While sovereign debt flare‑ups often start at the periphery, the central locus of systemic risk today lies squarely within the US fiscal–market nexus
Public debt has surged back to historic highs, but unlike the previous decade, the global economy no longer enjoys the rate cushion that once insulated sovereign balance sheets. In October 2024, the IMF’s Fiscal Monitor places global public debt above $100 trillion, warning that risks are “tilted to the upside.” Under severe scenarios, debt could rise by nearly 20 percentage points of GDP within three years. The IMF’s new Debt at Risk framework illustrates how quickly trajectories can deteriorate without credible fiscal adjustment. Meanwhile, UNCTAD reports developing‑economy external debt at $11.4 trillion, with interest burdens increasing sharply.
The U.S.: still the world’s swing factor
Because the US defines the global risk‑free curve, its fiscal arithmetic sets the tone for global sovereign borrowing. Congressional Budget Office projections place federal debt held by the public near 100% of GDP in 2025, with the trajectory rising under current law. Independent trackers estimate the 2025 federal deficit near 6% of GDP, with net interest costs surpassing $1 trillion for the first time. This has contributed to the rise in the New York Fed’s ACM term premium model, reflecting a higher required compensation for duration risk.
When does debt become dangerous?
There is no universal debt threshold that triggers unsustainability. A more reliable diagnostic is the interest–growth differential (r‑g). When borrowing costs “r” persistently exceed economic growth “g,” stabilizing debt requires increasingly large primary surpluses.
Research from the French Trésor and the ECB shows that (r‑g) can flip rapidly—and that high debt itself increases risk premia, creating a feedback loop: elevated debt boosts term premia, raising “r” relative to “g,” tightening fiscal constraints.
By this measure, the U.S. is not in crisis but is navigating a narrowing corridor of stability: debt is high, deficits are structurally large, and term premia exceed recent norms. Vulnerabilities remain. As Federal Reserve analyses highlight, leveraged Treasury basis trades continue to pose systemic risk by amplifying dislocations when funding tightens.
New evidence: The JGB “Air‑Pocket” problem
Japan’s government bond market—long a global anchor of stability—has issued an important warning. Since the end of yield curve control in March 2024, liquidity in the super‑long JGB sector has deteriorated. Recent intraday volatility in long‑dated JGBs has been significant. As the world’s second‑largest sovereign bond market, sudden “air pockets” in JGB liquidity suggest that term‑premium shocks are becoming more correlated and more contagious across global curves.
The implication: if thin market depth can trigger such moves in JGBs, the probability of a synchronized global steepening across Treasuries, Bunds, and JGBs has risen meaningfully.
Does a weaker dollar compound debt risk?
Dollar depreciation raises import costs, putting upward pressure on inflation risk premia and long‑dated yields. It also lifts marginal funding costs for the U.S., as foreign investors either reduce hedging or demand higher compensation for currency risk.
Dollar weakness does not trigger a sovereign crisis for a country issuing debt in its own currency. But paired with heavy issuance needs and elevated term premia, a weaker dollar makes fiscal stabilization materially more challenging. Term‑premium dynamics are now transmitted more quickly across borders and FX markets, tightening the feedback loop between currency weakness and sovereign financing costs.
Geo‑economic risk and the erosion of central bank independence
Geo‑economics is re‑emerging as nations weaponize sanctions, financial infrastructure, data chokepoints, and supply chains. These pressures inject volatility directly into the variables central to debt sustainability—inflation, growth, and term premia.
At the same time, central banks are facing increasing political pressure. The IMF warns that reduced independence risks a drift toward fiscal dominance, while recent research shows that political interference lifts inflation expectations and erodes credibility. This combination creates conditions for sovereign “accidents”—not via insolvency, but through a rapid loss of trust.
Bottom Line
While sovereign debt flare‑ups often start at the periphery, the central locus of systemic risk today lies squarely within the U.S. fiscal–market nexus. Debt becomes dangerous when persistent primary deficits coincide with a positive interest–growth differential, elevated term premia, liquidity fractures such as those in JGBs, and intensifying geo‑economic and political constraints on central banks.
In this environment, fixed‑income strategy should emphasize:
- Demanding higher duration compensation
- Tilting toward high‑quality credit
- Maintaining robust liquidity buffers
- Closely monitoring basis‑trade leverage
- Diversifying globally to manage cross‑market term‑premium correlations
The seeds of a crisis do not have to take root. But avoiding that outcome requires vigilance—something still absent from current market pricing. Identifying and properly valuing these vulnerabilities today is essential to preventing them from becoming unmanageable tomorrow.
Dominic Siciliano is a senior vice president, head of fixed income at iA Financial Group.
