The California Heat Assessment Tool

Created: 6/28/2019 - Updated: 2/27/2020


California’s climate is warming and residents increasingly endure extreme heat events that adversely impact public health. This exacerbates existing risks and will bring new challenges for different regions in the state, threatening the efficacy of traditional intervention strategies. Current thresholds for heat alerts are based on temperatures that exceed historical statistical thresholds, rather than temperatures that cause public health impacts. These ‘health-neutral’ thresholds may underestimate the health risks for the most sensitive populations. The California Heat Assessment Tool (CHAT) is based on new research that establishes local, health-based thresholds for extreme heat that help public officials, health professionals and residents understand what changing conditions mean for them. CHAT is part of California’s Fourth Climate Change Assessment, a state-mandated research program to assess climate change impacts in California, and was developed by Four Twenty Seven, Argos Analytics, the Public Health Institute and Habitat 7 with technical support from the California Department of Public Health.



We founded Four Twenty Seven as a mission-driven business to provide innovative tools and services to organizations seeking to understand climate impacts, assess risks to their operations or their stakeholders, and increase their resilience by developing and implementing climate adaptation measures. Our team is constituted of risk analysts, climate change and adaptation experts who bring years of experience working on climate mitigation and adaptation in the energy, industry, agricultural and food sector.