Today, Climate Central launches the Global Climate Shift Index (CSI-Global)—a new tool that quantifies the local influence of climate change on daily temperatures around the world.
Climate Central’s first-ever analysis using CSI-Global reveals the influence of human-caused climate change on daily average temperatures on each of the 365 days from October 1, 2021 to September 30, 2022 across the globe—including 1,000+ global cities.
Human-driven warming affected everyone, everywhere. Over the last 12 months, human-caused climate change affected temperatures experienced by 7.6 billion people. That’s nearly every person on the planet (96% of the global population).
People living near the equator and on small islands were especially impacted. Mexico, Brazil, western and eastern Africa, the Arabian Peninsula, and the Malay Archipelago experienced the strongest influence of human-caused climate change on temperatures over the 365 days analyzed.
At least 200 million people around the world felt the fingerprint of climate change on each of the 365 days analyzed. Global exposure peaked on October 9th 2021, when more than 1.7 billion people worldwide experienced temperatures that were made at least 3x more likely due to human-caused climate change.
Hotspots of human exposure: When accounting for urban population size, the total human exposure to daily temperatures altered by climate change was highest in Lagos, Nigeria; Mexico City, Mexico; and Singapore.
Fingerprints of climate change—everyday, everywhere
Scientists have been measuring the signals of human-driven global climate change for decades. We know how much planet-warming carbon dioxide we’ve released into the atmosphere since 1850 (660 billion metric tons). And we know how much global temperatures have increased since then (2°F, or 1.1°C).
But individual people don't experience global average temperatures. Instead, we mainly experience climate change through shifts in the daily weather patterns where we live. And now, using Climate Central’s Climate Shift Index (CSI), we can measure the influence of climate change on the temperatures that people experience everyday, everywhere. Learn more about the Climate Shift Index below.
Climate Shift Index (CSI) goes global
The Climate Shift Index launched in June 2022 and since then Climate Central has been operating a daily attribution service based on CSI and focused on the U.S. (CSI-USA) at the level of NOAA climate divisions.
Today, Climate Central is expanding the CSI tool to the rest of the globe (CSI-Global). We’re kicking off the global expansion with the first-ever global CSI analysis. This analysis reveals the influence of human-driven climate change on:
daily average temperatures
on each of the 365 days from October 1, 2021 to September 30, 2022
and locations across every continent—including 1,000+ major global cities
The global analysis also includes global population data to quantify how many people have experienced temperatures altered by climate change over the last 12 months.
Five ways to use CSI-Global now:
Sign up for alerts. Beginning today (October 27) and running through the scheduled end of COP27 (November 18), Climate Central will distribute daily emails summarizing CSI-Global scores on each day for 1,000+ cities. Sign up to receive these summaries and to be notified when we begin permanent ongoing services in 2023.
Use the tools. We are also creating an online tool to allow you to see which parts of the world are experiencing high CSI levels—every day.
Download the data. The city-level summary data from this global CSI analysis are available to download. Explore the data to see in more detail how climate change affected people in 1,000+ global cities over the last 12 months.
Read the report. A report released today, 365 Days on a Warming Planet, describes results of the global CSI analysis in detail.
Watch and share the video. A new video explains the science behind the CSI-Global tool and what it can tell us about the everyday impacts of climate change, worldwide.
Highlights from 365 Days on a Warming Planet, the global CSI analysis
Human-driven warming affected everyone, everywhere. Over the last 12 months, human-caused climate change had a detectable influence on the daily temperatures experienced by 7.6 billion people. That’s nearly every person on the planet (96% of the global population).
Those living near the equator and on small islands were especially impacted. Mexico, Brazil, western Africa, eastern Africa, the Arabian Peninsula, and the Malay Archipelago were global CSI hotspots over the 365 days from Oct 1, 2021 to Sept 30, 2022.
The single day when the most people were affected worldwide: The maximum population exposure occurred on October 9, 2021—when more than 1.7 billion people worldwide (more than 20% of the global population) experienced warm conditions that were made at least 3x more likely due to human-caused climate change.
Global cities are feeling the heat. An estimated 55% of the global population lives in cities, where urban heat islands worsen the risks posed by extreme heat. Climate Central’s analysis reveals that billions of people in 1,000+ global cities are already experiencing climate change in their daily lives.
Cities in small island developing states had the highest average CSI scores. Apia, Samoa and Ngerulmud, Palau were the top two cities in terms of average daily CSI scores (4.5, meaning temperature made at least 4.5x more likely due to climate change). Both cities also experienced the most total days with CSI scores of 3 or higher: 331 and 328 days, respectively—more than 90% of the 365 days analyzed.
Global cities with climate-boosted temperatures: 26 of the 1,000+ cities analyzed had at least 250 days (69% of the 365 days analyzed) with CSI levels of 3 or higher. These cities were all in east Africa, the Malay Archipelago, Mexico, Brazil, and small island developing states in the Caribbean and Oceania.
Urban hotspots of human exposure to climate change: Global cities range vastly in the size of their population. When accounting for the number of people in each of the 1,000+ cities analyzed (i.e., multiplying the population of each city by the total number of days in that city with CSI levels of 3 or higher), CSI-Global reveals that the total number of “people-days” over the study period exceeded 1 billion in:
Lagos, Nigeria (2.8 billion people-days)
Mexico City, Mexico (2.0 billion people-days)
Singapore (1.2 billion people-days)
By expanding globally, the CSI-Global fills critical data gaps in many parts of the world. In doing so, this analysis reveals that the people most affected by human-caused climate change right now are often from places that have contributed the least to the global carbon problem.
Over the last 12 months, people in these places have lived through more days altered by climate change than anywhere else on Earth. And if the climate continues to warm, those impacts will only intensify.
What is the Climate Shift Index? How does it work?
Thanks to advances in attribution science, we can now measure the influence of human-driven climate change on the temperatures that people experience everyday, everywhere—using the Climate Shift Index (CSI).
The Climate Shift Index (CSI) has 11 levels: five positive, five negative, and one representing no change. CSI levels indicate how climate change has altered the frequency of daily high, low, and average temperatures at a given location.
CSI levels from +1 to +5 indicate that human-caused climate change has made the observed or forecasted temperatures more likely or, equivalently, more common.
CSI levels from -1 to -5 indicate temperatures that are becoming less likely or less common due to human-caused climate change.
The Climate Shift Index is based on the ratio of the local frequency of a particular daily temperature in the current climate to the estimated frequency of that temperature in a world without human-caused climate change.
For more information on Climate Shift Index calculations:
POTENTIAL LOCAL STORY ANGLES
Journalists and meteorologists covering COP27 can sign up to receive email alerts summarizing daily CSI levels for the 1,000+ cities featured in this report, over the duration of COP27. Daily CSI-Global scores can provide readers with real-time understanding of the extent to which human-caused climate change made local heat extremes more likely.
The online map tool allows you to explore which parts of the world are experiencing high CSI levels—every day. And as of today, the city-level results from this global CSI analysis are available to download to explore in detail the exposure of urban residents on each continent to the fingerprints of human-caused climate change over the 365 days analyzed.
The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on climate change attribution and heat extremes. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists.