Nuclear Wastes in the Arctic Ocean. the Consequences of Past Dumping and Opportunities for Future Prevention

The view is expressed that the assessment of disposal of nuclear waste in the ocean (specifically the Arctic and Kara Seas) is critical to understanding Arctic pollution. Much needs to be done in deciding what we should do, even though many wastes are long-standing and persistent. in 1993, disclosures about Russian dumping of submarine nuclear reactors, nuclear fuel, and other radioactive wastes into the Arctic Ocean brought this region and its problems into the world spotlight and raised public concerns about the resulting health and environmental risks. As a result of this concern, the Congressional Office of Technology Assessment published a 1995 study, Nuclear Wastes in the Arctic (US Congress Office of Technology Assessment, 1995). This paper summarises and updates that study.     

Disposal of Mine Wastes Containing Pb and Zn Near the Ocean: An Assessment of Associated Environmental Implications in the Arctic

The past two decades have witnessed an increase in the exploration for, and development of, mineral resources at Arctic latitudes. Such effort has resulted in the commencement of production at a number of different localities in close proximity to the ocean. Since proximity to a source of transportation for the conveyance of concentrates to the market is a primary requirement governing the economic decisions for the mine to proceed, it is logical that ore deposits near a coastline are primary targets for development.

Closely tied to coastal mining developments is the need to dispose of tailings and waste rock in the most economical manner. Prior to the advent of heightened public awareness and environmental concern, and the enactment of pollution legislation, disposal practices were largely based upon convenience. Currently, however, proposed disposal and operating practices receive closer scrutiny, with a view to providing adequate protection for aquatic resources and habitat. This paper summarizes some of the features of three Arctic mines, wastes from which enter the marine environment, and compares the disposal practices used at each to measures of environmental change as indicated by metal concentrations in various media.     

武汉市“三废”排放的库兹涅茨特征及原因探析

通过分析武汉市1985-2001年近16年的“三废”排放量变化情况，发现武汉市“三废”的排放总量在波动中呈现上升趋势，但各类排放的时间规律相差明显。建立模型，将其人均GDP与“三废”排放的标准化值进行拟合，其计算结果显示：武汉市“三废”排放与人均GDP之间存在比较明显的三次曲线特征，在1985-1994年曲线呈持续下降趋势，而1995-2001年曲线初步显现出标准的环境库兹涅茨曲线。理论计算表明：武汉市“三废”排放的环境库兹涅茨曲线的转折点为人均GDP为12338．46元左右。通过环境经济学分析发现武汉市的经济发展、产业结构变动、能源结构变动和环境政策等4项因素是武汉市出现非标准环境库兹涅茨曲线的主要原因。     

Die Organisation der Früherkennung von Umweltproblemen im Rahmen der wissenschaftlichen Beratung der Umweltpolitik

This study is based on the theses that

1. early diagnosis is indispensable for the management of environmental problems in the context of precautionary policy, which have the character of a “creeping disaster” and that
2. the public must play the active role that is adequate within a democratic society.

In the context of the study, three existing advisory committees for environmental policy as well as two concepts which have not been put into effect are investigated. In the second part of the study the concepts and the working method of the three existing advisory committees are portrayed: the Council of Experts for Environmental Questions (SRU), the German Advisory Council on Global Change (WBGU), and the Office of Technology Assessment of the Federal Parliament (TAB). In part I, the concept of the Picht commission from 1972, which has never been implemented in this form was introduced. Part III deals with the critique of these committees and with an alternative concept of early diagnosis which has not yet been put into effect. In part IV, the work of the oldest of the committees, the SRU, is examined with respect to the three most important environmental problems of the last 15 years.     

Resource-associated divergence in the arctic marine amphipod<Emphasis Type="Italic"> Paramphithoe hystrix</Emphasis>

Host specialization has played an important role in the speciation of groups such as herbivorous insects and parasitic invertebrates. In this study, we provide evidence for its role in the diversification of the amphipod Paramphithoe hystrix Ross 1835 in Arctic marine waters. This species lives and feeds on the tissues of varied invertebrate hosts that are much larger than itself, including poriferans, hydrozoans and echinoderms, acting as a 'micropredator'. We examined the genetic structure of P. hystrix at sites in the Canadian Arctic where it is represented by a white form found on the light-coloured sea star Solaster endeca, a red form on the pink soft coral Gersemia rubriformis and by a spotted form with an unidentified host. These phenotypes occur in microallopatry, sometimes occupying alternate hosts just a few metres apart. Although their variation in host associates might have arisen from ingested host tissue, our results indicate that these morphs are genetically distinct. Mitochondrial (cytochrome c oxidase I) and nuclear (28S ribosomal RNA) gene sequences, as well as allozyme data all show strong genetic divergence between the three colour morphs, demonstrating their reproductive isolation. These results suggest that P. hystrix is a complex of at least three species, which may have arisen as a result of disruptive selection following host switches. Moreover, the depths of genetic divergence indicate that diversification of this complex was complete prior to the Pleistocene.Communicated by R.J. Thompson, St. John's     

Structural confirmation of the sea ice biomarker IP25 found in Arctic marine sediments

IP₂₅ is a highly branched isoprenoid and an organic geochemical biomarker that is produced by some Arctic sea ice diatoms. IP₂₅ has previously been used in Arctic palaeo sea ice reconstruction studies and as a tracer for studying Arctic food webs. Here, the molecular structure of IP₂₅ has been confirmed by ¹H and ¹³C NMR spectroscopy following large-scale extraction from marine sediments obtained from the Canadian Arctic and purification using a combination of open-column and HPLC chromatographic methods. The structure of IP₂₅ was consistent between the three different sampling locations and was identical to that found previously for this biomarker following synthesis from a closely related highly branched isoprenoid diene. Since this study represents the first structural characterisation of IP₂₅ in sediments, future analysis of sedimentary IP₂₅ for palaeo Arctic sea ice reconstructions can be carried out with much greater confidence.     

Schadstoff-Ferntransport in die Arktis

The Arctic is still considered as one of the few unpolluted regions in the world. This is true if one compares the Arctic region with middle latitude regions which are influenced more by human activities. However, the Arctic region is not isolated from all human impacts. In recent years, high concentrations of persistent pollutants (organic chemicals, metals) were detected in top predators of the Arctic food chain and indigenous peoples from the Canadian and Greenland Arctic, although no local contamination sources are known. The comprehensive, scientific investigation of the past 20 years confirmed that the combination of atmospheric and waterborne long-range transport is the major source of the high concentrations of persistent organic pollutants (POPs) in the pristine Arctic environment. However, also pelagic marine organisms (e.g. Atlantic cod, marine mammals) can transport large amounts of persistent pollutants in their lipids and introduce contaminants into the Arctic food web. Thus, the pollutants are transported into the Arctic and subsequently accumulated through the short and unbranched Arctic food web of the top predators. The most accepted theory nowadays describes the long-range transport of persistent pollutants as a combination of atmospheric and sea current transport, or as a ‘global distillation’ process. Depending on such physical properties of the substances as vapour pressure and the ambient tempeature, persistent (semivolatile) contaminants are transported over different distances prior to deposition (sea surface, sediment, soil). After the deposition, however, and depending on the weather conditions and surrounding temperature, persistent pollutants will be re-evaporated into the atmosphere and undergo further atmospheric transport to the Arctic region. This process is also called the ‘grasshopper effect’. The global transport of persistent pollutants into Arctic regions can be described as a repeatedly occurring combination of atmospheric and waterborne transport in which the main transport vehicle depends on the physical properties of the transported compound. The role of characteristic meteorological conditions in the respective climate zones through which the contaminant is transported must not be underestimated. Strong seasonal differences in temperature and precipitation rule the global weather situation. Therefore, seasonal pattern differences occur for the distribution of some persistent pollutants in the Arctic environment depending on average temperature, main wind and sea current directions, humidity and day time light conditions (causing photochemical degradation). The consumption of traditionally hunted marine mammals (seals, whales) was identified as one of the main reasons for high contamination burdens in the Canadian and Greenland Inuit populations. Consequences and counter measures against high contamination loads in the Arctic human populations and ecosystems are currently under discussion. However, no comprehensive measures concerning restrictions of hunting traditions are taken by the respective governments to date due to the primary social consequences which are to be expected. The advising experts argue that such a restriction would destroy the original social structures of the Inuit populations. Therefore, the drawbacks of such a hunting restriction would weigh heavier than the expected positive effects of the reduction of contaminant burdens ‘Arctic dilemma’.     

The ties that bind: Inter-clonal cooperation may help a fragile coral dominate shallow high-energy reefs

In Belize, shallow fore-reef buttresses are dominated byAgaricia tenuifolia Dana. The ecological importance of this fragile coral in such a high-energy environment may be explained in part by an unusual cooperative interaction between adjacent clones ofA. tenuifolia. The shallow buttresses are often composed primarily of many clones ofA. tenuifolia growing in close proximity. Surveys conducted at Carrie Bow Cay, Belize, in 1986 and 1987 showed that intraspecific contacts between different clones are common and occur far more frequently than interspecific encounters with other sessile taxa. In contrast to many other corals, contacts between non-clonemates ofA. tenuifolia do not result in competitive interactions, tissue bleaching or death, or significantly altered patterns of colony growth. Instead, inter-clonal contact stimulates localized morphological changes in the skeletons of both corals directly beneath the contact interface, which tend to anchor the two corals against each other, making them more resistant to breakage and detachment. By mechanically stabilizing clusters of otherwise fragile corals, these cooperative interactions potentially enhance the long-term survivorship and hence the fitness of interactingA. tenuifolia clones.The views expressed here are those of the author and do not necessarily reflect those of the Office of Technology Assessment     

Bioremediation of toxic metals mercury and cesium using three types of biosorbent: bacterial exopolymer,gall nut,and oak fruit particles

Cesium and mercury are two mono-valent elements which can be found in toxic industrial, medical, and nuclear wastes. Their presence in the environment has deleterious effects on the ecosystem, living organisms including humans. Due to the chemical nature of these metals, bioremediation by conventional methods is more difficult to achieve compared to other metals. In this study, we used three biosorbents (oak powder, gall nut, and bacterial exopolymer) for the bioremediation of Hg and Cs. Bio-polymer was produced in the GMS mineral broth. Synthetic wastes of Hg(NO₃)₂ and isotope Cs-133 as the single-metal solutions were used. The biorefining process was carried out in glass columns, made of Pyrex, with dimensions 20?×?7/2?cm² with a V-shaped bottom. The samples were analyzed using atomic absorption. The experimental results showed that eliminated metal percent by oak powder, gall nut, and bacterial exopolymer were, respectively, of 94.8%, 96%, and 13.8% for Hg and 7.8%, 4.4%, and 69.4% for Cs. The tests revealed that Ca⁺⁺, when used as flocculant, played a key role in both biosorption and bio-precipitation rates. Consequently, it was concluded that the investigated biosorbents could be use as an integrated biosorption system for the refinement of mixed wastes.     

Fractionation and speciation of arsenic in fresh and combusted coal wastes from Yangquan, northern China

In this study, the content and speciation of arsenic in coal waste and gas condensates from coal waste fires were investigated, respectively, using the digestion and sequential extraction methods. The fresh and fired-coal waste samples were collected from Yangquan, which is one of the major coal production regions in northern China. High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) was used to determine the concentrations of four major arsenic species [As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA)] in the extracts, while ICP-MS was used to measure total As content. Arsenic content in the investigated coal wastes and the condensate ranges between 23.3 and 69.3 mg/kg, which are higher than its reported average content in soils. Arsenic in coal waste exists primarily in the residual fraction; this is followed in decreasing order by the organic matter-bound, Fe–Mn oxides-bound, exchangeable, carbonates-bound, and water-soluble fractions. The high content of arsenic in the condensates indicates that combustion or spontaneous combustion is one of the major ways for arsenic release into the environment from coal waste. About 15% of the arsenic in the condensate sample is labile and can release into the environment under leaching processes. The water extractable arsenic (WEA) in the fresh coal waste, fired coal wastes, and the condensate varied between 14.6 and 341 μg/kg, with As(V) as the major species. Furthermore, both MMA and DMA were found in fresh coal wastes, fired coal wastes, and the condensate.     

Hazardous waste management in educational and research centers: a case study

The hazardous waste management (HWM) practice at Tehran University of Medical Sciences Central Campus, Iran, was investigated in this study. Four schools were selected and the required information such as type and amount of wastes, temporary storage methods, waste discharge frequency, and final waste disposal methods using sampling, questionnaires, interviews with laboratory staff, and reference to available documents were gathered. The quantity of hazardous waste generation per year excluding the uncontrolled wastewater was found to be 2.072 tons per year. The obtained results show that wastes having features of being infectious, toxic, ignitable, carcinogenic, corrosive, and reactive were present at 32%, 28%, 16%, 14%, 8%, and 2%, respectively. In the central campus, hazardous solid wastes managed with household solid wastes and hazardous liquid waste were discharged into the sinks without any kind of control; improper HWM practices are evident from the point of waste production to final disposal.     

Bioluminescence in the high Arctic during the polar night

This study examines the composition and activity of the planktonic community during the polar night in the high Arctic Kongsfjord, Svalbard. Our results are the first published evidence of bioluminescence among zooplankton during the Arctic polar night. The observations were collected by a bathyphotometer detecting bioluminescence, integrated into an autonomous underwater vehicle, to determine the concentration and intensity of bioluminescent flashes as a function of time of day and depth. To further understand community dynamics and composition, plankton nets were used to collect organisms passing through the bathyphotometer along with traditional vertical net tows. Additionally, using a moored bathyphotometer closed to the sampling site, the bioluminescence potential itself was shown not to have a diurnal or circadian rhythm. Rather, our results provide evidence for a diel vertical migration of bioluminescent zooplankton that does not correspond to any externally detectable changes in illumination.     

Simulating transport of 129I and idealized tracers in the northern North Atlantic Ocean

Transport of the radioactive tracer Iodine-129 (¹²⁹I, T _1/2 = 15.7 Myr) in the northern North Atlantic Ocean has been investigated using a global isopycnic Ocean General Circulation Model (OGCM) and observed data. ¹²⁹I originates mainly from the nuclear fuel reprocessing plants in Sellafield (UK) and La Hague (France), and is transported northwards along the Norwegian coast, and then into surface and intermediate layers in the Arctic Ocean through the Barents Sea and the Fram Strait, but also partly recirculating south along the eastern coast of Greenland. In the North Atlantic Subpolar Seas, ¹²⁹I is mainly found in dense overflow waters from the Nordic Seas being exported southwards in the Deep Western Boundary Current, and to a lesser extent in surface and intermediate layers circulating cyclonically within the Subpolar Gyre. Observed concentration of ¹²⁹I along a surface transect in the eastern Nordic Seas in 2001 is captured by the OGCM, while in the Nansen Basin of the Arctic Ocean the OGCM overestimates the observed values by a factor of two. The vertical profile of ¹²⁹I in the Labrador Sea, repeatedly observed since 1997 to present, is fairly realistically reproduced by the OGCM. This indicates that the applied model system has potential for predicting the magnitude and depth of overflow waters from the Nordic Seas into the North Atlantic Subpolar Seas. To supplement the information obtained from the ¹²⁹I distribution, we have conducted a number of idealized tracer experiments with the OGCM, including tracers mimicking pure water masses, and instantaneous pulse releases. New insight into time-scales of tracer transport in this region is obtained by utilizing a few recently developed methods based on the theory of Transit Time Distribution (TTD) and age of tracers. Implications for other types of “anomalies” in the northern North Atlantic Ocean, being anomalous hydrography or chemical tracers, and how they are interpreted, are discussed.     

Live discrimination of Calanus glacialis and C. finmarchicus females: can we trust phenological differences?

Two key players in the Arctic and subarctic marine ecosystem are the calanoid copepods, Calanus finmarchicus and C. glacialis. Although morphologically very similar, these sibling species have different life cycles and roles in the Arctic pelagic marine ecosystem. Considering that the distribution of C. glacialis corresponds to Arctic water masses and C. finmarchicus to Atlantic water masses, the species are frequently used as climate indicators. Consequently, correct identification of the two species is essential if we want to understand climate-impacted changes on Calanus-dominated marine ecosystems such as the Arctic. Here, we present a novel morphological character (redness) to distinguish live females of C. glacialis and C. finmarchicus and compare it to morphological (prosome length) and genetic identification. The characters are tested on 300 live females of C. glacialis and C. finmarchicus from Disko Bay, western Greenland. Our analysis confirms that length cannot be used as a stand-alone criterion for separation. The results based on the new morphological character were verified genetically using a single mitochondrial marker (16S) and nuclear loci (six microsatellites and 12 InDels). The pigmentation criterion was also used on individuals (n = 89) from Young Sound fjord, northeast Greenland to determine whether the technique was viable in different geographical locations. Genetic markers based on mitochondrial and nuclear loci were corroborative in their identification of individuals and revealed no hybrids. Molecular identification confirmed that live females of the two species from Greenlandic waters, both East and West, can easily be separated by the red pigmentation of the antenna and somites of C. glacialis in contrast to the pale opaque antenna and somites of C. finmarchicus, confirming that the pigmentation criterion is valid for separation of the two species.     

The Reuse of Urban and Industrial Waste in Tai-Lin-Pu Reclamation Project, Taiwan

This study introduces the principles of KMG's (Kaoshiung Municipal Government) dealing with the non-poisonous urban and industrial waste through reclamation of shore land in reinforcing a sense of coastal protection and land development in Tai-Lin-Pu coastal area, southern Taiwan.

Through a series of experimental studies, we found that substitutes of coarse aggregate with a broad spectrum of integrating slag powder, fly ash, and cementitious material can be obtained with a benefit up to 80% saving of cement. the integrated aggregates from the non-poisonous industrial wastes were subsequently made into armour units and used in the field tests at Tai-Lin-Pu coastal area, where the shorelines are seriously eroded. After being subjected to several severe typhoon advents, the results showed that the waste-made units used as the protection breakwater, together with construction wastes and excavated soil as the filling material, prove to be an effective practice in utilizing recycled urban waste to reclaim erosive shore lands. Moreover, this study also demonstrates that through detailed analysis of the waste characteristics, scrap material could be turned into valuable construction aggregates, and highlights the value of non-poisonous urban and industrial waste as a alternative resource for the shore protection engineering.     

Untersuchung von Abfällen mit biologischen Testverfahren zur Bewertung der Wassergefährdung

Wastes from three different types of waste treatment facilities were examined with bioassays to determine their hazard potential to waters (→Part I). All examined wastes showed toxic effects and have to be classified as hazardous to waters according to section 19g of the German Federal Water Management Act. The toxicity is probably caused by heavy metals in the leachates, especially copper. An evaluation pattern to classify wastes in the German system of Water Hazard Classes is presented. According to this proposal, a classification of the examined wastes into Water Hazard Class 1 seems to be appropriate. This classification does not describe the hazards resulting from the regular disposal on a landfill or from the utilisation of the treated wastes.     

Flexible incubation rhythm in northern fulmars: a comparison between oceanographic zones

Variation in the timing and abundance of marine food resources is known to affect the breeding behaviour of many seabirds, constraining our understanding of the extent to which these behaviours vary in different parts of a species’ range. We studied incubation shifts of northern fulmars (Fulmarus glacialis) breeding at two colonies in Arctic Canada (High Arctic oceanographic zone) and one colony in the UK (Boreal oceanographic zone) between 2001 and 2005. Fulmars in Arctic Canada had longer incubation shifts than previously reported at more southern colonies, presumably because marine productivity is lower early in the breeding season in the Arctic. Shift durations were particularly long at one colony in years with abnormally late, extensive sea-ice cover, although at the other Arctic colony, where sea-ice cover is predictably late every year, the duration of shifts was shorter than expected. At the Boreal colony, incubation shifts were much longer than expected, similar to Arctic colonies, and likely attributable to poor marine food supplies in the North Sea in recent years. Collectively, our data suggest that fulmars can adjust their incubation rhythm to compensate for poor marine feeding conditions, although this may incur a cost to body condition or reproductive success.     

Habitat type determines herbivory controls over CO2 fluxes in a warmer Arctic

High-latitude ecosystems store large amounts of carbon (C); however, the C storage of these ecosystems is under threat from both climate warming and increased levels of herbivory. In this study we examined the combined role of herbivores and climate warming as drivers of CO2 fluxes in two typical high-latitude habitats (mesic heath and wet meadow). We hypothesized that both herbivory and climate warming would reduce the C sink strength of Arctic tundra through their combined effects on plant biomass and gross ecosystem photosynthesis and on decomposition rates and the abiotic environment. To test this hypothesis we employed experimental warming (via International Tundra Experiment [ITEX] chambers) and grazing (via captive Barnacle Geese) in a three-year factorial field experiment. Ecosystem CO2 fluxes (net ecosystem exchange of CO2, ecosystem respiration, and gross ecosystem photosynthesis) were measured in all treatments at varying intensity over the three growing seasons to capture the impact of the treatments on a range of temporal scales (diurnal, seasonal, and interannual). Grazing and warming treatments had markedly different effects on CO2 fluxes in the two tundra habitats. Grazing caused a strong reduction in CO2 assimilation in the wet meadow, while warming reduced CO2 efflux from the mesic heath. Treatment effects on net ecosystem exchange largely derived from the modification of gross ecosystem photosynthesis rather than ecosystem respiration. In this study we have demonstrated that on the habitat scale, grazing by geese is a strong driver of net ecosystem exchange of CO2, with the potential to reduce the CO2 sink strength of Arctic ecosystems. Our results highlight that the large reduction in plant biomass due to goose grazing in the Arctic noted in several studies can alter the C balance of wet tundra ecosystems. We conclude that herbivory will modulate direct climate warming responses of Arctic tundra with implications for the ecosystem C balance; however, the magnitude and direction of the response will be habitat-specific.     

Temperature effects on accumulation and retention of radionuclides in the sea star,Asterias forbesi: implications for contaminated northern waters

Radioactive waste disposal and nuclear testing concentrated in high latitudes in the northern hemisphere have resulted in the accumulation of radionuclides in Arctic marine ecosystems, but little is known of the consequences for marine biota in these waters. Under controlled laboratory conditions in May through September 1994, we examined the bioaccumulation in sea stars, Asterias forbesi (Desor), or the radionuclides ²⁴¹Am, ⁵⁷Co and ¹³⁷Cs, all of which are important components of disposed radioactive wastes. Experiments at 2 and 12°C determined the relative importance of food (the bivalve, Macoma balthica) and water as sources of radionuclides and assessed the influence of temperature on radionuclide influx and efflux rates. The lower temperature greatly increased the retention of radionuclides ingested with food; for instance, the biological half-life (tb _1/2) of ²⁴¹Am in the sea stars was 31 d at 12°C, but was virtually infinite at 2°C. Retention of ingested ⁵⁷Co was also increased at 2°C (tb _1/2=41 d). ¹³⁷Cs was not accumulated from food. Low temperature significantly reduced net influx rates of ¹³⁷Cs from water, but did not affect net uptake of ²⁴¹Am or ⁵⁷Co. Temperature had little effect on the retention of all three isotopes obtained from the dissolved phase. These experiments suggest that extrapolation of results of previous radioecological studies, conducted at warmer temperatures, to polar or temperate winter environments may be problematic, and that nuclear waste isotopes obtained through trophic transfer may be retained far more efficiently in high latitude marine biota than by fauna from warmer ecosystems.     

Assessing the carbon balance of circumpolar Arctic tundra using remote sensing and process modeling.

This paper reviews the current status of using remote sensing and process-based modeling approaches to assess the contemporary and future circumpolar carbon balance of Arctic tundra, including the exchange of both carbon dioxide and methane with the atmosphere. Analyses based on remote sensing approaches that use a 20-year data record of satellite data indicate that tundra is greening in the Arctic, suggesting an increase in photosynthetic activity and net primary production. Modeling studies generally simulate a small net carbon sink for the distribution of Arctic tundra, a result that is within the uncertainty range of field-based estimates of net carbon exchange. Applications of process-based approaches for scenarios of future climate change generally indicate net carbon sequestration in Arctic tundra as enhanced vegetation production exceeds simulated increases in decomposition. However, methane emissions are likely to increase dramatically, in response to rising soil temperatures, over the next century. Key uncertainties in the response of Arctic ecosystems to climate change include uncertainties in future fire regimes and uncertainties relating to changes in the soil environment. These include the response of soil decomposition and respiration to warming and deepening of the soil active layer, uncertainties in precipitation and potential soil drying, and distribution of wetlands. While there are numerous uncertainties in the projections of process-based models, they generally indicate that Arctic tundra will be a small sink for carbon over the next century and that methane emissions will increase considerably, which implies that exchange of greenhouse gases between the atmosphere and Arctic tundra ecosystems is likely to contribute to climate warming.