The paper reviews surface air temperature records over the past 150 years, focusing on data homogeneity and estimation errors for hemispheric and global averages. It presents global temperature changes during two warming periods: 1925–1944 (0.37°C rise) and 1978–1997 (0.32°C rise). Warming has been more pronounced in areas with historically cool temperatures and less so in warm areas. Recent decades show greater increases in night minimum temperatures than day maximum temperatures, reducing the diurnal temperature range by 0.08°C per decade. The study discusses recent divergence between surface temperature trends and satellite measurements of lower tropospheric temperatures, and places the last 150 years in the context of the last millennium. The paper discusses the quality of raw land and marine temperature data, addressing long-term homogeneity and changes affecting data, such as urbanization and satellite measurements. It presents a comprehensive global surface temperature climatology on a 1°×1° grid, based on data from 1961–1990. The climatology indicates an annual average surface temperature of 14.0°C (14.6°C in the Northern Hemisphere, 13.4°C in the Southern Hemisphere). The annual cycle of global mean temperatures follows that of the land-dominated Northern Hemisphere, with a maximum in July of 15.9°C and a minimum in January of 12.2°C. The paper reviews methods for aggregating raw data to a regular grid, aiming to reduce spatial and temporal variations in data density. It discusses future improvements to the network. The accuracy of hemispheric and global temperature anomalies is assessed, particularly during the nineteenth century when coverage was poor. The surface temperature record is analyzed, comparing warming patterns during the 1978–1997 period with those of the earlier 1925–1944 period, which experienced a comparable rate of warming. It considers trends in areas affected by extreme temperatures, recent trends in Arctic temperatures, and the divergence of surface temperature trends from satellite retrievals of lower tropospheric temperature trends. The paper discusses the development of the absolute climatology and presents conclusions. It addresses the homogeneity of basic data, noting that changes in instrumentation, station location, and environmental factors can affect data. For land data, urbanization influences are considered, while for marine data, changes in instrumentation and measurement techniques are discussed. The paper also discusses the combination of land and marine components, and the aggregation of raw data for marine regions. It presents hemispheric and global anomaly time series, showing warming trends over the 1861–1997 period. The paper also discusses errors in estimation, including measurement and sampling errors, and their implications for temperature trends. The paper analyzes trends in the areas affected by extreme warmth, Arctic temperatures,The paper reviews surface air temperature records over the past 150 years, focusing on data homogeneity and estimation errors for hemispheric and global averages. It presents global temperature changes during two warming periods: 1925–1944 (0.37°C rise) and 1978–1997 (0.32°C rise). Warming has been more pronounced in areas with historically cool temperatures and less so in warm areas. Recent decades show greater increases in night minimum temperatures than day maximum temperatures, reducing the diurnal temperature range by 0.08°C per decade. The study discusses recent divergence between surface temperature trends and satellite measurements of lower tropospheric temperatures, and places the last 150 years in the context of the last millennium. The paper discusses the quality of raw land and marine temperature data, addressing long-term homogeneity and changes affecting data, such as urbanization and satellite measurements. It presents a comprehensive global surface temperature climatology on a 1°×1° grid, based on data from 1961–1990. The climatology indicates an annual average surface temperature of 14.0°C (14.6°C in the Northern Hemisphere, 13.4°C in the Southern Hemisphere). The annual cycle of global mean temperatures follows that of the land-dominated Northern Hemisphere, with a maximum in July of 15.9°C and a minimum in January of 12.2°C. The paper reviews methods for aggregating raw data to a regular grid, aiming to reduce spatial and temporal variations in data density. It discusses future improvements to the network. The accuracy of hemispheric and global temperature anomalies is assessed, particularly during the nineteenth century when coverage was poor. The surface temperature record is analyzed, comparing warming patterns during the 1978–1997 period with those of the earlier 1925–1944 period, which experienced a comparable rate of warming. It considers trends in areas affected by extreme temperatures, recent trends in Arctic temperatures, and the divergence of surface temperature trends from satellite retrievals of lower tropospheric temperature trends. The paper discusses the development of the absolute climatology and presents conclusions. It addresses the homogeneity of basic data, noting that changes in instrumentation, station location, and environmental factors can affect data. For land data, urbanization influences are considered, while for marine data, changes in instrumentation and measurement techniques are discussed. The paper also discusses the combination of land and marine components, and the aggregation of raw data for marine regions. It presents hemispheric and global anomaly time series, showing warming trends over the 1861–1997 period. The paper also discusses errors in estimation, including measurement and sampling errors, and their implications for temperature trends. The paper analyzes trends in the areas affected by extreme warmth, Arctic temperatures,