Pacific Sea Levels- Warming, ENSO, or Wind?

Apparently our Opposition Leader Bill Shorten, his deputy Tanya Plibersek, and immigration spokesman Richard Marles are heading off to the Pacific to discuss “the dangerous consequences of climate change”, all paid for by media baron Harold Mitchell, according to yesterday’s Weekend Australian.
They will visit Papua New Guinea, the Marshall Islands, and Kiribati (pronounced “Kiri-bahss”).
The President of Kiribati leads the complaints about the threat of global warming to his island nation. Kiribati has indeed seen foreshore erosion and salt water intrusion in recent years- just don’t mention causeway construction and underground water extraction.
Time for a reality check.
Sea level rise in Kiribati and the Marshalls has nothing to do with climate change and everything to do with the ENSO cycle, and winds in particular.
In this post I use data from the Australian Bureau of Meteorology’s Pacific Sea Level Monitoring Project at http://www.bom.gov.au/pacific/projects/pslm/. I also use NINO 4 data from http://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices and Trade Wind Index data from http://www.cpc.ncep.noaa.gov/data/indices/wpac850.
Fig. 1: Island nations in the Pacific Sea Level Monitoring Project, also showing the area of the NINO 4 index. (Click graphics to enlarge).

I have converted raw mean sea level data to monthly anomalies from 1995-2014 means, and scaled down NINO 4 and Trade Wind data, in order to make comparison easier.
This figure shows sea level data at all of the islands in the BOM’s Pacific Sea Level Monitoring Project.
Fig. 2: 12 month smoothed sea level anomalies, 1992-2015, for all islands in the Sea Level Monitoring Project. The vertical axis is in metres.

Point 1: While there is broad agreement on rises and falls, the timing of the rises and falls is very mixed- some rise at the same time as others fall.

This is clearly shown by Kiribati and the Marshalls- when one is rising the other is falling.
Fig. 3: 12 month sea level anomalies at Kiribati and Marshalls, 1992 to 2015.

Perhaps Mr Shorten can discuss why sea level changes at the Marshalls precede those at Kiribati by many months, such that they are presently moving in opposite directions.
Point 2: There is no doubt that from 1992 to 2015, throughout this region sea levels have been rising: both the Marshalls and Kiribati by 4.8 mm per year. However, since sea level rise occurs at different times, it cannot be due to temperature change. This is further reinforced by the next graphic.
Fig. 4: NINO sea surface temperature anomalies, January 1982- September 2015, 12 month means.

NINO 4 sea surface temperature anomalies since 1982 have almost zero (+0.01C per decade) trend (and the other indices show negative trend in sea surface temperatures). The tropical Pacific has not warmed.
At first glance, sea level change at these islands appears to correlate well with El Ninos and La Ninas, however close analysis shows a much more complex picture.
Fig. 5: 12 month running means of Kiribati sea level anomalies compared to NINO 4

Note that sea level changes several months before the NINO 4 index.
Fig. 6: 12 month running means of Marshall Islands sea level anomalies compared to the Trade Winds Index.

Note that the Trade Winds mostly change simultaneously with or some months before sea levels change.
Point 3: Sea level changes at Kiribati precede ENSO events, as measured by the NINO 4 index, but follow or match the Trades at the Marshalls (just to the north of the NINO 4 region).
However, in Figure 3 above, note that sea level anomalies at the Marshalls PRECEDE Kiribati.
So what is the cause of sea level rise in the western Pacific, which is an alarming 4.8mm per year at Kiribati and the Marshall islands?
Fig. 7: Trade Wind Index, December 1992 to September 2015

The Trade Winds have been increasing throughout the period of the Sea Level Monitoring Project, pushing surface water from east to west across the Pacific.
Fig. 8: Western Pacific winds at 1 November 2015

(From http://earth.nullschool.net/#current/wind/surface/level/orthographic=163.83,1.50,277 )
At Kiribati westerly wind pulses, which help to initiate and strengthen El Ninos, push water against the low coral cay and raise the sea level at the tide gauge, (located on the western side of Tarawa, which is in normal and La Nina years the leeward side).

 

Fig. 9:  Tarawa Atoll

When these winds slacken and trade winds strengthen, the sea level drops. In the rising sea level phase, the westerly winds push warmer water eastwards, and the weaker trades do not bring in as much cooler water from higher latitudes. Thus the rise in sea level at Kiribati precedes a rise in sea surface temperature, and the peak in sea level occurs about 5 months before the peak in NINO 4, one of the El Nino indicators.
Conversely, weaker trade winds bottom out some months before the bottom of sea levels at the Marshalls, which are to the north of the area affected by westerly wind pulses.
Therefore we can reassure Mr Shorten and his pals that sea level rise has little to do with climate change (unless alarmists claim that global warming will lead to stronger La Ninas, which lead to cooler temperatures- but I thought the plan was for more El Ninos).
Sea level rise is largely due to wind. And no doubt Mr Shorten will contribute to that.

Tags: climate, sea level