Global Surface Air Temperature

GloSAT - estimating how the global climate has changed over the industrial era

About GloSAT

The Paris Climate Agreement defines an ambition to limit global temperature change to between 1.5°C and 2°C above pre-industrial levels. In its Fifth Assessment report (AR5) the Intergovernmental Panel on Climate Change (IPCC) used a baseline of 1850-1900 for its definition of 'pre-industrial' as this is when most instrumental records begin. However, it has been estimated that global temperatures may have already increased by 0.0-0.2°C by this time, but this is uncertain due to a lack of data. Nonetheless, even using the 1850-1900 baseline, existing temperature datasets disagree on the amount of warming to date. This disagreement implies an uncertainty of more than 20% in the allowed carbon budget in order to meet the goals of the Paris Agreement, solely from the uncertainty in the observed surface temperature change. Differences between the global temperature datasets arise primarily from two structural uncertainties: the use of sea surface temperatures (SST) rather than air temperatures over the oceans, especially ice-covered regions, and differences in data coverage and interpolation strategies. This project addresses both of these uncertainties.

GloSAT Objectives

The overarching aim of GloSAT, a project funded by the Natural Environment Research Council, is to develop and analyse an extended and consistent global surface temperature climate record back to the 1780s, based on air temperature observations recorded across land, ocean and ice. This will be achieved through the production of a new, longer, and more reliable record of global surface temperature change. Existing estimates of global mean surface temperature combine air temperature over land and terrestrial ice-covered regions with sea surface temperature readings and take varying approaches for regions with sea-ice. The use of sea surface temperature measurements restricts the start date of the temperature record to around 1850, and the inconsistency of combining water and air temperatures limits confidence in estimates of climate sensitivity (an estimate of the temperature change that will result from a doubling of atmospheric CO2 concentration). The new GloSAT temperature record will give a longer and more consistent picture of global surface air temperature change, and its analysis will improve our understanding of climate change since the late 18th century.

Project partners National collaboration and world-class expertise

The GloSAT project brings together the National Oceanography Centre, the National Centre for Atmospheric Science and the Met Office along with the Universities of East Anglia, Edinburgh, Reading, Southampton and York. Funding for the project is provided via a Large Grant from the UK's Natural Environment Research Council.