If the role played by climate change in extreme weather events can be quantified, then the cost of related disaster can also be determined, hence we can place a financial figure on the component of climate change of these costs.

The last decade has witnessed a series of research findings that link extreme weather events to human instigated climate change.

The type of research referred to as “event attribution”, presents a more ideal means through which climate scientists can examine how the frequency and intensity of weather events like storms, heatwaves and droughts, are evolving as greenhouse gas concentration in the atmosphere continue to increase.

Packaged in a new pair of journal papers, the researchers have tried to create a new way through which the “attributable costs” of weather-related catastrophes can be quantified.

The focus of the research has been on floods and droughts that recently hit New Zealand and the 2017 Hurricane Harvey landfall in Texas.

By relying on event attribution as the scientific basis to quantify how extreme weather has evolved, the researchers took time to examine the links between the various changes in extreme weather events and the economic impact they cause.

If the role played by climate change in extreme weather events can be quantified, then the cost of related disaster can also be determined, hence we can place a financial figure on the component of climate change of these costs.

Eventually, these calculations will provide scientists with a price tag for climate change, based on its effect on extreme weather events.

Quantifying Attributable Costs

Considering the two research works, both of which were published in the Climatic Change journal, the floods and droughts in New Zealand for the 10 years from 2007 to 2017 and the August 2017 Hurricane Harvey in Texas were the point of reference.

According to the New Zealand Treasury, jointly, the two droughts of 2007 and 2013 caused a drop in New Zealand’s GDP by about NZ$4.8bn (US$3.4bn as at 2017 values).

Looking at the previously published techniques, which relied on climate models to project changes in the kinds of weather patterns common during the periods of severe drought in New Zealand, the climate change related cost was estimated at about NZ$800m (US$568m).

The scientific researchers also assessed the 12 most extreme rainfall events that caused a total of NZ$470m (US$334m) worth of insurance losses, by using methods applied elsewhere.

This process entailed running regional climate change models thousands of times over and over again, both with and without any human influence, and studying how the climate events at hand happened in each case.

On this basis, it’s estimated that about NZ$140m (US$99m) of the total insurance losses related to human influence on the climate.

Notably, the two sets of climate costs can’t be directly comparable as one measures reduction in economic performance while the other only measures insured losses.

The wisdom behind this is that event attribution can confirm that climate change is already causing substantial losses to New Zealand.

As such, we can conclude that climate change is not only a future monster, but one that is already here and costing us a lot.

Benchmarking Social Cost of Carbon Estimates

The experts also reviewed the human climate change fingerprint on the destruction caused by the 2017 Hurricane Harvey that battered Houston, Texas and believed to have been driven by torrential rainfall and widespread flooding.

The earlier published attribution research work based on independent methods was in consensus about the attributable changes in rains associated with Harvey: and these conclusions became the foundation on which the scientists’ cost estimates were based.

And the outcome of the study is shocking: An estimated US$67bn of the overall loss of US$90 billion related to the Hurricane is directly linked to climate change.

This is obviously a staggering estimate that would otherwise be achieved from the conventional economic models for climate change cost in the US such as the model developed by the Nobel Prize winner Nordhaus.

A 2017 research from the United States Environmental Protection Agency underpins this model on matters relating to “social cost of carbon”—ideally, this is the sum of financial damages brought about by every extra tonne of carbon released into the atmosphere.

Nordhaus’ model projects overall economic costs to the United States in 2017 from climate change to be about US$20 billion.

The common tools used to measure the costs of climate change are popularly referred to as “Integrated Assessment Models” (IAMs).

IAMs have been built with the hypothesis that the key economic impacts related to climate change emerge from long-term changes to agricultural output and practice related to average temperatures. Ideally, they generally assume that the effects of extreme weather events—generally infrequent by definition, are relatively negligible.

Virtually, the outcome from these groundbreaking research papers point to the fact that “top-down methodologies significantly underestimate the costs of climate change and that various event attribution methods could be used to create some sort of “bottom-up” review of these estimates.

Applying this approach more extensively could just be the thing to deliver a reliable check on IAM performance; adding another cherished line of evidence to help inform future projections relating to social cost of carbon.

In conclusion, there are numerous uncertainties in any projection of the effect of human influence on weather events and projections of costs related to climate change. While some of the impacts of extreme events are fairly well-documented including insurance losses, others are very challenging when it comes to measuring them and these include impacts on well-being and mental health.

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