The Maunder Minimum was a 70-year stretch from 1645 to 1715 when sunspots nearly vanished from the sun’s surface. During a normal solar cycle, the sun’s face is dotted with dark, magnetically active regions that wax and wane roughly every 11 years. During the Maunder Minimum, that cycle essentially flatlined. For one seven-year period (1645 to 1651), the recorded sunspot count was zero. Another eight-year gap of zero sunspots occurred from 1662 to 1670. Nothing like it has happened since.
What Happens During a Grand Solar Minimum
The sun doesn’t turn off during a grand minimum. It dims slightly. Reconstructions of the sun’s total energy output suggest it was roughly 1.25 watts per square meter lower during the Maunder Minimum than it is today, a reduction of about 0.09%. That sounds trivial, but it reflects real changes in the sun’s magnetic behavior. The solar wind, a stream of charged particles flowing outward from the sun, blew at lower speeds. The sun’s magnetic field weakened. And ultraviolet radiation, which makes up a small fraction of total output but plays an outsized role in atmospheric chemistry, dropped significantly. Estimates suggest the sun’s ultraviolet output at certain wavelengths was nearly 50% lower than modern levels.
The sun generates its magnetic activity through an internal process sometimes called the solar dynamo: hot plasma circulating deep inside the sun creates electrical currents, which in turn generate magnetic fields. Those fields rise to the surface and produce sunspots, solar flares, and other visible activity. During the Maunder Minimum, something suppressed this dynamo. The magnetic engine kept running, but at a fraction of its usual strength. Researchers have found evidence that a weak, roughly 8-year solar cycle persisted even during the deepest quiet, suggesting the dynamo never completely shut down.
The Maunder Minimum and the Little Ice Age
The Maunder Minimum overlaps with part of the Little Ice Age, a period of regional cooling in Europe and other parts of the Northern Hemisphere. Rivers that rarely freeze, like the Thames in London, froze solid. Crop failures and harsh winters were common. For decades, scientists debated whether the quiet sun caused this cold snap.
The current consensus is more nuanced. A 0.09% drop in solar output translates to a modest cooling effect, and many solar physicists argue the sun simply couldn’t have dimmed enough on its own to explain the Little Ice Age. Karel Schrijver, a solar physicist at Lockheed Martin’s Advanced Technology Center, and colleagues have pointed out that even during a prolonged minimum, a network of small bright features on the sun’s surface keeps its energy output above a certain floor. Volcanic eruptions were also frequent during this period, injecting reflective particles into the upper atmosphere and blocking incoming sunlight. Most researchers now view the Little Ice Age as driven by a combination of reduced solar output, heightened volcanic activity, and natural variability in ocean circulation, not by the quiet sun alone.
Regional Climate Effects
While the global temperature impact of a grand minimum is small, the regional effects can be surprisingly uneven. Research published in Nature Communications found that reduced ultraviolet radiation from the sun can alter pressure patterns in the atmosphere, particularly the Arctic and North Atlantic Oscillations. These are large-scale circulation patterns that steer winter weather across Europe, North America, and northern Asia. When ultraviolet output drops, the signal propagates downward through the atmosphere and reshapes how planetary waves move, ultimately shifting the jet stream.
The result is a patchwork of warming and cooling rather than uniform chill. Modeling studies project that a future grand minimum would produce enhanced cooling over northern Eurasia and the eastern United States during winter, with temperatures dropping 0.4 to 0.8°C relative to what they’d otherwise be. But other regions might see little change or even slight warming. The historical record bears this out in a striking way: the winter of 1685/86, right in the middle of the Maunder Minimum, was the fifth warmest winter in the entire 360-year Central England Temperature record. Grand solar minimums reshape where cold air goes, not just how much of it there is.
How Scientists Verify Ancient Solar Activity
Telescopic sunspot records go back to the early 1600s, which is why the Maunder Minimum is so well documented compared to earlier quiet periods. But scientists can also reconstruct solar activity much further back using tree rings and ice cores. The key is radiocarbon, a form of carbon produced when cosmic rays strike nitrogen atoms in the upper atmosphere. When the sun is magnetically active, its stronger magnetic field deflects more cosmic rays away from Earth, and less radiocarbon is produced. When the sun quiets down, more cosmic rays get through, and radiocarbon production rises.
Trees absorb this radiocarbon from the atmosphere as they grow, locking a year-by-year record into their rings. Ice cores preserve a similar signal through a different isotope, beryllium-10. By measuring these isotopes at annual resolution, researchers can trace the 11-year solar cycle thousands of years into the past. A 2024 study in Nature Communications used tree ring radiocarbon to map solar cycles across the entire first millennium BCE, finding a mean cycle length of 10.5 years and confirming that these isotope records reliably track solar behavior. This same technique has identified earlier grand minimums, like the Spörer Minimum (roughly 1460 to 1550), long before anyone was counting sunspots.
Could It Happen Again?
Grand solar minimums are a recurring feature of the sun’s long-term behavior, and another one will eventually occur. Several research groups have examined what that would mean for modern temperatures. The consistent finding, highlighted by NASA, is that a future grand minimum could cool the planet by as much as 0.3°C. That would, at best, slow human-caused warming briefly. It would not reverse it. Current greenhouse gas emissions are driving warming at a pace and scale that dwarfs the solar forcing difference between a grand minimum and normal activity. The 0.09% change in solar output during the Maunder Minimum is a small lever compared to the heat trapped by rising concentrations of carbon dioxide and methane.
A future grand minimum would still matter regionally. The modeling work on North Atlantic circulation patterns suggests that parts of northern Europe and the eastern United States could see winters that are relatively cooler than they’d otherwise be under continued warming, with shifts in precipitation patterns across Europe. But globally, the effect would be temporary and modest, a brief dip on a sharply rising curve.