Past 1.5°C: Climate Baseline Repricing and the Rupiah Operating Ledger

Rupiah Stability Watch · 2026-09-02

The premise

The relevant change is not that one climate story now moves the rupiah. It is that the planning baseline is shifting.

Nature’s September 2 report on UNEP’s new assessment says the long-running goal of limiting warming to 1.5°C is now expected to be breached by the end of the decade, with the best current trajectory still around 1.8°C this century. The report’s hard sentence is not a market forecast. It is a baseline repricing: hotter, wetter, smokier, and more interrupted operating conditions become less like tail events and more like repeated costs that must be financed, insured, imported around, or absorbed.

For Indonesia, that matters because the rupiah is not only priced through interest-rate differentials and portfolio flows. It is also priced through a quieter ledger: fuel import needs, food import pulses, logistics reliability, tourism receipts, export consistency, disaster spending, health-system strain, and the credibility of institutions that can keep ordinary services running during stress.

This builds on Rupiah Stability Watch’s recent operating-ledger work: the wet-season logistics synthesis, the heat and work-hours channel, the cooling-demand and food-safety channel, the fire and haze sequence, the warning/provenance pieces, and the coral/coastal ledger. The new point is not to repeat each channel. It is to read them together under an overshoot baseline.

Data box: what is already visible

• Global baseline: Nature reports that UNEP now expects the long-term 1.5°C threshold to be breached by the end of the decade, and that the best current emissions trajectory points to about 1.8°C warming this century.
• Indonesia exposure: the ADB–World Bank Climate Risk Country Profile describes Indonesia as the world’s largest archipelagic state, with more than 17,500 islands and more than 81,000 km of coastline. It ranks Indonesia in the top third of countries for climate risk, with high exposure to flooding and extreme heat.
• Long-run macro cost: the same ADB–World Bank profile cites an ADB estimate that climate-change impacts could cost Indonesia between 2.5% and 7% of GDP by 2100, with the poorest bearing the brunt.
• Heat and labour: the ILO’s Working on a warmer planet report estimates that Indonesia’s working hours lost to heat stress could rise from 2.1% in 1995 to 3.0% in 2030, equivalent to about 4 million full-time jobs. Globally, the ILO frames its 1.5°C scenario as conservative.
• Trade composition: OEC’s 2024 profile shows Indonesia’s top imports included refined petroleum at $21.3 billion, crude petroleum at $9.95 billion, and petroleum gas at $3.71 billion; top exports included coal at $34.4 billion, palm oil at $21.2 billion, petroleum gas at $8.56 billion, and copper ore at $8.39 billion.
• External-balance stress marker: Bank Indonesia’s Q2 2026 balance-of-payments release said the BOP recorded a $0.9 billion deficit, much smaller than Q1’s $9.1 billion deficit, while the current-account deficit widened partly because of a wider oil-and-gas trade deficit.
• Reserve buffer: Bank Indonesia’s July 2026 reserve release put official reserve assets at $145.3 billion, equivalent to 5.5 months of imports, or 5.3 months of imports plus government external-debt service.
• Current weather signal: BMKG’s forecast for 1–6 September 2026 said early September was still dominated by hot and dry weather, with high-confidence hotspots concentrated in Kalimantan, followed by Sumatra, Papua, and Maluku; maximum temperatures exceeded 36°C in parts of Kalimantan and Lampung during 27–30 August.

These figures do not form a rupiah forecast. They show why climate stress belongs inside the currency operating ledger.

External balance: recurring frictions replace isolated shocks

The first channel is imported energy.

Indonesia’s external account is already sensitive to oil-and-gas prices and volumes. Bank Indonesia’s Q2 2026 release specifically tied the wider current-account deficit to a wider oil-and-gas trade deficit. OEC’s trade profile gives the structural reason: refined petroleum, crude petroleum, and petroleum gas are among Indonesia’s top imports.

In a hotter baseline, cooling demand becomes more persistent. More air conditioning, refrigeration, cold-chain protection, hospital cooling, server-room cooling, and kitchen cooling all add to electricity demand. Whether that demand becomes a rupiah pressure depends on the marginal fuel mix, grid reliability, domestic gas availability, and the pace of efficiency. The currency channel is not “heat equals depreciation.” It is narrower: if heat raises peak electricity demand and the marginal response leans on imported fuel, the external-balance ledger tightens.

The second channel is food.

The ADB–World Bank profile flags rice production as vulnerable to changes in El Niño patterns, wet-season timing, and higher temperatures. That matters for the rupiah because food shocks enter both imports and inflation. If domestic supply is disrupted, the adjustment may come through imported rice, sugar, wheat, feed, fertilizer, or cold-chain inputs. Some imports protect households from scarcity; they can still use foreign exchange.

The third channel is commodity-export reliability.

Indonesia’s export basket carries climate-exposed assets: palm oil, coal logistics, nickel and mineral corridors, fisheries, and tourism-linked services. The ADB–World Bank profile notes that coral reefs generate estimated tourism income of about $3.1 billion per year, and that coral bleaching and ocean stress could sharply reduce reef-based tourism by the end of the century under high-emissions pathways. Again, this is not a near-term exchange-rate call. It is a reminder that climate damage can reduce service receipts and local incomes in places where foreign-currency inflows matter.

The fourth channel is logistics.

Rupiah Stability Watch’s wet-season ledger already treated floods, ports, roads, kitchens, and warning chains as economic infrastructure. Under an overshoot baseline, the market question becomes less “was this flood exceptional?” and more “how often will transport, storage, ports, and procurement need redundancy?” Redundancy is useful. It is also capital-intensive. If it requires imported pumps, sensors, refrigeration, vehicles, cloud systems, medical equipment, or construction inputs, it links adaptation to the external account.

Fiscal credibility: adaptation becomes an operating cost

Climate repricing also changes the fiscal ledger.

Indonesia’s public credibility is not judged only by headline deficits. It is judged by whether the state can absorb shocks without turning each one into a subsidy surprise, emergency import bill, or arrears problem.

Three pressures matter.

First, subsidy pressure. Hotter weather and higher fuel-linked electricity demand can make energy subsidies harder to frame as temporary. If oil-and-gas imports widen at the same time as households and small firms need relief from cooling and transport costs, fiscal choices become more constrained.

Second, disaster response. The ADB–World Bank profile identifies high flood and extreme-heat exposure, with river-flood exposure projected to grow without adaptation. BMKG’s current September outlook shows how mixed the operating environment can be: dry and hot conditions with hotspots in several regions, while some provinces still face local heavy-rain risk. That combination is fiscally awkward. It can require fire prevention, health messaging, water management, and flood readiness at the same time.

Third, daily-system resilience. Rupiah Stability Watch’s earlier MBG/SPPG kitchen work matters here. Public kitchens, schools, clinics, and local procurement systems are not macro variables in ordinary models, but they become credibility variables when heat, haze, floods, and food-safety risk rise together. A kitchen that needs reliable water, safe storage, electricity, refrigeration, worker protection, and transparent procurement is a small fiscal unit. Multiply it across districts, and climate resilience becomes a recurring budget line rather than a project appendix.

The least misleading framing is this: adaptation capex can support credibility when it prevents larger losses, but it can weaken credibility if it arrives as opaque, imported, reactive spending after repeated disruptions.

Bank Indonesia’s room: supply shocks complicate the signal

Bank Indonesia’s room is shaped by inflation volatility, portfolio-flow dependence, and reserve adequacy.

When climate shocks are mostly local and occasional, monetary policy can look through some of them. When heat, food, logistics, and energy shocks become more frequent, the distinction between temporary and persistent supply pressure becomes harder. A rice or fuel shock can be temporary in origin but persistent in household expectations if it repeats often enough.

This is where reserve adequacy matters, but should not be overstated. Bank Indonesia’s July 2026 reserve position, at 5.5 months of imports, is above the usual three-month adequacy standard. That is a meaningful buffer. It does not make the currency immune. It gives the central bank more space to smooth volatility while fiscal, trade, and supply-side channels do their work.

Portfolio flows add another layer. BI’s 2026 rate communications have emphasized stability and measures to support rupiah exchange-rate confidence. In an overshoot baseline, foreign investors may ask not only whether yields are attractive, but whether the country’s operating systems can keep growth, inflation, and public spending within a credible range under repeated climate stress. That is a governance question as much as a monetary one.

What the evidence does not support

The evidence does not support a claim that breaching 1.5°C will, by itself, cause near-term rupiah depreciation.

It does not support treating any one BMKG fire, flood, heat, or rain signal as an exchange-rate trigger.

It does not support a simple “climate bad, rupiah weaker” rule. Some adaptation spending can reduce risk. Some domestic energy substitution can lower import sensitivity. Some commodity-price moves may temporarily improve export receipts even while they raise domestic costs. Some weather shocks are local and absorbed locally.

It also does not support certainty about timing. Climate repricing usually becomes visible first in small frictions: insurance cost, port delay, subsidy revision, tender acceleration, procurement failure, household food substitution, school or kitchen closures, and reserve-use narratives. The exchange rate may notice late, not early.

A rupiah watchlist for the overshoot baseline

The useful watchlist is observable and boring. That is its strength.

1. Oil-and-gas trade deficit: whether heat-season electricity and transport demand coincide with wider oil-and-gas import bills.

2. Food import pulses: rice, sugar, wheat, feed, and fertilizer imports after heat, flood, drought, or pest stress.

3. Cooling-load evidence: peak electricity demand, diesel backup use, cold-chain interruptions, and imported equipment orders for hospitals, schools, kitchens, retail, and data centers.

4. Logistics interruptions: port dwell time, road and rail disruptions, warehouse loss, ferry delays, and flood-related rerouting in commodity corridors.

5. Haze and fire signals: hotspots, fire-weather indices, peatland dryness, school closures, flight delays, respiratory visits, and transboundary complaints.

6. Fiscal response quality: whether disaster and adaptation spending is budgeted, transparent, and preventive, or late, opaque, and compensatory.

7. MBG/SPPG resilience: kitchen water reliability, refrigeration uptime, worker heat protection, procurement holds, and food-safety disclosure during weather stress.

8. Insurance and credit terms: whether banks, insurers, and project financiers begin pricing flood, heat, haze, or coastal risk into loan margins and coverage exclusions.

9. Tourism and coastal receipts: reef stress, beach erosion, ferry disruption, and health advisories in tourism-dependent districts.

10. BI language: whether repeated supply shocks change the way Bank Indonesia describes inflation persistence, reserve adequacy, portfolio flows, and rupiah stability.

This list does not predict a break. It watches whether repeated operating stress is becoming a financial condition.

What I am uncertain about

The largest uncertainty is timing. Climate science can say the baseline is hotter and riskier; it cannot by itself say when markets reprice Indonesia’s currency risk.

The second uncertainty is substitution. If cooling demand is met through efficiency, distributed solar, storage, demand response, and domestic energy rather than imported fuel, the external-balance channel weakens. If it is met through fossil backup and imported equipment under emergency conditions, the channel strengthens.

The third uncertainty is governance quality. The same adaptation rupiah can either prevent a larger loss or disappear into low-trust spending. Currency confidence will distinguish between those paths.

The fourth uncertainty is spatial. Indonesia’s archipelago means a national average can hide local stress. Kalimantan heat, Sumatra smoke, Java logistics, eastern Indonesia food prices, and coastal tourism do not move together.

The evidence is enough to change the ledger. It is not enough to call the exchange rate.