Storm Ulysses

extremes, history, observations, weather

On 27th February 1903 a major windstorm hit the UK and Ireland, known as Storm Ulysses.

The 20th Century Reanalysis (20CRv3) includes a modern reconstruction of the storm, created by assimilating available observations of surface pressure into a state-of-the-art weather forecast model.

There is a problem however. The number of available observations over north-west Europe is limited as most have never been digitised from the original hand-written paper sources. Recently, the WeatherRescue.org project rescued millions of observations, allowing us to examine the value of this new data by rerunning 20CRv3 with the new data added.
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Warming patterns

Global warming does not mean the same amount of warming over the whole globe. There is a distinct spatial pattern to the long-term changes.

The first map below shows the total change in temperature since the early-industrial era, and the second map removes the global average warming to highlight regions of above and below average warming.

The largest warming is seen in the Arctic, and the land regions are clearly warming faster than the ocean. The striking blue area in the North Atlantic is a region of very little warming, and this is due to a decline in the strength of the Atlantic overturning circulation which brings warm water from the tropics to the northern latitudes.

All these features of the warming have been long predicted in climate model simulations, for example in IPCC AR4 and IPCC AR5.


Technical details: spatial pattern of warming uses approach described in Hawkins et al. (2020) using Berkeley Earth dataset, and the changes are relative to 1850-1900.

Arctic surprise

In 2007, IPCC AR4 produced this figure showing projections of changes in Arctic sea ice extent in the summer (July-September). The different colours represent a wide range of different scenarios for future emissions. Observations (1979-2020, added purple line) have decreased far more rapidly than projected in the CMIP3 models used at the time, when plotted on the same scale with the same reference period.

This demonstrates the concept of a climate-related ‘surprise’, or what might have been considered a low-likelihood event at the time.

The original figure is here. Also see Stroeve et al. (2012) for a CMIP5 comparison (Fig. 2a), and Notz et al. (2020) for a CMIP6 comparison (Fig. 2f).

What does a 1°C warmer world look like?

Global average temperature has risen by over 1°C since pre-industrial times, but the size of the change is not the same everywhere. The image below shows the temperature change observed in 5 individual years and for the 20-year average (2000-2019). For all of these examples the global average temperature was almost exactly +1°C warmer than the late 19th century.

In each individual year, the patterns can be quite different, with disparate regions of cooler and warmer temperatures. When averaging over 20-years, the overall pattern of warming is clearer: the Arctic is clearly warming much faster than the global average, and land areas are warming faster than ocean regions.


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Sensitivity of historical climate simulations to uncertain aerosol forcing

aerosols, GCMs, temperature

Earth’s climate has warmed by approximately 0.85 degrees over the period from 1880 to 2012 [IPCC, 2013] due to anthropogenic emissions of greenhouse gases. However, the rate of warming throughout the twentieth and early twenty-first centuries has not been uniform, with periods of accelerated warming and cooling.

Guest post by Andrea Dittus
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From the familiar to the unknown

temperature, variability

Changes in climate are often analysed in terms of trends or differences over time. However, for many impacts requiring adaptation, it is the amplitude of the change (the ‘signal’) relative to the local amplitude of climate variability (the ‘noise’) which is more relevant.

We consider the ‘signal-to-noise’ ratio in observations of local temperature, highlighting that many regions are already experiencing a climate which would be ‘unknown’ by late 19th century standards. The emergence of observed temperature changes over both land and ocean is clearest in tropical regions, in contrast to the regions of largest change which are in the northern extra-tropics.

[Details in: Observed emergence of the climate change signal: from the familiar to the unknown, by Hawkins, Frame, Harrington, Joshi, Rojas & Sutton]
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