Extreme drought events are predicted to increase with climate change, yet their impacts on ecosystem carbon dynamics under warming and elevated carbon dioxide (eCO ₂ ) remain unclear. In a peatland experiment with five warming treatments each under ambient carbon dioxide (aCO ₂ ) and eCO ₂ (+500 parts per million), a 2-month extreme drought in 2021 reduced net ecosystem productivity by 444.0 ± 65.8 and 736.6 ± 57.8 grams of carbon per square meter at +9°C under aCO ₂ and eCO ₂ , respectively—228.6 ± 56.8% and 381.9 ± 83.4% of the reduction at +0°C under aCO ₂ . This exacerbation was driven by warming-induced water table decline, prolonged low water tables, and CO ₂ -enhanced substrate availability through increased plant carbon inputs. Findings indicate that future climate will greatly amplify carbon loss during extreme drought, reinforcing positive carbon-climate feedbacks.

The Antarctic Peninsula (AP) climate is characterized by a high degree of variability, which poses a problem when attempting to put modern change in the context of natural variation. Therefore, novel methods are required to disentangle sometimes conflicting climate records from the region. In recent years, the development of Antarctic moss-cellulose isotopes as a proxy for summer terrestrial growing conditions has become more widespread, with the isotopes Δ¹³C and δ¹⁸O reflecting moss productivity and peatbank moisture conditions, respectively. Here, we used a combined Δ¹³C and δ¹⁸O isotope analysis of moss Chorisodontium aciphyllum cellulose from a peatbank located on Litchfield Island in the western AP to document changes in climate over the last 1700 years. High Δ¹³C values (>15‰) indicate warm and productive conditions on Litchfield Island from 1600 to 1350 cal yr BP (350 to 600 AD) and over the last 100 years. The δ¹⁸O record shows two distinct intervals of dry conditions at 1350–1000 cal yr BP (600–950 AD) and at 500–0 cal yr BP (1450–1950 AD). Our record indicates that terrestrial ecosystems in the AP have responded to regional climate driven by atmospheric circulation, such as the southern annular mode (SAM) and, to a lesser extent, changes in ocean circulation.