Climate Matters•November 9, 2023
Earth’s hottest 12-month streak
Earth just recorded its hottest 12-month streak (November 2022-October 2023).
Analysis using Climate Central’s Climate Shift Index shows how human-caused climate change influenced heat over the last 12 months in 175 countries and 920 cities.
Over that time, 90% of people worldwide (and 49% in the U.S.) experienced at least 10 days of temperatures very strongly influenced by climate change.
One-in-four people on Earth faced extreme, persistent, and dangerous heat waves driven by carbon pollution.
Out of 700 largest cities, Houston, Texas experienced the longest streak of extreme heat made more likely by carbon pollution: 22 days.
The rising frequency and intensity of heat waves across the globe is consistent with the consequences of carbon pollution — mainly from burning coal, oil, and natural gas.
Earth’s hottest 12-month stretch
The past 12 months have been hot — by the data, and by the experience of people around the world.
This year, Earth had its hottest Northern Hemisphere summer and hottest month (July) ever recorded. So it’s no surprise that the entire year is shaping up to be the hottest since records began in the 1800’s.
The rising frequency and intensity of extreme heat across the U.S. and around the globe is consistent with well-established science on the consequences of carbon pollution — mainly from burning coal, oil, and natural gas.
Ahead of global climate negotiations later this month, Climate Central analyzed the fingerprints of climate change on air temperatures and extreme heat waves over the past 12 months (November 1, 2022 to October 31, 2023).
Global fingerprints of climate change
Climate change attribution science quantifies whether and to what extent human-caused climate change altered the likelihood of specific extreme weather events.
Climate Central’s daily attribution system, the Climate Shift Index (CSI), applies the latest peer-reviewed methodology to map the influence of human-caused climate change on daily local temperatures and multi-day extreme heat events across the globe.
For example, a CSI level of 3 indicates that a local daily temperature was made at least three times more likely due to climate change.
Learn more about attribution science and the CSI here.
New Climate Central analysis using the Climate Shift Index (CSI) quantifies the influence of human-caused climate change on extreme heat in 175 countries and 920 cities during Earth’s record-hottest 12 month period (November 1, 2022 to October 31, 2023).
Nearly everyone on Earth experienced heat boosted by climate change
The past 12 months (November 1, 2022 to October 31, 2023) were Earth’s hottest on record. Over this period, the global average temperature was 1.3°C (2.3°F) above pre-industrial temperatures.
Over the last 12 months, 7.3 billion people (90% percent of the global population) experienced at least 10 days of temperatures strongly affected by climate change. These days had a CSI level of 3 or higher, indicating that human-caused climate change made those temperatures at least three times more likely.
During the same period, 5.8 billion people (73% of the global population) experienced more than a month’s worth of these temperatures.
Climate Central also analyzed how climate change influenced exposure to extreme heat (above the local 99th percentile) that persisted for at least five days.
Over the last 12 months, 1.9 billion people (one in four people) experienced an extreme heat streak that lasted at least five days and was strongly influenced by carbon pollution. These multi-day heat streaks had a CSI of 2 or higher, indicating that human-caused climate change made those temperatures at least two times more likely.
El Niño is just beginning to boost temperatures. Based on historical patterns, most of the global warming effect will be felt next year. Rapidly reducing carbon pollution every year is required to halt the warming trend.
In the U.S., widespread heat influenced by climate change
Nearly half (49%) of the U.S. population (162.6 million people) experienced 10 or more days at CSI level 3 or higher during the last 12 months.
Over one-quarter of the U.S. population (85.6 million people, or 26%) experienced 30 or more days with heat at CSI level 3 or higher during the same period.
Five of the 10 large global cities (of at least 1 million people) that experienced the most days with extreme heat (above the local 99th percentile) were in the U.S.: Houston (56 days), Austin (45 days), San Antonio (44 days), New Orleans (42 days), and Miami (34 days).
Out of 700 large global cities (of at least 1 million people), Houston, Texas experienced the longest streak of extreme heat made more likely by carbon pollution: 22 days.
New Orleans, La., tied with two cities in Indonesia (Tangerang and Jakarta) for having the second-longest streak of extreme heat (17 days).
During the last six months (May-October 2023), six U.S. states had average CSI levels of 1 or higher: Hawai’i (2.8), Louisiana (1.9), Texas (1.9), Florida (1.8), New Mexico (1.8), and Arizona (1.3).
Heat boosted by climate change around the world
Jamaica had the highest average CSI of any country analyzed (4.5 out of a maximum of 5). On the average day over the last 12 months, Jamaicans experienced average temperatures made at least four times more likely by human-caused climate change.
Guatemala (4.4) and Rwanda (4.1) also had average CSI levels above 4 during the last 12 months.
Out of 700 large cities (of at least 1 million people) analyzed, the two largest cities in the Dominican Republic experienced the most days with extreme heat (above the local 99th percentile): Santo Domingo (79 days) and Santiago (56 days). Santiago tied with Houston, Texas (56 days).
The influence of carbon pollution on heat was strongest in the developing world. Extreme heat driven by climate change is also accelerating among the world’s richest countries.
Three countries had an average CSI level of 1 or higher during the first six months analyzed (November 2022 to April 2023): Saudi Arabia, Indonesia, and Mexico.
Nine countries had an average CSI level of 1 or higher during the last six months analyzed (May to October 2023): Saudi Arabia, Indonesia, Mexico, India, Japan, Italy, Brazil, France, and Turkey. During this same period, the mean CSI increased in all G20 countries, with the exception of Germany and Russia.
LOCAL STORY ANGLES
CSI tools, data, custom maps, and local alerts
Here are four ways to use this attribution analysis from Climate Central:
Use the tools. Climate Central’s Climate Shift Index map tool shows which parts of the world are experiencing high CSI levels, every day. Explore the global CSI map for today, tomorrow, and any day of the study period (November 2022-October 2023).
Download the data. Data from this analysis are available to download and explore in more detail the daily global population exposure to high CSI levels, and summary conditions for 175 countries and 920 cities.
Access KML to create custom CSI maps. The Climate Shift Index is now available in KML format. Fill out this form to join our pilot project, receive the KML links, and create custom CSI maps.
Sign up for alerts. Sign up here to receive custom email alerts when strong CSI levels are detected in your local area.
Andrew Pershing, PhD (he/him/his)
VP for Science, Director of Attribution Science and Climate Fingerprinting | Climate Central
Relevant expertise: Climate change attribution
Contact: email@example.com (Peter Girard, VP for Communications)
Friederike Otto, PhD (she/her/hers)
Senior Lecturer in Climate Science | Grantham Institute for Climate Change and the Environment
Co-lead | World Weather Attribution
Relevant expertise: Climate change attribution; rapid attribution analysis of extreme weather events such as droughts, heat waves and storms
Joyce Kimutai, PhD (she/her/hers)
Principal Meteorologist | Kenya Meteorological Department
Research Associate in Climate Science | Grantham Institute for Climate Change and the Environment
Relevant expertise: Meteorology, analysis and interpretation of climate science
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
The Climate Shift Index® (CSI), Climate Central’s daily temperature attribution system, applies the latest peer-reviewed methodology to map the influence of climate change on temperatures across the globe, every day.
All Climate Shift Index (CSI) levels reported in this brief are based on daily average temperatures and ERA5 data from November 1, 2022 to October 31, 2023. See the frequently asked questions for details on computing the Climate Shift Index, including a summary of the multi-model approach described in Gilford et al. (2022). For detailed methodology, please refer to the Methods section of the full report: The hottest 12-month stretch in recorded history.