Climate Forcing Scenarios Research Articles

Eastern Bering Sea shelf environmental and lower trophic level responses to climate forcing: Results of dynamical downscaling from CMIP6

In this study we present projected changes in the Eastern Bering Sea shelf (EBS) biophysical processes in response to climate forcing scenarios from the Coupled Model Intercomparison Phase 6 (CMIP6). These changes are obtained by dynamical downscaling using a Bering Sea regional model. Surface atmospheric and ocean boundary forcing from three Earth System Models (ESMs) in CMIP6, and a low and a high emission scenario of Shared Socioeconomic Pathway (SSP126 and SSP585) of each of the ESMs are considered. Ensemble mean results suggest that, contrary to an anticipated increase in ocean stratification under warming, diminishing ice cover in response to climate forcing and resultant reduced surface freshening weakens EBS stratification in the melt season. Modeled ensemble mean phytoplankton and zooplankton biomass on the EBS exhibits subsurface maxima during the growing season; the amplitude of these maxima decreases with warming, along with a reduction in primary productivity and oxygen concentration over much of the EBS water column. Phenology of both phytoplankton and zooplankton biomass on the EBS shifts earlier, leading to an increase (decrease) in biomass averaged between April–July (August–November), while annually averaged biomass decreases under warming. Projected changes of primary and secondary plankton biomass at the end of the 21st century are not well separated between the SSP126 and SSP585 scenario in light of the large across model spread under each scenario. The projected ensemble mean warming amplitude of the EBS summer bottom temperature is largely unchanged between results forced by the Coupled Model Intercomparison Phase 5 Representative Concentration Pathway 8.5 (CMIP5 RCP8.5) and CMIP6 SSP585 scenarios. Likewise, the reduction rate of annual mean phytoplankton and large zooplankton biomass are comparable between RCP8.5 and SSP585 projections, even though the absolute amplitudes of biomass are sensitive to modeling parameters such as the solar irradiance attenuation curve. Hence, within the Bering Sea dynamical downscaling framework, projected long-term warming trends in EBS bottom temperature and plankton biomass reduction rates are robust responses to climate forcing.

Sustainability of Canada’s forestry sector may be compromised by impending climate change

Climate change poses a serious risk to long-term sustainable forest management, particularly when projecting future wood supply for forestry operations. However, few studies have accounted for the cumulative and interacting impacts of climate change on forest productivity and natural disturbances; even fewer have considered drought impacts when projecting wood supply. We modeled how disturbance- and drought-induced tree mortality will affect wood supply in three regions of Canada’s boreal forest over a 200-year period under three climate-forcing scenarios. We project strong declines in overall aboveground biomass due to increases in mortality caused mainly by increased drought and wildfire, particularly in drier, western regions. Using two management strategies, we show that maintaining current long-term sustainable harvesting levels will be extremely challenging depending on the level of anthropogenic climate forcing. Increased wildfire activity under severe climate forcing will strongly decrease the availability of harvestable stands. In western areas that are already water-limited, harvesting levels will need to be low to remain sustainable. Our results show that Canada’s future wood supply and sustainable forest management practices are highly vulnerable to changes in climate; hence adaptation actions are needed to lower these vulnerabilities.

Illustrative Analysis of Probabilistic Sea Level Rise Hazard

AbstractSea level rise results from several contributing physical processes, including ocean thermal expansion and glacier and ice sheet mass loss. Future projections of sea level remain highly uncertain due to several sources of aleatory and epistemic uncertainty. Quantifying different sources of sea level rise involves considering possible pathways of future radiative forcing and integrating models of different sea level rise processes. The probabilistic hazard analysis strategy has been proposed for combining sea level rise prediction models and climate forcing scenarios to examine sea level rise prediction uncertainty and the sources of this uncertainty. In this study we carry out an illustrative probabilistic sea level rise hazard analysis using ensembles of sea level rise predictions and emissions scenarios from the literature. This illustrative analysis allows us to estimate the probability that sea level rise will exceed a specified threshold at a given location and time and highlights how sea level rise uncertainty is sensitive to scenario inputs and sea level rise projection modeling choices. Probabilistic hazard is depicted for Earth using sea level rise hazard maps. We also demonstrate how hazard deaggregation can help us quantify the relative contributions of sea level rise sources, prediction models, and climate forcing scenarios to sea level rise hazard. The ice sheet contribution to sea level rise has a large impact on probabilistic projection of sea level rise due to the disagreements between current ice sheet models related to differences in modeling ice sheet instability.

Circumpolar permafrost maps and geohazard indices for near-future infrastructure risk assessments

Ongoing climate change is causing fundamental changes in the Arctic, some of which can be hazardous to nature and human activity. In the context of Earth surface systems, warming climate may lead to rising ground temperatures and thaw of permafrost. This Data Descriptor presents circumpolar permafrost maps and geohazard indices depicting zones of varying potential for development of hazards related to near-surface permafrost degradation, such as ground subsidence. Statistical models were used to predict ground temperature and the thickness of the seasonally thawed (active) layer using geospatial data on environmental conditions at 30 arc-second resolution. These predictions, together with data on factors (ground ice content, soil grain size and slope gradient) affecting permafrost stability, were used to formulate geohazard indices. Using climate-forcing scenarios (Representative Concentration Pathways 2.6, 4.5 and 8.5), permafrost extent and hazard potential were projected for the 2041–2060 and 2061–2080 time periods. The resulting data (seven permafrost and 24 geohazard maps) are relevant to near-future infrastructure risk assessments and for targeting localized geohazard analyses.

Pavement Risk Assessment for Future Extreme Precipitation Events under Climate Change

Pavement infrastructure is experiencing unanticipated climate conditions caused by global warming. Extreme weather events, such as extreme precipitations, are increasing in intensity and frequency, creating rising concern in pavement vulnerability and resilience analysis. Previous design approaches based on historical climate data may no longer be adequate for addressing future conditions. To promote pavement resilience under climate change, assessing pavement risk for extreme events is essential for prioritizing vulnerable infrastructure and developing adaptation strategies. The objective of this study is to develop a quantitative evaluation methodology for assessing pavement risk from extreme precipitations under climate change. Hazard analysis, fragility modeling, and cost estimation are the three major components for risk evaluation. An ensemble of 24 global climate models is used for predicting future extreme precipitations under various climate-forcing scenarios. The Mechanistic-Empirical Pavement Design Guide is employed to simulate performance change for performing fragility modeling. Risk assessment models considering a full range of hazards were used to quantify risk of asset value loss over specified analysis periods. Results indicate that future extreme precipitation events are expected to cause an increased medium risk of asset value loss. However, high uncertainties are involved in the estimation owing to variations in predicted climates. Major pavement damages do not necessarily equate with highest risk because the probability of occurrence of major damage is relatively lower. The proposed approach provides a practical tool for analyzing the interaction among extreme precipitation levels, pavement designs, damage states, occurrence probability, and asset value at risk.

Model-specification uncertainty in future area burned by wildfires in Canada

Climate change will drive significant changes in annual area burned (burning rates) in the boreal forest although the trends, which are highly variable among studies, which may be caused by model specifications. In order to investigate this, we used 100 models predicting burning rates that are based on two predictor datasets (annual or 30-year averages) and five statistical algorithms (generalised linear model (GLM), random forest, gradient-boosted model (GBM), regression trees, multivariate adaptive regression splines (MARS)) to build a consensus model projecting future burning rates in boreal Canada with three global climate models (GCMs) (CanESM2, HadGEM and MIROC) and three anthropogenic climate forcing scenarios (RCP 2.6, RCP 4.5 and RCP 8.5). Results of the ensemble models were then used to quantify and map the uncertainty created by model specifications. The consensus model projects strong increase (>4-fold by 2080s) in burning rates, particularly under high climate-forcing scenarios. Even with very high goodness-of-fit in the consensus model, the model-specification uncertainty for future periods (>200%) could still be much higher than that of different GCMs and RCP scenarios. When tallied, we show that the total uncertainty could greatly hinder our ability to detect significant trends in burning rates for much of Canada at the end of the 21st century.

Problems encountered when defining Arctic amplification as a ratio.

In climate change science the term ‘Arctic amplification’ has become synonymous with an estimation of the ratio of a change in Arctic temperatures compared with a broader reference change under the same period, usually in global temperatures. Here, it is shown that this definition of Arctic amplification comes with a suite of difficulties related to the statistical properties of the ratio estimator itself. Most problematic is the complexity of categorizing uncertainty in Arctic amplification when the global, or reference, change in temperature is close to 0 over a period of interest, in which case it may be impossible to set bounds on this uncertainty. An important conceptual distinction is made between the ‘Ratio of Means’ and ‘Mean Ratio’ approaches to defining a ratio estimate of Arctic amplification, as they do not only possess different uncertainty properties regarding the amplification factor, but are also demonstrated to ask different scientific questions. Uncertainty in the estimated range of the Arctic amplification factor using the latest global climate models and climate forcing scenarios is expanded upon and shown to be greater than previously demonstrated for future climate projections, particularly using forcing scenarios with lower concentrations of greenhouse gases.

Evaluating adaptation options for urban flooding based on new high-end emission scenario regional climate model simulations

Climate change adaptation studies on urban flooding are often based on a model chain approach from climate forcing scenarios to analysis of adaptation measures. Previous analyses of climate change impacts in Copenhagen, Denmark, were supplemented by 2 high-end scenario simulations. These include a regional climate model projection forced to a global temperature increase of 6°C in 2100 as well as a projection based on a high radiative forcing scenario (RCP8.5). With these scenarios, projected impacts of extreme precipitation increase significantly. For extreme sea surges, the impacts do not seem to change substantially compared to currently applied projections. The flood risk (in terms of expected annual damage, EAD) from sea surge is likely to increase by more than 2 orders of magnitude in 2100 compared to the present cost. The risk from pluvial flooding in 2000 is likely to increase by almost 4 and 8 times the current EAD for the RCP8.5 and 6°C scenario, respectively. For both hazards, business-as-usual is not a possible scenario, since even in the absence of policy-driven changes, significant autonomous adaptation is likely to occur. Copenhagen has developed an adaptation plan to pluvial flooding that makes the urban areas more robust and reduces the risk of flooding under the current climate to a very low level. The reduction in flood risk for the A1B scenario is substantial (corresponding to 0.2−0.3 times the current EAD in 2100), and even in the high-end scenarios, the risk is significantly reduced (corresponding to 0.6−1.0 and 1.2−2.1 times the current EAD for the RCP8.5 and 6°C scenario, respectively).

Impacts of human alteration of the nitrogen cycle in the US on radiative forcing

Nitrogen cycling processes affect radiative forcing directly through emissions of nitrous oxide (N2O) and indirectly because emissions of nitrogen oxide \((\hbox{NO}_{x})\) and ammonia (NH3) affect atmospheric concentrations of methane (CH4), carbon dioxide (CO2), water vapor (H2O), ozone (O3) and aerosols. The emissions of N2O are mostly from agriculture and they contribute to warming on both short and long time scales. The effects of \(\hbox{NO}_{{x}}\) and NH3 on CH4, O3, and aerosols are complex, and quantification of these effects is difficult. However, the net result on time scales of decades is likely one of cooling, which becomes less significant on longer time scales. Deposition of N onto ecosystems also affects sources and sinks of N2O, CH4, and CO2, but the dominant effect is changes in carbon (C) stocks. Primary productivity in most temperate ecosystems is limited by N, so inputs from atmospheric deposition tend to stimulate plant growth and plant litter production, leading in some cases to significant C sequestration in biomass and soils. The literature reviewed here indicates a range of estimates spanning 20–70 kg C sequestered per kg N deposited in forests, which are the dominant C sinks. Most of the sequestration occurs in aboveground forest biomass, with less consistency and lower rates reported for C sequestration in soils. The permanency of the forest biomass sink is uncertain, but data for the fate of forest products in the US indicate that only a small fraction of enhanced forest biomass C is sequestered in long-term harvest products or in unmanaged forests. The net effect of all of these N cycle processes on radiative forcing in the US is probably a modest cooling effect for a 20-year time frame, although the uncertainty of this estimate includes zero net effect, and a modest warming for a 100-year time frame. We know that N-cycling processes are important and that biotic feedbacks to climate change are unlikely to be properly modeled or assessed without including C–N interactions. However, due to the complexity of biological processes involving C–N–climate interactions, biogeochemical models are still poorly constrained with respect to ecosystem responses to impacts of N deposition and climate change. Only recently have N-cycling processes been incorporated into Earth system models for C–N interactions. The robustness of these models remains to be demonstrated. Much work remains for improving their representation in models used to simulate climate forcing scenarios.

Dendroclimatic relationships and possible implications for mountain birch and Scots pine at treeline in northern Sweden through the 21st centuryThis article is a contribution to the series Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition.

Changing climate in the Arctic is expected to have significant effects on the pattern and distribution of terrestrial vegetation. Species characteristic of specific zones in the mountains of northern Sweden have been shown to migrate up- and down-slope with changes in climate over the Holocene. This study evaluates the potential for Scots pine (Pinus sylvestris L.) to become a treeline dominant at Fennoscandian treelines, replacing mountain birch (Betula pubescens subsp. czerepanovii (Orlova) Hämet-Ahti). Data from paired mountain birch and Scots pine tree-ring chronologies for eight locations in northern Sweden are used to develop climate – tree ring width index (RWI) relationships. Modeled climate–RWI relationships are then used to predict the relative RWI values of the two species under a suite of climate-forcing scenarios using an ensemble of three global climate models. Results indicate that mountain birch and Scots pine RWI are both correlated with summer temperatures, but Scots pine is more likely than mountain birch to be influenced by moisture conditions. Predictions of RWI under future climate conditions indicate that mountain birch is unlikely to be replaced by Scots pine within the next century.

Climate change induced salinisation of artificial lakes in the Netherlands and consequences for drinking water production

In this paper we present a modelling study to investigate the impacts of climate change on the chloride concentration and salinisation processes in two man-made freshwater lakes in the Netherlands, Lake IJsselmeer and Lake Markermeer. We used a transient compartmental chloride and water balance model to elucidate the salinisation processes occurring under present conditions and assess future salinisation under two climate forcing scenarios. The model results showed that the Rhine River is the dominant determinant for the chloride concentration in both lakes, followed by drainage of brackish groundwater from the surrounding polders. The results further show that especially during dry years, seawater intrusion through the tidal closure dam is an important source of chloride to Lake IJsselmeer. The results from the climatic forcing scenarios show that Lake IJsselmeer is especially vulnerable to climate-induced salinisation whereas effects on Lake Markermeer are relatively small. Peak chloride concentrations at the raw water intake of the Andijk drinking water facility on Lake IJsselmeer are projected to increase to values above 250 mg/l in the most far-reaching climate change scenario W+ in 2050 for dry years. This is well above the maximum allowable concentration of 150 mg/l for chloride in drinking water. Modelling showed that climate change impacts the chloride concentrations in a variety of ways: 1) an increasing occurrence of low river flows from summer to autumn reduces the dilution of the chloride that is emitted to the Rhine with a constant load thereby increasing its concentration; 2) increased open water evaporation and reduced rainfall during summer periods and droughts increases the chloride concentration in the water; and 3) rises in sea level increase seawater intrusion through the tidal closure dam of Lake IJsselmeer. The processes described here are likely to affect many other tidal rivers or lakes and should be considered when planning future raw water intake stations for drinking water production or agricultural water supply.