Background: Extreme weather events driven by climate change are becoming increasingly frequent and severe globally, posing unprecedented pressure on health systems, especially on their emergency departments (EDs). The ED operates as the key link between acute impacts on public health caused by disasters and a wider healthcare sector response. Therefore, measuring surge capacity becomes an important aspect of assessing health system resilience to climate change. While there is a wealth of scientific literature on climate and health, to date no systematic review has established the relationship between disaster surge research and the documented patient-level outcomes linked to ED overcrowding in the context of different disaster types. Objective: The objective of this study was to conduct a systematic review of peer-reviewed articles assessing the impact of climate-related disasters – heat waves, floods and tropical cyclones, wildfires, compound events, and other types of weather events – on ED surge capacity and documenting the effects on patient-level measures such as deaths, length of stay (LOS) and time to treatment (TT2Tx). Methods: This systematic review was conducted in accordance with PRISMA 2020 guidelines, with searches performed across MEDLINE, Scopus, and Web of Science, alongside structured grey literature sources (WHO, IPCC, CDC, ACEP). In the preliminary search, 1,847 articles were identified, of which 312 duplicates were removed, and 1,535 abstracts excluded. From 68 full texts reviewed, 35 articles met all inclusion criteria. Results: There is consistent evidence of an association between climate-related disasters and ED surge in four main types of disasters. Heatwaves result in double the number of ED visits due to heat illnesses, while in the 2003 heatwave in Europe there were over 70,000 additional deaths recorded. In the aftermath of weather-related disasters, ED utilization increases by 1.22% during the first week following the event, with increased mortality persisting up to six weeks later. In the event of wildfire smoke exposure, there is a 57.1% rise in the number of asthma-related ED visits. Climate-related disasters independently cause an increased mortality rate in patients requiring hospital admission due to ED overcrowding by at least 5%, along with delay in critical interventions for sepsis, stroke, and acute myocardial infarction. There is limited evidence from low- and middle-income countries. Conclusions: Climate-related disasters are consistently associated with increased emergency department workload and measurable deterioration in patient outcomes, including increased mortality, delays in care, and prolonged hospital stays. These findings underscore the need to integrate climate-informed surge planning into emergency care systems and strengthen health system resilience through anticipatory, data-driven preparedness strategies.