The Long Heat

Climate change gradually weakens the systems that keep civilisation functioning, forcing societies to rebuild under harsher conditions and stricter rules.

Global temperatures peak at around 2.8–3°C above pre-industrial levels around 2110. They remain more than 2°C above that baseline for roughly two centuries, falling below 1.5°C only after 2300. The devastation comes from generations of sustained warming.

Wealthy countries have the resources to adapt. Poorer countries, especially in the tropics, lose much of their population as people flee extreme heat and destructive weather. Many of these weakened states are eventually absorbed into richer powers (see The Missing Century).

How the decline unfolds

1. The Grinding (2030–2080). Insurance withdraws from coasts and flood plains; property wealth evaporates for a generation. Simultaneous breadbasket failures in 2041 and 2058 break the faith that markets can feed everyone. Wet-bulb heat makes parts of South Asia, the Gulf and the Sahel seasonally uninhabitable at midday. Tens of millions move every decade.
2. The Northern Cold Shock (c. 2085). A partial collapse of the Atlantic Meridional Overturning Circulation (AMOC), centred on the Labrador Sea, cools north-west Europe while the rest of the world keeps heating. Britain, Scandinavia and the Low Countries face harsher winters and crop losses even as they absorb climate refugees. The event ends the idea of a single global climate story.
3. The Parasol Wars (2090–2130). A coalition of hot nations, led by China and India, begins stratospheric aerosol injection without global consent. Other states retaliate with counter-programmes or threaten the aircraft. Monsoons shift; blame is unprovable. The great fear is “termination shock”—rapid rebound warming if injection stops. The parasol is never switched off abruptly, but the possibility becomes a permanent lever of power.

4. The Contraction (2100–2180). Global population peaks near 10 billion in the 2080s, close to the UN's 2024 projection of 10.3 billion, and falls to about 6 billion by 2200. Collapsing birth rates and shortened lives account for most of the decline, compounded by regional famines and wars.

   Megacities fragment into federated districts. Strong states absorb their weaker neighbours' refugees, then their territory. It is rarely peaceful: absorbed peoples riot against custodians who ration their water, hosts turn on newcomers who come to outnumber them, and exile movements fight for flags that no longer fly.

Within surviving states, real authority shifts to cities, river-basin compacts and climate-refuge treaties. These institutions keep people alive while capitals retain their armies and debts. Refuge cities admit more people than they will trust with a vote, establishing a division between citizen and resident that outlasts the emergency (see Politics).

How humanity comes through it

Recovery rests on technologies already spreading in the 2020s, scaled by desperation and then by AI.

• Positive tipping points held. Solar, wind, batteries and EVs had already crossed self-reinforcing adoption thresholds by 2025. From the 2040s, energy gets cheaper even as everything else gets more expensive, making desalination, indoor agriculture and carbon removal possible at scale. Oil loses its central role in energy supply, and the Gulf loses influence as well as people.

• Carbon drawdown as two centuries of public works. Crews quarry and crush rock, spread mineral dust over farmland, and measure the carbon absorbed as it weathers. Coastal teams operate ocean alkalinity plants and monitor marine life. Inland crews tend forests adapted to hotter conditions, restore soils, cut firebreaks and replace trees lost to drought. Others maintain the pumps, railways, nurseries and monitoring stations that support the work.

  Much of it is repetitive, physically demanding and far from home; success is measured over decades. People join drawdown crews the way earlier generations joined armies—for wages, training, belonging and service. For a population struggling to find purpose after the AI Hollowing, repairing the world becomes a shared undertaking.

• The Basin Compacts. Rivers, rather than borders, become the unit of governance as upstream and downstream communities enter binding water treaties. These become the institutional seeds of The Settlement. Their real-world predecessors include the Great Lakes–St Lawrence River Basin Water Resources Compact of 2008, the Murray–Darling Basin Authority and the Mekong River Commission.

• Managed retreat and the Refuge Latitudes. Canada, Patagonia, Scandinavia, Siberia, Tasmania and the New Zealand highlands absorb hundreds of millions, alongside the Anatolian plateau and Himalayan foothills. Siberia's newcomers are mostly Chinese; Canada's are increasingly American. Old national identities blur as refuge cities develop creole cultures.

• Equality as adaptation. Dagomar Degroot and his colleagues' research on how societies survived climate disruption helps inspire a political doctrine after the Contraction: sthe survival of communities and broader civilisation depends on essential resources reaching everyone. In practice, this means guaranteed access enforced largely through rationing. The Settlement writes these guarantees into constitutions; the Mandate makes them state policy.

Fusion: the second hinge (2040s–2250s)

Renewables make energy cheap on Earth; fusion makes it dense and portable enough to support industry and transport beyond Mars. It arrives in three stages.

Control of these fuels gives power over interplanetary trade. Their sale builds Calder's fortune in the 2200s and 2220s and gives the Belt much of its bargaining power before the Ore Secession. Titan gains influence through the fuel trade and its supplies of nitrogen, needed for breathable atmospheres and agriculture.

During the 2400s, solar arrays built during the Mirror Race begin competing with fusion power. Falling demand for reactor fuel threatens suppliers' income and influence, helping drive the Ore Secession (see The long middle).

The Great Lift (2180s–2300s)

After the Contraction, the emerging blocs impose levies on surface industry to pay for climate damage and fund carbon drawdown. Space fusion powers off-world smelters and freighters, making both production and bulk transport cheaper. Industries increasingly find it cheaper to leave Earth than to pay the levies. Only then do the blocs ban most heavy industry from the surface.

Smelting, bulk chip fabrication, bulk chemistry and most power generation move to orbit, the Moon and the Belt. Embodied AI crews build the facilities, funded as climate repair, and workers and their families follow. Under the Fab Truce, Taiwan retains chip design, research and small-scale prototype production. Unlicensed workshops continue operating in the buffer, beyond the reach of the blocs' levies.

About ten million people live off Earth in 2180. By the 2340s, there are about half a billion. The Lift's young settlements grow about 1% a year through births exceeding deaths, while emigration rises from roughly half a million people a year in the 2180s to two million by the 2330s (see Why so many people live off Earth, in Reaching outward).

Those births are possible because the partial-gravity programme of the 2100s has already adapted human lines to low gravity. On the lightest worlds, children grow up in spin nurseries (see Designed children, in Ageing slowed, not ended).

From 2271, the Elevator, built jointly by all four blocs, carries most of the Lift's later freight and its poorest emigrants. Passenger capacity grows from about a million riders a year in the 2320s to six million by the 2430s, as ribbons are added and climbers speed up. From 2488, the bloc elevators carry emigrants too (see The Elevator, in Reaching outward).

After the 2340s, natural population growth averaging about 0.8% a year, together with steady emigration, brings the population beyond Earth to about three billion by 2497.

What is permanently lost by 2497

Almost all warm-water coral reefs, much of Bangladesh's delta, the Nile delta, many low island nations and a large share of Earth's species are gone. Sea level averages about four metres above its former level—from about three metres off Patagonia to five off New York—and continues rising slowly as ice sheets lose mass (see Cities).

Every child in 2497 learns the names of drowned cities the way we learn Pompeii.