9 Attribution
For too long, weather’s randomness has kept events such as these from being blamed squarely on climate change. Reporters in the late 1990s and early 2000s would ask climate scientists about climate change’s role in a weather-related disaster. All we could say was that we’d expect to see more of these events. Now, we can specify increased chances for specific events. This extends to forecasts: we can identify the places that are more likely to see wildfires, mudslides and fish die-offs. Such calculations dent both climate denial and a false sense of security. They take away the argument that ‘extreme weather happens anyway, so we don’t need to worry about it’. Extreme weather happens — and these metrics pinpoint what is becoming more likely, by how much and why.
Ametsoc (2021) Explaining Extreme Weather (pdf)
9.1 Attribution Studies Timeline
ClimateChangeNews
AR5 concluded that human influence on the climate system is “clear.” Today scientists say climate change is, without doubt, caused by us. A 2021 study concluded that humans have caused all of the warming observed since the preindustrial period.
Since the last IPCC report, there has been an explosion of attribution studies finding that specific heatwaves, droughts, tropical cyclones and other extreme events were more likely or intense because of climate change. Recent studies have shown that extreme events such as the Siberian heat wave in 2020 would never have happened without humans pumping greenhouse gases into the air.
Since AR5, attribution science has become more “impact-oriented”, Sjoukje Philip, a climate scientist from the World Weather Attribution (WWA) group, told Climate Home News. That means more studies focusing on the societal impacts of extreme weather events.
The increase in attribution studies is due to more precise climate models and peer-reviewed methods which allow scientists to rapidly and accurately analyse extreme events. Scientists are now able to carry out attribution studies within a few days of an event occurring.
Half of all attribution studies focus on heatwaves. Heatwaves are relatively easy to attribute because they are “very certain and the first response to climate change” and cover a large area, which makes it easier for climate models to pick up. Most of the rest look at extremes of rainfall leading to drought or floods. Only a handful have looked at hurricanes, which are hard to model due to their complexity and limited historical data. They reached relatively weak conclusions about the scale of human influence. That could change as new high-resolution models are being developed.
The majority of attribution studies focus on events in Europe and North America. This is because these regions have the most reliable climate data available.
Timeline of climate attribution studies
2004: First heatwave attribution study
The study found that climate change had at least doubled the likelihood of the European heatwave in 2003, which killed more than 70,000 people.
2011: First flooding attribution study
The first study to attribute greenhouse gas emissions’ contribution to flood risk in England and Wales. The scientists concluded that emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20% and in two out of three cases by more than 90%.
2014: Likelihood of European heatwaves analysis
The study found that summer heatwaves in Europe over the past 10-15 years were 10 times more likely due to climate change
2016: Mortality study of European heatwave
The first study to directly link deaths during the 2003 European heatwave to climate change. The scientists concluded that 506 of the 735 summer fatalities in Paris in 2003, and 64 of the 315 in London were a result of climate change.
2017: Bangladesh flooding study
World Weather Attribution analysis directly linked severe flooding in Bangladesh in 2017 to climate change.
2018: Cape Town water crisis analysis
The 2017 drought which led to Cape Town’s water crisis was made three times more likely by climate change, according to analysis by World Weather Attribution scientists.
2018: Extreme heat across Asia
Extreme heat across Asia in 2016 would have been impossible without climate change, scientists concluded in 2018.
2020: Siberian heatwave impossible without climate change
The prolonged Siberian heatwave in 2020 would have been almost impossible without climate change, according to rapid attribution analysis by the World Weather Attribution group.
2021: Australian bushfire season 30% more likely
Australia’s devastating bushfire season in 2019-202 was made significantly more likely because of climate change, according to World Weather Attribution scientists. The analysis showed that climate change led to weather conditions that increased the fire risk by at least 30%.
9.2 Map of Attribution Studies
Known as “extreme event attribution”, the field has gained momentum, not only in the science world, but also in the media and public imagination. These studies have the power to link the seemingly abstract concept of climate change with personal and tangible experiences of the weather.
Scientists have published more than 300 peer-reviewed studies looking at weather extremes around the world, from wildfires in Alaska (pdf) and hurricanes in the Caribbean to flooding in France and heatwaves in China. The result is mounting evidence that human activity is raising the risk of some types of extreme weather, especially those linked to heat.
To track how the evidence on this fast-moving topic is stacking up, Carbon Brief has mapped – to the best of our knowledge – every extreme-weather attribution study published to date.
The map above shows 355 extreme weather events and trends across the globe for which scientists have carried out attribution studies.
9.3 Bottom Trawling CO2 release
Time Magzine: How Industrial Fishing Creates More CO2 Emissions Than Air Travel
Bottom trawling is responsible for one gigaton of carbon emissions a year—a higher annual total than (pre-pandemic) aviation emissions. Not only does the practice contribute to climate change, it is extremely damaging to ocean biodiversity—the “equivalent of ploughing an old-growth forest into the ground, over and over and over again until there is nothing left”
Bottom trawling is also one of the least cost effective methods of fishing. Most locations have been trawled so many times, there is little left worth catching. Without government subsidies, no one would be making a penny.
Refuting a long-held view that ocean protection harms fisheries, the study found that well placed marine protected areas (MPAs) that ban fishing would actually boost the production of marine life by functioning as fish nurseries and biodiversity generators capable of seeding stocks elsewhere.
Sala
Marine sediments are the largest pool of organic carbon on the planet and a crucial reservoir for long-term storage29. If left undisturbed, organic carbon stored in marine sediments can remain there for millen-nia30. However, disturbance of these carbon stores can re-mineralize sed-imentary carbon to CO2, which is likely to increase ocean acidification, reduce the buffering capacityof the ocean and potentially add to the build-up of atmospheric CO2
Using satellite-inferred information on fishing activity by industrial trawlers and dredgers between 2016 and 2019, aggregated at a reso-lution of 1km2, we estimate that 4.9million km2 or 1.3% of the global ocean is trawled each year. This disturbance to the seafloor results in an estimated 1.47Pg of aqueous CO2 emissions, owing to increased carbon metabolism in the sediment in the first year after trawling. If trawling continues in subsequent years, emissions decline as sediment carbon stocks become exhausted. However, after 9 years of continuous trawling, emissions stabilize at around 40% of the first year’s emissions, or around 0.58Pg CO2 (Supplementary Fig.35). If the intensity and footprint of trawling remains constant, we estimate that sediment carbon emissions will continue at approximately 0.58Pg CO2 for up to around 400 years of trawling, after which all of the sediments in the top metre are depleted. Although 1.47Pg CO2 represents only 0.02% of total marine sedimentary carbon, it is equivalent to 15–20% of the atmospheric CO2 absorbed by the ocean each year32,33, and is compara-ble to estimates of carbon loss in terrestrial soils caused by farming34. Although an unknown fraction of the aqueous CO2 is emitted to the atmosphere, the increase in CO2 in the water column and sediment pore waters can have far-reaching and complex effects on marine carbon cycling, primary productivity and biodiversity.
Time Magzine BBC Sala (2021) Protecting the global ocean for biodiversity, food and climate - Nature Share
9.4 Company Attribution
A 2017 report by the Carbon Disclosure Project showed that 100 companies have been responsible for 71 per cent of global emissions since 1988. In 2019, a similar study from the Climate Accountability Institute found that just 20 companies were responsible for 35 per cent of all energy-related carbon dioxide and methane worldwide since 1965.