Linkages among climate change,crop yields and Mexico–US cross-border migration

Climate change is expected to cause mass human migration, including immigration across international borders. This study quantitatively examines the linkages among variations in climate, agricultural yields, and people''s migration responses by using an instrumental variables approach. Our method allows us to identify the relationship between crop yields and migration without explicitly controlling for all other confounding factors. Using state-level data from Mexico, we find a significant effect of climate-driven changes in crop yields on the rate of emigration to the United States. The estimated semielasticity of emigration with respect to crop yields is approximately −0.2, i.e., a 10% reduction in crop yields would lead an additional 2% of the population to emigrate. We then use the estimated semielasticity to explore the potential magnitude of future emigration. Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant, by approximately the year 2080, climate change is estimated to induce 1.4 to 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15–65 y) to emigrate as a result of declines in agricultural productivity alone. Although the results cannot be mechanically extrapolated to other areas and time periods, our findings are significant from a global perspective given that many regions, especially developing countries, are expected to experience significant declines in agricultural yields as a result of projected warming.     

Expert judgments about transient climate response to alternative future trajectories of radiative forcing

There is uncertainty about the response of the climate system to future trajectories of radiative forcing. To quantify this uncertainty we conducted face-to-face interviews with 14 leading climate scientists, using formal methods of expert elicitation. We structured the interviews around three scenarios of radiative forcing stabilizing at different levels. All experts ranked “cloud radiative feedbacks” as contributing most to their uncertainty about future global mean temperature change, irrespective of the specified level of radiative forcing. The experts disagreed about the relative contribution of other physical processes to their uncertainty about future temperature change. For a forcing trajectory that stabilized at 7 Wm^-2 in 2200, 13 of the 14 experts judged the probability that the climate system would undergo, or be irrevocably committed to, a “basic state change” as ≥0.5. The width and median values of the probability distributions elicited from the different experts for future global mean temperature change under the specified forcing trajectories vary considerably. Even for a moderate increase in forcing by the year 2050, the medians of the elicited distributions of temperature change relative to 2000 range from 0.8–1.8 °C, and some of the interquartile ranges do not overlap. Ten of the 14 experts estimated that the probability that equilibrium climate sensitivity exceeds 4.5 °C is > 0.17, our interpretation of the upper limit of the “likely” range given by the Intergovernmental Panel on Climate Change. Finally, most experts anticipated that over the next 20 years research will be able to achieve only modest reductions in their degree of uncertainty.     

Nonlinear response of summer temperature to Holocene insolation forcing in Alaska

Regional climate responses to large-scale forcings, such as precessional changes in solar irradiation and increases in anthropogenic greenhouse gases, may be nonlinear as a result of complex interactions among earth system components. Such nonlinear behaviors constitute a major source of climate “surprises” with important socioeconomic and ecological implications. Paleorecords are key for elucidating patterns and mechanisms of nonlinear responses to radiative forcing, but their utility has been greatly limited by the paucity of quantitative temperature reconstructions. Here we present Holocene July temperature reconstructions on the basis of midge analysis of sediment cores from three Alaskan lakes. Results show that summer temperatures during 10,000–5,500 calibrated years (cal) B.P. were generally lower than modern and that peak summer temperatures around 5,000 were followed by a decreasing trend toward the present. These patterns stand in stark contrast with the trend of precessional insolation, which decreased by ∼10% from 10,000 y ago to the present. Cool summers before 5,500 cal B.P. coincided with extensive summer ice cover in the western Arctic Ocean, persistence of a positive phase of the Arctic Oscillation, predominantly La Niña-like conditions, and variation in the position of the Alaskan treeline. These results illustrate nonlinear responses of summer temperatures to Holocene insolation radiative forcing in the Alaskan sub-Arctic, possibly because of state changes in the Arctic Oscillation and El Niño-Southern Oscillation and associated land–atmosphere–ocean feedbacks.     

From the Cover: Species distributions in response to individual soil nutrients and seasonal drought across a community of tropical trees

Tropical forest vegetation is shaped by climate and by soil, but understanding how the distributions of individual tree species respond to specific resources has been hindered by high diversity and consequent rarity. To study species over an entire community, we surveyed trees and measured soil chemistry across climatic and geological gradients in central Panama and then used a unique hierarchical model of species occurrence as a function of rainfall and soil chemistry to circumvent analytical difficulties posed by rare species. The results are a quantitative assessment of the responses of 550 tree species to eight environmental factors, providing a measure of the importance of each factor across the entire tree community. Dry-season intensity and soil phosphorus were the strongest predictors, each affecting the distribution of more than half of the species. Although we anticipated clear-cut responses to dry-season intensity, the finding that many species have pronounced associations with either high or low phosphorus reveals a previously unquantified role for this nutrient in limiting tropical tree distributions. The results provide the data necessary for understanding distributional limits of tree species and predicting future changes in forest composition.     

Soil metabolome response to whole-ecosystem warming at the Spruce and Peatland Responses under Changing Environments experiment

In this study, a suite of complementary environmental geochemical analyses, including NMR and gas chromatography-mass spectrometry (GC-MS) analyses of central metabolites, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) of secondary metabolites, and lipidomics, was used to investigate the influence of organic matter (OM) quality on the heterotrophic microbial mechanisms controlling peatland CO₂, CH₄, and CO₂:CH₄ porewater production ratios in response to climate warming. Our investigations leverage the Spruce and Peatland Responses under Changing Environments (SPRUCE) experiment, where air and peat warming were combined in a whole-ecosystem warming treatment. We hypothesized that warming would enhance the production of plant-derived metabolites, resulting in increased labile OM inputs to the surface peat, thereby enhancing microbial activity and greenhouse gas production. Because shallow peat is most susceptible to enhanced warming, increases in labile OM inputs to the surface, in particular, are likely to result in significant changes to CO₂ and CH₄ dynamics and methanogenic pathways. In support of this hypothesis, significant correlations were observed between metabolites and temperature consistent with increased availability of labile substrates, which may stimulate more rapid turnover of microbial proteins. An increase in the abundance of methanogenic genes in response to the increase in the abundance of labile substrates was accompanied by a shift toward acetoclastic and methylotrophic methanogenesis. Our results suggest that as peatland vegetation trends toward increasing vascular plant cover with warming, we can expect a concomitant shift toward increasingly methanogenic conditions and amplified climate–peatland feedbacks.

Peatlands contain an estimated one-third (1–3) or more (4) of global soil organic matter (OM). While much of this OM is locked away in frozen permafrost, thawing and nonpermafrost peatlands have also historically been significant net C sinks (5). Following its deposition in peatlands, microorganisms mediate the decomposition of soil OM to both CO₂ and CH₄. Because CH₄ has a much greater global warming potential compared with CO₂ (6, 7), whether peatlands exert a net warming or net cooling effect on climate depends on the balance between CO₂ uptake by primary producers and CO₂ and CH₄ emission from heterotrophic respiration (5). The relative production of CO₂:CH₄ from microbial respiration depends on the availability of terminal electron acceptors (TEAs) which promote CO₂ over CH₄ production, while under TEA-depleted conditions, peatland systems can approach a 1:1 production of CO₂ and CH₄ (8, 9). Hydrology plays a role, in that permanently inundated areas are more anoxic and the low availability of TEAs facilitates methanogenic conditions leading to higher CH₄ emission rates (5, 10). Active microbial consortia at a given place and time may also “tune” the CO₂:CH₄ production ratio by partitioning TEA pathways, speeding the rates of some reactions relative to others via production of enzyme catalysts, leading to heterogeneous C-gas production via the buildup of intermediates.Climate warming and the resulting ecosystem response, including lowered water tables and changes in vegetation community composition and production rates and composition, influence OM decomposition and the relative production of CO₂ and CH₄. Increasing primary production will increase the availability of fresh OM through increased litter inputs and elevated root exudates (e.g., ref. 11). Radiocarbon evidence from a number of peatlands shows that dissolved OM (DOM) contains more important substrates for methanogenesis than solid peat at any given depth (12–16). Thus, increases in the quantity of DOM input at the surface can increase CH₄ production at depth. The quality of OM available for decomposition, defined as energy yield upon oxidation under anoxic conditions, may also influence the rate and pathways of CH₄ production (12, 14). For example, sedge-dominated wetlands contain higher-quality OM for decomposition relative to Sphagnum-dominated bogs and, in turn, exhibit higher rates of CH₄ production and higher relative rates of acetoclastic methanogenesis (12, 14, 17, 18). Aside from altering vegetation and hydrology, temperature could exert a simple kinetic effect on microbial activity in peat, with warmer conditions leading to higher CO₂ and CH₄ production rates. Since CH₄ production has a higher Q₁₀ (Q₁₀ represents the proportional increase in metabolic rate or growth rate with a 10 ^oC increase in temperature) than CO₂ production, there would be a differential kinetic effect with CH₄ production being stimulated more than CO₂ for a given temperature increase (19–21).The Spruce and Peatland Responses under Changing Environments (SPRUCE; https://mnspruce.ornl.gov/) experiment is a whole-ecosystem warming and elevated air partial pressure of CO₂ (eCO₂) experiment in a regression design to test the impacts of climate drivers on ecosystem response in a nonpermafrost, undrained peatland. The SPRUCE group previously reported on an earlier phase of the experiment, referred to as deep-peat heating (DPH), in which the peat was heated at varying temperatures up to +9 °C above ambient before aboveground warming and eCO₂ started (22). During DPH, surface peat decomposition was increasingly methanogenic with temperature treatment, but there was no response of the peat below 25 cm to heating (22). In addition, no change in peat-associated microbial communities was observed with warming (22). Following the ∼1-y DPH treatment, aboveground warming from 0 to 6 m was added to the DPH experiment to achieve whole-ecosystem warming (23). Temperature treatment enclosures are duplicated and elevated air CO₂ concentrations (∼900 parts per million by volume [ppmv]) are applied in one of each of the temperature treatments. Under these conditions, surficial soil temperatures are higher than those measured during DPH which may exacerbate warming effects on CO₂ and CH₄ production (22). DOM in near-surface peat may become more concentrated and change composition with drying or shifts in the vegetation community (24, 25), which will also influence CO₂ and CH₄ production rates. Additionally, lagged responses in deep peat to warming became apparent only after more than 13 mo of DPH (26), leading us to examine the mechanisms mediating CO₂ and CH₄ production rates since the initiation of whole-ecosystem warming.This study assesses changes in CO₂ and CH₄ production with experimental warming driven primarily by changing OM quality and methanogenic activity. We hypothesized that increasing OM quality and microbial processing rates would facilitate increasingly methanogenic conditions. Multiple complementary and novel, high-resolution analytical approaches were employed to characterize the DOM. Each of these analyses provides molecular-level detail to elucidate both unique and overlapping subsets of molecular compounds comprising the DOM. While each technique presents its own limitations, their collective strengths can be leveraged in an integrated approach to provide a complementary analysis. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) allows semiquantitative analysis of large–molecular-weight (>∼100 to 1,000s Da) metabolites. One key advantage of this technique is the capability to resolve novel compounds and reveal key metabolic pathways (e.g., ref. 27). Gas chromatography-mass spectrometry (GC-MS) is capable of identifying smaller–molecular-weight compounds (typically <400 Da) in a semiquantitative way, allowing us to probe changes in critical small metabolites such as sugars. However, derivatization and drying during sample preparation can result in the loss of volatile compounds (28). To identify and quantify such volatile compounds (e.g., alcohols) and a range of carbohydrate compounds that are difficult to quantify using MS-based methods, ¹H liquid-state NMR was used. While the NMR method is truly quantitative, quantification requires standardization relative to a standard database (as does the GC-MS method). Thus, compound identification is limited to known compounds for which standard curves have already been developed. NMR is also less sensitive than many of the other techniques and cannot reliably identify compounds with concentrations less than ∼1 μM. Nevertheless, the quantitative nature of this technique provides valuable insights into the changes in some of the most metabolically important compounds (e.g., glucose, pyruvate). Metabolomic and metaproteomic analyses were coupled with analyses of microbial community composition and genomic potential (determined with 16S ribosomal RNA [rRNA] gene sequencing and shotgun metagenome approaches) to elucidate dominant methanogen taxa and pathways of methanogenesis. The results differentiate between upstream (e.g., increased substrate supply) and downstream (e.g., microbial inhibition) controls on CO₂ and CH₄ production dynamics in nonpermafrost, undrained peatlands during their response to warming.     

The effect of hGH deficiency on the insulin response to glucagon after oral glucose loading

Summary Six children and adolescents (aged from 2 6/12 to 16 years) with isolated hGH deficiency were subjected to a standard oral glucose tolerance test (OGTT) followed by the administration of IV glucagon at 180 mins. Three of them underwent a second test after several months of hGH therapy. Nine patients underwent a separate IV glucagon test and two of these patients had both tests. As controls served 14 endocrinologically normal children and adolescents, who underwent both tests. It was found that the patients with isolated hGH deficiency had lower basal plasma insulin and blood glucose levels and that their insulin response to IV glucagon even after oral glucose preloading was significantly lower than in the control group. This response was partially restored by several months of hGH treatment in the three patients tested. These findings are interpreted as further evidence for an insulinotrophic effect of hGH.Established Investigator of the Chief Scientist's Bureau, Ministry of Health     

NS5A mutations predict biochemical but not virological response to interferon-α treatment of sporadic hepatitis C virus infection in European patients

The NS5A region of the hepatitis C virus (HCV) genome has been reported by Japanese but not European investigators to be a significant factor in predicting interferon (IFN) response patients with HCV of genotype 1. We correlated the NS5A region with treatment outcome in patients with sporadic HCV infection. Twenty‐eight patients (10 men, 18 women, mean age 60 ± 2 years) with histologically proven HCV chronic hepatitis, genotype 1b, were treated with 6 MU IFN‐α for 6 months. The 6954–7073 area of the NS5A region was directly sequenced for nucleotide and amino acids mutations and the results were related to biochemical and virological response. None of the patients had a strain with nucleotide sequence identical to the Japanese HCV‐J. However, in five strains the nucleotide mutations led to synonymous amino acids and the amino acid sequences were identical to the prototype Japanese strain. Only 2/28 patients had four or more amino acid mutations (mutant strains) while 21 demonstrated an intermediate type and five belonged to the wild‐type. The most frequent non‐synonymous substitution was at position 6982 (A→G) corresponding to an amino acid change at codon 2218 (His→Arg). All patients with the wild‐type were biochemical nonresponders while the two patients with the mutant strains had a sustained biochemical response. Twenty‐three percent of the intermediate type had a sustained biochemical response. NS5A mutations predict the biochemical but not the virological response of patients. Virological response was poor and unrelated to the type of HCV strain. Biochemical responders had significantly lower amino acid mutations (1.14 ± 0.19) compared with nonresponders (2.57 ± 1.4, P < 0.003) as well as lower aminotransferase values (P < 0.01). Hence, mutational analysis of the NS5A region showed that our patients have a mutational profile similar to the European studies with a wild‐type that is slightly different from the Japanese HCV‐J sequence. The biochemical, but not the virological response to IFN‐α is similar to the Japanese studies, with no response of the patients with wild‐type sequence, a good response in the limited number of patients with mutant strains and 23% response rate in the patients with intermediate type sequences.     

The effect of short-term intravenous insulin administration on the glucagon response to a carbohydrate meal in adult onset and juvenile type diabetes

Summary These experiments were designed to determine whether the abnormal glucagon response of diabetics to a glucose meal can be restored to normal by the short-term administration of exogenous insulin in amounts sufficient to produce normal and above normal plasma insulin levels. The immunoreactive glucagon (IRG) response of nine nondiabetics to oral glucose was compared with that of ten juvenile and ten adult type diabetics. In the absence of exogenous insulin, the IRG response of diabetics was strikingly different from the nondiabetics, rising paradoxically, whereas in nondiabetics there was a decline in IRG. When plasma insulin levels were raised to normal by infusion of insulin (0.06 U/kg for 2 hr), the abnormal IRG response of adult type diabetics was not improved; the IRG response of the juvenile type patients was improved, but remained abnormal. Raising plasma insulin briefly to greater than normal concentrations inproved the IRG response during the glucose meal in both groups, but in the adult group total IRG suppression was still only half that of the nondiabetics; in the juvenile type group it was reduced to the nondiabetic level, but at glucose and insulin levels far above those of nondiabetics. The results are compatible with the view that the glucose-sensing function of the A-cells is, at least in part, mediated by or requires insulin. In juvenile diabetics, the abnormality is corrected by raising plasma insulin to above normal levels; adult onset diabetics appear to be less sensitive even to large doses of insulin during a carbohydrate load.This work presented in part at the International Glucagon Symposium, May 12, 1976, Dallas, Texas, the proceedings of which were published as a special supplement to Metabolism     

A case of hepatosplenic gamma-delta T-cell lymphoma with a transient response to fludarabine and alemtuzumab

Hepatosplenic gamma-delta T-cell lymphoma is a rare, usually fatal lymphoma and available literature on management is sparse. Allografting is probably the only curative option. We describe a further case with a dramatic, though transient response to Fludarabine and Alemtuzumab combination, following a failure of conventional chemotherapy. Given the dreadful prognosis with conventional chemotherapy, it is a regimen worth pursuing as a disease reduction strategy prior to allograft where appropriate.