence contributing to carbon-neutrality goals.

The Carnegie Planet Finder Spectrograph is being constructed for use at the Magellan Telescopes at Las Campanas Observatory in Chile. Its primary scientific objective is the detection of extrasolar planets through monitoring of stellar radial velocity variations. The spectrograph is being optimized for high precision measurement of these velocities with a resolution goal of 1 m s(-1). The optical design includes all spherical, standard optical glass and calcium fluoride lenses that function as both camera and collimator in a double-pass configuration. A prism cross-disperser is also used in double-pass and provides a minimum order separation of 4.0 arcsec. An R4 echelle grating is illuminated near true Littrow and provides complete wavelength coverage between 390 nm and 620 nm. Spectral resolution is 38,000 when using a 1 arcsec slit, although slit widths as small as 0.2 arcsec are available. An iodine cell is used to superimpose well-defined absorption features onto spectra to serve as a fiducial wavelength scale, and a thorium argon lamp is available for traditional wavelength calibrations. The spectrograph is currently under construction and is scheduled for commissioning in the second quarter of 2007.

The GMT-CfA, Carnegie, Catolica, Chicago Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has undergone conceptual design for consideration as a first light instrument at the Giant Magellan Telescope. G-CLEF has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability. We have defined the performance envelope of G-CLEF to address several of the highest science priorities in the Decadal Survey(1). The spectrograph optical design is an asymmetric, two-arm, white pupil design. The asymmetric white pupil design is adopted to minimize the size of the refractive camera lenses. The spectrograph beam is nominally 300 mm, reduced to 200 mm after dispersion by the R4 echelle grating. The peak efficiency of the spectrograph is >35% and the passband is 3500-9500 angstrom. The spectrograph is primarily fed with three sets of fibers to enable three observing modes: High-Throughput, Precision-Abundance and PRV. The respective resolving powers of these modes are R similar to 25,000, 40,000 and 120,000. We also anticipate having an R similar to 40,000 Multi-object Spectroscopy mode with a multiplex of similar to 40 fibers. In PRV mode, each of the seven 8.4m GMT primary mirror sub-apertures feeds an individual fiber, which is scrambled after pupil-slicing. The goal radial velocity precision of G-CLEF is partial derivative V < 10 cm/sec radial. In this paper, we provide a flowdown from fiducial science programs to design parameters. We discuss the optomechanical, electrical, structural and thermal design and present a roadmap to first light at the GMT.

Fiber-fed multi-object spectrographs have greatly enhanced the spectroscopic capabilities of the world's premiere telescopes, but their flexibility has typically been limited by a fixed effective slit size that constrains the available resolving power. We present a novel mechanism that, for the first time, equips a fiber-fed spectrograph with multiple discreet slits of different widths. In this paper, we detail the mechanical design of our variable slit mechanism, which is capable of positioning any one of six slits in front of the fibers immediately prior to injection into the spectrograph's optical train. Further, we present the details of related system necessary to achieve closed loop positioning of the slit mechanism given that no encoder is used. We also briefly discuss our use of open source and open hardware projects in the design. Finally, we describe the control system we have implemented for this subsystem.

The GMT-Consortium Large Earth Finder (G-CLEF) is an optical-band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose, high dispersion spectrograph that is fiber fed and capable of extremely precise radial velocity measurements. The G-CLEF Concept Design (CoD) was selected in Spring 2013. Since then, G-CLEF has undergone science requirements and instrument requirements reviews and will be the subject of a preliminary design review (PDR) in March 2015. Since CoD review (CoDR), the overall G-CLEF design has evolved significantly as we have optimized the constituent designs of the major subsystems, i.e. the fiber system, the telescope interface, the calibration system and the spectrograph itself. These modifications have been made to enhance G-CLEF's capability to address frontier science problems, as well as to respond to the evolution of the GMT itself and developments in the technical landscape. G-CLEF has been designed by applying rigorous systems engineering methodology to flow Level 1 Scientific Objectives to Level 2 Observational Requirements and thence to Level 3 and Level 4. The rigorous systems approach applied to G-CLEF establishes a well defined science requirements framework for the engineering design. By adopting this formalism, we may flexibly update and analyze the capability of G-CLEF to respond to new scientific discoveries as we move toward first light. G-CLEF will exploit numerous technological advances and features of the GMT itself to deliver an efficient, high performance instrument, e.g. exploiting the adaptive optics secondary system to increase both throughput and radial velocity measurement precision.

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph, which has been selected as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas Observatory. We designed G-CLEF as a general-purpose echelle spectrograph with a precision radial velocity (PRV) capability goal of 0.1 m/s, which will enable it to detect/measure the mass of an Earth-sized planet orbiting a Solar-type star in its habitable zone. This goal imposes challenging requirements on all aspects of the instrument and some of those are best incorporated directly into the optical design process. In this paper we describe the preliminary optical design of the G-CLEF instrument and briefly describe some novel solutions we have introduced into the asymmetric white pupil echelle configuration.

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has been selected as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas Observatory in Chile's Atacama desert region. We designed G-CLEF as a general-purpose echelle spectrograph with precision radial velocity (PRV) capability used for exoplanet detection. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec, necessary for detection of Earth-sized planets orbiting stars like our Sun in the habitable zone. This goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures. Stability in instruments of this type is typically affected by changes in temperature, orientation, and air pressure as well as vibrations caused by telescope tracking. For these reasons, we have chosen to enclose G-CLEF's spectrograph in a thermally insulated, vibration isolated vacuum chamber and place it at a gravity invariant location on GMT's azimuth platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology and budget are also significant design drivers. All of the previously listed considerations must be managed while ensuring that performance requirements are achieved.

One of the first light instruments for the Giant Magellan Telescope(1) (GMT) will be the GMT-Consortium Large Earth Finder (G-CLEF). It is an optical band echelle spectrograph that is fiber fed to enable high stability. One of the key capabilities of G-CLEF will be its extremely precise radial velocity (PRV) measurement capability. The RV precision goal is 10 cm/sec, which is expected to be achieved with advanced calibration methods and the use of the GMT adaptive optics system. G-CLEF, as part of the GMT suite of instruments, is being designed within GMT's automated requirements management system. This includes requirements flow down, traceability, error budgeting, and systems compliance. Error budgeting is being employed extensively to help manage G-CLEF technical requirements and ensure that the top level requirements are met efficiently. In this paper we discuss the G-CLEF error budgeting process, concentrating on the PRV precision and instrument throughput budgets. The PRV error budgeting process is covered in detail, as we are taking a detailed systems error budgeting approach to the PRV requirement. This has proven particularly challenging, as the precise measurement of radial velocity is a complex process, with error sources that are difficult to model and a complex calibration process that is integral to the RV measurement. The PRV budget combines traditional modeling and analysis techniques, where applicable, with semi-empirical techniques, as necessary. Extrapolation from existing PRV instruments is also used in the budgeting process.

We describe the Carnegie-Spitzer-IMACS (CSI) Survey, a wide-field, near-IR selected spectrophotometric redshift survey with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on Magellan-Baade. By defining a flux-limited sample of galaxies in Spitzer Infrared Array Camera 3.6 mu m imaging of SWIRE fields, the CSI Survey efficiently traces the stellar mass of average galaxies to z similar to 1.5. This first paper provides an overview of the survey selection, observations, processing of the photometry and spectrophotometry. We also describe the processing of the data: new methods of fitting synthetic templates of spectral energy distributions are used to derive redshifts, stellar masses, emission line luminosities, and coarse information on recent star formation. Our unique methodology for analyzing low-dispersion spectra taken with multilayer prisms in IMACS, combined with panchromatic photometry from the ultraviolet to the IR, has yielded high-quality redshifts for 43,347 galaxies in our first 5.3 deg(2) of the SWIREXMM-LSS field. We use three different approaches to estimate our redshift errors and find robust agreement. Over the full range of 3.6 mu m fluxes of our selection, we find typical redshift uncertainties of sigma(z)/(1 + z) less than or similar to 0.015. In comparisons with previously published spectroscopic redshifts we find scatters of sigma z/(1 + z) = 0.011 for galaxies at 0.7 <= z <= 0.9, and sigma z/(1 + z) = 0.014 for galaxies at 0.9 <= z <= 1.2. For galaxies brighter and fainter than i = 23 mag, we find sigma z/(1 + z) = 0.008 and sigma z/(1 + z) = 0.022, respectively. Notably, our low-dispersion spectroscopy and analysis yields comparable redshift uncertainties and success rates for both red and blue galaxies, largely eliminating color-based systematics that can seriously bias observed dependencies of galaxy evolution on environment.