Range Of Emission Scenarios Research Articles

Projected increases in surface melt and ice loss for the Northern and Southern Patagonian Icefields

The Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI) have increased their ice mass loss in recent decades. In view of the impacts of glacier shrinkage in Patagonia, an assessment of the potential future surface mass balance (SMB) of the icefields is critical. We seek to provide this assessment by modelling the SMB between 1976 and 2050 for both icefields, using regional climate model data (RegCM4.6) and a range of emission scenarios. For the NPI, reductions between 1.5 m w.e. (RCP2.6) and 1.9 m w.e. (RCP8.5) were estimated in the mean SMB during the period 2005–2050 compared to the historical period (1976–2005). For the SPI, the estimated reductions were between 1.1 m w.e. (RCP2.6) and 1.5 m w.e. (RCP8.5). Recently frontal ablation estimates suggest that mean SMB in the SPI is positively biased by 1.5 m w.e., probably due to accumulation overestimation. If it is assumed that frontal ablation rates of the recent past will continue, ice loss and sea-level rise contribution will increase. The trend towards lower SMB is mostly explained by an increase in surface melt. Positive ice loss feedbacks linked to increasing in meltwater availability are expected for calving glaciers.

Future Changes in Wet and Dry Season Characteristics in CMIP5 and CMIP6 simulations

AbstractClimate change will result in more dry days and longer dry spells, however, the resulting impacts on crop growth depend on the timing of these longer dry spells in the annual cycle. Using an ensemble of Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6) simulations, and a range of emission scenarios, here we examine changes in wet and dry spell characteristics under future climate change across the extended tropics in wet and dry seasons separately. Delays in the wet seasons by up to two weeks are projected by 2070-2099 across South America, Southern Africa, West Africa and the Sahel. An increase in both mean and maximum dry spell length during the dry season is found across Central and South America, Southern Africa and Australia, with a reduction in dry season rainfall also found in these regions. Mean dry season dry spell lengths increase by 5-10 days over north-east South America and south-west Africa. However, changes in dry spell length during the wet season are much smaller across the tropics with limited model consensus. Mean dry season maximum temperature increases are found to be up to 3°C higher than mean wet season maximum temperature increases over South America, Southern Africa and parts of Asia. Longer dry spells, fewer wet days, and higher temperatures during the dry season may lead to increasing dry season aridity, and have detrimental consequences for perennial crops.

A modified impulse-response representation of the global near-surface air temperature and atmospheric concentration response to carbon dioxide emissions

Abstract. Projections of the response to anthropogenic emission scenarios, evaluation of some greenhouse gas metrics, and estimates of the social cost of carbon often require a simple model that links emissions of carbon dioxide (CO2) to atmospheric concentrations and global temperature changes. An essential requirement of such a model is to reproduce typical global surface temperature and atmospheric CO2 responses displayed by more complex Earth system models (ESMs) under a range of emission scenarios, as well as an ability to sample the range of ESM response in a transparent, accessible and reproducible form. Here we adapt the simple model of the Intergovernmental Panel on Climate Change 5th Assessment Report (IPCC AR5) to explicitly represent the state dependence of the CO2 airborne fraction. Our adapted model (FAIR) reproduces the range of behaviour shown in full and intermediate complexity ESMs under several idealised carbon pulse and exponential concentration increase experiments. We find that the inclusion of a linear increase in 100-year integrated airborne fraction with cumulative carbon uptake and global temperature change substantially improves the representation of the response of the climate system to CO2 on a range of timescales and under a range of experimental designs.

Validation of a Pattern Scaling Approach for Determining the Maximum Available Renewable Freshwater Resource

Abstract A pattern scaling approach allows projection of regional climate changes under a wide range of emission scenarios. A basic assumption of this approach is that the spatial response pattern to global warming (scaling pattern) is the same for all emission scenarios. Precipitation minus evapotranspiration (PME) over land can be considered to be a measure of the maximum available renewable freshwater resource, and estimation of PME is fundamentally important for the assessment of water resources. The authors assessed the basic assumption of pattern scaling for PME by the use of five global climate models. A significant scenario dependency (SD) of the scaling pattern of PME was found over some regions. This SD of the scaling pattern of PME was mainly due to the SD and the nonlinear response of large-scale atmospheric and oceanic changes. When the SD of the scaling pattern of PME is significant in a target area, projections of the impact of climate change need to carefully take into consideration the SD. Although the SD of the anthropogenic aerosol scaling patterns tended to induce SDs of precipitation and evapotranspiration scaling patterns, the SDs of precipitation and evapotranspiration tended to cancel each other out. As a result, the SD of the PME scaling pattern tended to be insignificant over most regions where the SD of anthropogenic aerosol scaling patterns were significant. The authors could not find large impacts of land use change on PME scaling pattern, but the former may influence the latter on different time scales or spatial scales.

Multimodel ensemble projections of future climate extreme changes in the Haihe River Basin, China

Exploring the characteristic of the extreme climatic events, especially future projection is considerably important in assessing the impacts of climatic change on hydrology and water resources system. We investigate the future patterns of climate extremes (2001–2099) in the Haihe River Basin (HRB) derived from Coupled General Circulation Model (CGCM) multimodel ensemble projections using the Bayesian Model Average (BMA) approach, under a range of emission scenarios. The extremes are depicted by three extreme temperature indices (i.e., frost days (FD), growing season length (GSL), and Tmin >90th percentile (TN90)) and five extreme precipitation indices (i.e., consecutive dry days (CDD), precipitation ≥10 mm (R10), maximum 5-day precipitation total (R5D), precipitation >95th percentile (R95T), and simple daily intensity index (SDII)). The results indicate frost days display negative trend over the HRB in the 21st century, particularly in the southern basin. Moreover, a greater season length and more frequent warm nights are also projected in the basin. The decreasing CDD, together with the increasing R10, R5D, R95T, and SDII in the 21st century indicate that the extreme precipitation events will increase in their intensity and frequency in the basin. Meanwhile, the changes of all eight extremes climate indices under A2 and A1B scenarios are more pronounced than in B1. The results will be of practical significance in mitigation of the detrimental effects of variations of climatic extremes and improve the regional strategy for water resource and eco-environment management, particularly for the HRB characterized by the severe water shortages and fragile ecological environment.

Multi-model ensemble projections in temperature and precipitation extremes of the Tibetan Plateau in the 21st century

Projections of changes in climate extreme are important in assessing the potential impacts of climate change on social and natural systems. This article presents future projections of climate extremes in the Tibetan Plateau constructed from ensembles of coupled general circulation models (CGCMs) contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), under a range of emission scenarios. The extremes of temperature and precipitation are described by seven indices, namely, the frost day (FD), percentage of nights when T min > 90th percentile (TN90), consecutive dry days (CDD), annual count of days when precipitation >=10 mm (R10), maximum 5-day precipitation total (R5D), simple daily intensity index (SDII), and annual total precipitation when precipitation > 95th percentile (R95T). Results indicate that frost days decrease over the Tibetan Plateau in the 21st century. More frequent warm nights are also projected in the plateau. The increases of these temperature extremes under A2 and A1B scenarios are more pronounced than under B1. Heavy precipitation events for single days and pentads are projected to increase in their intensity over most parts of Tibetan Plateau. CDD, R10, R5D, R95T and SDII collectively suggest more extreme precipitation in the region (2011–2020). In addition, impacts of climate extremes changes on local water resources and fragile ecosystem are discussed as an extension of this article. The findings will be beneficial to project regional responses in this unique region to global climate change, and then to formulate regional strategies against the potential menaces of climate change.

Vegetation feedback under future global warming

It has been well documented that vegetation plays an important role in the climate system. However, vegetation is typically kept constant when climate models are used to project anthropogenic climate change under a range of emission scenarios in the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios. Here, an atmospheric general circulation model, and an asynchronously coupled system of an atmospheric and an equilibrium terrestrial biosphere model are forced by monthly sea surface temperature and sea ice extent for the periods 2051–2060 and 2090–2098 as projected with 17 atmosphere–ocean general circulation models participating in the IPCC Fourth Assessment Report, and by appropriate atmospheric carbon dioxide concentrations under the A2 emission scenario. The effects of vegetation feedback under future global warming are then investigated. It is found that the simulated composition and distribution of vegetation during 2051–2060 (2090–2098) differ greatly from the present, and global vegetation tends to become denser as expressed by a 21% (36%) increase in global mean leaf area index, which is most pronounced at the middle and high northern latitudes. Vegetation feedback has little effect on globally averaged surface temperature. On a regional scale, however, it induces statistically significant changes in surface temperature, in particular over most parts of continental Eurasia east of about 60°E where annual surface temperature is expected to increase by 0.1–1.0 K, with an average of about 0.4 K for each future period. These changes can mostly be explained by changes in surface albedo resulting from vegetation changes in the context of future global warming.

Characterizing uncertainty in modeling primary terrestrial ecosystem processes

The simulation results from models participating in the Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP) highlight the role of positive carbon‐climate feedback in accelerating growth of atmospheric CO2. The large range among models in the strength of this feedback indicates the uncertainty in our understanding of the response of the land and the oceans to continued climate warming and increasing CO2. Most of this uncertainty is associated with the response of terrestrial ecosystems to changes in climate and atmospheric CO2. The reasons for differences between models' responses to transient climate and CO2 forcing are not easily identified because of their complex parameterizations and spatially distributed processes. In this paper, we show that a simple box model can reasonably reproduce the globally averaged primary land‐atmosphere CO2 fluxes and carbon pools of two complex terrestrial ecosystem models (TEMs) over a range of emission scenarios. The parameters of the box model are calculated by fitting the box model to each TEM's response to transient climate and CO2 forcing. This approach is also applied to terrestrial carbon cycle components of carbon‐climate models participating in the C4MIP study. The resulting set of parameter values based on a common box model structure yields a wide range of parameter values, which suggests an absence of clear consensus in modeling primary terrestrial ecosystem processes and provides some insight into the reasons for divergent responses of terrestrial carbon cycle components.

Projected changes in temperature and precipitation extremes over the Yangtze River Basin of China in the 21st century

Projections of changes in climate extremes are important in assessing the potential impacts of climate change on societal and natural systems. We analyze future projections of climate extremes derived from an ensemble of coupled general circulation models (CGCMs) contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), under a range of emission scenarios. The extremes are described by seven indices based on temperature and precipitation (HWDI, TN90, CDD, R10, R5D, SDII, and R95T). The region of our focus is the Yangtze River Basin (YRB) in southern China. Results show a longer duration of heatwave over YRB in the 21st century than today, particularly in the headstream area. More frequent warm nights are also projected in the region. The increases of these temperature extremes under A2 and A1B scenarios are more pronounced than in B1. The change patterns of CDD and R10 are less uniform in the region compared to the other indices. Heavy precipitation events for single days and pentads are projected to increase in their intensity over the YRB. In addition, a larger fraction of the total annual precipitation is projected to occur during heavy precipitation events, i.e. events that exceed the 95th percentile.

Temperature and concentration feedbacks in the carbon cycle

Feedback processes in the carbon budget are investigated in a manner that parallels the treatment of feedback processes in the energy budget. The analysis is applied to simulations with the CCCma earth system model CanESM1 using a range of emission scenarios. For the atmosphere there is a positive “carbon‐temperature” feedback which acts to increase CO2 flux to the atmosphere as temperatures warm. There is also a negative “carbon‐concentration” feedback which acts to remove CO2 from the atmosphere via enhanced uptake of CO2 by the land and ocean as CO2 concentration increases. While the positive feedback associated with temperature change is reasonably linear and consistent as temperature increases, the feedback associated with CO2 concentration is not. The negative carbon‐concentration feedback weakens with increasing CO2 concentration thereby enhancing atmospheric CO2 and accelerating global warming. The behaviour of the inferred carbon‐concentration feedback is different for different emission scenarios implying a dependence on state variables other than CO2 concentration. The carbon‐concentration feedback behaviour inferred for a particular scenario may not, therefore, be used to infer system behaviour for other scenarios.

Going to the extremes

Projections of changes in climate extremes are critical to assessing the potential impacts of climate change on human and natural systems. Modeling advances now provide the opportunity of utilizing global general circulation models (GCMs) for projections of extreme temperature and precipitation indicators. We analyze historical and future simulations of ten such indicators as derived from an ensemble of 9 GCMs contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), under a range of emissions scenarios. Our focus is on the consensus from the GCM ensemble, in terms of direction and significance of the changes, at the global average and geographical scale. The climate extremes described by the ten indices range from heat-wave frequency to frost-day occurrence, from dry-spell length to heavy rainfall amounts. Historical trends generally agree with previous observational studies, providing a basic sense of reliability for the GCM simulations. Individual model projections for the 21st century across the three scenarios examined are in agreement in showing greater temperature extremes consistent with a warmer climate. For any specific temperature index, minor differences appear in the spatial distribution of the changes across models and across scenarios, while substantial differences appear in the relative magnitude of the trends under different emissions rates. Depictions of a wetter world and greater precipitation intensity emerge unequivocally in the global averages of most of the precipitation indices. However, consensus and significance are less strong when regional patterns are considered. This analysis provides a first overview of projected changes in climate extremes from the IPCC-AR4 model ensemble, and has significant implications with regard to climate projections for impact assessments.

Going to the Extremes

Projections of changes in climate extremes are critical to assessing the potential impacts of climate change on human and natural systems. Modeling advances now provide the opportunity of utilizing global general circulation models (GCMs) for projections of extreme temperature and precipitation indicators. We analyze historical and future simulations of ten such indicators as derived from an ensemble of 9 GCMs contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), under a range of emissions scenarios. Our focus is on the consensus from the GCM ensemble, in terms of direction and significance of the changes, at the global average and geographical scale. The climate extremes described by the ten indices range from heat-wave frequency to frost-day occurrence, from dry-spell length to heavy rainfall amounts. Historical trends generally agree with previous observational studies, providing a basic sense of reliability for the GCM simulations. Individual model projections for the 21st century across the three scenarios examined are in agreement in showing greater temperature extremes consistent with a warmer climate. For any specific temperature index, minor differences appear in the spatial distribution of the changes across models and across scenarios, while substantial differences appear in the relative magnitude of the trends under different emissions rates. Depictions of a wetter world and greater precipitation intensity emerge unequivocally in the global averages of most of the precipitation indices. However, consensus and significance are less strong when regional patterns are considered. This analysis provides a first overview of projected changes in climate extremes from the IPCC-AR4 model ensemble, and has significant implications with regard to climate projections for impact assessments.

Are Scientists underestimating climate change?

The consensus view of climate scientists, as represented by the 2001 Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report, is that the enhanced greenhouse effect likely will lead to global average surface warming by 2100 of between 1.4° and 5.8°C,and global sea level rise of between 9 and 88 centimeters. This assumes the climate sensitivity is in the range 1.5°–4.5°C for an equilibrium doubling of preindustrial carbon dioxide concentrations, and the Special Report on Emissions Scenarios (SRES) range of emissions scenarios [IPCC, 2000]. However, recent developments suggest that this dated IPCC view might underestimate the upper end of the range of possibilities and shift the probabilities toward an increasing risk of greater warmings and sea level rises by 2100.

The IPCC Third Assessment Report on the Scientific Basis of Climate Change

The Intergovernmental Panel on Climate Change (IPCC) has recently completed its Third Assessment Report on the Scientific Basis of Climate Change. The report builds on previous IPCC assessment reports in 1990 and 1995 and has been in preparation for the past three and a half years through the work of more than 500 scientists world wide who have been taking stock of the research findings reported in some 4000 peer—reviewed scientific papers. The report consists of a Summary for Policymakers, a Technical Summary and an underlying detailed report of fourteen chapters. The Summary for Policymakers was approved on a line by line basis by an intergovernmental session of the science working group (Working Group 1) of the IPCC, held in Shanghai, China on 17–20 January 2001, with the participation of some 45 of the 122 Lead Authors and official government delegations from 99 countries. The report concludes that, although many uncertainties remain, the past five years of observations and research have provided stronger evidence than hitherto of a human impact on global climate and increased confidence in the capability of climate models to project future global climate trends for a range of emission scenarios through the twenty first century. This article, which is based, in part, on the author's experience as Principal Delegate of Australia to the IPCC and as a member of the IPCC Bureau since 1994, describes the operation of the IPCC assessment process and the preparation, approval and main conclusions of the science component of the Third Assessment Report.

Nitrogen deposition and strategies for the control of acidification and eutrophication across Great Britain

It is now recognised that a multi-pollutant, multi-effect approach needsto be adopted to address the range of problems caused by atmosphericpollution. In this paper we use a relatively simple trajectory model (HARM)to explore the coupled behaviour of sulphur dioxide (SO2),oxides of nitrogen (NOx) and ammonia (NH3) andthe possible effects of future reductions in emissions of these pollutantson depositions of S and N across Great Britain. The performance of HARM withrespect to concentrations and depositions of NOy andNHx is assessed by comparison with data from nationalmonitoring networks. A range of emissions scenarios are modelled and theeffects of these reductions on critical loads exceedance are explored usingthe critical loads function (CLF), which allows both the acidification andeutrophication effects of S and N deposition to be explored simultaneously.Spatial variations in the reductions of deposition of S and/or N required tomeet critical loads are described. Reductions in emissions of the precursorsof strong acids (SO2 and NOx) yield benefits interms of ammonium deposition as a result of their coupled chemistry. Thedevelopment of strategies to control nitrogen deposition will need to take this non-linearity in to account.

Comparison of longterm greenhouse projections with the geologic record

Previous climate modeling studies suggest that temperature increases beyond 2100 AD due to greenhouse gas changes could be comparable to the Cretaceous. However, these projections have not been tested against a range of emission scenarios, nor have estimates of past temperature change been well restrained quantitatively. Herein we use a 1D energy balance model (EBM) with an upwelling‐diffusion ocean model to explore the temperature response to extreme cases of unrestricted and severely restricted greenhouse gas increases. Results are compared against revised estimates of global temperature change over the last 100 million years. For four of the six scenarios, global temperature projections by the years 2400–2700 equal or exceed levels of the Eocene or Cretaceous warm periods. The two exceptions involve scenarios with relatively low climate sensitivity and stringent conservation measures, but even in these projections temperatures are as warm as any time in the last 30 million years. These calculations suggest that regardless of emission scenario or system sensitivity, future greenhouse warming will be large even on a geological scale.