Climate Central’s Climate Shift Index measures global warming’s effect on our daily temperatures.
Carbon dioxide is the most abundant greenhouse gas on the planet. A greenhouse gas leads to global warming by trapping heat instead of allowing it to escape back into the atmosphere at night.
Carbon dioxide levels have fluctuated over the last 100,000 years, but it's only since the Industrial Revolution that CO2 levels have been rising exponentially because of human activity. This leads to a direct and clear rise in global temperatures, which leads to a direct and clear rise in ocean temperatures, which leads to all of the climate change impacts we feel.
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Climate Central has created the Climate Shift Index to quantify the effects of global warming on temperatures. By using CO2 as the driving force, the CSI looks at our current climate and then compares it to our past climate when CO2 levels were lower.
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By making this comparison, the CSI assigns a number to the high and low temperatures that can range from -5 to +5. Anything on the positive side means that climate change made the temperatures more likely. A +5 means that the temperature on that day was five times more likely because of human-driven climate change. Or conversely, the temperature would have been five times less likely without human-driven climate change.
Here are the key points about the Climate Shift Index and specifically how it applies to July of 2023:
- July 2023 was marked by record-shattering global average temperatures and widespread local heat extremes — which are among the deadliest weather-related hazards.
- Analysis using the Climate Shift Index, Climate Central’s daily temperature attribution tool, indicates that human-caused climate change made July’s extreme heat far more likely.
- At least 2 billion people around the world — one-quarter of the global population — felt a very strong influence of climate change each day in July.
- Those living near the equator and on small islands experienced the strongest influence of human-caused climate change on temperatures during July.
- Levels of July heat in the southern U.S., Mexico, Central America, and the Caribbean would have been extremely unlikely without human-caused climate change.
- In the U.S., 244 million people — 73% of the population — experienced at least one July day with temperatures made at least three times more likely due to human-caused climate change.
- U.S. cities with the strongest climate fingerprints on July heat were: Cape Coral, Fla.; Sarasota, Fla.; Bonita Springs, Fla.; Santa Fe, N.M.; Miami, Fla.; Mesa, Ariz.; Albuquerque, N.M.
Read the full analysis here.
