The world has just experienced its hottest 12-month period in recorded history, with the average global temperature over 1.3 degrees Celsius above pre-industrial levels between November 2022 and October this year.
Analysis of international data, conducted by Climate Central scientists, found that human-induced climate change had significantly elevated temperatures around the world.
The report warned that El Niño was only just beginning to boost temperatures and, based on historical patterns, most of the effect would be felt next year.
While Australia did not experience the same level of extremes compared to many other parts of the world, a hot and dry summer was expected.
The study found that a quarter of people around the world experienced a five-day heat wave that could be quantitatively linked to human-induced climate change.
Andrew Pershing, vice president for science at Climate Central, said the findings were important in the lead up to international climate negotiations being held at the end of the month.
“The whole point of this attribution science is to make the connection between what people are experiencing and climate change” he said.
“These impacts are only going to grow as long as we continue to burn coal, oil and natural gas — that is the ultimate driver of the changes that we’re seeing around the planet.”
Climate fingerprints
To understand the role climate change has had on heat, the scientists used a peer reviewed methodology they have called the Climate Shift Index (CSI), which uses models to understand what daily temperatures would have been with no carbon pollution in the atmosphere.
“The challenge is that we have these global numbers of 1.3 degrees [Celsius] … super important numbers when we’re thinking about tracking the global climate — but this is not what people experience. We experience our daily weather,” Dr Pershing said.
The CSI quantifies how much human-caused climate change has influenced the odds of people experiencing extreme daily temperatures locally.
It found most people on the planet had experienced temperatures very strongly affected by climate change.
Hover to explore how temperatures in different parts of the world were made hotter by climate change
The list of countries most impacted by climate change was dominated by small islands and developing countries, particularly in the Caribbean and Indo-Pacific.
Joyce Kimutai, a principal meteorologist at the Kenya Meteorological Department, said increased temperatures were hitting vulnerable populations hardest.
“Looking at the climate shift index, we could see that close to 5.8 billion people actually, in this past year, experienced temperatures higher than the normal monthly averages,” she said.
“But if you look closely, you find that it’s actually more than half of the countries in all regions of the world.”
The analysis found impacts in developed nations were also accelerating, with unusually high temperatures in the last six months hitting Saudi Arabia, Mexico and Indonesia in particular.
Heat streaks
World Weather Attribution lead scientist Friederike Otto said the events that had by far the strongest climate change fingerprints were heatwaves.
“For heatwaves, climate change is really an absolute game changer,” Dr Otto said.
“The physics is very clear, because we have more greenhouse gases in the atmosphere from burning fossil fuels, the atmosphere overall is warmer and in a warm atmosphere we see more heatwaves.”
In the past 12 months, the analysis found that a quarter of the world’s population experienced a five-day heat streak made at least two times more likely because of human-caused climate change.
The heatwaves in the United States were exceptionally bad, with Houston, Texas suffering through a 22-day heat streak.
Twelve cities in the US experienced streaks of five days or more, with an average Climate Shift Index of 5, meaning that climate change boosted the likelihood of that weather by at least a factor of five.
Cities in Indonesia were also hit hard by extreme heat waves, with both Jakarta and Tangerang experiencing a 17-day heat streak, that was also made five times more likely because of climate change.
An upward trend
The record-breaking temperatures around the world were in line with what scientists had predicted for greenhouse gas emission levels in the atmosphere, Climate Central’s Dr Pershing said.
“In some ways it is not surprising. We should expect to set records because we live on a warming planet,” he said.
“We have too much carbon dioxide in the atmosphere, more and more every year that drives temperatures up.”
While Dr Pershing said it was difficult to tease apart how much the normal weather cycles of La Niña and El Niño played, the record breaking 12-months was consistent with the long-term warming trend.
“That’s something where I think further analysis will come out as people look retrospectively at this year,” he said.
“What we expect is that next year we will have one of these anomalies where we stick up well above that trend, and that will be once the full effect of El Niño really comes into play.”
Meteorologist Dr Kimutai said there would continue to be yearly variations.
“They [temperatures] might be up and down, which is a feature of the atmosphere anyway, of the system,” she said.
“But we are seeing a constant trend, a constant upward trend in the warming of the planet.”