Source: AGU Advances
Rising carbon dioxide (CO2) levels are known to raise temperatures in Earth’s atmosphere. But slow feedback processes, including heat storage in the ocean and changes in the carbon cycle, mean that sometimes, such temperature changes don’t manifest right away; it can take decades, or even millennia, for Earth to reach equilibrium.
However, different climate models generate vastly different estimates of when such an equilibrium will be reached. One reason for these differences is the “pattern effect,” or the way uneven sea surface temperature changes can create distinct ocean warming patterns that affect atmospheric circulation and thus cloud cover, precipitation, and heat transfer. This complex interplay of factors can increase or decrease warming and shape the climate’s sensitivity to greenhouse gases.
One way to help predict what long-term warming patterns might look like is to turn to the past. Unearthing patterns in paleoclimate data, especially from times when Earth experienced a warmer climate, can provide insight into future warming patterns. Zhang et al. analyzed 10 million years of sea surface temperature records to determine the relative warming of different ocean regions under rising CO2 levels.
The study used the Western Pacific Warm Pool, the planet’s largest and warmest surface water body, as a reference point, comparing its sea surface temperature data with those of 17 other ocean sites to establish a global warming pattern.
The researchers then compared the warming shown in these paleoclimate data with the results of several models that simulate warming on the basis of an abrupt quadrupling of CO2 compared to preindustrial levels. They found the paleoclimate data and modeled results showed similar millennia-scale warming patterns, especially at higher latitudes. When both were compared to the past 160 years of sea surface temperature measurements, however, there were some differences in warming patterns. Modern warming is still in a transient state, influenced by ocean heat uptake, whereas the paleopattern represents the full equilibrium response.
It will take thousands of years to reach a new equilibrium, the researchers note. The study suggests that compared to the current transient warming, future warming patterns will be stronger at middle and high latitudes, including the North Pacific, North Atlantic, and Southern oceans. This high-latitude warming will likely be stronger than previous estimates suggested, and it is more pronounced in millennial-level than in century-level projections. (AGU Advances, https://doi.org/10.1029/2025AV001719, 2025)
—Rebecca Owen (@beccapox.bsky.social), Science Writer