The effect of ENSO on sea-level in the South-western Pacific and Australia

In a previous post, I explored the connection between ENSO ((El Niño/La Niña Southern Oscillation) and sea-levels at Darwin and Fremantle on the west coast of Australia, in particular, the remarkably close correlation between smoothed monthly average levels and a smoothed, trended multiple of the SOI (Southern Oscillation Index).

It had already occurred to me that if the correlation was so convincing, that perhaps it might be possible to adjust monthly average data by the multiple of SOI to remove its effect and reveal the underlying pattern and trend of sea-level change at such strongly-affected locations. First attempts showed that the tenfold multiple I'd used to show correlation was too high, and that a multiple of 7 was "just right" for ENSO adjustment. Lower multipliers didn't reduce the variability ("lumpiness") sufficiently, and too high a value increased variability in the opposite direction. Lucky 7 turned out to be the "Goldilocks" factor. Here's my revised chart for Darwin:

... and with 7 times SOI subtracted from monthly values

The revised chart for Fremantle for the same period

... and with 7 times SOI subtracted from monthly values

Those two removals are quite convincing, I'd say - "extreme ironing" indeed. Note that the trends for both removals are slightly higher than the originals, despite the post-1990s upticks having been removed. It's because the earlier trend from the mid-1970s was down, which effectively pulled the trend-lines down.

High rates of rise in the western Pacific (as shown by satellite sea-level maps) have been a thorn in the side of some sceptics for some time. They conveniently ignore the fact that sea-levels along the Pacific coasts of the Americas show low or negative rates on the maps, supported by tide-gauge data, and that the high rates in the west are also supported by tide-gauge data, when exactly the same time-spans as the satellite maps are compared. They also ignore the reasoned, researched and informed voices which explain that both phenomena are effects of ENSO.

The island of Pohnpei (Federated States of Micronesia) is in that western "hotspot", and using PSMSL data for the two tide-gauges covering the period I've been able to recreate the record from 1974-2012.

The "ENSO profile" being clear, I went ahead and adjusted the monthly data as before.

Majuro atoll is in the Marshall Islands group, and I've extended my previous reconstruction to end 2012, and added the SOI plot. Note that sea-level is lagging SOI on the extreme right.

Kwajelein is also in the Marshall Islands, not that far from Majuro. Sea level is clearly leading SOI on the right.

The uptick is the subject of a couple of recent posts on wattsupwiththat.com, ENSO not being very high on the list of possible reasons under discussion. Nils-Axel Mörner thinks it's due to subsidence because of recent building, but then he would, he doesn't understand ENSO and the magnitude of its effects. Here's the latest data to June 2013 for Majuro from the South Pacific Sea Level and Climate Monitoring Project.

As you can see, the uptick has now reversed, following the SOI back to zero.

Pago Pago, American Samoa, shows a less-satisfactory correlation overall, but it's still reasonably convincing. It also shows  the sharp recent uptick.

I've had a look at correlation on the eastern side in California, but it's less clear. California is well north of the equator, and ENSO is the Southern Oscillation after all. I'll see if I can find an SOI widget (or make one) for my sidebar. I'll add captions with source data links very soon.

Sea-level in Australia and the Southern Oscillation Index

I've read a fair bit about the Southern Oscillation Index (SOI) over the years, about how much ENSO (El Niño/La Niña Southern Oscillation) affects sea-level in the Pacific. I've noted effects, particularly the El Niño "dip" in the western and central Pacific, and the corresponding "spike" in the east (especially the US Pacific shore). However, my impression was that it was just the extremes, El Niño and the less-well defined La Niña that had any real effect on Pacific sea-level. Before I continue, it's worthwhile quoting what Australia's Bureau of Meteorology has to say about the SOI; it's succinct and informative:

The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin.

Sustained negative values of the SOI below −8 often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in winter and spring rainfall over much of eastern Australia and the Top End. You can read more about historical El Niño events and their effect on Australia in the Detailed analysis of past El Niño events.

Sustainted [sic] positive values of the SOI above +8 are typical of a La Niña episode. They are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal. You can read more about historical La Niña events and their effect on Australia in the Detailed analysis of past La Niña events. 

The ENSO Wrap-Up includes the latest 30-day SOI value, as well as other information on indicators of El Niño and La Niña events.

 The graph below shows monthly values of the SOI in recent years.

  Source:BOM

On the following page they have links to data tables; Wanting to create a spreadsheet of monthly SOI values (from 1876!) I was dismayed to find the table to be structured as years down and months across. However, using Excel's Copy and Paste-Special/Transpose functions I was able to do it, laboriously year by year. Here's the result for 1959 to May 2013. The reason for the not-so-obvious start year will become obvious very soon.

SOI index 1959-2013    Data source: BOM

I've added a 25-month (2 year) centred moving average to smooth out the spikes without suppressing the signal. A 13-month MA would seem to be more appropriate, but gives too "lumpy" a trace; a 37-month MA smooths just too much. Like Goldilocks' porridge the 25-month MA is "just right".

Comparing the SOI plot with a sea-level plot is easy, but I wondered if I could add the SOI to a sea-level chart in some way. One problem is that the signal is relatively small, and the other is that it varies around a (flat, obviously) zero value. I hit on the wheeze of "magnifying" the SOI signal, and normalising the start of the SOI moving average with the start of the sea-level moving average, incrementing the magnified SOI by the monthly sea-level-trend increment. I tried a factor of 10 for magnification, on the basis that the SOI signal is based on air pressure at sea level, and one hPa change leads to a 10 mm sea-level change (in the opposite direction). My assumption may not have had much maths behind it, but the "porridge effect" operated and it was "just right". Here's the result for Darwin:

Darwin complete sea-level record 1959-2012       Data source: BOM/NTC

I don't now what you think, but I'd call that a rather good correlation, especially over the right-hand half of the chart. Here's one for Fremantle over the same period.

Fremantle sea-level 1959-2013  Data source: BOM/NTC

For both Darwin and Fremantle, note that the recent (since 1994) sharp upward trend has begun a downward reverse, more clearly predicted on the SOI chart which extends to last month (May 2013). The large and broad downward bulge around 1983 corresponds with the intense (some would say most intense on record) El Niño of 1982-3. It shows up well on the 25m MA sea-level plot for Darwin (and most Australian stations), but sea-level rose at Fremantle during that event. All the other El Niños show up on both charts; the broad low during the early 1990s (1991-2 and 1994-5 El Niños, with just 1993 between) and the intense but shorter 1997-8 El Niño. The 2010 El Niño was a more subdued affair.

I think it's clear that the SOI doesn't just affect variations in sea-level, it drives them, at least on the west coast of Australia. In a future post I'll look at other Oz stations for correlation, and where correlation is poor, explore possible reasons.

Australia's CSIRO - manufacturing sea level hockeysticks?

The CSIRO's "State of the Climate" report was published today (14th March 2010). Missing a link to the report in the newspaper article summarising the dire consequences of climate change in store for Diggers Down Under, I did a Google News search, and came up with a rather interesting ABC page on the release of the report, titled "Sea Levels are Rising", which is not exactly news, but never mind that. Below the obligatory (and of course irrelevant) statement

It notes that the long-term warming trend has not changed, with each decade having been warmer than the previous decade since the 1950s.

... is an "interactive data visualisation" which "explores sea level rise patterns across Australia using data sets provided to the ABC by CSIRO". What struck me immediately was the uptick in sea level at three of the 62 tide gauge stations on the superimposed charts below the interactive map. I've selected Wyndham (WA) on the map - which shows the largest 2010 uptick. I've almost completed an interactive map for Australia myself (similar to the "South Pacific Seal Level 2011" in the reference pages, top-right sidebar), so I'm familiar with the chart for Wyndham. That uptick is definitely not kosher, not kosher at all. here it is:

Source: ABC

... and the RHS embiggened:

Source: ABC

By reading the data points from the ABC chart, I've established that all the preceding annual data points are correct, but 2010 stands out like a sore thumb Here's the corresponding chart for Wyndham, over the same time period, 1993-2010, with the last two points from the ABC chart added in red:

Data Source: NTC

The lower pair of points are Darwin (346) and Carnarvon (322). If the offsets from the real data for all three stations are added, they total 526, which averaged over all 62 stations comes to 526/62 = 8 mm rounded down. If that's deducted from the all-station average for 2010 (dark green line), it brings it down from 120 mm to 112, which means that the three outliers have increased that 112 figure by almost 11%.

I considered whether this might not be deliberate fiddling (generous and understanding to a fault!), but possibly a result of using incomplete data for 2010, for example January-June, but that doesn't explain it - any average with January as a start point is much lower than the ABC/CSIRO figures. Not only that, but 2009/10 were El Niño years, and there's usually a drop in sea level during one of these events; it shows up (though much less pronounced than 1997/8) at most stations except some in the far south. One such rogue plot might be a genuine error, but three? Here are my plots for Darwin and Carnarvon:

Data Source: NTC

Data Source: NTC

I've checked a random sample of the other stations on that rather clever (I'm green with envy - don't take that as weakness) interactive page, and can detect no further excursions from NTC data whatsoever, even for Hobart, home of the CSIRO. Currently, this is a mystery within an enigma, to paraphrase Churchill's description of Russia at the beginning of WW2.

UPDATE 15th March 2012

I've tracked down the source of two of the "adjustments". The CSIRO (funded by the Australian taxpayer) doesn't obtain its sea level data from the National Tidal Centre (funded by the Australian taxpayer, and where you'd expect them to get it as I do), but from an independent archiver, the Permanent Service for Mean Sea Level, based in Liverpool, UK. It's one which I use regularly for data unobtainable elsewhere, but I'm surprised that the CSIRO uses it. The PSMSL relies on data submission from national or other bodies which collect it, and it's rarely up-to-date, often months or even years of the latest data are missing. This explains why CSIRO web pages and publications quote sea level statistics up to Dec. 2010 for the NTC SEAFRAME stations, even though the NTC publish the data monthly.

Anyway, PSMSL has, apparently arbitrarily, adjusted 2010 monthly data for Carnarvon and Wyndham upwards by 140 mm and 260 mm respectively, with no acknowledgement (as is customary) on the station pages. here's a chart for Wyndham for 2009-10 illustrating what's been done:

Data Sources: PSMSL & NTC

That 260 mm is larger by 63 mm than the change in sea level at Wyndham since the gauge was installed in 1966, and larger than estimates of global sea level rise since 1900, so it's no small matter. What are they playing at? The Darwin data (to 2010) at PSMSL appears to be identical to the NTC data (except measured from a different baseline, which is irrelevant), so where did that 128 mm adjustment come from? Sherlock is on the case, with his (t)rusty magnifying glass at the ready. No violin though. On second thoughts, perhaps I'll just ask them. Watch this space for exciting developments.

Sea Level in Australia - the Inexorable Rise in Alarmism

Is the sea-level around the Australian coast rising at an alarming rate? The Australian Climate Commission would have citizens and policy-makers in Australia and elsewhere believe that it is. In their 2011 report "The Critical Decade - Climate science, risks and responses" the following map is shown (mm per year)

Figure 8. Local sea-level rise (mm/year) around Australia from the early 1990s to 2008

Looks scary, doesn't it? In the southwest, somewhere near Perth, 8.1 mm/year, implying a rise of 81 cm in a century. In the north, somewhere near Darwin, a slightly lower value. Are these figures correct? As quoted "from the early 1990s to 2008" they are, but they are also very misleading - at most of the (as yet) unidentified monitoring stations shown on that map, there has been no significant sea-level rise after 1998. I can also show that most, if not all of the rise around Australia in the second half of the 20th century occurred during 1997 and 1998. during what's been called "one of the most severe ENSO events in history". ENSO is short for "El Niño/La Niña-Southern Oscillation"  for those not familiar with the mnemonic.This is not what the Climate Commission, the CSIRO, nor the Australian government want known.

Here's my version, based on the same data, but starting from 1999, at the end of the late 90s ENSO "ramp" which grossly distorts the "early 1990s to 2008" rates shown above.

Local sea-level rise (mm/year) around Australia from 1999 to 2010

Looks rather less scary, doesn't it? Let's see where the CC got their data, and why there's such a massive difference between those two maps.

The Battle of the Bulge

National Geographic News tells us:

Earth Has "Spare Tire"—And Ice Melt's Keeping It That Way 

Waistline bulge has stopped slimming, thanks to massive melting.

Earth isn't losing its "spare tire" as fast as it should be, according to new research—and it's definitely not because the planet's not getting enough water.

In fact, melting ice from Antarctica and Greenland (map) is giving the oceans huge infusions of water, which then gets pulled toward the Equator—counteracting a millennia-old slimming trend around the planet's middle, experts say. 

.....

Overall, the current ice loss is causing Earth's bulge to grow at a rate of seven millimeters a decade, Wahr and Nerem found—exactly enough to counteract the long-term rebound, at least temporarily.

This must mean that sea-level rise in the equatorial regions is higher than elsewhere, so let's look at a few places. The largest open body of water is the Pacific ocean, and Hawaii isn't that far from the equator (21°N)