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1000 year rainfall study suggests droughts and floods used to be longer, worse

A study done on… golly, Antarctic Ice, allegedly shows that in the catchment area for Newcastle in NSW, Australia, the last 100 years have been pretty darn nice, compared to the past when droughts and big-wet periods used to last a lot longer.

Set aside, for a moment, that the ice cores are thousands of kilometers away and in a totally different climate, if they are right, if, then natural climate change is much worse than our short climate records are telling us. And if our current records are so inadequate and don’t represent the “old-Normal”, then we have a flying pigs of predicting the “New Normal”. Has the climate changed at all, or is the new one just like the old old one?

Hydroclimatologist and lead author, Dr Carly Tozer from the ACE CRC said the research showed exposure to drought and flood risk was higher than previously estimated.

“The study showed that modern climate records, which are available for the past one hundred years at best, do not capture the full range of rainfall variability that has occurred,” Dr Tozer said.

“The wet and dry periods experienced since 1900 have been relatively mild when we look at the climate extremes of the past millennium.”
“Looking back over the past thousand years, we see that prolonged wet periods and droughts of five years or longer are a regular feature of the climate.”

The press release and interview can tell us that we are “underestimating” the risk of drought and flood, which sounds like the usual “worse than expected” scare story beat up in the media — but it is different. This time we are underestimating the risk of natural causes of floods and droughts:

“Water resources infrastructure in Australia is still mostly designed based on statistics calculated from about the last 100 years of instrumental rainfall and streamflow observations,” Dr Kiem said.

“What this study shows is that existing water management plans likely underestimate the true risk of drought and flood due to the reliance on data and statistics obtained from only the relatively short instrumental period.”

The ABC and The Conversation don’t draw the bleeding obvious next step: If follows — as day after night, that if we’ve underestimated natural climate change — then the models have been overestimating the influence of CO2.

There is no mention of climate change in the ABC interview. None on The Conversation either. You might feel relieved that these stories didn’t beat us over the head with the usual doctrine: “climate change will be worse than we thought, spend more money, buy a windmill”. But they should have mentioned climate change.  They should have connected the dots for what this means — the climate is likely to get more extreme in future, but it’s less likely that “carbon dioxide” is the cause.  They certainly wouldn’t have hesitated if the study suggested that 20th century was “unprecedented”, or “hotter”, “wetter” or “drier” than the last thousand years.

As for the Antarctic rainfall indicator of Newcastle…

Carly Tozer, The Conversation

There is no direct indicator of rainfall patterns for Australia before weather observations began. But, strange as it may sound, there is a link between eastern Australian rainfall and the summer deposition of sea salt in Antarctic ice. This allowed us to deduce rainfall levels by studying ice cores drilled from Law Dome, a small coastal ice cap in East Antarctica.

How can sea salt deposits in an Antarctic ice core possibly be related to rainfall thousands of kilometres away in Australia? It is because the processes associated with rainfall variability in eastern Australia – such as the El Niño/Southern Oscillation (ENSO), as well as other ocean cycles like the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) – are also responsible for variations in the wind and circulation patterns that cause sea salt to be deposited in East Antarctica (as outlined in our previous research).

Color me not-yet-convinced about the accuracy of the rain-gauge in Antarctica. But the central message is that we ought prepare ourselves for worse weather, and it’s hard to argue with that. Fortunately, we can download the actual paper (link below) and look, say, at Figure 4 ourselves.

UPDATE: Reader Neville reminds me of an earlier study Australia has had megadroughts for the last thousand years says ice core study. Strikingly the correlations between Antarctica and NSW catchments were better than most of the rest of Australia (map at the link).


C. R. Tozer et al.: An ice core derived 1013-year catchment-scale annual rainfall reconstruction, The paper will be available for download from Hydrology and Earth System Sciences from 0900 AEST, 11 May 2016.

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