Search

Antarctic ice cores can help determine ice mass loss from the Antarctic Ice Sheet (AIS) during past warm periods. We compile Last Interglacial (LIG) δ18O${\delta }^{18}O$measurements from eight Antarctic cores and compare these to new isotope‐enabled LIG simulations, which explore three plausible LIG AIS elevation and extent scenarios. We find that these simulations capture less than 10% of East Antarctic core‐mean δ18O${\delta }^{18}O$changes. Although our simulations do not fully explain the changes, they capture some inter‐core geographical δ18O${\delta }^{18}O$variations. Some LIG AIS configurations show higher skill than PI AIS configurations in simulating the inter‐core differences. The remaining discrepancies between the simulated and observed core‐mean water isotope changes suggest that LIG simulations also need to include the influences of reduced Antarctic sea ice, a warmer Southern Ocean, and resultant shifts in vapor source regions to produce a more satisfactory match to δ18O${\delta }^{18}O$observed at ice core sites. Reconstructions of Antarctic Ice Sheet (AIS) retreat during past warm periods provide important constraints for projections of future ice mass loss and sea level rise. The Last Interglacial (LIG) is a particularly useful example, when global temperatures were 1±1oC$\pm {1}^{o}C$warmer than preindustrial (PI) conditions, to explore future sea level rise projections associated with the successful implementation of the Paris Agreement. Here, we use data from six East Antarctic ice cores and two new, unpublished records from West Antarctica that capture LIG conditions. Water isotopes in ice cores are sensitive to changes in temperature, AIS elevation, atmospheric circulation pattern, sea ice area, and ocean conditions. We compare model simulations of the LIG with ice core data and find that elevation changes, an important indicator of ice mass loss, explain only around 9% of the isotope change captured in East Antarctic ice cores. Due to the limitation of our simulations in the coastal regions, our West Antarctic coastal sites are more challenging. In summary, we find that while the range of our simulations does not fully explain average East Antarctic PI‐to‐LIG isotope changes, they do capture some of the geographical variations in isotope change patterns. A compilation of Last Interglacial δ18O${\delta }^{18}O$ice core records shows anomalies of +${+}$1.5‰ and +${+}$3.3‰ for 127 kyr BP and LIG‐peak core‐meanSimulations run with plausible LIG Antarctic Ice Sheet (AIS)configurations, alongside greenhouse gas and orbital changes, capture <${< } $10% of core‐mean differencesTwo LIG AIS configurations yield lower geographical errors at 127 kyr, compared to their PI configurations A compilation of Last Interglacial δ18O${\delta }^{18}O$ice core records shows anomalies of +${+}$1.5‰ and +${+}$3.3‰ for 127 kyr BP and LIG‐peak core‐mean Simulations run with plausible LIG Antarctic Ice Sheet (AIS)configurations, alongside greenhouse gas and orbital changes, capture <${< } $10% of core‐mean differences Two LIG AIS configurations yield lower geographical errors at 127 kyr, compared to their PI configurations

Regional carbon budget assessments attribute and track changes in carbon sources and sinks and support the development and monitoring the efficacy of climate policies. We present a comprehensive assessment of the natural and anthropogenic carbon (C‐CO2) fluxes for Australasia as a whole, as well as for Australia and New Zealand individually, for the period from 2010 to 2019, using two approaches: bottom‐up methods that integrate flux estimates from land‐surface models, data‐driven models, and inventory estimates; and top‐down atmospheric inversions based on satellite and in situ measurements. Our bottom‐up decadal assessment suggests that Australasia's net carbon balance was close to carbon neutral (−0.4 ± 77.0 TgC yr−1). However, substantial uncertainties remain in this estimate, primarily driven by the large spread between our regional terrestrial biosphere simulations and predictions from global ecosystem models. Within Australasia, Australia was a net source of 38.2 ± 75.8 TgC yr−1, and New Zealand was a net CO2sink of −38.6 ± 13.4 TgC yr−1. The top‐down approach using atmospheric CO2inversions indicates that fluxes derived from the latest satellite retrievals are consistent within the range of uncertainties with Australia's bottom‐up budget. For New Zealand, the best agreement was found with a national scale flux inversion estimate based on in situ measurements, which provide better constrained of fluxes than satellite flux inversions. This study marks an important step toward a more comprehensive understanding of the net CO2balance in both countries, facilitating the improvement of carbon accounting approaches and strategies to reduce emissions. Human activities—including the extraction and use of fossil fuels (coal, oil, and natural gas), cement production, and land‐use change (e.g., land clearing), release carbon dioxide (CO2) to the atmosphere, while biospheric processes such as the CO2uptake by forests and revegetation remove CO2from the atmosphere. In this study, we assess the balance of natural and human‐driven sources and sinks of CO2for Australia and New Zealand (referred to as the Australasia carbon budget) for 2010–2019. Our findings indicate that Australasia was close to carbon neutral, with large uncertainties, suggesting that the CO2sinks from vegetation in this region largely offset the CO2emissions from human activities. An independent assessment using the latest satellite observations and modeling shows consistent results for Australia. For New Zealand, a national system of ground observations and modeling agreed better with the bottom‐up budget than satellite‐derived flux estimates. We synthesize Australasia's carbon C‐CO2budget (together with Australia and New Zealand) based on bottom‐up and top‐down approachesAustralasia's bottom‐up carbon budget suggests that this region was close to neutral (−0.4 ± 77.0 TgC yr−1) from 2010 to 2019Australasia's annual CO2balance fluctuates significantly, particularly in Australia, shifting from a strong carbon sink to a strong carbon source We synthesize Australasia's carbon C‐CO2budget (together with Australia and New Zealand) based on bottom‐up and top‐down approaches Australasia's bottom‐up carbon budget suggests that this region was close to neutral (−0.4 ± 77.0 TgC yr−1) from 2010 to 2019 Australasia's annual CO2balance fluctuates significantly, particularly in Australia, shifting from a strong carbon sink to a strong carbon source

Government policies currently commit us to surface warming of three to four degrees Celsius above pre-industrial levels by 2100, which will lead to enhanced ice-sheet melt. Ice-sheet discharge was not explicitly included in Coupled Model Intercomparison Project phase 5, so effects on climate from this melt are not currently captured in the simulations most commonly used to inform governmental policy. Here we show, using simulations of the Greenland and Antarctic ice sheets constrained by satellite-based measurements of recent changes in ice mass, that increasing meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, and that meltwater from Antarctica will trap warm water below the sea surface, creating a positive feedback that increases Antarctic ice loss. In our simulations, future ice-sheet melt enhances global temperature variability and contributes up to 25 centimetres to sea level by 2100. However, uncertainties in the way in which future changes in ice dynamics are modelled remain, underlining the need for continued observations and comprehensive multi-model assessments.