Global public debt is on track to match the size of the world economy in the coming years, new projections from the International Monetary Fund show.

Why it matters: That gloomy fiscal outlook in major economies risks triggering market turmoil around the world.

• And global trends — aging societies, geopolitical strife and populist pitches across the political spectrum — suggest the need for more spending, not less.

By the numbers: Global public debt is estimated to top $100 trillion by year-end — or roughly 93% of global GDP, according to new projections from the fund.

• IMF economists expect cumulative global debt will approach 100% of world GDP by 2030, with the two largest economies — the U.S. and China — leading the increase.
• The U.S. is pretty much already there, with a debt-to-GDP ratio of about 100%.

Between the lines: IMF economists suggest that actual outcomes will probably be worse.

• In the group's semiannual Fiscal Monitor Report, researchers say such estimates are often subject to an "optimism bias" and actual global debt levels turn out higher than projected by an average of 6 percentage points of GDP after three years.

The big picture: The estimates don't (and couldn't) fully account for how much governments will have to increase spending to address health care in an increasingly older population, defense, the green transition and more.

• This all assumes a benign economic backdrop and a stable interest rate environment; any potential shock could force higher spending.

Where it stands: The IMF says current economic conditions — cooling inflation, interest rate cuts — provide the environment to rein in spending.

• "With inflation moderating and central banks lowering policy rates, economies are better positioned now to absorb the economic effects of fiscal tightening," the authors write.

Yes, but: That looks politically unfeasible. For instance, both U.S. presidential candidates are campaigning on policies that would add to fiscal deficits to varying degrees.

• The latest projection from the Congressional Budget Office — which doesn't account for campaign promises — shows debt held by the public will be 122% of GDP by 2034.
• "The political discourse on fiscal issues has increasingly tilted toward higher government spending in recent decades," the IMF researchers write.

Threat level: High debt levels in the world's largest economies — paired with the unknown path of fiscal and monetary policy down the line — could rattle financial markets in such a way that spills over into higher borrowing costs for other nations.

• A separate report this week from the World Bank shows the world's poorest countries cumulatively have more debt now than at any point in the past 18 years.

What they're saying: "The debt problems in advanced economies will have consequences — but it's not like the consequences these economies have," Ayhan Kose, the World Bank's deputy chief economist, tells Axios.

What do policy wonks do in the weeks leading up to a deeply consequential election? Model the fiscal and economic impacts of the candidates' policies, of course.

Driving the news: Three reports out in the last 24 hours offer mainstream economists' best guesses as to how the tax and immigration policies the two candidates propose would play out.

State of play: The Yale Budget Lab modeled the effect of former President Trump's proposed 10% across-the-board levy on all imports and a 60% tariff on Chinese imports.

• The group finds it would raise about $2.7 trillion in federal revenue over the next decade, but that this number would fall by as much as 26% depending on how aggressively other countries retaliate.
• It finds that the purchasing power of American households would decrease by $1,900-$7,600, depending on factors like how much they substitute away from imported goods and how the Federal Reserve reacts.

The Tax Foundation modeled all Trump tax proposals, finding that his agenda would, taken together, increase long-run GDP and wages by 0.8% and employment by about 600,000 jobs.

Yes, but: In the Tax Foundation's projections, the contribution to growth comes mainly from extending business-friendly provisions of Trump's 2017 tax legislation, which, in this model, will encourage more capital investment and productivity.

• The group finds those provisions would add 2.4% to GDP while Trump's tariffs (and retaliation from overseas) subtract 1.7%.

And a new paper out this morning from scholars at the Brookings Institution, Niskanen Center, and American Enterprise Institute estimates the economic impact of the two candidates' immigration approaches.

• They find net migration over the coming decade could range from 25.6 million people in a scenario in which Trump wins and is maximally aggressive in restricting immigration to 35.7 million people if Harris wins and is maximally aggressive in encouraging it.
• The numbers are quite similar in scenarios where either candidate wins but acts more moderately.