Transition Into The Anthropocene (TITAN)

Transition Into The Anthropocene (TITAN): Learning about the climate system from data of the 19th and early 20th century

This project will use a novel climate modelling approach to improve our understanding of drivers of climate variability on decadal timescales in Europe and North America.

Identifying the causes of observed changes in our climate requires an understanding of the natural variability of the climate system and of the response of the climate to external influences. Our present knowledge is heavily weighted towards changes observed over the recent few decades and primarily focussed on the influence of greenhouse gases.

This project focuses on the early Anthropocene, namely the 19th through to the early 20th century. This period covers the emergence from an unusually cold period, the so-called ‘Little Ice Age’, and shows periods of warming including the still enigmatic early 20th century warming.

Global mean surface temperature anomalies (°C), relative to the period 1901 to 1950, from observations (black) and simulations (blue) [from Climate Change 2007: Working Group I: The Physical Science Basis]

Newly available observational data now make it possible to analyse this period in detail. This data has recently become available to researchers thanks to projects such as Old Weather, where members of the public transcribe ships’ logs of Arctic and worldwide weather observations made by United States ships since the mid-19th century.

‘Fingerprints’ for climate changes in response to external drivers, such as changes in atmospheric composition, solar radiation, and volcanism will be used to estimate the contribution by these factors to observed changes over the 19th and early 20th century. These fingerprints will be based on a large, multi-model ensemble of state-of-the-art climate model simulations.

The project will use targeted model simulations to help determine the role of sea surface temperature patterns and atmospheric and oceanic circulation in setting temperature records in the 1930s and 1940s.

The result will inform us about the causes of climate change over the early Anthropocene and will give us an estimate of the natural variability of climate based on a far longer time period. We will be able to give probabilistic estimates of the climate’s transient sensitivity to greenhouse gas increases and will have an improved understanding of the response of sea ice, precipitation, and temperature extremes to warming.

weather@home contribution

The Titan project is being led from the University of Edinburgh and’s role will be to focus on the contribution of different climate drivers (greenhouse gases, aerosols) to extreme weather events of the early 20th century, including the “dust bowl” years in North America and the series of very cold European winters in the 1940s.

Dust storm approaching Stratford, Texas, 1935 [Photo from NOAA Photo Library]

We will use long term daily station data from the US and Europe reaching back to the 19th century to find changes in extremes of daily, monthly and seasonal minimum and maximum temperature, as well as extreme monthly and seasonal temperatures over the period.

Using this information we will perform a large ensemble of simulations of the 1930s and 1940s within the weather@home project, using the atmospheric model HadAM3P and regional models over the EU and North America, to identify causes of, and contributors to, early 20th century weather extremes.

As with our other weather attribution studies, there will be more than one ensemble– one will be driven by observed sea surface temperatures, and the observed atmospheric composition of greenhouse gases and aerosols. At least two  ‘counterfactual’ ensembles will be simulated in addition to that: one with  the greenhouse gas response removed, representing the “world that might have been” without anthropogenic greenhousre gas forcing and the other one without some key climate relevant aerosols in the atmosphere.

This modelling work will help answer one of the key questions for this project: what role did atmospheric circulation and greenhouse gas increases play in temperature extremes observed over the early 20th century, and what can we learn from it?