Early last glacial maximum in the southern Central Andes reveals northward shift of the westerlies at similar to 39 ka

The latitudinal position of the southern westerlies has been suggested to be a key parameter for the climate on Earth. According to the general notion, the southern westerlies were shifted equatorward during the global Last Glacial Maximum (LGM: ~24–18 ka), resulting in reduced deep ocean ventilation, accumulation of old dissolved carbon, and low atmospheric CO2 concentrations. In order to test this notion, we applied surface exposure dating on moraines in the southern Central Andes, where glacial mass balances are particularly sensitive to changes in precipitation, i.e. to the latitudinal position of the westerlies. Our results provide robust evidence that the maximum glaciation occurred already at ~39 ka, significantly predating the global LGM. This questions the role of the westerlies for atmospheric CO2, and it highlights our limited understanding of the forcings of atmospheric circulation.

Abundance and distribution of the eastern North Pacific Steller sea lion (Eumetopias jubatus) population

The eastern Steller sea lion (Eumetopias jubatus) population comprises animals that breed along the west coast of North America between California and southeastern Alaska. There are currently 13 major rookeries (>50 pups): five in southeastern Alaska, three in British Columbia, two in Oregon, and three in California. Overall abundance has increased at an average annual rate of 3.1% since the 1970s. These increases can largely be attributed to population recovery from predator-control kills and commercial harvests, and abundance is now probably as high as it has been in the last century. The number of rookeries has remained fairly constant (n=11 to 13) over the past 80 years, but there has been a northward shift in distribution of both rookeries and numbers of animals. Based on the number of pups counted in a population-wide survey in 2002, total pup production was estimated to be about 11,000 (82% in southeastern Alaska and British Columbia), representing a total population size as approximately 46,000−58,000 animal

Bioenergetic responses of sub-adult sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea) to temperature with special discussion regarding its southernmost distribution limit in China

1. This paper investigated the bioenergetic responses of the sea cucumber Apostichopus japonicus (wet weights of 36.5 +/- 1.2 g) to different water temperatures (5, 10, 15, 20, 25 and 30 degrees C) in the laboratory. 2. Results showed that theoretically the optimal temperatures for energy intake and scope for growth (SFG) of sub-adult A. japonicus was at 15.6 and 16.0 degrees C, respectively. The aestivation threshold temperature for this life-stage sea cucumber could be 29.0 degrees C by taking feeding cessation as the indication of aestivation. 3. Our data suggests that A. japonicus is thermo-sensitive to higher temperature, which prevents it from colonising sub-tropical coastal zones. Therefore, water temperature plays an important role in its southernmost distribution limit in China. 4. The potential impact of global ocean warming on A. japonicus might be a northward shift in the geographical distribution. Crown Copyright (C) 2009 Published by Elsevier Ltd, All rights reserved.

High dispersal potential has maintained long-term population stability in the North Atlantic copepod Calanus finmarchicus

The cool-water copepod Calanus finmarchicus is a key species in North Atlantic marine ecosystems since it represents an important food resource for the developmental stages of several fish of major economic value. Over the last 40 years, however, data from the Continuous Plankton Recorder survey have highlighted a 70 per cent reduction in C. finmarchicus biomass, coupled with a gradual northward shift in the species's distribution, which have both been linked with climate change. To determine the potential for C. finmarchicus to track changes in habitat availability and maintain stable effective population sizes, we have assessed levels of gene flow and dispersal in current populations, as well as using a coalescent approach together with palaeodistribution modelling to elucidate the historical population demography of the species over previous changes in Earth's climate. Our findings indicate high levels of dispersal and a constant effective population size over the period 359 000–566 000 BP and suggest that C. finmarchicus possesses the capacity to track changes in available habitat, a feature that may be of crucial importance to the species's ability to cope with the current period of global climate change.

Expressed sequence tag-derived microsatellites for the cool-water marine copepod Calanus finmarchicus

The copepod Calanus finmarchicus is the major contributor to zooplankton biomass in the North Atlantic and Norwegian Sea, but recent studies have shown a 70% decrease in abundance as well as a northward shift in the species' range. Insights into dispersal capabilities gained from population genetic studies will be crucial in predicting the response of C. finmarchicus communities to climate change and, consequently, we have developed a set of expressed sequence tag-derived microsatellite markers to allow fine-scale elucidation of population structuring and dispersal. Ten polymorphic markers displayed between two and 19 alleles, with levels of expected heterozygosity ranging from 0.044 to 0.924.

High dispersal potential has maintained long-term population stability in the North Atlantic copepod Calanus finmarchicus

The cool-water copepod Calanus finmarchicus is a key species in North Atlantic marine ecosystems since it represents an important food resource for the developmental stages of several fish of major economic value. Over the last 40 years, however, data from the Continuous Plankton Recorder survey have highlighted a 70 per cent reduction in C. finmarchicus biomass, coupled with a gradual northward shift in the species's distribution, which have both been linked with climate change. To determine the potential for C. finmarchicus to track changes in habitat availability and maintain stable effective population sizes, we have assessed levels of gene flow and dispersal in current populations, as well as using a coalescent approach together with palaeodistribution modelling to elucidate the historical population demography of the species over previous changes in Earth's climate. Our findings indicate high levels of dispersal and a constant effective population size over the period 359 000-566 000 BP and suggest that C. finmarchicus possesses the capacity to track changes in available habitat, a feature that may be of crucial importance to the species's ability to cope with the current period of global climate change.

Unique genetic variation at a species' rear edge is under threat from global climate change

Global climate change is having a significant effect on the distributions of a wide variety of species, causing both range shifts and population extinctions. To date, however, no consensus has emerged on how these processes will affect the range-wide genetic diversity of impacted species. It has been suggested that species that recolonized from low-latitude refugia might harbour high levels of genetic variation in rear-edge populations, and that loss of these populations could cause a disproportionately large reduction in overall genetic diversity in such taxa. In the present study, we have examined the distribution of genetic diversity across the range of the seaweed Chondrus crispus, a species that has exhibited a northward shift in its southern limit in Europe over the last 40 years. Analysis of 19 populations from both sides of the North Atlantic using mitochondrial single nucleotide polymorphisms (SNPs), sequence data from two singlecopy nuclear regions and allelic variation at eight microsatellite loci revealed unique genetic variation for all marker classes in the rear-edge populations in Iberia, but not in the rear-edge populations in North America. Palaeodistribution modelling and statistical testing of alternative phylogeographic scenarios indicate that the unique genetic diversity in Iberian populations is a result not only of persistence in the region during the last glacial maximum, but also because this refugium did not contribute substantially to the recolonization of Europe after the retreat of the ice. Consequently, loss of these rear-edge populations as a result of ongoing climate change will have a major effect on the overall genetic diversity of the species, particularly in Europe, and this could compromise the adaptive potential of the species as a whole in the face of future global warming.

Climate impacts of recent multidecadal changes in Atlantic Ocean Sea Surface Temperature: A multimodel comparison

During the twentieth century sea surface temperatures in the Atlantic Ocean exhibited prominent multidecadal variations. The source of such variations has yet to be rigorously established—but the question of their impact on climate can be investigated. Here we report on a set of multimodel experiments to examine the impact of patterns of warming in the North Atlantic, and cooling in the South Atlantic, derived from observations, that is characteristic of the positive phase of the Atlantic Multidecadal Oscillation (AMO). The experiments were carried out with six atmospheric General Circulation Models (including two versions of one model), and a major goal was to assess the extent to which key climate impacts are consistent between the different models. The major climate impacts are found over North and South America, with the strongest impacts over land found over the United States and northern parts of South America. These responses appear to be driven by a combination of an off-equatorial Gill response to diabatic heating over the Caribbean due to increased rainfall within the region and a Northward shift in the Inter Tropical Convergence Zone (ITCZ) due to the anomalous cross-equatorial SST gradient. The majority of the models show warmer US land temperatures and reduced Mean Sea Level Pressure during summer (JJA) in response to a warmer North Atlantic and a cooler South Atlantic, in line with observations. However the majority of models show no significant impact on US rainfall during summer. Over northern South America, all models show reduced rainfall in southern hemisphere winter (JJA), whilst in Summer (DJF) there is a generally an increase in rainfall. However, there is a large spread amongst the models in the magnitude of the rainfall anomalies over land. Away from the Americas, there are no consistent significant modelled responses. In particular there are no significant changes in the North Atlantic Oscillation (NAO) over the North Atlantic and Europe in Winter (DJF). Additionally, the observed Sahel drying signal in African rainfall is not seen in the modelled responses. Suggesting that, in contrast to some studies, the Atlantic Multidecadal Oscillation was not the primary driver of recent reductions in Sahel rainfall.

A phyloclimatic study of Cyclamen

Background: The impact of global climate change on plant distribution, speciation and extinction is of current concern. Examining species climatic preferences via bioclimatic niche modelling is a key tool to study this impact. There is an established link between bioclimatic niche models and phylogenetic diversification. A next step is to examine future distribution predictions from a phylogenetic perspective. We present such a study using Cyclamen (Myrsinaceae), a group which demonstrates morphological and phenological adaptations to its seasonal Mediterranean-type climate. How will the predicted climate change affect future distribution of this popular genus of garden plants? Results: We demonstrate phylogenetic structure for some climatic characteristics, and show that most Cyclamen have distinct climatic niches, with the exception of several wide-ranging, geographically expansive, species. We reconstruct climate preferences for hypothetical ancestral Cyclamen. The ancestral Cyclamen lineage has a preference for the seasonal Mediterranean climate characteristic of dry summers and wet winters. Future bioclimatic niches, based on BIOCLIM and Maxent models, are examined with reference to a future climate scenario for the 2050s. Over the next 50 years we predict a northward shift in the area of climatic suitability, with many areas of current distribution becoming climatically unsuitable. The area of climatic suitability for every Cyclamen species is predicted to decrease. For many species, there may be no areas with a suitable climate regardless of dispersal ability, these species are considered to be at high risk of extinction. This risk is examined from a phylogenetic perspective. Conclusion: Examining bioclimatic niches from a phylogenetic perspective permits novel interpretations of these models. In particular, reconstruction of ancestral niches can provide testable hypothesis about the historical development of lineages. In the future we can expect a northwards shift in climatic suitability for the genus Cyclamen. If this proves to be the case then dispersal is the best chance of survival, which seems highly unlikely for ant-dispersed Cyclamen. Human-assisted establishment of Cyclamen species well outside their native ranges offers hope and could provide the only means of dispersal to potentially suitable future environments. Even without human intervention the phylogenetic perspective demonstrates that major lineages could survive climate change even if many species are lost.

Decreased frequency of North Atlantic polar lows associated with future climate warming

Every winter, the high-latitude oceans are struck by severe storms that are considerably smaller than the weather-dominating synoptic depressions1. Accompanied by strong winds and heavy precipitation, these often explosively developing mesoscale cyclones—termed polar lows1—constitute a threat to offshore activities such as shipping or oil and gas exploitation. Yet owing to their small scale, polar lows are poorly represented in the observational and global reanalysis data2 often used for climatological investigations of atmospheric features and cannot be assessed in coarse-resolution global simulations of possible future climates. Here we show that in a future anthropogenically warmed climate, the frequency of polar lows is projected to decline. We used a series of regional climate model simulations to downscale a set of global climate change scenarios3 from the Intergovernmental Panel of Climate Change. In this process, we first simulated the formation of polar low systems in the North Atlantic and then counted the individual cases. A previous study4 using NCEP/NCAR re-analysis data5 revealed that polar low frequency from 1948 to 2005 did not systematically change. Now, in projections for the end of the twenty-first century, we found a significantly lower number of polar lows and a northward shift of their mean genesis region in response to elevated atmospheric greenhouse gas concentration. This change can be related to changes in the North Atlantic sea surface temperature and mid-troposphere temperature; the latter is found to rise faster than the former so that the resulting stability is increased, hindering the formation or intensification of polar lows. Our results provide a rare example of a climate change effect in which a type of extreme weather is likely to decrease, rather than increase.

A review on Northern Hemisphere sea-ice, storminess and the North Atlantic Oscillation: observations and projected changes

The Arctic has undergone substantial changes over the last few decades in various cryospheric and derivative systems and processes. Of these, the Arctic sea ice regime has seen some of the most rapid change and is one of the most visible markers of Arctic change outside the scientific community. This has drawn considerable attention not only from the natural sciences, but increasingly, from the political and commercial sectors as they begin to grapple with the problems and opportunities that are being presented. The possible impacts of past and projected changes in Arctic sea ice, especially as it relates to climatic response, are of particular interest and have been the subject of increasing research activity. A review of the current knowledge of the role of sea ice in the climate system is therefore timely. We present a review that examines both the current state of understanding, as regards the impacts of sea-ice loss observed to date, and climate model projections, to highlight hypothesised future changes and impacts on storm tracks and the North Atlantic Oscillation. Within the broad climate-system perspective, the topics of storminess and large-scale variability will be specifically considered. We then consider larger-scale impacts on the climatic system by reviewing studies that have focused on the interaction between sea-ice extent and the North Atlantic Oscillation. Finally, an overview of the representation of these topics in the literature in the context of IPCC climate projections is presented. While most agree on the direction of Arctic sea-ice change, the rates amongst the various projections vary greatly. Similarly, the response of storm tracks and climate variability are uncertain, exacerbated possibly by the influence of other factors. A variety of scientific papers on the relationship between sea-ice changes and atmospheric variability have brought to light important aspects of this complex topic. Examples are an overall reduction in the number of Arctic winter storms, a northward shift of mid-latitude winter storms in the Pacific and a delayed negative NAO-like response in autumn/winter to a reduced Arctic sea-ice cover (at least in some months). This review paper discusses this research and the disagreements, bringing about a fresh perspective on this issue.

The large-scale circulation change at the end of the Baiu season in Japan as seen in ERA40 data

The time evolution of the circulation change at the end of the Baiu season is investigated using ERA40 data. An end-day is defined for each of the 23 years based on the 850 hPa θe value at 40˚Nin the 130-140˚E sector exceeding 330 K. Daily time series of variables are composited with respect to this day. These composite time-series exhibit a clearer and more rapid change in the precipitation and the large-scale circulation over the whole East Asia region than those performed using calendar days. The precipitation change includes the abrupt end of the Baiu rain, the northward shift of tropical convection perhaps starting a few days before this, and the start of the heavier rain at higher latitudes. The northward migration of lower tropospheric warm, moist tropical air, a general feature of the seasonal march in the region, is fast over the continent and slow over the ocean. By mid to late July the cooler air over the Sea of Japan is surrounded on 3 sides by the tropical air. It is suggestive that the large-scale stage has been set for a jump to the post-Baiu state, i.e., for the end of the Baiu season. Two likely triggers for the actual change emerge from the analysis. The first is the northward movement of tropical convection into the Philippine region. The second is an equivalent barotropic Rossby wave-train, that over a 10-day period develops downstream across Eurasia. It appears likely that in most years one or both mechanisms can be important in triggering the actual end of the Baiu season.

Intensified Asian summer monsoon and its variability in a coupled model forced by increasing greenhouse gas concentrations

The Asian summer monsoon response to global warming is investigated by a transient green-house warming integration with the ECHAM4/OPYC3 CGCM. It is demonstrated that increases of greenhouse gas concentrations intensify the Asian summer monsoon and its variability. The intensified monsoon results mainly from an enhanced land-sea contrast and a northward shift of the convergence zone. A gradual increase of the monsoon variability is simulated from year 2030 onwards. It seems to be connected with the corresponding increase of the sea surface temperature variability over the tropical Pacific.

Dynamical evolution of North Atlantic ridges and poleward Jet Stream displacements

The development of a particular wintertime atmospheric circulation regime over the North Atlantic, comprising a northward shift of the North Atlantic eddy-driven jet stream and an associated strong and persistent ridge in the subtropics, is investigated. Several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the North Atlantic Oscillation and East Atlantic pattern. First, the authors identify a close relationship between northward shifts of the eddy-driven jet, the establishment and maintenance of strong and persistent ridges in the subtropics, and the occurrence of upper-tropospheric anticyclonic Rossby wave breaking over Iberia. Clear tropospheric precursors are evident prior to the development of the regime, suggesting a preconditioning of the Atlantic jet stream and an upstream influence via a large-scale Rossby wave train from the North Pacific. Transient (2–6 days) eddy forcing plays a dual role, contributing to both the initiation and then the maintenance of the circulation anomalies. During the regime there is enhanced occurrence of anticyclonic Rossby wave breaking, which may be described as low-latitude blocking-like events over the southeastern North Atlantic. A strong ridge is already established at the time of wave-breaking onset, suggesting that the role of wave-breaking events is to amplify the circulation anomalies rather than to initiate them. Wave breaking also seems to enhance the persistence, since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking.

Evaluation of coupled ocean-atmosphere simulations of northern hemisphere extratropical climates in the mid-Holocene

We have used the BIOME4 biogeography–biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean–atmosphere general circulation models to mid-Holocene changes in orbital forcing in the mid- to high-latitudes of the northern hemisphere. All the models produce: (a) a northward shift of the northern limit of boreal forest, in response to simulated summer warming in high-latitudes. The northward shift is markedly asymmetric, with larger shifts in Eurasia than in North America; (b) an expansion of xerophytic vegetation in mid-continental North America and Eurasia, in response to increased temperatures during the growing season; (c) a northward expansion of temperate forests in eastern North America, in response to simulated winter warming. The northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in North America are supported by palaeovegetation data. The expansion of xerophytic vegetation in mid-continental North America is consistent with palaeodata, although the extent may be over-estimated. The simulated expansion of xerophytic vegetation in Eurasia is not supported by the data. Analysis of an asynchronous coupling of one model to an equilibrium-vegetation model suggests vegetation feedback exacerbates this mid-continental drying and produces conditions more unlike the observations. Not all features of the simulations are robust: some models produce winter warming over Europe while others produce winter cooling. As a result, some models show a northward shift of temperate forests (consistent with, though less marked than, the expansion shown by data) and others produce a reduction in temperate forests. Elucidation of the cause of such differences is a focus of the current phase of the Palaeoclimate Modelling Intercomparison Project.