The chapter "Observations: Atmosphere and Surface" assesses the scientific literature on atmospheric and surface observations since the IPCC Fourth Assessment Report (AR4). It identifies the most likely changes in physical climate variables or climate forcing agents based on current knowledge, following the IPCC AR5 uncertainty guidance. The chapter highlights significant changes in atmospheric composition, radiation budgets, temperature, hydrological cycle, extreme events, and atmospheric circulation. Key findings include: - Well-mixed greenhouse gases (GHGs) such as carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) have increased in atmospheric abundance from 2005 to 2011. - The global mean stratospheric ozone has declined since pre-1980 values, with most of the decline occurring before the mid-1990s. - Global stratospheric water vapour trends are uncertain due to large variability and short data records. - Aerosol column amounts have declined over Europe and the eastern USA since the mid-1990s, while increasing over eastern and southern Asia since 2000. - Global mean surface temperature has increased since the late 19th century, with each of the past three decades being successively warmer than all previous decades. - The number of heavy precipitation events over land has likely increased in more regions than it has decreased, with the highest confidence in North America and Europe. - Atmospheric circulation features have moved poleward, involving a widening of the tropical belt, a poleward shift of storm tracks and jet streams, and a contraction of the northern polar vortex. - Confidence in long-term changes in remaining aspects of the global circulation is low due to observational limitations or limited understanding. The chapter also discusses the challenges in developing homogeneous long-term records from different observational sources and the importance of accounting for non-climatic artefacts in raw observations.The chapter "Observations: Atmosphere and Surface" assesses the scientific literature on atmospheric and surface observations since the IPCC Fourth Assessment Report (AR4). It identifies the most likely changes in physical climate variables or climate forcing agents based on current knowledge, following the IPCC AR5 uncertainty guidance. The chapter highlights significant changes in atmospheric composition, radiation budgets, temperature, hydrological cycle, extreme events, and atmospheric circulation. Key findings include: - Well-mixed greenhouse gases (GHGs) such as carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) have increased in atmospheric abundance from 2005 to 2011. - The global mean stratospheric ozone has declined since pre-1980 values, with most of the decline occurring before the mid-1990s. - Global stratospheric water vapour trends are uncertain due to large variability and short data records. - Aerosol column amounts have declined over Europe and the eastern USA since the mid-1990s, while increasing over eastern and southern Asia since 2000. - Global mean surface temperature has increased since the late 19th century, with each of the past three decades being successively warmer than all previous decades. - The number of heavy precipitation events over land has likely increased in more regions than it has decreased, with the highest confidence in North America and Europe. - Atmospheric circulation features have moved poleward, involving a widening of the tropical belt, a poleward shift of storm tracks and jet streams, and a contraction of the northern polar vortex. - Confidence in long-term changes in remaining aspects of the global circulation is low due to observational limitations or limited understanding. The chapter also discusses the challenges in developing homogeneous long-term records from different observational sources and the importance of accounting for non-climatic artefacts in raw observations.