Carbon Brief is a UK-based website designed to “improve the understanding of climate change, both in terms of the science and the policy response”. It is funded by the European Climate Foundation and is based in London. The article cited , and included, below received a highly-commended award for investigative journalism from the Royal Statistical Society. Originally published in 2017, it is updated annually.
Scientists have published more than 230 peer-reviewed studies looking at weather events around the world, from Hurricane Katrina to Russia’s 2010 heatwave. The result is mounting evidence that human activity is raising the risk of some types of extreme weather, especially those linked to heat.
Carbon Brief’s analysis suggests 68% of all extreme weather events studied to date were made more likely or more severe by human-caused climate change. Heatwaves account for 43% such events, droughts make up 17% and heavy rainfall or floods account for 16%.
To track how the evidence on this fast-moving topic is stacking up, Carbon Brief has mapped – to the best of their knowledge – every extreme event attribution study from a peer-reviewed journal.
The map below shows 260 extreme weather events across the globe for which scientists have carried out attribution studies. The different symbols show the type of extreme weather; for example, a heatwave, flood or drought. The colours indicate whether the attribution study found a link to human-caused climate change (red), no link (blue) or was inconclusive (grey).
Use the plus and minus buttons in the top-left corner, or double click anywhere, to zoom in on any part of the world. Click on a weather event to reveal more information, including a quote from the original paper to summarise the findings and a link to the online version.
The filter on the left allows users to select a specific type of weather event to look at or, for example, only those found to be influenced by climate change.
The software used to make the map currently only works with a Web Mercator projection (as used by virtually all major online map providers). It is worth noting that this – like all map projections – offers a somewhat distorted view of the world.
It is important to note that the weather events scientists have studied so far are not randomly chosen. They can be high-profile events, such as Hurricane Harvey, or simply the events that occurred nearest to scientific research centres. (More on this later.)
The 260 weather events in the map are covered by 234 individual scientific papers. Where a single study covers multiple events or different locations, these have been separated out.
Combining the evidence over the past 20 years, the literature is heavily dominated by studies of extreme heat (31%), rainfall or flooding (20%) and drought (18%). Together, these make up more than two-thirds of all published studies (68%). The full list is available in this Google sheet.
As the chart below shows, the number of events studied each year has grown rapidly over time; from eight in 2012 to 59 in 2018. Note that the studies typically follow a year or so after the event itself as the writing and peer-review process for journal papers can take many months.
The majority of studies included here have been published in the annual “Explaining extreme events” special issues of the Bulletin of the American Meteorological Society (BAMS). Each bumper volume typically contains around 20-30 peer-reviewed studies of events from the previous year. Other studies have been found through the Climate Signals database and online searches through journals.
Specific types of event can be displayed in the chart below by clicking on the category names at the top.
Number of attribution studies by extreme weather event type and year. Note: the total number of events dipped in 2017 because the Bulletin of the American Meteorological Society special report for that year was published in early 2018 rather than late 2017.
Most of the categories of extreme weather are self-explanatory, but “storms” and “oceans” require a bit of explanation.
For ease of presentation, the “storms” category includes both tropical cyclones (i.e. hurricanes, typhoons) and extratropical storms. The “oceans” category encompasses studies looking at sea surface temperatures and storm surges, such as those generated by Typhoon Haiyan in the Philippines and Hurricane Sandy (pdf, p17) along the eastern US seaboard.
There are also some new categories of events in this update, including “coral bleaching” and “ecosystem services”, reflecting the ongoing developments in attribution science.
For example, two studies focusing on 2016 found that El Niño and human-caused climate change combined to bring drought and poor harvests to southern Africa (pdf, p91), and that enhanced warming of sea surface temperatures increased the risk (pdf, p144) of coral bleaching on the Great Barrier Reef.
Such studies show that attribution studies are increasingly considering the impacts of extremes, rather than focusing purely on the weather event. One of the first of these “impact attribution” studies was published in 2016. It estimated that 506 of the 735 fatalities in Paris during the 2003 European heatwave were down to the fact that climate change had made the heat more intense than it would otherwise have been. The same was true for 64 of the 315 fatalities in London, the study said.
This shift towards impacts “is quite significant”, says Prof Peter Stott, who leads the climate monitoring and attribution team at the Met Office Hadley Centre and has been a co-editor of the BAMS reports since they began in 2012. He tells Carbon Brief:
“Impacts are hard to do because you have to establish a significant link between the meteorology and the impact in question. As editors, we’ve been trying to encourage more studies on impacts because it’s the impacts rather than the meteorology per se that tends to motivate these types of study – and if we only have the attribution on the meteorological event then we only have an indirect link to the relevant impact.”
Finally, some attribution research has also looked at the human influence on changes in general indicators of climate change, such as global average temperature or sea level rise. These have not been included in the attribution map as the focus here is on extremes.
Turning to the results of the attribution studies that have been published so far, scientists found that human-caused climate change has altered the likelihood or severity of an extreme weather event in 78% of cases studied (68% made more severe or likely and 10% made less so).
In Carbon Brief’s first edition of this analysis in 2017, 68% of events were found to have a human impact (with 63% made more severe or likely and 6% less so).
Note that events are classified here as having an human impact if climate change is found to have influenced at least one aspect of that event. For example, a study of the 2011 East Africa drought found that climate change contributed to the failure of the “long rains” in early 2011, but that the lack of “short rains” in late 2010 was down to the climate phenomenon La Niña. This event is, thus, designated as having a human impact.
For the majority of events affected by climate change, the balance has shifted in the same direction. That is, rising temperatures made the event in question more severe or more likely to occur. These events are represented by the red in the chart below. Clicking on the red “slice” reveals that heatwaves account for 43% of such events, droughts for 17% and rainfall or flooding for 16%. Return to the original chart, and do the same with the other slices to see the proportion of different weather types in each category.
In 11% of studied weather events, scientists found climate change had made the event less likely or less severe (pale orange in the chart above).
Unsurprisingly, this category includes blizzards and extreme cold snaps. However, it also features a few studies that suggest climate change has lessened the chances of heavy rainfall, and another that found rising temperatures have made agricultural drought in California less likely.
With thanks and acknowledgements to Carbon Brief.
The complete article can be found at
Later sections of the article contains sections on:
heavy rain and flooding