Climate change exacerbated floods caused by a tropical storm that shut down a large portion of New Zealand last month in one of the country’s costliest catastrophes, according to experts, but they were unable to precisely determine how much it exacerbated the tragedy.

Global warming caused by the combustion of fossil fuels contributed to the downpours from Cyclone Gabrielle, which featured at least six hours of deluges of over an inch per hour (20 millimetres per hour) of pounding rain, according to a research conducted Tuesday by 23 experts from across the world. Normal approaches to estimate how much climate change contributed to the tragedy were insufficiently conclusive for scientists due to the lack of weather data, the tiny size of the impacted area, and the region’s naturally high weather variability.

Sam Dean, co-author and scientist at New Zealand’s National Institute of Water and Atmospheric Research, stated, “Climate change is a major worry for floods in New Zealand, and you have to realise that these are enormous volumes of rainfall.” “I have no question whatsoever, based on my expertise as a climate scientist, that climate change has had a 30% effect on the event, but do we know the precise percentage? No, we don’t.”

The work has not yet been peer-reviewed, the scientific gold standard, because it is so new. Yet, the scientists at World Weather Attribution use well-established methods for attributing climate change — comparing an actual occurrence to models of what would have occurred in the absence of rapid warming — and publish their findings in papers that have been peer-reviewed.

More than 200,000 houses were without electricity for days, a national emergency was proclaimed, and the storm inflicted $8 billion ($13 billion New Zealand) in devastation to Aotearoa, the indigenous Mori name for New Zealand. According to the Meteorological Office of New Zealand, some locations received up to 400 millimetres (15.7 inches) of rainfall in just two days. The storm claimed eleven lives.

MetService reports that the cyclone came just a few weeks after heavy floods in the region had saturated the ground and nearly matched New Zealand experts’ worst-case forecasts.

In a pre-warming environment that was 2.1 degrees Fahrenheit (1.2 degrees Celsius) colder than it is now, heavy rainfall over two days was around 30% more severe and four times as common. Nevertheless, the scientists stated that these numbers are subject to significant uncertainty due to a lack of data.

In addition, scientists conduct computer models to determine if global warming has an effect. But, the region that was inundated is so tiny that most computer models could not account for it. Those who were able to do so discovered a significantly smaller climatic imprint than the historical data indicates, or virtually none.

Yet, experts are persuaded that climate change plays an influence, even if they cannot quantify it.

Michael Mann, a climate scientist from the University of Pennsylvania who was not a member of the study team, stated that the group is likely underestimating the impact of climate change on the destruction in New Zealand because climate models are insufficient to describe all of climate change’s effects on extreme weather.

“There is extra energy and moisture in every storm as a result of human-caused warming, regardless of whether a research formally credits it,” he added.

In addition to climate change, researchers discovered that a just concluded global weather-altering phenomena known as La Nina and an ocean heat wave contributed to Gabrielle’s effect.

Friederike Otto, a climate scientist at Imperial College London and co-author and team leader of the study, stated, “Every extra degree of warming will exacerbate these kinds of disasters.” “Climate change is not something that occurs in the distant future or to someone else; rather, it impacts people, especially vulnerable communities, all over the world today.”

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