Implications For Future Climate Research Articles

Annual Report 2021

CAGE investigates the natural release of the greenhouse gas methane from the Arctic seafloor. Vast amounts of methane are trapped at shallow depths below the seafloor as gas hydrates, ice-like mixtures of gas and water. Current warming makes these shallow Arctic greenhouse gas reservoirs particularly vulnerable to thawing. CAGE investigates the processes involved, how these affect the ecosystem, the ocean and the atmosphere, and implications for future climate and environment.

Implications of future climate- and land-change scenarios on grassland bird abundance and biodiversity in the Upper Missouri River Basin

Over the past decades, numerous threats from climate- and land-use change to ecosystems have been identified. Grassland ecosystems are among the most endangered in the world and ongoing grassland declines in the Great Plains have been a major concern for avian biodiversity conservation. Threat mitigation may include biofuel cultivation, CO2 emissions reductions, and land conservation strategies. However, spatially explicit and species-specific population responses to future scenarios remain unknown. We show how future land-use and climate scenarios may affect abundance and biodiversity patterns for grassland birds in the Upper Missouri River Basin. We used georeferenced abundance records, 20 environmental predictors, and gradient boosting machines to create spatial abundance models for 24 grassland bird species. Models were scored to current conditions and seven future landcover/climate-change scenarios to spatially predict changes in bird abundance for 2050. Model accuracy varied by species (0.2% ≤ NRMSE ≤ 39.3%) but spatial predictions were highly accurate (.03 ≤ MAE ≤ 7.67). Mean abundances declined for eight species in at least one scenario, whereas abundances increased for 16 species. Multi-species change analyses identified areas of decreasing abundance, particularly in the southeast, whereas increasing were predicted at higher elevations to the west. Important predictors included temperature, forest distance, and elevation. Predicted abundances varied by species and geography. Abundances and distributions expanded for most species, but multi-species declines also occurred in many low-elevation areas. These models may improve understanding of species-specific responses to environmental change by identifying emerging areas of avian conservation concern.

Evaluating the Implications of Climate Projections on Heat Hardiness Zones for Green Infrastructure Planning

Background: Green Infrastructure (GI) is widely being promoted as an adaptation strategy for urban flooding. Like urban flooding, tree species could be impacted by future climatic conditions. However, there have been limited studies on the implications of future climate on GI planning, mostly due to the lack of climate data at higher spatial resolutions. Objective: In this paper, we analyze the implications of climate projections on heat hardiness zones since this could impact the GI landscape in the coming years. This is an extension of our earlier work on evaluating impacts of climate projections on plant hardiness zones. </P><P> Method: Using downscaled daily temperature data from ten Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models for the historical (1980 - 2005) and projected (2025 - 2050) periods, we analyzed future heat hardiness zones in the watershed bounding Knox County, TN. We analyzed the implications of these outputs for the current list of suggested native and non-native tree species selected for GI in the study area. Results: All the models suggest that a considerable part of the study area will move into the next warmer heat zone. While most trees remain suitable for GI, several are at the limit of their ideal heat zones. Conclusion: The insights from this study will help guide the selection and placement of GI across the study area. Specifically, it should help green infrastructure planners design better mitigation and adaptation strategies to achieve higher returns on investments as more cities are now investing in GI projects.

Thermal energy and stress properties as the main drivers of regional distribution of coral species richness in the Indian Ocean

AbstractAimLarge‐scale variation in species richness results from multiple environmental controls. We proposed to identify the main factors that influence species richness of reef corals to provide insight into natural forces and their implications for future climate impacts.LocationIndian Ocean.MethodsWe applied quantile regression (QR) to predict coral species richness and to evaluate the influence of reef area, biogeographical connection – represented by reef area up‐current, geological provinces defined by plate tectonics, latitude, longitude and mainland‐island separation, the physico‐chemical factors of photosynthetically active radiation (PAR), salinity and primary productivity and seven properties of sea surface temperature (mean, minimum, maximum, standard deviation, range, kurtosis and skewness) on coral species richness. Predictions at three quantiles (0.50, 0.75 and 0.95) were compared against ordinary least squares regression (OLS) analysis.ResultsAll four models successfully predicted species richness, with the 95% QR model showing the best fit. According to this model, reef area, number of reefs up‐current and mean‐SST had positive effects while maximum and kurtosis‐SST had negative effects on richness. The distribution of observed richness values in relation to the regression line suggested this model revealed the main limiting factors. High predicted richness sites were located in the region from Western Australia to Central Indian Ocean Islands and southern India, the Mozambique Channel and East Africa and Southern Red Sea and Gulf of Aden. Sites with low predicted richness were Arabian/Persian Gulf and Gulf of Oman, South Africa and south‐west Madagascar, Gulf of Kutch, Bay of Bengal and the Mascarenes.ConclusionsTemperature properties played a prominent role in influencing species richness mainly as latent energy and stress rather than thermal stability. These thermal properties indicate the conditions needed to promote coral diversity and selecting climate refugia for conservation management.

Variability and trends in surface seawater pCO2 and CO2 flux in the Pacific Ocean

AbstractVariability and change in the ocean sink of anthropogenic carbon dioxide (CO2) have implications for future climate and ocean acidification. Measurements of surface seawater CO2 partial pressure (pCO2) and wind speed from moored platforms are used to calculate high‐resolution CO2 flux time series. Here we use the moored CO2 fluxes to examine variability and its drivers over a range of time scales at four locations in the Pacific Ocean. There are significant surface seawater pCO2, salinity, and wind speed trends in the North Pacific subtropical gyre, especially during winter and spring, which reduce CO2 uptake over the 10 year record of this study. Starting in late 2013, elevated seawater pCO2 values driven by warm anomalies cause this region to be a net annual CO2 source for the first time in the observational record, demonstrating how climate forcing can influence the timing of an ocean region shift from CO2 sink to source.

Changes to the tropical circulation in the mid-Pliocene and their implications for future climate

Abstract. The two components of the tropical overturning circulation, the meridional Hadley circulation (HC) and the zonal Walker circulation (WC), are key to the re-distribution of moisture, heat and mass in the atmosphere. The mid-Pliocene Warm Period (mPWP; ∼ 3.3–3 Ma) is considered a very rough analogue of near-term future climate change, yet changes to the tropical overturning circulations in the mPWP are poorly understood. Here, climate model simulations from the Pliocene Model Intercomparison Project (PlioMIP) are analyzed to show that the tropical overturning circulations in the mPWP were weaker than preindustrial circulations, just as they are projected to be in future climate change. The weakening HC response is consistent with future projections, and its strength is strongly related to the meridional gradient of sea surface warming between the tropical and subtropical oceans. The weakening of the WC is less robust in PlioMIP than in future projections, largely due to inter-model variations in simulated warming of the tropical Indian Ocean (TIO). When the TIO warms faster (slower) than the tropical mean, local upper tropospheric divergence increases (decreases) and the WC weakens less (more). These results provide strong evidence that changes to the tropical overturning circulation in the mPWP and future climate are primarily controlled by zonal (WC) and meridional (HC) gradients in tropical–subtropical sea surface temperatures.

Implications of future climate on water availability in the western Canadian river basins

ABSTRACTPrecipitation, temperature, and evaporative demand are the most dominant factors affecting water availability in a region. This study examines projected changes in these hydro‐climatic variables over western Canada under two greenhouse gas emissions scenarios using statistically downscaled, high resolution climate data generated by six Global Climate Models (GCMs) from the latest Coupled Model Intercomparison Project (CMIP5). Potential changes in the spatial and seasonal distributions of water availability over nine major western Canadian river basins are examined by computing the 3‐ and 12‐month standardized precipitation and evapotranspiration indices (SPEI‐3 and SPEI‐12). While individual GCM projections vary on the rate and seasonality of changes, they all indicate similar spatial and temporal patterns. The highest projected increases in precipitation and temperature are primarily in the northern basins, with some decreases in summer precipitation in the southern basins. The evolution of the SPEI‐12 values for the southern basins such as Columbia, Saskatchewan, Fraser and Athabasca indicate a gradual increase in the magnitude and duration of water deficit, while the reverse was found for most of the northern basins such as Peel/Lower Mackenzie, Liard, and Northern Pacific that show a gradual increase in water surplus on an annual basis. The SPEI‐3, however, shows that almost all river basins in western Canada, with the exception of Peel/Lower Mackenzie that are located in the extreme north of the study region, are projected to experience decreasing water availability in summer. In general, the study highlights the potential changes in the spatial and seasonal distribution of western Canadian water resources and sets the stage for a more detailed and process based hydro‐climate modelling study to be conducted in the region.

Eurasian snow cover variability in relation to warming trend and Arctic Oscillation

Two distinct modes of snow cover variability over Eurasia are investigated using cyclostationary empirical orthogonal function (CSEOF) analysis. The first mode of Eurasian snow cover extent (SCE) represents a seasonally asymmetric trend between spring and fall. The spring SCE shows a decreasing trend, while the fall SCE particularly in October exhibits a clear increasing trend. This seasonally asymmetric trend of SCE is closely linked to Arctic sea ice decline accompanied by warming in the northern Eurasia. The decreased SCE during spring is primarily attributed to the warm air temperature anomalies, while the increased SCE in October results from the loss of sea ice and the ensuing moisture transport to the atmosphere, which is realized as increased snow in October. The second mode of Eurasian SCE, on the other hand, is closely related to Arctic Oscillation (AO), which is a dominant mode of Northern Hemisphere atmospheric variability. The snow cover variability over Europe during winter is largely affected by AO variability, rather than the warming signal represented by the first CSEOF mode. Detailed descriptions of the two distinct modes of Eurasian SCE and their interactions with oceanic and atmospheric variables are presented along with possible implications for future climate.

Climate and biogeochemical response to a rapid melting of the West Antarctic Ice Sheet during interglacials and implications for future climate

interglacials onto the global climate‐carbon cycle system using the Earth system model of intermediate complexity LOVECLIM. Prescribing a meltwater pulse in the Southern Ocean that mimics a rapid disintegration of the WAIS, a substantial cooling of the Southern Ocean is simulated that is accompanied by an equatorward expansion of the sea ice margin and an intensification of the Southern Hemispheric Westerlies. The strong halocline around Antarctica leads to suppression of Antarctic Bottom Water (AABW) formation and to subsurface warming in areas where under present‐day conditions AABW is formed. This subsurface warming at depths between 500 and 1500 m leads to a thermal weathering of the WAIS grounding line and provides a positive feedback that accelerates the meltdown of the WAIS. Our model results further demonstrate that in response to the massive expansion of sea ice, marine productivity in the Southern Ocean reduces significantly. A retreat of the WAIS, however, does not lead to any significant changes in atmospheric CO2. The climate signature of a WAIS collapse is structurally consistent with available paleoproxy signals of the last interglacial MIS5e. Citation: Menviel, L., A. Timmermann, O. E. Timm, and A. Mouchet (2010), Climate and biogeochemical response to a rapid melting of the West Antarctic Ice Sheet during interglacials and implications for future climate, Paleoceanography, 25, PA4231, doi:10.1029/2009PA001892.

Implications of future climate and atmospheric CO2 content for regional biogeochemistry, biogeography and ecosystem services across East Africa

AbstractWe model future changes in land biogeochemistry and biogeography across East Africa. East Africa is one of few tropical regions where general circulation model (GCM) future climate projections exhibit a robust response of strong future warming and general annual‐mean rainfall increases. Eighteen future climate projections from nine GCMs participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment were used as input to the LPJ dynamic global vegetation model (DGVM), which predicted vegetation patterns and carbon storage in agreement with satellite observations and forest inventory data under the present‐day climate. All simulations showed future increases in tropical woody vegetation over the region at the expense of grasslands. Regional increases in net primary productivity (NPP) (18–36%) and total carbon storage (3–13%) by 2080–2099 compared with the present‐day were common to all simulations. Despite decreases in soil carbon after 2050, seven out of nine simulations continued to show an annual net land carbon sink in the final decades of the 21st century because vegetation biomass continued to increase. The seasonal cycles of rainfall and soil moisture show future increases in wet season rainfall across the GCMs with generally little change in dry season rainfall. Based on the simulated present‐day climate and its future trends, the GCMs can be grouped into four broad categories. Overall, our model results suggest that East Africa, a populous and economically poor region, is likely to experience some ecosystem service benefits through increased precipitation, river runoff and fresh water availability. Resulting enhancements in NPP may lead to improved crop yields in some areas. Our results stand in partial contradiction to other studies that suggest possible negative consequences for agriculture, biodiversity and other ecosystem services caused by temperature increases.

Surface temperatures of the Mid-Pliocene North Atlantic Ocean: implications for future climate

The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions. With continents basically in their current positions and atmospheric CO2 similar to early twenty-first century values, the cause of Mid-Pliocene warmth remains elusive. Understanding the behaviour of the North Atlantic Ocean during the Mid-Pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change. Under the framework of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) sea surface reconstruction, we synthesize Mid-Pliocene North Atlantic studies by PRISM members and others, describing each region of the North Atlantic in terms of palaeoceanography. We then relate Mid-Pliocene sea surface conditions to expectations of future warming. The results of the data and climate model comparisons suggest that the North Atlantic is more sensitive to climate change than is suggested by climate model simulations, raising the concern that estimates of future climate change are conservative.

Ozone depletion due to increasing anthropogenic trace gas emissions: role of stratospheric chemistry and implications for future climate

The response of the atmosphere to increasing emissions of radatively active trace gases (COz, CH,, N 2 0 , o3 and CFCs) is calculated by means of a l-dimensional coupled chemical-radiativetransport model. We identify the sign and magnitude of the feedback between the chemistry and thermal structure of the atmosphere by examining steady state changes in stratospheric ozone and surface temperature in response to perturbations in trace gases of anthropogenic origin. Next, we assess the possible decline in stratospheric ozone and its effect on troposphere-stratosphere temperature trends for the period covering the pre-industrial era to the present. Future trends are also considered using projected 'business-as-usual' trace gas scenario (scenario BAU) and that expected as a result of global phase-out of production of CFCs by the year 2000 (scenario MP). The numerical experiments take account of the effect of stratospheric aerosol loading due to volcanic eruptions and the influence of the thermal inertia of the ocean. Results indicate that the trace gas increase from the period 1850 to 1986 could already have contributed to a 3 to 10 % decline in stratospheric ozone and that this decline is expected to become more pronounced by the year 2050, amounting to a 43 % ozone loss at 40 km for the scenario BAU. The total column ozone Increase of 1.5 % obtained in our model calculations for the present-day atmosphere is likely to change sign with time leading to a net decrease of 12.7 % by the middle of next century. The equilibrium surface warming for the period 1850 to 1986 is found to be 0.7 K and our calculations indicate that thls warming will reach 2.6 K by the year 2050. As a result of radiativechemical interactions, a large stratospheric cooling (16.4 K) is likely by the middle of the next century. In case the control measures on production of CFCs as laid down in the London Amendment of the Montreal Protocol are implemented by all countries and a global phase-out of CFCs takes place by the year 2000, the ozone loss at 40 km could be restricted to 17 % by the year 2050 (net column decrease of only 2.9%). This would, however, only marginally reduce the stratospheric cooling to 12.6 K. The greenhouse warming at the surface expected by the middle of the next century with enforcement of the Montreal Protocol restrictions is likely to be 2 K.