Reports of Hawai'i's Climate Death are Greatly Exaggerated

Over at the Huffington Post, this headline caught my eye: "Climate Change Will Ruin Hawaii, New Study Suggests."

The article is based on a report by the University of Hawaii's Sea Grant program.  Here is a statement from the University of Hawaii report:

Air temperature has exhibited a consistent increasing trend in Hawai'i over the last 100 years, the rate of which has quadrupled in the last 40 years to over 0.3 F (0.17 C) per decade.

I'm not sure how they define "consistent" in climate science, but in the real world it means "always acting or behaving in the same way ... continuing to happen or develop in the same way ... free from variation or contradiction."

Four NOAA National Weather Service climate sub-regions exist for Hawaii: Hilo, Honolulu, Kahului, and Lihue.  Not a single one of these regions has anything remotely close to an increasing trend in air temperatures over the past three decades.  Lihue has a near-perfect non-correlation, and Hilo, Honolulu, and Kahului all have highly non-significant trends (i.e., no trends) with negative correlations toward cooling, not warming.  This is part of a "consistent increasing trend in Hawai'i over the last 100 years" in air temperature that has accelerated in recent decades?  No chance.

Even over the last 40 years, the Hilo, Kahului, and Lihue regions all show non-significant trends with negative – cooling – correlations. This appears to entirely contradict the University of Hawaii report. Honolulu does have an overall increasing trend in air temperatures over the past 40 years, but not over the last 30 years. To fully explain this, some data visualization is required.

It is abundantly clear that there is no "consistent" increasing trend in air temperature at Honolulu over the "last 40 years" (i.e., since 1974).  The climate warmed for the first 20 years of this time frame and has then cooled.  Yes, there is still an overall increasing trend since 1974, but it is not consistent, nor is it at 0.3 F per decade.  Indeed, the parametric trend over the last 40 years is only 0.19 F per decade, whereas the non-parametric Mann-Kendall-based trend analysis yields only 0.20 F per decade.  Since 1984 – the most recent 30-year period for climate change analyses – the trend is non-significant with a negative correlation towards cooling.

To recap, the University of Hawaii report claims that "air temperature has exhibited a consistent increasing trend in Hawai'i over the last 100 years, the rate of which has quadrupled in the last 40 years to over 0.3 F per decade."  When we look at the data, instead we find that three of the four climate sub-regions in Hawaii have correlations towards cooling – not warming – air temperatures over the past 40 years, and all four sub-regions have cooling correlations over the past 30 years.  That is not a consistent and accelerating warming rate.

On the contrary, air temperatures in Hawaii appear to be declining over the most recent decades, which should be cause to doubt the corresponding claim that "Hawai'i is projected to continue warming, with a range of +4-5 F (2.2-2.8 C) for high emissions scenarios by the year 2085."  Continue warming?  It doesn't look like it has been warming for at least 30, and more probably 40, years.  The real question is whether Hawaii will continue cooling.

The University of Hawaii report notes that "with increased temperatures, some residents could face increased vulnerability to extreme heat and its associated illnesses such as heatstroke and cardiovascular and kidney disease."  Extreme heat concerns in Hawaii?  Since records began in 1950, the Hilo region has never had a day with a maximum temperature above 95 F (a common benchmark for extreme heat employed in the National Climate Assessment and elsewhere in the scientific literature).  Not one.  Records go back to 1890 in the Honolulu area, and not a single day above 95 F in 125 years.  For the Kahului area, only five total days of extreme heat since records begin in 1955: one each in 1973, 1983, 1994, 1995, and 1997.  None since 1997.  No trend here.  Finally, not a single day above 95 F in the Lihue region since its records began in 1905.

Over the last three decades, extreme maximum temperatures at Lihue have a perfect non-correlation, Hilo and Kahului have non-significant correlations towards lower extreme maximum temperatures (aka, cooling), and Honolulu actually does have a highly significant declining – not increasing – trend in extreme maximum temperatures.  Looks like extreme heat is becoming less of a threat in Hawaii during recent decades, not more. Same general pattern for mean maximum temperatures as well – no significant trends anywhere except in the Honolulu area, whose mean maximum temperatures are going down over the last 30 years, not up.

How about this prediction?

For the southern shoreline of O'ahu, the frequency of heavy rainfall is projected to increase through 2040, with those heavy rainfall events becoming less extreme.

For the Honolulu area (aka, "the southern shoreline of O'ahu"), the number of days per year with more than two inches of rainfall has a near statistically significant declining – not increasing – trend since records begin in 1878.  Also a negative correlation over the past 30 years.  The number of days with more than an inch of rain each year does have a significant declining trend since 1878, and a near-significant declining trend over the past 30 years as well.  The maximum daily rainfall quantity for each year also has a near significant decreasing trend since 1878, and a negative correlation since 1984, too.

All this suggests that heavy precipitations events on the southern shoreline of O'ahu are not becoming more common or extreme over time.  Rather, they are becoming less common and less extreme.  The report even notes that "at rain gauge stations across Hawai'i, the number of high intensity rain events has decreased by 27% while the frequency of low intensity rain events has increased. Rainfall has become less intense for the western islands [O'ahu and Kaua'i] over the last 60 years."

So climate change up to the present has led to less extreme precipitation on the southern shoreline of O'ahu, but in the future it will make it more extreme?  And even if, somehow, in the future the precipitation events on the southern shoreline of O'ahu do increase back up to their historical norms, this will spell out the ruination of Hawaii?  A return to normal will be extreme – sounds like Orwellian doublespeak.

And while I would agree that "Hawai'i's total annual average rainfall ... has decreased over the last century," it is also critical to note – as I did in my previous piece on climate change in the Aloha State – there have been no significant trends in annual precipitation for any of the Hawaiian sub-regions since 1970 and, in three of the four Hawaiian sub-regions, we also have no data available for a century.

Thus, I am just not seeing supporting apocalyptic evidence that climate change is going to ruin Hawaii.  Time to tone down the hysteria and just report the facts, although that may be asking for too much from the Huffington Post and climate science community.

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