Emergence of climate change temperature and precipitation signals over South America ​

Abstract This study investigates the emergence of climate change signals in December-February (DJF) and June-August (JJA) temperature and annual precipitation across South America relative to a 1901–1930 reference period. We use a combination of observational gridded datasets (BEST, CRU and GPCC) and CMIP6 model simulations within a global warming level (GWL) framework to examine for emergence. Results reveal marked contrasts between variables, regions, and data sources, highlighting the role of internal variability and observational uncertainty in emergence assessments. For seasonal temperature, both observations and models indicate that climate change signals have likely already emerged in tropical South America at GWLs below 1°C. Although substantial discrepancies exist between observational datasets in the timing and spatial patterns of emergence, CRU and BEST show a consistent latitudinal gradient, with earlier emergence at lower latitudes and delayed (or absent) emergence toward southern regions. Model simulations further suggest that nearly the entire continent may experience temperature signal emergence by the 1.5°C GWL, with the highest GWL of emergence in south-eastern South America. In contrast, annual precipitation exhibits limited and largely non-robust emergence in observations, strongly influenced by internal variability and limited by data availability constraints, particularly in northern regions. Precipitation projections display high spatial heterogeneity and inter-model spread. Only in southwestern South America a robust drying signal is consistently identified, with an emergence between the 1.0°C and 1.5°C GWL. Overall, findings highlight the need for cautious interpretation of observational emergence diagnostics while underscoring the value of model-based assessments for understanding future climate signal emergence in South America, relevant to adaptation planning.