Rainfall’s natural variation hides climate change signal

Posted: February 23, 2018 by oldbrew in climate, Natural Variation, research

Flooding in Houston from Hurricane Harvey 2017 [image credit: BBC]

This looks like another way of saying nobody can be sure what is natural variation and what – if anything – isn’t, when it comes to rainfall patterns at least. Or if they think they can work something out, it would have to be over a lot longer period than currently available data allows. Result: decision makers must fly blind as Phys.org suggests – probably by making assumptions based on poorly-performing climate models.

New research from The Australian National University (ANU) and ARC Centre of Excellence for Climate System Science suggests natural rainfall variation is so great that it could take a human lifetime for significant climate signals to appear in regional or global rainfall measures.

Even exceptional droughts like those over the Murray Darling Basin (2000-2009) and the 2011 to 2017 Californian drought fit within the natural variations in the long-term precipitation records, according to the statistical method used by the researchers.

This has significant implications for policymakers in the water resources, irrigation and agricultural industries.

“Our findings suggest that for most parts of the world, we won’t be able to recognise long term or permanent changes in annual rainfall driven by climate change until they have already occurred and persisted for some time,” said Professor Michael Roderick from the ANU Research School of Earth Sciences.

“This means those who make decisions around the construction of desalination plants or introduce new policies to conserve water resources will effectively be making these decisions blind.

“Conversely, if they wait and don’t act until the precipitation changes are recognised they will be acting too late. It puts policymakers in an invidious position.”

To get their results the researchers first tested the statistical approach on the 244-year-long observational record of precipitation at the Radcliffe Observatory in Oxford, UK. They compared rainfall changes over 30-year-intervals. They found any changes over each interval were indistinguishable from random or natural variation.

They then applied the same process to California, which has a record going back to 1895, and the Murray Darling Basin from 1901-2007. In both cases the long dry periods seem to fit within expected variations.

Finally, they applied the process to reliable global records that extended from 1940-2009. Only 14 per cent of the global landmass showed, with 90 per cent confidence, increases or decreases in precipitation outside natural variation.

Continued here.

  1. Ron Clutz says:

    They are looking for a nanosignal in records like this:

  2. Ron, not sure what your graph shows. I think one has to narrow the area up to see any pattern. In a large country as Australia there are many areas of different climate. In the north east of Australia in which areas are tropical going into sub-tropical. These are affected by cyclones from the east and rainfall is associated with El Nino (dry) and La Nina (wet). The north west of Australia is monsoonal with storms (monsoons) and cyclones coming from the west over the Indian ocean affected by the Indian Ocean dipole.. The middle of Australia is dry and it can at times be affected by cyclonic weather coming from either east or west.
    I live in sub-tropical area on the east coast. I have for my place a 125 yr record of rainfall. This comes mainly from an official weather station 5Kms away but now closed. I have been getting daily readings for the last 10 years. There are 4 official weather stations within 15 km radius and there have been another 5 which have only been recently closed but two private stations open in the last 5 years. I have plotted a graph of high (> 2350mm) and low (< 1250mm) for the annual rainfall at my place. It is easy to see a pattern of flood time and drought time. The frequency appears to be around 10-11 years. (When I lived in Sydney NSW that was also the frequency of major bushfires.- 1980, 1990 & 2001.) For the rainfall at my place it appears that important drought periods may have a frequency around 60 years. We also had a dry period from 200 to 2008 and this was followed by floods 2011-2013. The wettest period was 1893 to 1899 (which had records for annual 3998mm-1898 and monthly for January (1898) February (1819mm-1893) and March (1898). This was followed by what was called the Federation drought and at my place the rainfall for 1902 was 519mm less than a third of the 125yr average of 1806mm
    The ANU is known as a hotbed of climate alarmists with one of the worst Prof Will Steffen (who was mentioned in the climategate emails corresponding with Jones and others). There is nothing excellent about the ARC centre.

  3. oldbrew says:

    The Sun doesn’t behave like clockwork so the long-term climate isn’t likely to either. How they expect to separate natural variation from supposed ‘other’ influences, without any element of guesswork or subjective opinion, is a mystery.

  4. Phoenix44 says:

    “Our findings suggest that for most parts of the world, we won’t be able to recognise long term or permanent changes in annual rainfall driven by climate change until they have already occurred and persisted for some time.”

    Er, think that’s true for everywhere and everything.

    Pretty difficult to identify any kind of “permanent change” until it’s persisted for some time.

  5. Bitter@twisted says:

    “Centre of excellence”

  6. Paul Vaughan says:

    Heads or tails it’s the devil either way.
    The sampling regime is a joke on the users.
    It’s a shell game in a fluid stream of phase changes.
    All avenues to climate justice are twisted, frozen, or evaporated by conjuring arts.
    The time series magicians keep moving the shells and changing the phase of the peas.
    At the magical “center of excellence” is the conjuring art of scrambled aggregation criteria.
    Dark magic is A PURELY LOGICAL COIN with deception on one side and ignorance on the other.

  7. ivan says:

    I have to ask, what climate change signal and how would they know it if it was there or is it just groupthink like all of the climate hype?

  8. Rather than El Nino and La Nina which maybe defined differently I meant SOI -10 for a considerable period is dry and SOI +10 for a considerable period means wet for SE Qld. I have looked at these periods and the frequency is in the order of 10-11 years with a range of about 9 to 13 years. SOI is determined from the difference of atmospheric pressure between Tahiti and Darwin. and has been measured since about 1860. There have been papers relating atmospheric pressures to sea surface temperatures. I have also noted that there seems to be some relationship with tide heights at Darwin to Darwin atmospheric pressures. There are definitely influences of the moon but the 10-11 year cycle maybe due to the sun influenced by Jupiter
    Anyway I repeat there is a pattern not random variation.

    [reply] sounds a lot like the solar cycle

  9. stpaulchuck says:

    this is just like the “ozone hole” brouhaha of a couple years ago based on around 30 years of data… of a planet billions of years old. Ridiculous inductive fallacy reasoning writ large.

    Even though we have a whole lot more weather data we’re still talking about hundreds of years so not even enough direct measurement going back past the last ice age but merely cooked up analogs. At least these guys were the first to come out in public and say, “We don’t know.” Thank you.
    “Science is the belief in the ignorance of the experts” – Richard Feynman

  10. Gamecock says:

    ‘New research from The Australian National University (ANU) and ARC Centre of Excellence for Climate System Science’

    Led by Captain Obvious.

  11. hunter says:

    Once again skeptics of the climate consensus are proven to be correct.