Seasonal attribution experiment

What was the climateprediction.net Seasonal Attribution Experiment?

The climateprediction.net Seasonal Attribution Project uses computing time donated by the general public to run state-of-the-art high-resolution model simulations of the world's climate. These simulations are used to determine the extent to which the risk of occurrence of extreme weather events is attributable to human-induced climate change.

We focus on extreme weather events that occur on a seasonal timescale, and in our current project we focus specifically on the United Kingdom floods of Autumn 2000 which occurred during the wettest autumn ever recorded, causing widespread damage and an estimated insured loss of £ 1.3 billion.

• Half of the climate model simulations we run are of the Autumn 2000 period, specifically including within them the effects of human-induced climate change caused by the emission of greenhouse gases. We call these the "Industrial Autumn 2000" simulations.
• The other half will simulate a representation of the the Autumn 2000 climate had there not been any human-induced emissions of greenhouse gases over the last century. We call these the "Non-Industrial Autumn 2000" simulations.
• By then comparing the results of these Industrial and Non-industrial simulated climates, and recording the occurrence of floods like that of Autumn 2000 in each of them, we can determine how the frequency of occurrence (or 'risk') of such a flood has changed, and therefore how much risk is attributable to human-induced emissions of greenhouse gases over the last century.

There is also an article with more details about the science behind this project.

We are also collaborating with other research groups who are interested in using our simulations to perform similar attribution studies, for snowmelt in western North America, and heatwaves in South Africa and India.

Why look at attributing extreme weather events in this way?

Recent extreme weather events, having large societal and economic impacts have prompted the debate about effects of human activity on the world's climate. One way to answer this question is to compare the world's current climate with what it would look like had it not been for human activity - similar to the way an epidemiologist might compare samples of smokers and non-smokers to attribute the effects of smoking to lung cancer. The problem is that we cannot observe what a climate without the presence of human activity looks like, since we can only observe the current state of the climate. Hence we have to resort to simulations of such a climate using state-of-the-art climate models.

Furthermore, small differences in how we initialize these simulations can have a significant impact on the end results - reflecting the fact that we do not have completely perfect models and that in the real world small differences in what is going on now can have significant effects on what happens in the future (to quote a famous statement, 'The flap of a butterfly's wings in Brazil can set off a tornado in Texas', the so called butterfly effect). To account for this uncertainty we will run a large number of simulations of each climate - again, similar to how an epidimiologist might study a large number of patients to have confidence in his results. Also, because the Autumn 2000 flood event was in itself extreme this further necessitates running a large number of simulations before we might expect to reproduce an event of that magnitude. We are currently aiming to complete about 10,000 simulations for each of the Industrial and Non-Industrial Autumn 2000 climates.

We focus particularly on the United Kingdom Autumn 2000 floods because, aside from causing widespread damage, they occurred during the wettest autumn since records began in 1766. Thus we might expect any signal of such an event in the simulations to be more prominent and easier to detect than if we had investigated less severe and/or shorter lived weather phenomena. Also, it is only relatively recently that models have been developed with the required resolution to sufficiently capture the storms and weather patterns associated with the Autumn 2000 floods.

Attributing the risk of extreme weather events to climate change in this way also has very interesting implications for liability for such events.

How can I help?

We aim to complete around 10,000 climate model simulations of each of the Autumn 2000 climates. Running all these simulations, however, is very computationally expensive because they are so many and because the model is of high spatial resolution - it's beyond our own resources. This where your can help and participate in our project!. We invite you to download and run one of these simulations on your own computer and so help in determining the risk of occurrence of the United Kingdom Autumn 2000 floods attributable to human-induced climate change.

The simulation will run automatically as a background process on your computer when you switch your computer on, and you can schedule when you want it to run. It should not affect any other tasks you use your computer for. It will simulate the world's weather for a one year period from April 2000 - March 2001, so as to capture important atmospheric conditions surrounding and including the Autumn 2000 period. As it runs, you can watch the weather patterns on your, unique, version of the world evolve. A single simulation run continuously takes approximately 3-4 weeks on a computer with a Pentium 4 processor. Once completed, the results are sent back to us via the Internet, but you do not need to be continuously connected to the Internet whilst the simulation is in progress otherwise, and you will be able to see a summary of your results on this web site.

What climate model are you using and what is 'BOINC'?

For our simulations we use the state-of-the-art HadAM3-N144 climate model, which was developed at the Hadley Centre for Climate Prediction and Research. It is a high spatial resolution version of the standard Unified Model used by the UK Met Office (learn more about climate modelling and the Unified Model). At the earth's surface it has a horizontal resolution of approximately 100km² at mid-latitudes enabling it to reasonably capture the storms and weather patterns associated with the Autumn 2000 floods flooding. Specifically, in the simulations we record daily surface temperature, precipitation, 500hPa geopotential height and surface winds over the Atlantic-European region. Monthly temperature, precipitation, 500hPa geopotential height, mean sea-level pressure and soil moisture over the entire globe is also output to assess larger scale weather systems. Furthermore, daily temperatures and precipitation over the Northwest US, India and South Africa are recorded for related attribution projects investigating snowmelt and heatwaves.

To distribute and manage the running of simulations on participating computers we use 'BOINC' (Berkeley Open Infrastructure for Network Computing) software. BOINC allows the user to control the run behaviour of a simulation on their computer. This includes allowing you to schedule when you want to run the simulation, how much of your computers resources to dedicate to the project, selecting a screen-saver mode, and interactive visualisation of your simulation.

Who are we?