Earlier in the era of our warming climate, atmospheric and climate scientists lacked the computer power and database to make reliable estimates of how much a role climate change was playing in individual extreme weather events. A newer scientific subdiscipline has evolved in recent years and is proving to be useful in not only gauging probabilities of a causal link, but in making estimates important to future efforts at climate change mitigation and adaptation measures to deal with the inevitable impacts. I was first introduced to attribution science in email exchanges several years ago with Penn State’s renowned climate scientist, Professor Michael Mann.
A group called World Weather Attribution, or WWA, organized in 2014 to better ascertain the probabilities of climate involvement in extreme weather events. Some of the research partners in WWA include Oxford University, the National Center for Atmospheric Research, Princeton University, the Royal Netherlands Meteorological Institute and several other European scientific centers. WWA is hosted at Oxford’s Environmental Change Institute, or ECI.
ECI explains the fundamental premise as to how WWA’s work is performed: “ECI’s unique approach uses very large ensembles of simulations of regional climate models to run two different analyses: to represent the current climate as it was observed, and to represent the same events in the world that might have been without human-induced climate change.”
When, for example, humankind’s industrial greenhouse gases and their proven warming effects are removed in these model comparisons, it becomes mathematically more apparent how extreme weather events and patterns have been ramped up in frequency and intensity by human activity. Model run comparisons with our added greenhouse gases versus those without our inputs of carbon dioxide and methane can reveal stark differences. Past extreme weather events can be simulated in the models to make these comparisons.
WWA analyzed a recent catastrophic weather event, the flooding in mid-July in Germany and other parts of central Europe.
The event details were just released this past Monday.
• The crux of WWA’s findings on attribution: “Climate change increased the intensity of the maximum 1-day rainfall event in the summer season in this large region by about 3 – 19% compared to a global climate 1.2 °C cooler than today. The increase is similar for the 2-day event.
• "The likelihood of such an event to occur today compared to a 1.2 °C cooler climate has increased by a factor between 1.2 and 9 for the 1-day event in the large region. The increase is again similar for the 2-day event.”
Another recent example more familiar to Americans concerns the unprecedented heat wave in the Pacific Northwest earlier this summer.
That event, covering British Columbia, Washington and Oregon was so far outside the range of known climatology going back centuries it has been determined its extreme peaks would be impossible without human influence. To refresh your memory, on June 28 Quillayute, Wash., located 3 miles from cold Pacific waters at the edge of a rainforest on the Olympic Peninsula, reached 110 degrees. Quillayute’s previous all time high, like Buffalo’s, was 99 degrees. Seattle-Tacoma Airport hit an all time record high of 108 degrees on a day when the average high is 74. Lytton, B.C., reached 121 degrees, the hottest temperature in Canada’s history, before being destroyed by wildfire the following day. Here are WAA’s analysis and conclusions, which are alarming (and peer-reviewed).
On this linked page, you may also click on other events now determined to be nearly impossible without human-activity induced warming.
Even now, California wildfires are roaring far ahead of schedule, largely but not exclusively tied to a climate-induced megadrought.
Lake Mead and Lake Powell reservoirs are at record low levels, as is the Colorado River, with water supply deliveries having been slashed and a major hydroelectric generation plant in central California now shut down. Dwindling snowpacks in the Sierra Nevada add to the water crises.
Attribution science has complex issues when dealing with droughts in arid parts of the world, such as the southwest. Droughts in such regions have always been a part of the environment, and some in the past have been very lengthy and severe. Yet, this current extreme long-term weather and climate event has unquestionable links in its severity to the warming climate when examined in the framework of attribution science. A 2020 study in the journal Science concluded 46% of this megadrought’s severity is tied to the human-caused warming climate. Such percentages in some other global arid region droughts are not always quite that high.
The same global warming produces quite the opposite effect in wetter regions, enhancing and increasing extreme heavy precipitation events, as I detailed in my Tuesday article.