The research themes running through the series. Most reports sit in more than one, so the themes overlap by design.
By the 2090s, 4.3 to 9.3 billion people will live with frequent heat, extreme rain or long dry spells, up from 3.4 billion. The exposed population ages fast: heat exposure among people 65 and over rises nearly tenfold, to 1.3 billion. If schooling keeps rising and protecting as it has, harm falls by 70–84% in three pathways, but under SSP3 protection only holds harm level, and heat harm rises 39%.
By 2087, most of humanity will live in sub-Saharan Africa or South Asia. By the 2090s, the median person would live at a mean annual temperature of 26–28 °C, up from 22 °C, and the worst-off quarter beyond 28.5–29.4 °C, with one to more than two months of dangerous heat a year, in air already six times dirtier than the WHO guideline. A low-emissions, high-development path keeps unprecedented heat to 0.6 billion people instead of 3.8 billion.
In 2022 the median fuel importer's bill jumped from 4.5% to 7.4% of GDP, and the jump tracked how much each country imported, not how clean its power was (r = −0.08). Import bills are mostly oil and gas for transport, heat and industry, so the transition protects only when it reaches those uses. When it does, it also cuts the 86% of fossil air-pollution deaths borne by importers and the emissions behind climate risk.
The life-expectancy gap between developing and high-income countries fell from 25 years in 1960 to 8.4 today, but it closed four times faster before 2000 than since, and coverage growth has halved since 2015. Sri Lanka, Thailand and Viet Nam show good health at low cost, yet in the median low-income country governments spend $7 a person on health, households pay nearly half of all costs, and an essential package would cost 11% of GDP.
Since 1975 the world's urban centres have added 2.1 billion people, and growth has leaned into the floodplain: the urban population in 100-year river flood zones tripled to 507 million while cities as a whole grew 2.3 times, with one new resident in six settling in a flood zone. Six in ten new city dwellers settled in cities exposed to at least one major hazard, and 746 million now live where two or more compound. Most of the growth still to come is unbuilt — the cheapest moment for safer settlement decisions.
Multi-domain shock years rose from about 6% of countries a year before 2020 to 9% since, after 33% in 2020. The observed network has a sink: economic shocks, internet shutdowns and governance shocks raise the next year's risk of displacement or mortality shocks 2.5, 2.0 and 1.6 times. Low-income countries carry eleven times the multi-domain burden of rich ones, and twenty countries with 705 million people face a 30% or higher modelled risk of multi-domain shocks in 2026.
1.66 billion people live where two or more climate hazards overlap, but only 158 million of them also have limited means to adapt. They are concentrated in the heat-and-drought belt from Senegal to Pakistan and on cyclone coasts from Madagascar to Haiti. By 2050 that overlap nearly triples to 455 million, led by Nigeria. Halving poverty and strengthening coping would cut it to 263 million, more than lower emissions alone (356 million), though not in the most fragile states.
By 2087, most of humanity will live in sub-Saharan Africa or South Asia. By the 2090s, the median person would live at a mean annual temperature of 26–28 °C, up from 22 °C, and the worst-off quarter beyond 28.5–29.4 °C, with one to more than two months of dangerous heat a year, in air already six times dirtier than the WHO guideline. A low-emissions, high-development path keeps unprecedented heat to 0.6 billion people instead of 3.8 billion.
Countries vulnerable in 2000 have closed their human-development gap at about 0.3% a year, a half-life of two centuries. Those that avoided reversals closed it three times faster, while reversals erased 13% of their gains. Higher human development makes reversals shallower and polycrisis risk lower (r = −0.84). Faster convergence with halved reversals would bring 38 of 60 vulnerable countries past an HDI of 0.70 by 2050, against 17 at the recent pace.
Forty-eight countries, 36 of them in sub-Saharan Africa, are trapped in two or more degradation cycles, and they hold 78% of the world's extremely poor. Polluting cooking fuel, missing sanitation and forest loss move together even among countries at the same income. Fifty-two countries escaped at least one cycle after 2000, through clean-cooking drives, sanitation campaigns and forest recovery, and cut extreme poverty by a median 26 points, more than twice as much as those that stayed trapped. Air pollution is the cycle growth has not broken.
Multi-domain shock years rose from about 6% of countries a year before 2020 to 9% since, after 33% in 2020. The observed network has a sink: economic shocks, internet shutdowns and governance shocks raise the next year's risk of displacement or mortality shocks 2.5, 2.0 and 1.6 times. Low-income countries carry eleven times the multi-domain burden of rich ones, and twenty countries with 705 million people face a 30% or higher modelled risk of multi-domain shocks in 2026.
Very hot days are deadlier when the air is dirty: across 620 cities, a very hot day raised deaths by 12.8% when particle pollution was high against 5.3% when it was low. And the two hazards travel together — in 2024 ozone was higher on hot days in 131 of 149 large cities. About 2.6 billion people live in countries that are both hot and polluted, three-quarters of the population of lower-middle-income countries against 4% in high-income ones.
The first report in this theme.
No site analysed reaches the 35 °C wet-bulb ceiling before about 4.4 °C of global warming; the binding line is lower. Healthy young adults lose the ability to cool themselves in humid heat near 30.5 °C, a level 11 of 161 sites reached for at least an hour in 2024. Under current policies, about 2.8 °C, the cities touching it would hold 161 million people, up from 9 million today — around the Gulf, across South Asia and in eastern China.
Scarcity is an accelerant, not a detonator. Drought cuts cereal yields by about 6% and doubles the odds of a crop failure, but in the same country an ordinary dry year barely changes the risk of war. Severe droughts raise the chance a new conflict starts the next year by about 60%, and in fragile states local droughts shift fighting toward communal and militia violence. Violence concentrates where scarcity meets weak states: 24 such countries, 7% of humanity, suffered 37% of conflict deaths in 2016–24.
The first report in this theme.
By 2087, most of humanity will live in sub-Saharan Africa or South Asia. By the 2090s, the median person would live at a mean annual temperature of 26–28 °C, up from 22 °C, and the worst-off quarter beyond 28.5–29.4 °C, with one to more than two months of dangerous heat a year, in air already six times dirtier than the WHO guideline. A low-emissions, high-development path keeps unprecedented heat to 0.6 billion people instead of 3.8 billion.
Heat cut work capacity enough in 2024 to put about $490 billion of output at risk, a conservative estimate from hourly heat stress in 149 cities. The Lancet Countdown's broader estimate is $1.09 trillion. Either figure is of the same order as all climate damages in the DICE model at 1.5 °C. The loss is regressive (3% of hours in lower-middle-income countries against 0.2% in rich ones) and convex: one extra degree adds 73%, two nearly triple it. Moving work out of the afternoon recovers 20–30%.
The first report in this theme.
The 2023 headline was six of nine planetary boundaries breached; by 2025–26 it is seven, all worsening. Measured as a multiple of the disturbance each boundary allows, humanity has used 2.1 times its CO₂ allowance, 3.1 times its climate-forcing allowance, about 2.7–2.9 times its nitrogen and phosphorus allowances and 11 to 111 times its extinction allowance. Each boundary translates into a budget, a floor, a ceiling or a ban — and the ozone layer shows a breached boundary can be brought back.
The poorest half of humanity breathes 66% of the world's fine-particle exposure above the WHO guideline. Exposure peaks not in the poorest countries but in lower-middle-income ones, where industry, dense cities and solid-fuel cooking coincide: their population-weighted average is 42.5 µg/m³, against 12.5 in high-income countries. Since 2010 three in four high-income countries have cleaned their air, against fewer than half of lower-middle-income ones.
The first report in this theme.
Scarcity is an accelerant, not a detonator. Drought cuts cereal yields by about 6% and doubles the odds of a crop failure, but in the same country an ordinary dry year barely changes the risk of war. Severe droughts raise the chance a new conflict starts the next year by about 60%, and in fragile states local droughts shift fighting toward communal and militia violence. Violence concentrates where scarcity meets weak states: 24 such countries, 7% of humanity, suffered 37% of conflict deaths in 2016–24.
The life-expectancy gap between developing and high-income countries fell from 25 years in 1960 to 8.4 today, but it closed four times faster before 2000 than since, and coverage growth has halved since 2015. Sri Lanka, Thailand and Viet Nam show good health at low cost, yet in the median low-income country governments spend $7 a person on health, households pay nearly half of all costs, and an essential package would cost 11% of GDP.
The first report in this theme.
The 2023 headline was six of nine planetary boundaries breached; by 2025–26 it is seven, all worsening. Measured as a multiple of the disturbance each boundary allows, humanity has used 2.1 times its CO₂ allowance, 3.1 times its climate-forcing allowance, about 2.7–2.9 times its nitrogen and phosphorus allowances and 11 to 111 times its extinction allowance. Each boundary translates into a budget, a floor, a ceiling or a ban — and the ozone layer shows a breached boundary can be brought back.
The first report in this theme.
No site analysed reaches the 35 °C wet-bulb ceiling before about 4.4 °C of global warming; the binding line is lower. Healthy young adults lose the ability to cool themselves in humid heat near 30.5 °C, a level 11 of 161 sites reached for at least an hour in 2024. Under current policies, about 2.8 °C, the cities touching it would hold 161 million people, up from 9 million today — around the Gulf, across South Asia and in eastern China.
The first report in this theme.
The life-expectancy gap between developing and high-income countries fell from 25 years in 1960 to 8.4 today, but it closed four times faster before 2000 than since, and coverage growth has halved since 2015. Sri Lanka, Thailand and Viet Nam show good health at low cost, yet in the median low-income country governments spend $7 a person on health, households pay nearly half of all costs, and an essential package would cost 11% of GDP.
The life-expectancy gap between developing and high-income countries fell from 25 years in 1960 to 8.4 today, but it closed four times faster before 2000 than since, and coverage growth has halved since 2015. Sri Lanka, Thailand and Viet Nam show good health at low cost, yet in the median low-income country governments spend $7 a person on health, households pay nearly half of all costs, and an essential package would cost 11% of GDP.
Heat cut work capacity enough in 2024 to put about $490 billion of output at risk, a conservative estimate from hourly heat stress in 149 cities. The Lancet Countdown's broader estimate is $1.09 trillion. Either figure is of the same order as all climate damages in the DICE model at 1.5 °C. The loss is regressive (3% of hours in lower-middle-income countries against 0.2% in rich ones) and convex: one extra degree adds 73%, two nearly triple it. Moving work out of the afternoon recovers 20–30%.
The first report in this theme.
The world adds 1.43 billion people by 2050, 69% of them in cities and 57% in sub-Saharan Africa. People living with 30 or more days a year above a 35 °C heat index more than double, from 1.9 to 4.1 billion. Warming drives 1.74 billion of that rise and population growth 0.44 billion, and growth lands disproportionately in hot places. City dwellers in 100-year flood zones, 507 million today, are heading for 630–690 million.
Droughts have barely become more frequent, but they have become hot. Half of warm-season drought months in 1995–2024 were also extremely hot, up from three in ten in 1951–80 and seven in ten in 2021–24. Dry-to-wet whiplash is up 30%, and hot-dry years produce the great smoke and dust events. By the 2090s, 0.34 billion people would live with two or more compound hazards on a low-emissions path, 5.2 billion on a high one.
The first report in this theme.