The Lancet Countdown: tracking progress on health and climate change was established to provide an independent, global monitoring system dedicated to tracking the health dimensions of the impacts of, and the response to, climate change. The Lancet Countdown tracks 41 indicators across five domains: climate change impacts, exposures, and vulnerability; adaptation, planning, and resilience for health; mitigation actions and health co-benefits; finance and economics; and public and political engagement. This report is the product of a collaboration of 27 leading academic institutions, the UN, and intergovernmental agencies from every continent. The report draws on world-class expertise from climate scientists, ecologists, mathematicians, geographers, engineers, energy, food, livestock, and transport experts, economists, social and political scientists, public health professionals, and doctors. The Lancet Countdown’s work builds on decades of research in this field, and was first proposed in the 2015 Lancet Commission on health and climate change, which documented the human impacts of climate change and provided ten global recommendations to respond to this public health emergency and secure the public health benefits available (panel 1). 1.. Present day changes in heat waves, labour capacity, vector-borne disease, and food security provide early warning of the compounded and overwhelming impact on public health that are expected if temperatures continue to rise. Trends in climate change impacts, exposures, and vulnerabilities show an unacceptably high level of risk for the current and future health of populations across the world. 2.. A lack of progress in reducing emissions and building adaptive capacity threatens both human lives and the viability of the national health systems they depend on, with the potential to disrupt core public health infrastructure and overwhelm health services. 3.. Despite these delays, a number of sectors have seen the beginning of a low-carbon transition, and it is clear that the nature and scale of the response to climate change will be the determining factor in shaping the health of nations for centuries to come. 4.. Ensuring a widespread understanding of climate change as a central public health issue will be crucial in delivering an accelerated response, with the health profession beginning to rise to this challenge. Vulnerability to extremes of heat has steadily risen since 1990 in every region, with 157 million more people exposed to heatwave events in 2017, compared with 2000, and with the average person experiencing an additional 1·4 days of heatwaves per year over the same period (indicators 1.1 and 1.3). For national economies and household budgets, 153 billion hours of labour were lost in 2017 because of heat, an increase of more than 62 billion hours (3·2 billion weeks of work) since 2000 (indicator 1.4). The direct effects of climate change extend beyond heat to include extremes of weather. In 2017, a total of 712 extreme weather events resulted in US$326 billion in economic losses, almost triple the total losses of 2016 (indicator 4.1). Small changes in temperature and precipitation can result in large changes in the suitability for transmission of important vector-borne and water-borne diseases. In 2016, global vectorial capacity for the transmission of the dengue fever virus was the highest on record, rising to 9·1% for Aedes aegypti and 11·1% for Aedes albopictus above the 1950s baseline. Focusing on high-risk areas and diseases, the Baltic region has had a 24% increase in the coastline area suitable for epidemics of Vibrio cholerae, and in 2016, the highlands of sub-Saharan Africa saw a 27·6% rise in the vectorial capacity for the transmission of malaria from the 1950 baseline (indicator 1.8). A proxy of agricultural yield potential shows declines in every region, with 30 countries having downward trends in yields, reversing a decades-long trend of improvement (indicator 1.9.1). Decreasing labour productivity, increased capacity for the transmission of diseases such as dengue fever, malaria, and cholera, and threats to food security provide early warning of compounding negative health and nutrition effects if temperatures continue to rise. Global inertia in adapting to climate change persists, with a mixed response from national governments since the signing of the Paris Agreement in 2015. More than half of global cities surveyed expect climate change to seriously compromise public health infrastructure, either directly, with extremes of weather disrupting crucial services, or indirectly, through the overwhelming of existing services with increased burdens of disease (indicator 2.2). Globally, spending for climate change adaptation remains well below the $100 billion per year commitment made under the Paris Agreement. Within this annual spending, only 3·8% of total development spending committed through formal UN Framework Convention on Climate Change (UNFCCC) mechanisms is dedicated to human health (indicator 2.8). This low investment in adaptive capacity is magnified in specific regions around the world, with only 55% of African countries meeting International Health Regulation core requirements for preparedness for a multihazard public health emergency (indicator 2.3). Multiple examples of stagnated mitigation efforts exist, with a crucial marker of decarbonisation—the carbon intensity of total primary energy supply—remaining unchanged since 1990 (indicator 3.1). A third of the global population, 2·8 billion people, live without access to healthy, clean, and sustainable cooking fuel or technologies, which is the same number of people as in 2000 (indicator 3.4). In the transport sector, per-capita global road-transport fuel use increased by 2% from 2013 to 2015, and cycling comprises less than 10% of total journeys taken in three quarters of a global sample of cities (indicators 3.6 and 3.7). The health burden of such inaction has been immense, with people in more than 90% of cities breathing polluted air that is toxic to their cardiovascular and respiratory health. Indeed, between 2010, and 2016, air pollution concentrations worsened in almost 70% of cities around the globe, particularly in low-income and middle-income countries (LMICs; indicator 3.5.1). In 2015 alone, fine particulate matter (ie, atmospheric particulate matter with a diameter of less than 2·5 μm [PM_2·5]) was responsible for 2·9 million premature deaths, with coal being responsible for more than 460 000 (16%) of these deaths, and with the total death toll (from other causes including particulates and emissions such as nitrogen oxide) being substantially higher (indicator 3.5.2). Of concern, global employment in fossil-fuel extractive industries actually increased by 8% between 2016, and 2017, reversing the strong decline seen since 2011 (indicator 4.4). At a time when national health budgets and health services face a growing epidemic of lifestyle diseases, continued delay in unlocking the potential health co-benefits of climate change mitigation is short-sighted and damaging for human health. Despite this stagnation, progress in the power generation and transport sectors provide some cause for optimism, with many positive trends being observed in the 2017 report, and which continue in the present 2018 report. Notably, coal use continues to decline (indicator 3.2) and more renewable energy was installed in 2017 than energy from fossil fuels (indicator 3.3). However, maintaining the global average temperature rise to well below 2°C necessitates wide-reaching transformations across all sectors of society, including power generation, transport, spatial infrastructure, food and agriculture, and the design of health systems. These transformations, in turn, offer levers to help tackle the root causes of the world’s greatest public health challenges. About 712 climate-related extreme events were responsible for US$326 billion of losses in 2017, almost triple the losses of 2016 (indicator 4.1). Crucially, 99% of the losses in low-income countries remained uninsured. Indicators of investment in the low-carbon economy show that the transition is already underway, with continued growth in investment in zero-carbon energy, and growing numbers of people employed in renewable energy sectors (indicators 4.2 and 4.4). Furthermore, investment in new coal capacity in 2017, was at its lowest in at least 10 years, with 2015 potentially marking a peak in coal investment. Correspondingly, global subsidies for fossil fuels continued to decrease, and carbon pricing only covers 13·1% of global greenhouse-gas emissions, a number that is expected to increase to more than 20% when planned legislation in China is implemented in late 2018 (indicators 4.6 and 4.7). However, the rise of employment in fossil fuel industries in 2017 reversed a 5 year downward trend, and will be a key indicator to follow closely. A better understanding of the health dimensions of climate change allows for advanced preparedness, increased resilience and adaptation, and a prioritisation of mitigation interventions that protect and promote human wellbeing. To this end, coverage of health and climate change in the media has increased substantially between 2007, and 2017 (indicator 5.1). Following this trend, the number of academic journal articles published on health and climate change has almost tripled over the same period (indicator 5.2). These figures often follow internationally important events, such as the UNFCCC’s Conference of the Parties (COP), along with temporary rises in mentions of health and climate change within the UN General Debate (UNGD; indicator 5.3). The extended heatwaves across the northern hemisphere in the summer of 2018, might prove to be a turning point in public awareness of the seriousness of climate change. 2017 saw a substantial rise in the number of medical and health professional associations actively responding to climate change. In the USA, the US Medical Society Consortium on Health and Climate represents 500 000 physicians. This organisation follows the formation of the UK Health Alliance on Climate Change, which brings together many of the UK’s royal medical and nursing colleges and major health institutions. Organisations like the European Renal Association–European Dialysis and Transplant Association and the UK’s National Health Service (NHS) are committing to reducing the contributions of their clinical practice emissions. The NHS achieved an 11% reduction in emissions between 2007, and 2015. Several health organisations have divested, or are committing to divest, their holdings in fossil fuel companies, including the Royal Australasian College of Physicians, the Canadian Medical Association, the American Public Health Association, and the World Medical Association (indicator 4.5). Given that climate change is the biggest global health threat of the 21st century, responding to this threat, and ensuring this response delivers the health benefits available, is the responsibility of the health profession; indeed, such a transformation will not be possible without it. The 2015 Lancet Commission made ten global recommendations to accelerate the response to climate change and deliver the health benefits this response could offer. A summary of the progress made against these recommendations using the 2018 Lancet Countdown’s indicators is presented in panel 1. Here, global leadership is increasingly provided by China, the EU, and many of the countries that are most vulnerable to climate change.

The KEMRI/Centers for Disease Control and Prevention (CDC) Health and Demographic Surveillance System (HDSS) is located in Rarieda, Siaya and Gem Districts (Siaya County), lying northeast of Lake Victoria in Nyanza Province, western Kenya. The KEMRI/CDC HDSS, with approximately 220 000 inhabitants, has been the foundation for a variety of studies, including evaluations of insecticide-treated bed nets, burden of diarrhoeal disease and tuberculosis, malaria parasitaemia and anaemia, treatment strategies and immunological correlates of malaria infection, and numerous HIV, tuberculosis, malaria and diarrhoeal disease treatment and vaccine efficacy and effectiveness trials for more than a decade. Current studies include operations research to measure the uptake and effectiveness of the programmatic implementation of integrated malaria control strategies, HIV services, newly introduced vaccines and clinical trials. The HDSS provides general demographic and health information (such as population age structure and density, fertility rates, birth and death rates, in- and out-migrations, patterns of health care access and utilization and the local economics of health care) as well as disease- or intervention-specific information. The HDSS also collects verbal autopsy information on all deaths. Studies take advantage of the sampling frame inherent in the HDSS, whether at individual, household/compound or neighbourhood level.

Background: Aedes aegypti is the principal vector for several important arbovirus diseases, including dengue, chikungunya, yellow fever, and Zika. While recent empirical research has attempted to identify the current global distribution of the vector, the seasonal, and longer-term dynamics of the mosquito in response to trends in climate, population, and economic development over the twentieth and the twenty-first century remains to be elucidated. Methods: In this study, we use a process-based mathematical model to estimate global vector distribution and abundance. The model is based on the lifecycle of the vector and its dependence on climate, and the model sensitivity to socio-economic development is tested. Model parameters were generally empirically based, and the model was calibrated to global databases and time series of occurrence and abundance records. Climate data on temperature and rainfall were taken from CRU TS3.25 (1901–2015) and five global circulation models (CMIP5; 2006–2099) forced by a high-end (RCP8.5) and a low-end (RCP2.6) emission scenario. Socio-economic data on global GDP and human population density were from ISIMIP (1950–2099). Findings: The change in the potential of global abundance in A. aegypti over the last century up to today is estimated to be an increase of 9.5% globally and a further increase of 20 or 30% by the end of this century under a low compared to a high carbon emission future, respectively. The largest increase has occurred in the last two decades, indicating a tipping point in climate-driven global abundance which will be stabilized at the earliest in the mid-twenty-first century. The realized abundance is estimated to be sensitive to socioeconomic development. Interpretation: Our data indicate that climate change mitigation, i.e., following the Paris Agreement, could considerably help in suppressing risks of increased abundance and emergence of A. aegypti globally in the second half of the twenty-first century.

We report and explore changes in child mortality in a rural area of Kenya during 2003–2009, when major public health interventions were scaled-up. Mortality ratios and rates were calculated by using the Kenya Medical Research Institute/Centers for Disease Control and Prevention Demographic Surveillance System. Inpatient and outpatient morbidity and mortality, and verbal autopsy data were analyzed. Mortality ratios for children less than five years of age decreased from 241 to 137 deaths/1,000 live-births in 2003 and 2007 respectively. In 2008, they increased to 212 deaths/1,000 live-births. Mortality remained elevated during the first 8 months of 2009 compared with 2006 and 2007. Malaria and/or anemia accounted for the greatest increases in child mortality. Stock-outs of essential antimalarial drugs during a time of increased malaria transmission and disruption of services during civil unrest may have contributed to increased mortality in 2008–2009. To maintain gains in child survival, implementation of good policies and effective interventions must be complemented by reliable supply and access to clinical services and essential drugs.

Background: The rollout of antiretroviral therapy (ART) is one of the largest public health interventions in Eastern and Southern Africa of recent years. Its impact is well described in clinical cohort studies, but population-based evidence is rare. Methods: We use data from seven demographic surveillance sites that also conduct community-based HIV testing and collect information on the uptake of HIV services. We present crude death rates of adults (aged 15–64) for the period 2000–2011 by sex, HIV status, and treatment status. Parametric survival models are used to estimate age-adjusted trends in the mortality rates of people living with HIV (PLHIV) before and after the introduction of ART. Results: The pooled ALPHA Network dataset contains 2.4 million person-years of follow-up time, and 39114 deaths (6893 to PLHIV). The mortality rates of PLHIV have been relatively static before the availability of ART. Mortality declined rapidly thereafter, with typical declines between 10 and 20% per annum. Compared with the pre-ART era, the total decline in mortality rates of PLHIV exceeds 58% in all study sites with available data, and amounts to 84% for women in Masaka (Uganda). Mortality declines have been larger for women than for men; a result that is statistically significant in five sites. Apart from the early phase of treatment scale up, when the mortality of PLHIV on ART was often very high, mortality declines have been observed in PLHIV both on and off ART. Conclusion: The expansion of treatment has had a large and pervasive effect on adult mortality. Mortality declines have been more pronounced for women, a factor that is often attributed to women's greater engagement with HIV services. Improvements in the timing of ART initiation have contributed to mortality reductions in PLHIV on ART, but also among those who have not (yet) started treatment because they are increasingly selected for early stage disease.