What would happen if all the satellites stopped working?

Numerical weather prediction depends overwhelmingly on satellite observation, which supplies the great majority of the data assimilated into forecast models and is the only meaningful source over oceans and sparsely populated regions. Losing it would cut useful forecast range from around a week to roughly a day or two, with severe consequences for aviation, shipping, agriculture and storm warning — hurricane track forecasts in particular have improved by a factor of several since satellite coverage became routine. Navigation and timing would fail as described for GPS, and satellite communications would take out remote connectivity, maritime links and much broadcast distribution, though undersea fibre carries the bulk of international internet traffic and would survive. Earth observation for climate monitoring, deforestation, ice cover and disaster response would stop. The compounding hazard is Kessler syndrome, in which collision debris causes further collisions and makes some orbits unusable for generations, which is the version of this scenario that would not be quickly reversible.

How confident this is

This is a reasoned extrapolation rather than an observation. The mechanism is understood, but the scale of the consequences depends on assumptions that could reasonably be argued differently.

Everyday systems

• What would happen if everyone on Earth jumped at the same time? Essentially nothing. All of humanity together is about one ten-trillionth of Earth's mass.
• What would happen if the internet went down? Payments fail first, then logistics — most physical supply chains now depend on network connectivity rather than the other way round.
• What would happen if all the power went out worldwide? Water supply is the first life-critical failure — most tap water is pumped, and pumping stops when the grid does.
• How much space would it take for everyone on Earth to stand in one place? About 2,000 square kilometres — smaller than Luxembourg, and less than twice the area of Los Angeles.
• What would happen if GPS stopped working? Timing, not navigation, is the real dependency — mobile networks, power grids and financial systems all use GPS clocks.
• What would happen if money stopped existing? Trade would collapse to what barter can support, and something money-like would be reinvented within weeks.
• What would happen if all refrigeration stopped? Food waste would rise enormously and the vaccine cold chain would fail — refrigeration is a public health system, not a convenience.
• What would happen if the water supply stopped? Three days for drinking, but sanitation fails first — waterborne disease is what historically kills people in a water outage.
• What would happen if all digital data was lost? Ownership would be the deepest problem — land registries, bank balances and medical records exist almost entirely as data.