The hottest 12-month stretch in recorded history

See the full report: The hottest 12-month stretch in recorded history How carbon pollution affected countries and major cities worldwide from November 2022 to October 2023

Download data: for 175 countries, 154 states/provinces, and 920 major cities

Leading up to COP28, Climate Central scientists assessed worldwide air temperatures for climate fingerprints over the past 12 months (November 1, 2022 to October 31, 2023).

Analysis using the Climate Shift Index (CSI) — Climate Central’s daily local temperature attribution system — indicates that human-caused climate change significantly elevated temperatures over the last 12 months. The analysis looks at daily average temperatures and heat waves and includes data for 175 countries, 154 states/provinces, and 920 major cities.

With an average warming of more than 1.3°C, the past 12 months were the hottest on record. El Niño is just beginning to boost temperatures, but based on historical patterns, most of the effect will be felt next year. Rapidly reducing carbon pollution every year is required to halt the warming trend.

Over the entire year-long period, 90% percent of people (7.3 billion) experienced at least 10 days of temperatures very strongly affected by climate change, and 73% (5.8 billion) experienced more than a month’s worth of these temperatures. These days had a CSI of 3 or higher; CSI level 3 indicates that human-caused climate change made those temperatures at least three times more likely.

We also examined exposure to dangerous, extreme temperatures, especially where conditions persisted for at least 5 days. We found that 1 in 4 people (1.9 billion) experienced a five-day heat wave (at minimum) that 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.

Our findings confirm that climate burdens are both inequitable and emerging everywhere around the world. Least developed countries and small island nations had higher exposure to climate-driven heat, but climate change touched every country, and intense heat waves occurred in the U.S., Europe, India, and China.

Major funding provided by the Bezos Earth Fund, The Schmidt Family Foundation, and the William and Flora Hewlett Foundation.