Short answers, pulled from the story.
Global surface temperature (GST) is the average temperature of Earth's surface at a given time. It is calculated by combining sea surface temperature and near-surface air temperature over land, weighted by their respective areas. The current annual global mean surface temperature is about 15 degrees Celsius.
Global average surface temperature has warmed by 1.09 degrees Celsius from the 1850-1900 baseline to 2011-2020, based on multiple independently produced datasets. Land surfaces warmed by 1.59 degrees Celsius over that period, while sea surface temperatures warmed by 0.88 degrees Celsius.
The Central England temperature data series is the longest-running temperature record, starting in 1659. It is a single-location dataset. Quasi-global instrumental records begin around 1850, while the GloSAT reference analysis released on the 15th of December 2025 extends gridded global data back to the 1780s.
Scientists use proxy data including tree ring widths, coral growth, ice core isotope ratios, ocean and lake sediments, borehole temperatures, and glacier lengths to reconstruct past temperatures. Ice cores from Antarctica's Dome Concordia extend the record to 800,000 years, and the Guliya core from a low-latitude high-altitude region spans more than 700,000 years.
The period from 2015 through 2025 included all eleven of the warmest years on record since 1850. The year 2024 ranks first, followed by 2023, which was 1.48 degrees Celsius above the 1850-1900 average according to the Copernicus Climate Change Service, and was declared the warmest on record almost immediately after it ended.
The 1998 El Nino was among the strongest of the 20th century, making 1998 the warmest year on record by a substantial margin at the time. The apparent slowdown in warming from 1998 to 2012 was partly driven by La Nina conditions and was less pronounced in later, improved datasets than in those available in 2012. Warming resumed clearly after 2012, with every year from 2015 onward warmer than any year prior to 2015.