Global Surface Air Temperature (GloSAT)

Department Name: Science and Technology


Surface temperature is the longest instrumental record of climate change and the measure used in the Paris Climate Agreement that aims to 'prevent dangerous anthropogenic interference with the climate system'. The Agreement defines an ambition to limit global temperature change to 1.5C or 2C above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) used a baseline of 1850-1900 for its definition of 'pre-industrial' as this is when existing instrumental records begin. It has been estimated that global temperatures may have already increased by 0.0-0.2C by this time, but this is uncertain due to lack of data. However, even using the 1850-1900 baseline, existing temperature datasets disagree on the amount of warming to date and this disagreement implies more than 20% uncertainty in the allowed carbon budget to meet the goals of the Paris Agreement solely due to uncertainty in observed surface temperature change. These differences between temperature datasets arise mostly 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.

To best inform decision-makers, records of temperature change must be as accurate, consistent, and long as possible. Existing global datasets start in 1850 or later, but we will extend the record a further 70 years back to the late 18th century. Current knowledge of this period comes from instrumental measurements in Europe, palaeo-proxies (tree-rings, corals or ice cores), and climate models. We will dramatically extend the spatial coverage of the early measured record in this 70-year period, which is important for understanding natural climate variability and the climate response to different radiative forcings. For example, the longer record includes the period of 5 large volcanic eruptions and extra cycles of multi-decadal climate oscillations. The new record will allow us to better disentangle the contributions of anthropogenic and natural factors on the climate system and quantify the effect humans have already had on Earth's temperature, and hence on future climate.

A major inconsistency has been past use of air temperature over land but SST over oceans. Recent advances mean we can produce a marine air temperature record to construct the first global air temperature dataset over ocean, land and ice, stretching back to the late 18th century. Our dataset will be independent from SST, currently the most uncertain component of global temperature. We will improve land, marine and cryosphere air temperature observations to make them more homogeneous and extend the global record further back in time. This requires fundamental research to better understand the bias and noise characteristics of historical observations and develop new error models. We will adopt sophisticated statistical techniques to allow the estimation of air temperature everywhere, even when there are gaps in the observations. We will expand the historical climate record with new ship's logbook and weather station digitisations focused on early data, sparse periods and regions, and the interfaces between land, ocean and ice. We will engage the public in the digitisation effort building on recent successful citizen science initiatives.

We will analyse the new surface air temperature record to better understand how temperatures have changed since the late 18th century. This longer record will give a better understanding of natural climate variations, both variability generated internally within the climate system and that due to external forcing factors such as volcanic eruptions and solar changes. This improved understanding of natural variability will enable us to more cleanly isolate the characteristic "fingerprints" of man-made climate change allowing us to more confidently detect and attribute human-induced changes

Planned Impact

The most recent Climate Change Public Attitude Tracking Survey in the UK found that
74% of respondents were either 'very' or 'fairly' concerned about climate change. Global political concern over the issue is reflected by the Paris Agreement negotiated by 196 parties at the 21st Conference of Parties in 2015. The UK has committed to reducing greenhouse emissions by 80% by 2050. Clean growth is a key element of the government's industrial strategy.

The most visible measure of climate change for both policymakers and the public is the historical temperature record, which measures how global temperatures have changed over the past 170 years, and shows periods of rapid warming in the early 20th century and for the whole of the last 50 years. However the record is not long enough to give a complete picture of temperature change since before the start of the industrial revolution, or how exceptional recent temperature change is in comparison to pre-industrial conditions. The current historical temperature record mixes air and water temperatures in a way which creates confusion when comparing with climate model predictions.

This project will produce a new global surface air temperature dataset starting in around 1780 - at least 70 years longer than any other and stretching back almost to the start of the industrial revolution. The length of the record, the use of air temperatures for both land and oceans, and improvements to our understanding of the historical measurements will make this new dataset the benchmark for the understanding human impact on the climate for both policymakers and the general public.

Temperature data underpins national and international policy on climate change. The UN Framework Convention on Climate Change (UNFCCC) process will benefit from improved quantification of temperature change since the pre-industrial period to feed into their regular 'global stocktake' which will monitor progress towards achieving the aims of the Paris Agreement to limit global temperature change to 1.5 or 2C above pre-industrial levels.

A range of datasets with differing spatial and temporal resolutions will be produced to represent improving data coverage over time, and incorporating new analyses of the level of confidence in the data at any point in time. This information will feed into national & international climate assessments, such as the annual State of the Climate Report, the UK Climate Change Risk Assessments, and future Intergovernmental Panel on Climate Change reports. The climate science community will also benefit from an improved understanding of natural climate variations, such as those due to volcanic eruptions and internal ocean-atmosphere interactions: the new dataset will be widely used to compare to other observational datasets, weather model reanalyses and climate model simulations. This will improve our understanding of past climate change and weather extremes, and implications for future change, providing data for risk management in both government and industry.

An important part of GloSAT will be the digitisation of historical observations from their current paper or scanned image formats. Much of this will be achieved through public engagement and citizen science digitisation, building on the highly successful project, which has already rescued more than 2.5 million weather observations using thousands of volunteers. The rescued observations will be added to international weather observation databases such as ICOADS, ISTI, ISPD and the Copernicus Climate Data Store for the entire climate community to use. The use of citizen science for digitisation will also be exploited as an opportunity to engage the public in science and to communicate climate science.


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Blunden J (2021) State of the Climate in 2020 in Bulletin of the American Meteorological Society

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Cropper T (2023) Quantifying Daytime Heating Biases in Marine Air Temperature Observations from Ships in Journal of Atmospheric and Oceanic Technology

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Kent EC (2021) Historical Estimates of Surface Marine Temperatures. in Annual review of marine science

Description Publications part-funded by GloSAT have been used as supporting evidence in the Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6).
First Year Of Impact 2022
Sector Environment
Impact Types Policy & public services

Title CLASSnmat: monthly, global, gridded night marine air temperature data 
Description Climate Linked Atlantic Sector Science (CLASS)nmat is a global dataset of monthly mean night marine air temperature (NMAT) that is produced on a 5° latitude by 5° longitude regular grid and covers the period 1880 to 2019. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact This dataset will be used in the forthcoming Bulletin of the American Meteorological Society (BAMS) annual State of the Climate report for 2019 as a comparison against other global temperature datasets. 
Description Poster presentation and discussions at 1st Royal Meteorological Society Climate Change Forum 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The 1st Royal Meteorological Society Climate Change Forum runs under the theme "Risks and Resilience: Emerging challenges in a post Paris world" took place at Coin Street Conference Centre, London on the 4th June 2019. This event brought together the UK climate science community and was a unique chance to discuss current needs, research challenges and policy requirements in an interdisciplinary way.

The interactive format of the day consisted of keynote lectures in the morning, an extended poster and networking session over lunch and interactive round table discussion in the afternoon.

Speakers in the morning from government, parliament and advisory bodies helped to understand recent challenges of the UK society and government. The poster session featured recent highlights in climate change research including natural, social sciences and interdisciplinary research approaches. It also covered climate actions from the private and public sector, science communication and the science-policy dialogue. This session provided an opportunity for exchanging knowledge from within the UK climate research community in interdisciplinary ways. The round tables in the afternoon explored science challenges for future research and society as well as current challenges the climate science community is facing.
Year(s) Of Engagement Activity 2019