Population decline of the saguaro cactus throughout its distribution is associated with climate change.

BACKGROUND AND AIMS: Climate change is a global phenomenon species are experiencing, which in arid regions will translate into more frequent and intense drought. The Sonoran Desert is becoming hotter and drier, and many organisms are rapidly changing in abundance and distribution. These population attributes directly depend on the dynamics of the population, which in turn depends on the vital rates of its individuals; yet few studies have documented the effects of climate change on the population dynamics of keystone species such as the saguaro cactus (Carnegiea gigantea). Although saguaros have traits that enable them to withstand present environmental conditions, climate change could make them vulnerable if forced beyond their tolerance limits. METHODS: We evaluated the effect of climate change on 13 saguaro populations spanning most of the species' distribution range. Using field data from 2014 to 2016, we built an integral projection model (IPM) describing the environmentally-explicit dynamics of the populations. We used this IPM, along with projections of two climate change and one no-change scenarios, to predict population sizes (N) and growth rates (λ) from 2017 to 2099 and compared these scenarios to demonstrate the effect of climate change on saguaro's future. KEY RESULTS: We found that all populations will decline, mainly due to future increases in drought, mostly hindering recruitment. However, the decline will be differential across populations, since those located near the coast will be affected by harsher drought events than those located further inland. CONCLUSIONS: Our study demonstrates that climate change and its associated increase in drought pose a significant threat to the saguaro cactus populations in the Sonoran Desert. Our findings indicate that the recruitment of saguaros, vital for establishing new individuals, is particularly vulnerable to intensifying drought conditions. Importantly, regional climate trends will have different impacts on saguaro populations across their distribution range.

Spatially explicit downscaling and projection of population in mainland China.

Spatially explicit population data is critical to investigating human-nature interactions, identifying at-risk populations, and informing sustainable management and policy decisions. Most long-term global population data have three main limitations: 1) they were estimated with simple scaling or trend extrapolation methods which are not able to capture detailed population variation spatially and temporally; 2) the rate of urbanization and the spatial patterns of settlement changes were not fully considered; and 3) the spatial resolution is generally coarse. To address these limitations, we proposed a framework for large-scale spatially explicit downscaling of populations from census data and projecting future population distributions under different Shared Socio-economic Pathways (SSP) scenarios with the consideration of distinctive changes in urban extent. We downscaled urban and rural population separately and considered urban spatial sprawl in downscaling and projection. Treating urban and rural populations as distinct but interconnected entities, we constructed a random forest model to downscale historical populations and designed a gravity-based population potential model to project future population changes at the grid level. This work built a new capacity for understanding spatially explicit demographic change with a combination of temporal, spatial, and SSP scenario dimensions, paving the way for cross-disciplinary studies on long-term socio-environmental interactions.

Climate migration amplifies demographic change and population aging.

The warnings of potential climate migration first appeared in the scientific literature in the late 1970s when increased recognition that disintegrating ice sheets could drive people to migrate from coastal cities. Since that time, scientists have modeled potential climate migration without integrating other population processes, potentially obscuring the demographic amplification of this migration. Climate migration could amplify demographic change-enhancing migration to destinations and suppressing migration to origins. Additionally, older populations are the least likely to migrate, and climate migration could accelerate population aging in origin areas. Here, we investigate climate migration under sea-level rise (SLR), a single climatic hazard, and examine both the potential demographic amplification effect and population aging by combining matrix population models, flood hazard models, and a migration model built on 40 y of environmental migration in the United States to project the US population distribution of US counties. We find that the demographic amplification of SLR for all feasible Representative Concentration Pathway-Shared Socioeconomic Pathway (RCP-SSP) scenarios in 2100 ranges between 8.6-28 M [5.7-53 M]-5.3 and 18 times the number of migrants (0.4-10 M). We also project significant aging of coastal areas as youthful populations migrate but older populations remain, accelerating population aging in origin areas. As the percentage of the population lost due to climate migration increases, the median age also increases-up to 10+ y older in some highly impacted coastal counties. Additionally, our population projection approach can be easily adapted to investigate additional or multiple climate hazards.

Probabilistic County-Level Population Projections.

Population projections provide predictions of future population sizes for an area. Historically, most population projections have been produced using deterministic or scenario-based approaches and have not assessed uncertainty about future population change. Starting in 2015, however, the United Nations (UN) has produced probabilistic population projections for all countries using a Bayesian approach. There is also considerable interest in subnational probabilistic population projections, but the UN's national approach cannot be used directly for this purpose, because within-country correlations in fertility and mortality are generally larger than between-country ones, migration is not constrained in the same way, and there is a need to account for college and other special populations, particularly at the county level. We propose a Bayesian method for producing subnational population projections, including migration and accounting for college populations, by building on but modifying the UN approach. We illustrate our approach by applying it to the counties of Washington State and comparing the results with extant deterministic projections produced by Washington State demographers. Out-of-sample experiments show that our method gives accurate and well-calibrated forecasts and forecast intervals. In most cases, our intervals were narrower than the growth-based intervals issued by the state, particularly for shorter time horizons.

The impact of Covid-19 on demographic components in Spain, 2020-31: A scenario approach.

While considerable attention has been paid to the impact of Covid-19 on mortality and fertility, few studies have attempted to evaluate the pandemic's effect on international migration. We analyse the impact of Covid-19 on births, deaths, and international migration in Spain during 2020, comparing observed data with estimated values assuming there had been no pandemic. We also assess the consequences of three post-pandemic scenarios on the size and structure of the population to 2031. Results show that in 2020, excess mortality equalled 16.2 per cent and births were 6.5 per cent lower than expected. Immigration was the most affected component, at 36.0 per cent lower than expected, while emigration was reduced by 23.8 per cent. If net migration values recover to pre-pandemic levels in 2022, the size and structure of the population in 2031 will be barely affected. Conversely, if levels do not recover until 2025, there will be important changes to Spain's age structure.

Trajetórias socioeconômicas compartilhadas no Brasil: cenários para a dinâmica populacional e os desafios à adaptação e mitigação / Shared socioeconomic pathways in Brazil: Scenarios for population dynamics and the challenges to adaptation and mitigation / Trayectorias socioeconómicas compartidas en Brasil: escenarios de dinámica poblacional y desafíos para la adaptación y mitigación

Resumo Dentre os múltiplos avanços científicos na compreensão das relações entre mudanças climáticas e dinâmica populacional, uma das principais inovações ocorreu na atual geração de modelagem climática, com a inclusão de um conjunto de cenários em que as questões populacionais são centrais. Baseados em narrativas de trajetórias socioeconômicas, estes cenários traçam alternativas para os desenvolvimentos sociais futuros, que, por sua vez, consideram projeções populacionais multidimensionais, construídas a partir das variáveis sexo, idade e escolaridade. Tais projeções incorporam heterogeneidades populacionais relevantes para a adaptação, sendo, potencialmente, mais sensíveis às mudanças na dinâmica demográfica e à compreensão da relação população e ambiente. No Brasil, contudo, tanto os pressupostos como as implicações desta abordagem são quase inexistentes. O presente artigo aborda esta discussão para o país, considerando seus aspectos teóricos e metodológicos. Destacam-se algumas das inferências da abordagem das shared socioeconomic pathways (SSPs) - trajetórias socioeconômicas compartilhadas - para construir projeções populacionais no nível subnacional, enfatizando os ganhos potenciais desta agenda no campo de população e ambiente.

Abstract During the past decades, there were scientific advances to better comprehend climate change and population dynamics. One of the main ones was the inclusion of a set of scenarios in current generation of climate modelling, with population as its human core. These are the shared socioeconomic pathways that result in population projections constructed by multi-dimensional demography, with population disaggregated by, sex, age and educational attainment. Such projections incorporate relevant population heterogeneities to adaptation and are potentially more sensitive to capture changes in demographic dynamics. This paper addresses this discussion for Brazil, considering both theoretical and methodological aspects. We highlight some of the implications of SSPs approach to construct population projections at the subnational level, emphasizing the benefits this agenda could bring to the population and environment fields.

Resumen Los avances en la ciencia para una mejor comprensión de las relaciones entre el cambio climático y la dinámica de la población se han producido en varios campos durante las últimas tres décadas. Una de las principales innovaciones se observa en la generación actual de modelos climáticos, con la inclusión de un conjunto de escenarios en los que los temas de población son centrales. Estos escenarios, denominados trayectorias socioeconómicas compartidas, esbozan alternativas para futuros desarrollos sociales que, a su vez, consideran proyecciones poblacionales multidimensionales, construidas a partir de las variables sexo, edad y educación. Estas proyecciones incorporan heterogeneidades de población relevantes para la adaptación y son potencialmente más sensibles a los cambios en la dinámica demográfica. Este artículo aborda esta discusión para Brasil, considerando sus aspectos teóricos y metodológicos. Se destacan algunas de las implicaciones del enfoque para construir proyecciones de población en el ámbito subnacional, con énfasis los logros que esta agenda puede traer al campo de población y medio ambiente.

Local area population projections dataset for Australia.

A new dataset of population projections for local areas of Australia is described. The areas comprise SA3 areas of the Australian Statistical Geography Standard, which mostly range in population between 30,000 and 130,000. The projections are launched from the 2020 Estimated Resident Populations published by the Australian Bureau of Statistics and extend out to 2035. They are available by sex and five year age group up to 80-84 with 85+ as the final age group and in five year projection intervals. The projections were prepared using the synthetic migration cohort-component model, a new model for population projections which requires much less input data than conventional projection models, and therefore involves much lower costs and production time. Despite this, a recent evaluation demonstrated respectable forecast accuracy, and greater accuracy than equivalent simple projection models producing populations by age and sex. The age-sex projections are constrained to independent age-sex national projections and local area projections of total populations. The dataset consists of local area projections for the whole of the country which is consistent in methods, input data, and projection outputs due to the use of one model. This is rare in Australia because local area projections are most commonly prepared by individual State/Territory Governments using different methods, data sources, projection assumptions (which can be influenced by State/Territory population policies), and time periods. These nationally consistent projection data should be useful for a wide range of local area planning, policy, and research purposes, such as childcare demand, school enrolments, power and water usage, aged care provision, store and business site selection, living arrangements and household projections, labour force projections, and transport modelling.

Contrasting seasonal effects of climate change influence density in a cold-adapted species.

Many ecological processes are profoundly influenced by abiotic factors, such as temperature and snow. However, despite strong evidence linking shifts in these ecological processes to corresponding shifts in abiotic factors driven by climate change, the mechanisms connecting population size to season-specific climate drivers are little understood. Using a 21-year dataset and a Bayesian state space model, we identified biologically informed seasonal climate covariates that influenced densities of snowshoe hares (Lepus americanus), a cold-adapted boreal herbivore. We found that snow and temperature had strong but conflicting season-dependent effects. Reduced snow duration in spring and fall and warmer summers were associated with lowered hare density, whereas warmer winters were associated with increased density. When modeled simultaneously and under two climate change scenarios, the negative effects of reduced fall and spring snow duration and warmer summers overwhelm the positive effect of warmer winters, producing projected population declines. Ultimately, the contrasting population-level impacts of climate change across seasons emphasize the critical need to examine the entire annual climate cycle to understand potential long-term population consequences of climate change.

Projections of dependency and associated social care expenditure for the older population in England to 2038: effect of varying disability progression.

OBJECTIVES: to assess the effect of recent stalling of life expectancy and various scenarios for disability progression on projections of social care expenditure between 2018 and 2038, and the likelihood of reaching the Ageing Society Grand Challenge mission of five extra healthy, independent years at birth. DESIGN: two linked projections models: the Population Ageing and Care Simulation (PACSim) model and the Care Policy and Evaluation Centre long-term care projections model, updated to include 2018-based population projections. POPULATION: PACSim: about 303,589 individuals aged 35 years and over (a 1% random sample of the England population in 2014) created from three nationally representative longitudinal ageing studies. MAIN OUTCOME MEASURES: Total social care expenditure (public and private) for older people, and men and women's independent life expectancy at age 65 (IndLE65) under five scenarios of changing disability progression and recovery with and without lower life expectancy. RESULTS: between 2018 and 2038, total care expenditure was projected to increase by 94.1%-1.25% of GDP; men's IndLE65 increasing by 14.7% (range 11.3-16.5%), exceeding the 8% equivalent of the increase in five healthy, independent years at birth, although women's IndLE65 increased by only 4.7% (range 3.2-5.8%). A 10% reduction in disability progression and increase in recovery resulted in the lowest increase in total care expenditure and increases in both men's and women's IndLE65 exceeding 8%. CONCLUSIONS: interventions that slow down disability progression, and improve recovery, could significantly reduce social care expenditure and meet government targets for increases in healthy, independent years.

Will the COVID-19 pandemic affect population ageing in Australia?

The COVID-19 pandemic has caused extensive disruption to economies and societies across the world. In terms of demographic processes, mortality has risen in many countries, international migration and mobility has been widely curtailed, and rising unemployment and job insecurity is expected to lower fertility rates in the near future. This paper attempts to examine the possible effects of COVID-19 on Australia's demography over the next two decades, focusing in particular on population ageing. Several population projections were prepared for the period 2019-41. We formulated three scenarios in which the pandemic has a short-lived impact of 2-3 years, a moderate impact lasting about 5 years, or a severe impact lasting up to a decade. We also created two hypothetical scenarios, one of which illustrates Australia's demographic future in the absence of a pandemic for comparative purposes, and another which demonstrates the demographic consequences if Australia had experienced excess mortality equivalent to that recorded in the first half of 2020 in England & Wales. Our projections show that the pandemic will probably have little impact on numerical population ageing but a moderate effect on structural ageing. Had Australia experienced the high mortality observed in England & Wales there would have been 19,400 excess deaths. We caution that considerable uncertainty surrounds the future trajectory of COVID-19 and therefore the demographic responses to it. The pandemic will need to be monitored closely and projection scenarios updated accordingly.

Undocumented Older Latino Immigrants in the United States: Population Projections and Share of Older Undocumented Latinos by Health Insurance Coverage and Chronic Health Conditions, 2018-2038.

OBJECTIVES: This article focuses on the older Latino undocumented population and anticipates how their current demographic characteristics and health insurance coverage might affect future population size and health insurance trends. METHODS: We use the 2013-2018 American Community Survey as a baseline to project growth in the Latino 55 and older undocumented population over the next 20 years. We use the cohort component method to estimate population size across different migration scenarios and distinguish between aging in place and new immigration. We also examine contemporary health insurance coverage and chronic health conditions among 55 and older undocumented Latinos from the 2003-2014 California Health Interview Survey. We then project health insurance rates in 2038 among Latino immigrants under different migration and policy scenarios. RESULTS: If current mortality, migration, and policy trends continue, projections estimate that 40% of undocumented Latino immigrants will be 55 years or older by 2038-nearly all of whom will have aged in place. Currently, 40% of older Latino undocumented immigrants do not have insurance. Without policies that increase access to insurance, projections estimate that the share who are uninsured among all older Latinos immigrants will rise from 15% to 21%, and the share who is both uninsured and living with a chronic health condition will rise from 5% to 9%. DISCUSSION: Without access to health care, older undocumented immigrants may experience delayed care and more severe morbidity. Our projections highlight the need to develop and enact policies that can address impending health access concerns for an increasingly older undocumented Latino population.

Demographic perspectives in research on global environmental change.

The human population is at the centre of research on global environmental change. On the one hand, population dynamics influence the environment and the global climate system through consumption-based carbon emissions. On the other hand, the health and well-being of the population are already being affected by climate change. A knowledge of population dynamics and population heterogeneity is thus fundamental to improving our understanding of how population size, composition, and distribution influence global environmental change and how these changes affect population subgroups differentially by demographic characteristics and spatial distribution. The increasing relevance of demographic research on the topic, coupled with availability of theoretical concepts and advancement in data and computing facilities, has contributed to growing engagement of demographers in this field. In the past 25 years, demographic research has enriched climate change research-with the key contribution being in moving beyond the narrow view that population matters only in terms of population size-by putting a greater emphasis on population composition and distribution, through presenting both empirical evidence and advanced population forecasting to account for demographic and spatial heterogeneity. What remains missing in the literature is research that investigates how global environmental change affects current and future demographic processes and, consequently, population trends. If global environmental change does influence fertility, mortality, and migration, then population estimates and forecasts need to adjust for climate feedback in population projections. Indisputably, this is the area of new research that directly requires expertise in population science and contribution from demographers.

The call of the emperor penguin: Legal responses to species threatened by climate change.

Species extinction risk is accelerating due to anthropogenic climate change, making it urgent to protect vulnerable species through legal frameworks in order to facilitate conservation actions that help mitigate risk. Here, we discuss fundamental concepts for assessing climate change risks to species using the example of the emperor penguin (Aptenodytes forsteri), currently being considered for protection under the US Endangered Species Act (ESA). This species forms colonies on Antarctic sea ice, which is projected to significantly decline due to ongoing greenhouse gas (GHG) emissions. We project the dynamics of all known emperor penguin colonies under different GHG emission scenarios using a climate-dependent meta-population model including the effects of extreme climate events based on the observational satellite record of colonies. Assessments for listing species under the ESA require information about how species resiliency, redundancy and representation (3Rs) will be affected by threats within the foreseeable future. Our results show that if sea ice declines at the rate projected by climate models under current energy system trends and policies, the 3Rs would be dramatically reduced and almost all colonies would become quasi-extinct by 2100. We conclude that the species should be listed as threatened under the ESA.

Use of Counterfactual Population Projections for Assessing the Demographic Determinants of Population Ageing.

Counterfactual population projections have been used to estimate the contributions of fertility and mortality to population ageing, a method recently designated as the gold standard for this purpose. We analyse projections with base years between 1850 and 1950 for 11 European countries with long-run demographic data series to estimate the robustness of this approach. We link this approach with stable population theory to derive quantitative indicators of the role of fertility and mortality; consider ways of incorporating net migration; and examine the effect of using alternative indicators of population ageing. A number of substantive and technical weaknesses in the counterfactual projection approach are identified: (1) the conclusions are very sensitive to the choice of base year. Specifically, the level of base year fertility has a major influence on whether fertility or mortality is considered the main driver of population ageing. (2) The method is not transitive: results for two adjacent intervals are unrelated to results for the combined period. Therefore, overall results cannot be usefully allocated between different sub-intervals. (3) Different ageing indices tend to produce similar qualitative conclusions, but quantitative results may differ markedly. (4) Comparisons of alternative models should be with a fixed fertility and mortality projection model rather than with the baseline values as usually done. (5) The standard counterfactual projections approach concatenates the effects of initial age structure and subsequent fertility and mortality rates: methods to separate these components are derived.

A New Measure of Fertility Replacement Level in the Presence of Positive Net Immigration.

In most more developed countries, the total fertility rate (TFR) is below 2.1 and net immigration is positive. This paper proposes and calculates for 22 populations for 2011-15 a 'Current Migration Replacement TFR' which in combination with the mortality and absolute net migration for that period generates a stationary population equal in size to the mid-period population. The results show the Current Migration Replacement TFR ranges widely from 0.60 for Singapore to 2.05 for Slovakia. That the Current Migration Replacement TFR is below the 2011-15 TFR in 14 of the 22 countries shows that, when considered in combination with current migration and mortality, in most of the countries the current 'below 2.1' TFR is coherent with population increase, not population decline, over the long run. For New Zealand, Australia, Norway, Sweden and the UK continued current fertility in combination with constant mortality and constant absolute net migration is coherent with more than doubling of the current population size. The value of this measure for illustrating the interconnected population size implications of sub-replacement fertility and immigration, for sub-categorisation of 'post-transitional' populations by population growth prospects, and for guiding population policy is discussed.

Future air pollution related health burdens associated with RCP emission changes in the UK.

Three Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) are used to simulate future ozone (O3), nitrogen dioxide (NO2), and fine particulate matter (PM2.5) in the United Kingdom (UK) for the 2050s relative to the 2000s with an air quality model (AQUM) at a 12 km horizontal resolution. The present-day and future attributable fractions (AF) of mortality associated with long-term exposure to annual mean O3, NO2 and PM2.5 have accordingly been estimated for the first time for regions across England, Scotland and Wales. Across the three RCPs (RCP2.6, RCP6.0 and RCP8.5), simulated annual mean of the daily maximum 8-h mean (MDA8) O3 concentrations increase compared to present-day, likely due to decreases in NOx (nitrogen oxides) emissions, leading to less titration of O3 by NO. Annual mean NO2 and PM2.5 concentrations decrease under all RCPs for the 2050s, mostly driven by decreases in NOx and sulphur dioxide (SO2) emissions, respectively. The AF of mortality associated with long-term exposure to annual mean MDA8 O3 is estimated to increase in the future across all the regions and for all RCPs. Reductions in NO2 and PM2.5 concentrations lead to reductions in the AF estimated for future periods under all RCPs, for both pollutants. Total mortality burdens are also highly sensitive to future population projections. Accounting for population projections exacerbates differences in total UK-wide MDA8 O3-health burdens between present-day and future by up to a factor of ~3 but diminishes differences in NO2-health burdens. For PM2.5, accounting for future population projections results in additional UK-wide deaths brought forward compared to present-day under RCP2.6 and RCP6.0, even though the simulated PM2.5 concentrations for the 2050s are estimated to decrease. Thus, these results highlight the sensitivity of future health burdens in the UK to future trends in atmospheric emissions over the UK as well as future population projections.

Projections of Older European Migrant Populations in Australia, 2016-56.

Many of the European migrant populations which settled in Australia in the three decades after World War Two are now much older, and their aged care and health care needs are changing. While there is a considerable literature on individual aspects of ageing in many migrant groups (particularly as it pertains to culturally appropriate aged care), little research attention has been given to population aspects of ageing and its implications. The aim of this paper is to address this lacuna by presenting projections of Australia's Europe-born older migrant population from 2016 to 2056. The population projections were created by a cohort-component model modified to accommodate multiple birthplace populations. Findings show the older Europe-born population is projected to experience a slight increase over the next few years, reach a peak of just under one million in the early 2030s, and then undergo a gradual decline thereafter. The Europe-born share of Australia's 65+ population will fall, from 25.5% in 2016 to 10% by 2056. Populations born in Western and Southern Europe are likely to decline throughout the projection horizon while, the Northern Europe-born and Ireland-born older populations are projected to grow continually. The populations born in the UK and South Eastern Europe initially grow before decline sets in. To a large extent the future population size of these older migrant groups will be the result of cohort flow. We discuss the implications of the coming demographic changes for government policy and culturally appropriate service provision.

Using future age profiles to improve immigration projections.

Young adults migrate more than older people. As populations in many countries get older, this may affect out-migration-and thus immigration to other countries. This is not usually accounted for in projections of future immigration, even though considerable ageing is expected globally. We show how United Nations projections of future age profiles in origin regions can be combined with those regions' emigration rates by age group to improve national projections of immigration to a destination country, exemplified by Norway. Using various methods for projecting future migration, we show that projected immigration tends to be lower when taking expected ageing in origin regions into account. This may have a considerable effect on population projections: for Norway, taking changing age profiles in origin regions into account in immigration projections would have an effect on the projected population of Norway equivalent to that of reducing the fertility assumptions by 0.1 children per woman.

Past and projected growth of Australia's older migrant populations.

In recent years, Australia's older population (aged 65 and over) has been growing rapidly, accompanied by a shift in its country of birth composition. Although a great deal of research has been undertaken on past and current aspects of Australia's migrant groups, little attention has been paid to future demographic trends in older populations. The aim of this paper is to examine recent and possible future demographic trends of Australia's migrant populations at the older ages. We present population estimates by country and broad global region of birth from 1996 to 2016, and then new birthplace-specific population projections for the 2016 to 2056 period. Our findings show that substantial growth of the 65+ population will occur in the coming decades, and that the overseas-born will shift from a Europe-born dominance to an Asia-born dominance. Cohort flow (the effect of varying sizes of cohorts moving into the 65+ age group over time) will be the main driver of growth for most older birthplace populations. The shifting demography of Australia's older population signals many policy, planning, service delivery and funding challenges for government and private sector providers. We discuss those related to aged care, health care, language services, the aged care workforce, regulatory frameworks and future research needs in demography and gerontology.

Ageing of the Aboriginal and Torres Strait Islander population: numerical, structural, timing and spatial aspects.

OBJECTIVES: To assess levels of numerical, structural, timing and spatial aspects of ageing of the Aboriginal and Torres Strait Islander population. METHODS: Population projections for 15 Australian regions were created by a multi-state cohort-component model. RESULTS: The older (45-plus) population grew from 29,815 in 1986 to 167,259 in 2016. In the subsequent 30 years, we project growth to 448,785 people. Growth rates of the older population vary: from 200% in the 60-64-year-old group to 800% growth in the 85-plus age group by mid-century. This strong numerical ageing is reflected in a shift in structural ageing by about six percentage points. Selected areas outside of capital cities are structurally older than many cities. Numerical ageing is strongest in capital cities and New South Wales. Cohort flow is the primary driver of ageing. CONCLUSIONS: Numerical and structural ageing is projected to increase significantly to mid-century with important spatial variations. Population ageing is largely irreversible. Implications for public health: High numerical growth in the older Aboriginal and Torres Strait Islander population poses implications for increased demand for a range of health and care services. Variations in spatial and timing aspects of ageing indicate demand will peak earlier in some geographical locations relative to others.