A peer-reviewed study published in Nature Geoscience has found that during Earth’s most extreme ancient warming periods, between 66 and 47.8 million years ago, rainfall across mid-latitude regions became sharply more intermittent, with shorter wet seasons and longer dry gaps. The findings, drawn from a global compilation of plant fossils, soil chemistry, and river deposits, carry a pointed warning for the present: current climate models may significantly underestimate how erratic precipitation patterns could become as carbon dioxide levels continue to climb.
Ancient Hothouse Earth Had Erratic, Unpredictable Rain
The early Paleogene, spanning roughly 66 to 47.8 million years ago, was one of the warmest stretches in Earth’s history. Atmospheric CO2 concentrations during that era reached two to four times modern levels, according to a synthesis paper in Science that assembled a transparent, integrated carbon dioxide record for the past 66 million years. Continents were arranged differently and ice sheets were largely absent, but the period offers the closest natural analog for the kind of warming trajectory human emissions are now driving, even if the exact rates and sources of carbon release differ from today’s fossil-fuel-driven surge.
What researchers found in the Nature Geoscience study is that this extreme warmth did not simply bring more rain everywhere. Instead, precipitation became more intermittent across mid-latitude regions, a pattern reconstructed through a multi-proxy framework including paleosols, fossilized plant assemblages, and sedimentary records of ancient rivers and lakes. Wet seasons shortened while the intervals between rain events stretched, and storms tended to arrive in more intense bursts. That distinction matters because it means total annual rainfall could remain stable or even increase while the timing and intensity of individual events shift in ways that stress ecosystems, agriculture, and water infrastructure designed around smoother seasonal cycles.
Extreme Rain Events Can Spike Even When Averages Hold Steady
A separate modeling study focused on the Paleocene-Eocene Thermal Maximum, or PETM, roughly 56 million years ago, reinforces this disconnect between averages and extremes. Published in Earth and Planetary Science Letters, the research showed that extreme precipitation events surged regionally during the PETM even when mean precipitation did not change proportionally. Simulations indicated that in some basins, the heaviest downpours intensified far more than the seasonal totals, pointing to a climate system in which warmer air and oceans loaded more moisture into individual storms without necessarily transforming every aspect of the hydrological cycle in lockstep.
Complementary evidence from a Nature Communications analysis found that hothouse warmth corresponded to exceptionally dry conditions in subtropical continental interiors, linked to carbon-cycle disruptions and orbital variations that reshaped atmospheric circulation. The PETM itself involved carbon releases on the order of thousands of petagrams, a scale that dwarfs annual human emissions but offers a window into how the climate system responds when carbon loading is rapid and sustained over millennia. Taken together, these studies paint a picture of ancient warming that did not produce uniformly wetter or drier conditions but instead amplified the swings between both extremes, sometimes within the same region and even within the same year.
Modern Climate Models May Be Too Conservative
One of the sharpest takeaways from this body of research is that present-day climate simulations appear to lowball the degree of rainfall disruption that extreme warming can produce. Comparisons between paleoclimate data and model outputs indicate that today’s models underestimate how irregular rainfall can become during periods of extreme warmth, according to scientists working with the Woodwell Climate Research Center. If models trained on recent observational data cannot reproduce the rainfall patterns recorded in 50-million-year-old rocks, their projections for the next century deserve scrutiny, particularly in regions where agriculture, reservoir operations, and urban drainage systems depend on relatively predictable seasonal moisture.
This is not merely an academic concern. NOAA’s CarbonTracker CT2022, a carbon-cycle reanalysis product covering atmospheric trends from 2000 through 2020, documents the ongoing acceleration of CO2 in the modern atmosphere and the steady narrowing of the gap between present-day concentrations and those inferred for the early Paleogene. While human emissions are unfolding on a much shorter timescale than ancient carbon pulses, the paleoclimate record suggests that rainfall intermittency scales with warming in ways current models do not fully capture. That implies that flood maps, drought probabilities, and design standards for bridges, dams, and stormwater systems may be systematically optimistic about how often and how severely precipitation will depart from historical norms.
Sahel Storms Offer a Real-Time Preview
The ancient record is not the only evidence pointing toward growing rainfall volatility. Satellite observations covering 1982 through 2016 show that the frequency of extreme Sahelian storms tripled over that period, according to research published in Nature. The most intense organized convective systems in the region grew both stronger and more common, even as seasonal rainfall totals did not increase at a comparable rate. That pattern (extreme events climbing while averages lag) mirrors the decoupling identified in the PETM modeling work and echoes the intermittency reconstructed for the early Paleogene, suggesting that similar physical mechanisms may already be at play in today’s tropics and subtropics.
The Sahel finding carries direct implications for flood risk in one of the world’s most climate-vulnerable regions, where hundreds of millions of people depend on seasonal rains for subsistence farming and pastoral livelihoods. A sharp rise in the most violent storms can turn fields into flash-flood channels, destroy infrastructure, and erode already thin safety nets, even if the total amount of rain over the season looks familiar on paper. Recent assessments by World Weather Attribution, summarized in a Reuters climate newsletter, have highlighted how La Niña conditions can further tilt the odds toward both floods and droughts in vulnerable regions, underscoring that natural climate patterns are now interacting with long-term warming to reshape rainfall extremes in ways that echo, on a smaller scale, the disruptions seen in deep time.
Planning for a More Intermittent Future
For policymakers, engineers, and land managers, the message from both fossils and satellites is that focusing on average rainfall alone is no longer sufficient. The Paleogene reconstructions, the PETM modeling, and the Sahel observations all point toward climates where the spacing, intensity, and seasonality of storms change more dramatically than the annual totals. In such a world, water systems designed around historical norms can fail in opposite directions: reservoirs can run dry during prolonged gaps between storms, then face sudden overtopping when rare deluges arrive, while soils swing between desiccation and erosion in ways that challenge traditional cropping calendars.
Adapting to this more intermittent regime means stress-testing infrastructure and policies against a wider range of plausible futures than current models may suggest. That could include revising design standards for drainage and flood defenses to account for sharper downpours, investing in flexible water storage and distribution that can bridge longer dry spells, and diversifying crops and farming practices to cope with both drought and waterlogging. The deep-time perspective does not dictate exact timelines or local outcomes, but it does provide a sobering boundary condition: when the planet has been this warm before, rainfall patterns did not simply shift smoothly. They fractured into more erratic, harder-to-manage extremes, and there is growing evidence that the early stages of that transition are already underway.
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*This article was researched with the help of AI, with human editors creating the final content.
