A University of Western Australia Oceans Institute study of long-lived Caribbean sclerosponges reconstructs ocean temperatures back to 1700, suggesting warming may have surpassed 1.5°C as early as 2020.

The study suggests warming began about eight decades earlier than IPCC estimates and that 2020 temperatures rose above 1.7°C above pre-industrial levels, implying an accelerated warming timeline.

Regardless of debates over exact thresholds, the article stresses that immediate and substantial emission reductions are essential to mitigate climate risks.

Researchers used strontium-to-calcium ratios in Caribbean sclerosponges as climate archives, arguing these records may be less distorted by ocean currents than some proxies, to reconstruct historical sea temperatures.

Some scientists caution against relying on a single regional proxy, advocating for more data and regional or climate-system corroboration before revising widely used baseline thresholds.

Even as the study circulates, other indicators already point to warming near or beyond the 1.5°C threshold, with January 2025 identified as the hottest on record at roughly 1.7°C above pre-industrial levels, underscoring the urgency of cutting emissions.