For most of the past four decades, the investment case for long-duration government bonds was straightforward. Yields fell steadily from the early 1980s highs, bond prices rose, and when equities sold off, bonds appreciated as investors sought safety. The 60/40 portfolio — 60% equities, 40% bonds — was not just a rule of thumb; it was a genuinely diversified structure that worked because of the reliable negative correlation between the two asset classes.

That era has ended. The question now is not whether the long bond bull market is over — it clearly is — but what the structural consequences are for investors who built portfolios on the assumption that bonds would always cushion equity drawdowns.

What has happened to long bond yields

30-year US Treasury yields have returned to levels not seen since before the 2008 global financial crisis. The same pattern is visible across developed markets: Japan, the United Kingdom, Germany, and Australia have all seen long-end yields rise materially from their post-GFC lows.

The mechanics are straightforward. Bond prices and yields move inversely — when yields rise, existing bond holdings fall in value. An investor holding a 30-year Treasury bond purchased at the yield lows of 2020–2021 has experienced a capital loss of 30–40% in nominal terms. For a portfolio that held these bonds as a "safe" asset, that outcome was deeply unexpected.

The structural causes

The yield rise is not simply a consequence of the post-COVID inflation spike and the central bank response to it. The Bloomberg analysis identifies three structural forces that are likely to keep long-end yields elevated:

  • Fiscal deficits and borrowing volume. The US government is running a structural deficit of approximately 6–7% of GDP outside of recession conditions — a level previously associated only with wartime or acute economic crises. The volume of Treasury issuance required to finance this deficit is placing sustained upward pressure on yields. Other developed-market governments face similar, if less extreme, dynamics.
  • Inflation persistence. The post-COVID inflation episode demonstrated that supply-side shocks can produce inflation that is more persistent than central bank models predicted. With structurally higher defence spending, energy transition costs, and deglobalisation trends, the inflation baseline for the 2020s appears higher than the 2010s. Investors demand a higher yield to hold fixed-rate bonds when inflation uncertainty is elevated.
  • Maturity shortening by governments. Governments are increasingly reluctant to lock in long-term borrowing at current yields, and are financing their deficits with shorter-maturity debt. This shifts the duration risk to investors rather than issuers — and reduces the supply of long bonds at the same time as institutional demand for duration is rising.

Jeff Gundlach's warning

Jeff Gundlach of DoubleLine Capital — one of the most closely followed fixed income investors in the world — has been explicit about the implications. His analysis of US fiscal sustainability concludes that the current trajectory of deficit spending and debt accumulation is not consistent with stable long-term yields.

"The United States is on an unsustainable fiscal path. The bond market will eventually force a reckoning — either through higher yields, inflation, or both." — Jeff Gundlach, DoubleLine Capital

Gundlach's practical conclusion is notable: he recommends gold over Treasury bonds as the safe-haven asset for this environment, and suggests that investors seeking diversification from US equity risk should look to emerging markets — specifically India — rather than assuming US Treasuries will provide it.

The broader implications for borrowers

Higher long-term yields do not stay in bond portfolios. They transmit through the economy to every borrower with fixed-rate debt: mortgage holders, auto loan borrowers, corporate issuers, and governments themselves. The cost of refinancing debt that was issued at 2020–2021 lows has risen substantially, and the full impact of that refinancing cycle is still working through the system.

For Australian investors, the direct interest rate channel is less pronounced than in the US (Australian mortgages are predominantly variable rate), but the equity market channel is significant. A higher risk-free rate compresses the valuation premium that equity markets — particularly growth equities — can command. The mechanism is simple: if you can earn 5% risk-free on a government bond, you require a higher expected return from equities to justify the additional risk.

What this means for portfolio construction

The end of the long bond era does not mean that bonds have no place in portfolios. For investors with genuine short-term liquidity needs, for those in or approaching retirement who require income predictability, and for portfolios with matched liability structures, bonds remain essential. What changes is the assumption about what they will do in a crisis.

A portfolio constructed on the premise that long-duration government bonds will rise when equities fall is relying on a correlation that held for four decades but has now broken down. The 2022 calendar year — in which both Australian and US 60/40 portfolios delivered their worst returns in four decades — was not an anomaly. It was a preview.

The practical response is to seek diversification from sources that do not rely on the bond-equity correlation: real assets with inflation-linked cash flows, private credit with contracted returns, and equity exposures with geographic and factor diversification that are not simply correlated proxies for US technology.

These are not novel ideas. They are the investment principles that endowment funds and sovereign wealth vehicles have applied for decades. The Long Bond Era made them look unnecessary. Its end makes them essential.