Emissions released since 2015 warmed Europe's hottest week every year since 2021, a GRL study finds

The cooler version of June 2025 exists only inside a model. The week itself happened once, in a world that already held a decade of post-Paris emissions, so the comparison is between an observed event and a generated one ^[2]. The Stanford group extended a method it published in 2024 to run that comparison for a single slice of human emissions, the part released since 2015 ^[19].

Jared Trok, a doctoral student in Earth system science at the Stanford Doerr School of Sustainability, described the core difficulty in statistical terms ^[22]. "It's a signal-to-noise issue," Trok said. "The role of random, natural variability in specific weather events is large, which makes it difficult to detect the influence from a small amount of human emissions." ^[12]

Two numbers come out of the comparison, and they answer different questions. The probability, above 99% for the June 2025 event, is about direction: the decade's emissions made that week hotter than it would otherwise have been ^[5]. The magnitude is roughly a third of a degree Celsius, and it applies to average daily temperatures in some regions ^[6]. It is not the peak of the hottest afternoon, and it is not a global-mean figure of the sort the Paris targets are written in ^[8].

Heat killed several thousand people across Europe in 2025, and June that year was the hottest observed in the region until heat waves broke the record in 2026 ^[10]. "That third of a degree temperature change may seem small," Trok said, "but a large body of literature shows that small changes in temperature can have meaningful impacts on the damages caused by those extreme weather events." ^[11] Another study found that changes in daily temperature have disproportionate impacts on electricity demand, mortality rates, agricultural yields and labor productivity across the United States ^[16].

Almost one-fifth of all carbon dioxide from burning fossil fuels has been released in the decade since the Paris Agreement was adopted, most of it from oil, natural gas and coal ^[7]. Attribution work has generally run against the whole record since the mid-19th century ^[20]. Ten years is about 6% of that roughly 170-year span, so the tested window is short in time and heavy in carbon ^[21]. That is where a decade-scale signal would be easiest to find.

Noah Diffenbaugh, a co-author and professor at the Stanford Doerr School of Sustainability, stated the forward claim directly ^[22]. "This study highlights that we can expect the kinds of extreme heat waves we've been experiencing recently to intensify even more in the coming years," he said ^[14].

Several thousand lawsuits are underway seeking to hold oil companies and other fossil fuel producers accountable for loss and damage caused by extreme weather linked to global warming ^[17]. This study isolates a date range, and those suits need a producer. Its authors describe attributing specific damages from specific weather events to subsets of human-caused emissions as challenging ^[18].