According to the Financial Times, mortgage-backed securities can trigger a self-reinforcing feedback loop that pushes Treasury yields higher still. The warning lands with the US 10-year Treasury yield at 5.31%, roughly 156 basis points above the Federal Reserve's 3.75% funds rate target. That gap tells investors the bond market is pricing a policy stance meaningfully looser than where long-term borrowing costs actually sit.
Mortgage Bonds and the Convexity Feedback Loop
The mechanism the FT describes centres on a property of mortgage bonds known as negative convexity. When Treasury yields rise, mortgage rates follow, and homeowners stop refinancing. The expected life of outstanding mortgage-backed securities stretches out just as their market value falls. Portfolio managers who hedge these holdings respond by selling Treasuries to rebalance duration, and that selling pushes yields higher again.
This is not a new phenomenon. It surfaced during the 1994 bond market rout and again in episodes since the 2008 financial crisis, when mortgage hedging flows amplified moves that started elsewhere. What makes the current setting notable is the starting point: a 10-year yield already at 5.31%, a level that leaves less room for absorption before refinancing activity collapses further and convexity hedging intensifies.
When mortgage rates rise, homeowners refinance less, which extends the duration of outstanding mortgage bonds. Portfolio managers then sell Treasuries to maintain their hedge ratios, pushing yields higher still.
The Fed-Market Divergence and Why It Matters
The 10-year yield at 5.31% against a 3.75% Fed funds rate and 2.6% US inflation reading creates a curve shape that signals the market expects term premium, not policy tightening, to drive long rates from here. NYT Dealbook frames this tension directly, describing markets as buoyant and under pressure at once. Equity trading on the day bears that out: the Dow fell 1.15%, the S&P 500 dropped 0.67%, the Russell 2000 slid 1.24%, and the VIX jumped 4.53% to 15.69. European benchmarks moved in the same direction, with the DAX down 1.5% and the Euro Stoxx 50 off 1.61%.
Risk assets outside equities told a similar story. Gold fell 1.09% to $4,115 an ounce and silver dropped 2.3% to $60.17, an unusual pairing with equity weakness that suggests investors were raising cash broadly rather than rotating into traditional havens. Bitcoin fell 3.84% to $82,992 and Ethereum dropped 5.76%, a decline that tracked the equity sell-off closely enough to reinforce how tightly digital assets now move with broader risk sentiment. Readers tracking that correlation can find more detail at Coinhours' coverage of crypto's macro sensitivity. The composite sentiment reading of 76, still labelled risk-on, suggests the market has not yet priced a sustained yield shock, which leaves room for further repricing if the mortgage bond dynamic the FT describes plays out.
A Familiar Spectre: Rate-Rigging Convictions Quashed
Separately, the BBC reports that convictions against bankers jailed for rigging interest rate benchmarks have been quashed. The timing is a reminder that benchmark integrity has been a recurring fault line in fixed income markets. The original rate-rigging cases centred on manipulation of reference rates that underpinned trillions of dollars in lending and derivatives contracts globally.
The echo today is different in mechanism but similar in theme: markets that look orderly on the surface can carry structural vulnerabilities that only become visible under stress. The 1990s and 2000s history of central bank benchmark-setting, covered in The History of Central Banking Part 1 and Part 2, shows how often confidence in rate-setting mechanisms has been tested and rebuilt.
Background: What Treasury Yields Tell Investors
Treasury yields function as the benchmark against which nearly all other borrowing costs are set, from mortgages to corporate bonds. A full explanation of how yields are determined and why they matter for portfolio construction is available at Treasury Yields. The short version: when yields rise faster than growth expectations justify, it tightens financial conditions across the economy, independent of what the central bank's policy rate says.
The RBA's own cash rate sits at 4.6%, with Australian inflation at 2.4%, a narrower gap than the one visible in the US data. That contrast underscores how US-specific dynamics, including the mortgage bond market structure, are driving the current yield story rather than a globally synchronised rate-setting cycle.
What Comes Next for Bond Investors
The FT's warning does not predict a crisis. It describes a mechanical risk that becomes more relevant as yields climb and refinancing activity slows. Investors holding long-duration bond exposure should watch the 10-year yield's path from 5.31% as closely as they watch the Fed funds rate itself, because the next leg higher may originate inside the mortgage market rather than at the Federal Reserve's next meeting.