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2010 Literature Review Archives - Impacts and Adaptation

Bentz, B.J., J. Régnière, C.J. Fettig, E.M. Hansen, J.L. Kayes, J.A. Hicke, R.G. Kelsey, J.F. negron and S.J. Seybold. 2010. Climate change and bark beetles of the western United States and Canada: Direct and Indirect Effects. Bioscience, Vol 60(8), pp. 602-613.

A new study combines climate projections with population models to predict the future success of mountain pine beetle and spruce bark beetle.  Higher temperatures are predicted to increase the probability of population success for both species.    

Bentz and colleagues project future changes in the probability of population success of two species of bark beetles (mountain pine beetle and spruce beetle) in the United States and Canada.  The response of bark beetle populations to climate change is influenced directly by temperature changes (impacts on cold tolerance and life-cycle timing) and indirectly through impacts on host trees (physiology and distribution) and on other species associated with the beetle (e.g., fungal symbionts).  The authors note that their projections are based only on bark beetle success.  To develop the predictions, mechanistic population models for the two species were driven by projections of daily precipitation and maximum and minimum temperatures to 2100 AD generated using the Canadian Regional Climate Model driven by the IPCC emission scenario SRES A2, a relatively high emission scenario.  The model used to predict spruce beetle population success shows markedly higher outbreak potential for the boreal forests of Canada for 2071-2100 based on temperature related impacts on developmental timing alone (future forest distribution and changes in cold tolerance of the spruce beetle are not considered).  Greater probability of mountain pine beetle population success is predicted for parts of the current range that have seen increased mountain pine beetle induced mortality over the past decade (in Canada this includes high elevation forests of the Canadian Rocky mountains as well as lodgegpole pine forests in central B.C.).  The authors note that the probability of mountain pine beetle range expansion across jack pine forests into eastern pine forests remains low to moderate throughout this century.


Boyce, D.G., M.R. Lewis and B. Worm. 2010. Global phytoplankton decline over the past century. Nature, Vol 466, pp 591-596, doi:10.1038/nature09268.

A new record of phytoplankton abundance identifies a global rate of decline of ~1% of the global median per year over the past century.  The authors associate the long-term decline with increasing sea surface temperatures around the globe.


Marine phytoplankton account for roughly half of planetary primary production, drive ocean ecosystems and influence biogeochemical cycles (e.g. carbon cycle) and the climate system.  Satellite-derived records of phytoplankton abundance exist only from the late 1970s and little is known about long-term trends in phytoplankton concentration.  Canadian researchers from Dalhousie University present a new compilation of phytoplankton data from around the globe.  Boyce and colleagues combined records of ocean transparency and in situ chlorophyll measurements to estimate phytoplankton biomass at local, regional and global scales since 1899. At the local scale (defined as 10o x10o cells), phytoplankton declines were identified in almost 60 percent of the cells with sufficient data.  Declines were concentrated in high latitude areas (>60o) and with increasing distance from land (i.e. in the open oceans in agreement with satellite data).   The authors divided the global ocean into ten regions and phytoplankton declines were identified in 8/10 regions (increases were found in the North and, more strongly in the Southern Indian Ocean).   The trend for the global ocean was also negative indicating an annual rate of decline of roughly 1% of the global median.  The authors identified statistically significant relationships between basin-scale climate indices and interannual to interdecadal fluctuations in regional phytoplankton series.  The century-scale declines in phytoplankton observed in most regions were linked most strongly with sea surface temperatures (SSTs) which have increased over much of the global ocean.   In tropical and subtropical regions, increased SSTs are thought to inhibit nutrient availability in the upper ocean through changes in the depth of the mixing layer and water column stability.   The authors note that this mechanism does not explain the phytoplankton declines in polar regions.


Byrne, R.H., S. Mecking, R.A. Feely,R., and X. Liu. 2010. Direct observations of basin-wide acidification of the North Pacific. GRL 37,L02601, doi:10.1029/2009GL040999, 2010.

Analysis of North Pacific Ocean data confirm that the acidity of sea water in the upper mixed layer has increased across the basin over the past 15 years.  The increase can be attributed to rising concentrations of atmospheric CO 2 .

In recent years, researchers have been warning policy makers that rising CO2 concentrations, in addition to causing an enhanced greenhouse effect, will cause increasing ocean acidity (pH decline) , with potentially serious implications for shell fish, coral reefs and other parts of marine ecosystems.  A new study published in Geophysical Research Letters by a team of American oceanographers now provides the first clear evidence than an entire ocean basin may already be undergoing such changes.  The investigators compare data from sea water samples taken along a longitude line in the North Pacific between 22 and 56°N latitude in 1991 and again in 2006.  While little change was noted below depths of 800 m, the upper 500 m layer showed an average net decline in pH over the 15 years of -0.06.  This decrease in the upper ocean appears to be due to both natural and anthropogenic causes. However, trends in the mixed layer of the upper 100 m of -0.0017/year are consistent with that expected due to the rise of CO2 concentrations in the atmosphere above, and hence may be entirely due to anthropogenic factors.  The authors project that future acidity trends in the upper ocean will continue to follow changes in atmospheric concentrations of CO2.


Carrie, J., F. Wang, H. Santei, R.W. Macdonald, P. M. Outridge and G. A. Stern. 2010. Increasing contaminant burdens in an Arctic fish, Burbot (Lota lota) in a warming climate. Environ. Sci. Technol. 44:1:316-322.

An increasing mercury burden in arctic burbot has occurred despite declining or stable atmospheric concentrations. Climate warming, leading to decreases in ice cover and increases in algal production, is proposed to have increased the amount of bioavailable mercury.

The Mackenzie River Basin (MRB) of the Northwest Territories has been experiencing one of the strongest climate warming trends in North America with snow cover and ice season decreasing in response. In this study, samples of Mackenzie River burbot were collected between 1985-2009 and analysed for mercury (Hg) burdens (and other contaminants). A sediment core from a near-by lake, serving as a proxy for regional trends, revealed an increase in algal-derived organic matter and a 1.5 fold increase in total Hg over the last 30 years despite declining or stable atmospheric Hg concentrations. Similar increases in sediment Hg have been reported for other Arctic and sub-Arctic lakes. Mercury burdens in the burbot were shown to have increased approximately 2-fold since 1985. The authors propose that the greater amounts of algal organic matter in northern lakes may increase both the scavenging of Hg from the water column and the conversion of algal-bound inorganic Hg to bioavailable MeHg (methylmercury). Therefore, climate warming, leading to changes in environmental conditions that increase algal productivity, may indirectly increase contaminant burdens in arctic burbot. The results of this study add to the emerging literature documenting the importance of climate and environmental conditions on the biogeochemical cycling of Hg.


Coffroth, M.A., D.M. Poland, E.L. Petrou, D.A. Brazeau and J.C. Holmberg. 2010. Environmental symbiont acquisition may not be the solution to warming seas for reef-building corals. PLoS ONE, Vol 5, Issue 10, e13258, doi: 10.1371/journal.phone.0013258.

A recent study suggests that reef-building corals will not be able to acclimatize to increasing sea surface temperatures by acquiring new, heat-tolerant algal symbionts from the environment.

Coral reefs worldwide are in decline and much of the mortality is related to coral bleaching associated with rising sea surface temperatures (SSTs).  Coral bleaching occurs when corals lose their photosynthetic algal symbionts and hence, an important supply of nutrients.  Bleaching can occur when sea surface temperatures are only slightly above the annual mean and severe bleaching can result in coral death.  Previous studies have suggested that coral reefs may be able to recover from bleaching events through acquisition of more stress-tolerant symbionts from the surrounding environment (i.e. exogenous symbionts).  Coffroth and colleagues evaluate this possibility by exposing experimentally bleached samples of coral reefs (Carribean finger coral from the Florida Keys National Marine Sanctuary) to symbiont types not normally found in these reefs and monitored subsequent symbiont uptake under normal water temperatures (simulating a recovery phase).  They found that although some of the colonies did acquire some exogenous symbionts from the water column, the acquisition was temporary indicating that the new symbiotic relationship was unstable.  Stable recovery occurred only with symbiont types present before bleaching (i.e. resident in situ symbiont populations).  The authors conclude that these results have important implications with regards to the response of reef-building corals to climate change.  They suggest that the acquisition of new symbionts is unlikely to provide a stable means of acclimatizing to increasing SSTs because only corals that already host heat-tolerant symbiont strains may be able to acclimatize.


Prowse, T., R. Shrestha, B. Bonsal and Y. Dibike. 2010. Changing spring air-temperature gradients along large northern rivers: Implications for severity of river-ice floods. GRL Vol 37, L19706, doi:10.1029/2010GL044878.

Future climate warming is shown to induce earlier arrival of ice melt conditions and reduced air temperature gradients along large northward flowing Arctic rivers, including the Mackenzie. These changes suggest that river ice break-up conditions will be less severe in the future. Flood potential is more difficult to project.

Along high-latitude northward flowing rivers, such as the Mackenzie River in Canada, spring flood extremes are strongly influenced by both the volume and timing of snowmelt and by ice conditions along the river. Typically, a spring flood wave generated in the warmer headwaters moves progressively downstream. Depending on the amount of resistance presented by ice on the river, flooding can result. A team of Environment Canada scientists have investigated how future climate may alter air temperature gradients along four major Arctic rivers and what impact such changes might have on the timing and severity of spring ice break-up. Their research focused on the lower 2000-km stretches of the Mackenzie River in Canada, and the Lena, Yenisey and Ob Rivers in Russia. Japanese reanalysis data was used as a source of current climate information, while future climate projections were obtained from ensemble means of projections with the IPCC SRES A2 scenario by four GCMs. Current and future air-temperature data were regridded to a common 50-km resolution using an interpolation method. The spring 0°C isotherm (I0°C) was defined as the first day of the year when a 31-day running daily mean temperaturecrossed 0°C. Under future climate, the movement of the I0°C downstream closely tracks current conditions in terms of overall duration, but with earlier dates, that varied from 7.5 -  16.5 days earlier (averaged over the entire 2000-km stretch) for the 4 rivers by mid-century, to 13.6 – 25.5 days earlier towards the end of the century. Downstream warming is significantly greater than upstream warming under future climate conditions, which reduces gradients in air temperature between upstream and downstream river sections.  Despite some inter-model variations, the general tendency then is toward an earlier arrival of melt conditions and greater warming in the downstream direction. It is suggested that these changes are likely to lead to thinner river ice cover at the time of break-up and generally less severe ice break-up conditions. However, it remains more difficult to project changing flood risks since a number of other factors are involved in determining this.


Ridgwell,A. and D.N., Schmidt. 2010. Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nature Geoscience 3:196-200.

Earth system model simulations suggest that rising atmospheric CO 2 concentrations will cause changes in ocean chemistry and biota over the next few millennia that will likely be unprecedented in the past 65 million years. 


In addition to causing global warming, rising atmospheric CO2concentrations are projected to result in ocean acidification.  Two British ocean modelers have recently used an Earth system model called GENIE-1 to undertake a multi-millennia simulation of the response of ocean chemistry to projected rises in atmospheric CO2concentrations under a very conservative emissions scenario (using the IS92a scenario to 2100, then a steady decline in global emissions until atmospheric concentrations stabilize, with a total net emission of 2180 GtC). They then compared results to simulations of changes that took place during the Palaeocene-Eocene period that included a thermal maximum some 55 million years ago.  During this period, atmospheric CO2 concentrations were also high, global temperatures changed rapidly and the biodiversity of benthic calcifying organisms in the deep ocean appear to have decreased markedly.  The comparison suggests that changes in marine chemistry during the next few millennia will likely significantly exceed that of the Palaeocene-Eocone thermal maximum, thus making them unprecedented in the past 65 million years.


Rode, K.D., S.C. Amstrup and E.V. Reghehr. 2010 Reduced body size and cub recruitment in polar bears associated with sea ice decline. Ecological Applications Vol 20(3), pp 768-782.

A long-term study of polar bears in the southernBeaufort Seaprovides evidence of an association between sea ice extent and measures of growth and cub recruitment. Declines in growth were coincident with a long-term reduction in sea ice availability. Reproductive success was lower following years with lower availability of optimal sea-ice habitat. 

Growth rates in mammals are largely dependent on nutrient availability which can reflect changes in environmental conditions over time and space.  Previous studies have identified a relationship between reductions in sea ice and polar bear size (polar bears use the ice as a platform from which to hunt seals) but long-term studies have been limited to the southern portions of their range, primarily in Hudson Bay.  Rode et al describe a long-term monitoring study (1982-2006) of the size, condition and reproductive success of polar bears in the southern Beaufort Sea off the coast of Alaska and relate changes in these aspects to inter-annual and long-term variations in the availability of sea ice habitat.  The authors report an overall decline in mean skull size and body length in polar bears greater than three years of age and a decline in body size of young bears over this period coincident with a long-term reduction in sea ice availability.  Reduced litter mass, number of yearlings per female and body size in young bears are recorded following years with low sea ice availability.  The authors conclude that the reduced availability of sea ice habitat imposed nutritional limitations that reduced body size and reproduction in this polar bear population.


Sinervo, B., F. Mendez-de-la-Cruz, D.B. Miles  et al. 2010. Erosion of lizard diversity by climate change and altered thermal niches. Science Vol 328, pp 894-899, doi: 10.1126/science.1184695.

A recent study identifies links between lizard extinctions and rapid spring temperature increases which restrict activity during the breeding period.  Global projections of future loss suggest that lizard species extinction rates may be as high as 20% by 2080 and local extinction rates may be as high as 39%.

It is anticipated that global climate change will cause range shifts and species extinctions but data to validate whether any such events have already occurred are scarce.  Sinervo et al. compared recent and historical (back to 1975) surveys of 48 lizard species at 200 sites with intact habitat in Mexico and found that 12% of local populations were extinct by 2009.  The authors explored climatological and biological data to identify the causes of these extinctions and were able to relate rapid increases in winter-spring maximum temperatures to an increase in the amount of time lizards must spend in cool refuges to avoid overheating.  Time spent in these refuges during spring decreases foraging time precisely when reproductive energy demands are highest, thus limiting reproductive success.  A physiological model based on these relationships is validated using observed climate and lizard population data from around the globe (available for 34 lizard families at 1216 geo-referenced sites).  The model simulations correctly identify local lizard population extinctions on four other continents thus validating the model and suggesting that climate-related local extinctions have already occurred.  Genetic modeling suggests that genetic adaptation is not feasible given the rapidity of current and projected climate changes.  The authors also use their extinction model to develop future projections of extinctions worldwide based on simulations from three global climate models.  Future projections (for scenario A2a, IPCC 3rd Assessment Report) suggest that by 2080, 39% of lizard populations and 20% of all lizard species will be extinct.


Sushama, L., N. Khaliq and R. Laprise. 2010. Dry spell characteristics over Canada in a changing climate as simulated by the Canadian RCM. Global and Planetary Change 74, 1-14.)

A study using the Canadian regional climate model projects an increased risk in the future of growing season conditions conducive to drought in the already drought-prone Southern Prairies region, southernmost Ontario and Quebec, and the Maritimes.

Global climate models generally project wetter winter and spring seasons across Canada in the future but dryer summers in southern Canada, although there is greater uncertainty about the latter. A new study by Canadian scientists investigates changes in dry spells over Canada in the future using the Canadian Regional Climate Model (RCM) which, with its higher spatial resolution, may be better able to resolve changes in extreme events at regional scales.  A 140-year simulation spanning the period 1961-2100 was conducted using the fourth generation RCM with boundary conditions provided by a simulation with the Canadian global climate model (CGCM3) driven by a relatively high emission scenario (IPCC SRES A2). The RCM’s ability to simulate current dry spell conditions was first evaluated for the period 1971-2000 using data from Environment Canada’s precipitation network. Some model biases were detected. Projected changes in mean number of dry days (days with very little to no rain) and ‘dry spells’ (extended periods of dry days), and maximum dry spell return periods were investigated for the April-September period. For most of Canada, a decrease in mean number of dry days and an increase in mean number of dry spells are projected.  For southern Canada, including the Windsor-Quebec corridor and parts of the Maritimes, the opposite pattern is expected, with increases in mean number of dry days and decreases in mean number of dry spells. The authors explain that in higher latitudes, the expectation is for more precipitation generally which will break up the longer dry spells experienced currently into a greater number of dry spells of shorter duration. The projected decrease in the number of dry spells for the southern regions is associated with longer dry spells in future climate; a result that was also reflected in the return period analysis for maximum dry spells.  Overall, the regions with the highest sensitivity to projected changes in dry periods are shown to be the large region encompassing the southern Prairies, along with the Windsor-Quebec corridor and Maritime region.


Williams, B. and A.G. Grottoli. 2010. Recent shoaling of the nutricline and thermocline in the western tropical Pacific. Geophysical Research Letters, Vol 37, L22601, doi: 10.1029/2010GL044867.

 

A new study based on stable isotope records from corals identifies a decrease in the depth of the warm surface layer in the western tropical Pacific.  This is consistent with a weakening of atmospheric circulation over the tropical Pacific projected by many climate models in response to global warming.

The mean state of the tropical Pacific Ocean influences global climate through atmospheric and oceanic teleconnections to remote regions.  Recent modeling studies have suggested that impacts of increasing atmospheric greenhouse gas concentrations in the tropical Pacific may include a weakening of the Walker circulation (which affects the easterly trade winds, oceanic upwelling, convection and precipitation patterns etc.) and a shoaling (i.e. rise) in the depth of the nutricline and thermocline in the western tropical Pacific (WTP).  Both the nutricline and thermocline give an indication of the depth at which warm, nutrient poor surface waters are separated from cool, nutrient rich waters and are closely related in the WTP.  Since there are insufficient direct observational records to identify changes in nutricline and thermocline depth, Williams and Grottoli used proxy records, in this case, dated, high-resolution stable isotope records from corals. They sampled soft corals and black corals from reefs near Palau (in the WTP) growing at three depths (5m, 85m and 105m).  These corals are not restricted to near-surface waters because their food source is particulate organic matter in the water column. Changes in food source with depth produce differences in the isotope geochemistry of the coral skeleton, providing a proxy for the past depth of the nutricline and associated thermocline.  The results indicate that, since the 1970s, the nutricline and thermocline have shoaled and primary productivity has increased in the WTP.  The authors note that the magnitude and duration of this shoaling is unprecedented over the past 115 years.  These are the first subsurface proxy records (below 20m) to indicate that the Walker circulation has weakened over the 20th century consistent with recent modeling studies of the impacts of global warming on this region.