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Mountains and high elevation regions are often viewed as climate change “hotspots” which are responding particularly rapid to global climate forcing and may anticipate or amplify what is occurring elsewhere. Accelerating mountain climate change has widespread impacts ranging from an enhanced loss of snow and ice, through impacts on the hydrological regimes, to changes in ecological zonation as species move uphill. We examine global evidence for elevation contrasts in temperature trends (also known as elevation-dependent warming, EDW) and precipitation changes. We performed a meta-analysis of existing studies, which used in-situ station temperature and precipitation data from mountain regions as reported by the IPCC, and we analysed global gridded datasets (observations, reanalyses and model hindcasts). In both cases, we examined the elevation dependency of temperature and precipitation changes since 1900. The meta-analysis indicates that studies using pairs of station groups (in mountains and nearby low elevation areas) show a tendency towards enhanced warming at higher elevations. However, when all past studies of observations are combined globally, no systematic difference in warming rates for high vs. low elevation groups is found. Thus, on a global scale, local and regional features may obscure EDW. Precipitation changes in mountain areas based on station data are inconsistent, and a global elevational gradient in precipitation trends does not emerge. Gridded datasets (CRU, GISTEMP, GPCC, ERA5, CMIP5) show increased warming rates at higher elevations in specific regions (e.g. Andes for CMIP5 and Greater Alpine Region for ERA5), but again, there is no universal amplification of warming in mountains. The agreement between datasets is weak for temperature. Changes in precipitation show a tendency towards weaker (stronger) increase at higher (lower) elevations, especially in mid-latitudes. This means that the orographic effect may be weakening on a global scale, which may be a result of both thermodynamics and changes in atmospheric circulation.

Changing climate and human demographics in the world's mountains will have increasingly profound environmental and societal consequences across all elevations. Quantifying current human populations in and near mountains is crucial to ensure that any interventions in these complex social-ecological systems are appropriately resourced, and that valuable ecosystems are effectively protected. However, comprehensive and reproducible analyses on this subject are lacking. Here, we develop and implement an open workflow to quantify the sensitivity of mountain population estimates over recent decades, both globally and for several sets of relevant reporting regions, to alternative input dataset combinations. Relationships between mean population density and several potential environmental covariates are also explored across elevational bands within individual mountain regions (i.e. "sub-mountain range scale"). Globally, mountain population estimates vary greatly-from 0.344 billion (5% of the corresponding global total) to 2.289 billion (31%) in 2015. A more detailed analysis using one of the population datasets (GHS-POP) revealed that in ∼35% of mountain sub-regions, population increased at least twofold over the 40-year period 1975-2015. The urban proportion of the total mountain population in 2015 ranged from 6% to 39%, depending on the combination of population and urban extent datasets used. At sub-mountain range scale, population density was found to be more strongly associated with climatic than with topographic and protected-area variables, and these relationships appear to have strengthened slightly over time. Such insights may contribute to improved predictions of future mountain population distributions under scenarios of future climatic and demographic change. Overall, our work emphasizes that irrespective of data choices, substantial human populations are likely to be directly affected by-and themselves affect-mountainous environmental and ecological change. It thereby further underlines the urgency with which the multitudinous challenges concerning the interactions between mountain climate and human societies under change must be tackled.

Numerous applications, including generating future predictions via numerical modelling, establishing appropriate policy instruments, and effectively tracking progress against them, require the multitude of complex processes and interactions operating in rapidly changing mountainous environmental systems to be well monitored and understood. At present, however, not only are environmental available data pertaining to mountains often severely limited, but interdisciplinary consensus regarding which variables should be considered absolute observation priorities remains lacking. In this context, the concept of so-called Essential Mountain Climate Variables (EMCVs) is introduced as a potential means to identify critical observation priorities and thereby ameliorate the situation. Following a brief overview of the most critical aspects of ongoing and expected future climate-driven change in various key mountain system components (i.e. the atmosphere, cryosphere, biosphere and hydrosphere), a preliminary list of corresponding potential EMCVs – ranked according to perceived importance – is proposed. Interestingly, several of these variables do not currently feature amongst the globally relevant Essential Climate Variables (ECVs) curated by GCOS, suggesting this mountain-specific approach is indeed well justified. Thereafter, both established and emerging possibilities to measure, generate, and apply EMCVs are summarised. Finally, future activities that must be undertaken if the concept is eventually to be formalized and widely applied are recommended.

Summary The numerous processes implicated in the rapid and profound climate-driven changes that are underway across the world's mountains must be well monitored, understood, and—as far as possible—accurately projected. However, not only are the available environmental data upon which such activities hinge often severely limited, but interdisciplinary consensus regarding which variables should be considered observation priorities also remains elusive. Here, the concept of Essential Mountain Climate Variables (EMCVs) is introduced as a potential means of ameliorating the situation. After a review of climate-driven environmental change in mountains, a preliminary set of corresponding EMCVs is proposed. Variables pertaining to several disciplines naturally feature prominently. In addition, several are not currently considered to hold broader global relevance, which justifies our mountain-specific approach. Established and emerging possibilities to measure, generate, and apply EMCVs are then summarized. Finally, future activities toward the concept’s formalization are recommended. Ultimately, the approach hopes to increase the utility of mountainous environmental data to both fundamental science and decision making related to environmental management, risk mitigation, and adaptation.

Abstract The Heidrun TLP drilling riser system has been designed and fabricated using a titanium alloy for the riser pipe body arid flanges, the booster line and the fasteners. This is the first use of this material in this application. The process described in this paper includes several engineering stages, a materials qualification and testing stage and the fabrication stage, all of which took place over a four and one half year period. The use of titanium for the riser allowed the optimization of associated components of the system; the tensionless, the sub sea wellhead and drilling connector and the surface handling systems which resulted in considerable weight and cost savings to the Heidrun Project. At the time of this writing the riser has not been used in service from the TLP, but has been used in both factory acceptance testing of the various components and through an extensive system integration testing program which involved both surface and sub sea trials. This paper describes these processes and highlights several design innovations and key leanings about the use of titanium in an offshore drilling environment. Introduction The Heidrun field was discovered in 1985 and is located in the Norwegian continental shelf, blocks 6507/7 and 6507/8 of the Haltenbenken area. These blocks were awarded to the operators, Conoco Norway Inc. and Statoil in 1984 and 1986, respectively, in the license rounds for production licenses numbers 095 and 124. The Tension Leg Platform (TLP) location is 65 19'33" North, 0719'03" East in a mean water depth of 1132 ft. (345 m) re. Figure 1. The Heidrun field consists of three main producing reservoirs with total estimated recoverable oil reserves of more than 750 million barrels (120 million m') and around 1,800 billion standard cubic feet (50 billion Sm') of gas. The Heidrun Field is currently the most northerly development on the Norwegian continental shelf and weather conditions are extremely hostile. During design and development of the Heidrun TLP, Conoco Norway Inc. utilized previous experience and expertise gained from the Hutton TLP in the UK sector, located in a water depth of 482 ft, (147m) and the worlds first TLP, and the Jolliet Tension Leg Wellhead Platform (TLWP) in the Gulf of Mexico, located in a water depth of 1759 R. (536m). The Heidrun TLP is the worlds first concrete TLP and has a total displacement of 290,621 T. The Heidrun drilling and production template has 56 well slots, 8 export-import riser tie-in porches, 8 dual-purpose slots, measures 176 × 125 × 20 fl. (51 × 38 × 6m) and weighs 2290 tones, re. Figures 2 and 3. Well slots are positioned at 9.84 ft. (3m) centers minimum and the overall system is designed for simultaneous drilling and production. Ten TLP wells were pre-drilled and partially completed prior to installation of the TLP, the drilling of the remaining 46 wells requires a high pressure drilling riser and are being performed subsequent to the TLP installation. The 7" (177.8 mm) well completions are performed through the 10-3/4" (273 mm) OD production riser.