Last year was probably the hottest on record worldwide. On regional and local scales, 2014 also broke many records. Across Europe as a whole, and in 19 individual European countries, it was the warmest year recorded.
The Central England Temperature series – the longest instrumental temperature record in the world, extending all the way back to 1659 – also experienced its warmest year last year.
In a study published today in Environmental Research Letters, my colleagues and I examined this record-breaking year in central England to try and answer the question: has human-induced climate change altered the likelihood of very warm years in that region?
To find the answer, we used two very different methods.
The first involved the use of different sets of climate model simulations. We examined climate models that include both natural influences on the climate, such as solar fluctuations and volcanic eruptions, and human influences such as greenhouse gas emissions. We then compared these with simulations that only take account of natural influences (without the human influence) over the past century.
For each set of models, we worked out the likelihood of very warm years in central England, and then compared the results. We found that human-induced climate change has increased the likelihood of very warm years in central England by at least 13-fold.
The second method involved the observed temperature record, rather than models. We studied more than a century of the Central England Temperature series, to work out the distribution pattern of all the warmest years back to 1900.
This allowed us to compare the “return times” for warm years like 2014 in the current climate, versus the climate of a century ago. We found that the likelihood of very warm years in central England has very likely increased by at least 22-fold between 100 years ago and today.
What do the different numbers tell us?
Both methods show large increases in the likelihood of very warm years in central England related to human-induced climate change. These numbers are consistent given that they are based primarily on different data sets and slightly different relative likelihoods (using simulations of a natural climate in the first method and the observed climate of 100 years ago in the second). What’s more, the range of uncertainties on these values have large overlaps.
The key conclusion is that there is strong evidence that human-induced climate change is already significantly and substantially increasing the likelihood of very warm years in central England. This is remarkable, given that central England is such a small region of the world and has a highly variable climate.
Another way to put it is that, even in such a small region with such wide-ranging weather, we are still able to detect a clear “fingerprint” of human-induced climate change over the relatively short time span of a century.
As the climate continues to warm we would expect the likelihood of very warm years in central England to increase further because of human-induced climate change.