Bold statement: Humans may have warmed the planet longer and more extensively than our standard baselines suggested, and this reshapes how we think about today’s climate challenges. But here’s where it gets controversial: what we call the starting point for “preindustrial” warming isn’t as fixed as many assume, and that nuance matters for how we measure today’s temperature rise and pin responsibility.
Chris Mooney, a Pulitzer Prize–winning journalist and CNN Climate contributor, reports on a striking new temperature dataset that pushes our climate timeline back to 1781. The conventional historical record, used to gauge modern warming and to frame targets like 1.5°C (2.7°F), typically begins in 1850. The new dataset, named GloSAT, expands the window to the late 18th century, offering a longer view of natural variability and human influence.
The reason this matters is that greenhouse gases rose by about 2.5 percent between 1750 and 1850. That increase likely caused some warming that the 1850-based baselines don’t fully capture. In other words, the planet may have already warmed before the widely cited 1850 threshold, and the early portion of warming has been underappreciated in many calculations.
Lead author Colin Morice of the UK Met Office Hadley Centre explains that 1850 was chosen more for practical data reasons than because it marks the true onset of industrial activity. The GloSAT team presents a cooler Earth for the late 1700s through 1849 compared with the 1850–1900 period, which is typically treated as the preindustrial baseline. Yet, not all early warming is attributable to human activity; major volcanic eruptions in the early 1800s cooled the planet by injecting reflective particles into the stratosphere.
Ed Hawkins of the National Centre for Atmospheric Science notes that 1815’s Tambora eruption is well documented, while the 1808 eruption’s location remains uncertain. The cooling from these events likely contributed to the late-18th-to-mid-19th-century warming recovery, though some portion of the early warming could still be linked to human influence.
The Intergovernmental Panel on Climate Change (IPCC) has long estimated a small amount of human-caused warming between 1750 and 1850, roughly 0 to 0.2°C. The GloSAT researchers fall in the middle of this range. In a complementary study led by Andrew Ballinger at the University of Edinburgh, the team used GloSAT data and climate models to quantify human-driven warming between 1750 and 1850 at about 0.09°C, with the remainder explained by natural variability and volcanic activity. Another scientist, Piers Forster, arrives at a similar conclusion via a different method: a plausible total human contribution of roughly 0.1–0.2°C when looking further back than 1850.
The project rests on an array of historical observations, from early modern Europe to North America and beyond. Records such as the Central England Temperature series (which starts in 1659) and temperature data from Uppsala, Sweden (begun in 1722) build the backbone for GloSAT. The Bavarian Alps’ Hohenpeissenberg station has documented temperatures since 1781, offering a rare continuous thread through turbulent times—Napoleonic wars included. Researchers emphasize that these local measurements must be combined with ocean data to approximate global temperatures, since the oceans cover about 70% of the planet.
To reconstruct ancient warmth, the GloSAT team relies on marine air temperatures measured aboard ships—rather than seawater temperatures—because ship data were more consistently recorded in the 18th century. This choice tends to yield slightly lower warming estimates for the overlap period with modern datasets. The team openly notes gaps and higher uncertainty for the years before 1850, where data are sparse and unevenly distributed.
So, what does a potential extra early warming imply for today? It doesn’t automatically derail climate goals or shift when impacts arrive, but it does alter our understanding of the total human imprint on the climate system. Some researchers urge caution against overinterpreting early warming as a direct forecast of future changes; others suggest it could recalibrate how aggressively we must act to limit further disruption.
In sum, the new GloSAT findings prompt a reevaluation of pre-1850 warming and remind us that the timeline of human influence is more nuanced than a single starting year. They invite a broader conversation about how baselines shape policy goals and public perception, and they underscore the importance of integrating historical observations with modern climate models to grasp the full scope of humanity’s impact on the planet.
