A new report published by the EOCD describes the world of 2050 sustaining 9.2 billion people. (credit: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring)

If you look at a graph of our instrumental temperature records (like this one) you’ll see that temperatures seem to bounce around idly until after 1900, at which point a sustained rise becomes apparent. As a result, the pre-industrial temperature is typically pegged at the value it had in the late 1800s.

But a recent study published in Nature uses paleoclimate records from the 1500s to show that industrial-era warming first became apparent in the Northern Hemisphere in the mid-1800s. This paper suggests that humanity’s climate influence can be seen earlier than previously thought, so current models may underestimate the magnitude of human-caused climate change.

Paleoclimate data is reconstructed by combining observed climate data with known geochemical or biological markers of temperature. This information is analyzed using a statistical model that allows scientists to estimate temperatures for unobserved time points. For example, scientists can combine information from tree rings for years that have temperature readings to learn about how the temperatures affect tree growth. They can then use tree rings to make inferences about the climate in time periods before we started recording climate data, based on the changes that they see in the rings.