Insights into climate change and reliability of GloSAT from integrating climate proxy, model and instrumental sources

Climate proxies are not just for extending the record before the instrumental period but also have value in assessing the instrumental record itself (e.g. global trends: Anderson et al. 2013; Indian Ocean SST: Pfeiffer et al. 2017). This PhD will apply such comparisons to periods and regions where the insight from proxies will be most valuable. One focus will be Europe in the early instrumental period (pre-1900 and especially GloSAT's new extension before 1850) where different thermometer exposures contribute to summer temperature biases and there is a wealth of summer-sensitive well-replicated tree-ring data supplemented by documentary evidence.

Another focus will be tropical temperature trends in comparison with information from coral records (PAGES 2k Consortium 2017). Novel approaches will strengthen the project, including utilising information from the Last Millennium Reanalysis (Tardif et al. 2018) and applying improved approaches to tree-ring analysis (signal-free Regional Curve Standardisation) to yield more reliable multi-centennial trends.

There are undoubtedly significant uncertainties is the proxy-based multi-centennial trends which the PhD project will explore. Even where these are too large to constrain the GloSAT instrumental uncertainties from, say, 1800-present, the proxies will also provide independent information on decadal-multidecadal temperature variability and the PhD project will utilise this to evaluate the instrumental variations over comparable time-spans. For example, there are differences in temperature changes over 1800-1850 and 1850-1900 between different datasets and the climate proxies might contribute to resolving these issues.

The overall outcome will be an independent evaluation of GloSAT temperature and optimised climate change information in the case study regions.

References

Anderson et al. (2013) Global warming in an independent record of the past 130 years. Geophys. Res. Lett., 40, 189-193, doi: 10.1029/2012GL054271.
PAGES2k Consortium (2017) A global multiproxy database for temperature reconstructions of the Common Era. Sci. Data, 4,170088, doi: 10.1038/sdata.2017.88
Pfeiffer et al. (2017) Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates. Scientific Reports 7, 14434, https://doi.org/10.1038/s41598-017-14352-6
Tardif et al. (2018) Last Millennium Reanalysis with an expanded proxy database and seasonal proxy modeling, Clim. Past Discuss., https://doi.org/10.5194/cp-2018-120

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 WeatherRescue.org 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.