Sea levels in the Pacific

I recently visited Port Vila, capital of the Pacific island nation of Vanuatu (the photo above is from the Port Vila waterfront). Port Vila is the site of a sea-level measuring station. It is interesting that, although local newspapers are deeply concerned about sea level rise, the average sea level rise between 1993 and 2017 at Port Vila was essentially zero (see chart below, which uses LOESS smoothing of monthly measurements).

How can this be? Aren’t global sea levels rising at 2–3 mm per year? Well, “global sea level” is a rather theoretical concept. Ocean temperatures are not uniform. Some islands are rising out of the ocean. Others are sinking. Air pressure, and the El Niño Southern Oscillation cycle, have a huge effect on sea levels too. As they say, it’s complicated.

The NASA map below shows that some areas of the Pacific have actually seen a long-term reduction in sea level (independent of any upward or downward movement of land). Other areas, of course, have seen quite rapid increases (the increases and decreases average out to a rise of about 3 mm per year). The map covers data only up to 2008, however. Since 2008 was roughly the peak for the Port Vila data, it doesn’t quite explain the last decade of the graph above. If I had to guess, I’d assume that some of those sea-level-decrease areas on the map had shifted a bit.


I’m off soon to Vanuatu for a holiday. Above (click to zoom) is a map of this island nation (produced using the raster package of R, with my own colour palette). The map outlines are from (which is missing an island, unfortunately). Elevation data is from the Shuttle Radar Topography Mission (with additional void fill using a lower-resolution dataset).

The overlay in red shows light visible at night (from NASA’s Earth at Night). Apart from the two main towns of Luganville and Port Vila, the active volcanoes on Ambrym and Tanna are clearly visible (take a closer look at Ambrym’s lava lake here).

Not highlighted is the active volcano on Ambae, an island which held 4% of the nation’s population until it was recently evacuated – consider helping the evacuees via Anglican Aid.

Pencil charts for visualising colours

As a result of a discussion with a photographer friend of mine, I’ve been thinking (not for the first time) about visualising the colour palette of images. Consider this sunset, for example (a picture I took in Adelaide 8 years ago):

The photograph is rich in yellow and orange. However, the apparent blue in the sky is actually grey, and the apparent grey of the sea is actually brown. If we postulate a standard set of 35 plausible pencil colours, and map each pixel to the closest-matching pencil colour, we get this (I have done the comparison in RGB space):

Then we can visualise the colour palette of the image by showing the wear on the virtual pencils, if each virtual pencil has been used to colour the corresponding pixels. It can be seen that a lot of orange, brown, and grey was used (click to zoom):

Conversely, this beach scene (photographed in Vanuatu in 2016) is rich in blues:

The warm light greys of the beach don’t quite find an exact match among the pencils, but the other colours match fairly well:

And here is the pencil visualisation (click to zoom):

If, rather than using a standard set of colours, we extract the pencil colours from the image itself (image quantisation), fewer pencils will, of course, be required:

The fit to the original image will be much closer as well:

So this is a trick to remember for another day – pencil visualisations!

Visiting Vanuatu again

I recently made another trip to the island nation of Vanuatu, which means blog-writing has been a bit thin. Above is one of the country’s many beautiful tropical beaches. I think you can see why I haven’t been writing much!

I was in Vanuatu for the 14 November supermoon, which was the closest approach of the moon to Earth since 1948 and until 2034. Below is a rather bad photo of the event, taken with my mobile phone.

Let me also give a shout-out to the friendly staff of Air Vanuatu, who did a great job in their shiny new Boeing 737-800.

Islands of Vanuatu

Here is an experiment in simple data visualisation – the larger islands of Vanuatu, plotted by area and population density (on logarithmic axes, so that lines of constant population are straight). Santo is the largest island, while Efate (where the capital, Port Vila, is located) has the highest population density. The mean population density for the nation as a whole is 22.3 people per sq km.

The islands on the plot are drawn to scale, using the maps package of R. For the islands shown, the population varies from 322 (Hiu) to 86,250 (Efate). Area data is from this table, while population data is from the 2015 Vanuatu National Population Estimates.

The plot sheds some light on local issues: the high population density of Tanna makes land particularly precious, while the lower population density of Santo – comparable to Mali, NSW (Australia), or Nevada (USA) – makes infrastructure more expensive.

Visiting Vanuatu

Recently I took my own advice and visited the island nation of Vanuatu. I had a great time! Since the islands are volcanic and surrounded by coral reefs, the beach sand ranges from pure white to basaltic black, with an intermediate grey-brown in some cases, like the beach in my photo above.

Vanuatu has a range of interesting wildlife (though no native land mammals other than bats). Birds of Vanuatu include the Vanuatu kingfisher (Todiramphus farquhari, above), which I did not see. There are 120 other bird species, including visiting seabirds. Butterflies of Vanuatu (of which I saw many) include the Monarch butterfly (Danaus plexippus) and several subspecies of the Canopus Swallowtail (Papilio fuscus, below).

Underwater, Vanuatu provides wonderful opportunities to see marine life while diving or snorkelling. The Flickr photographs below are by Diane Brook (click images to zoom):


Vanuatu update

The Red Cross has produced this damage assessment map for Vanuatu (click to zoom):

The photos below show aid arriving – delivering aid from Australia (below left, photo: Australian Defence Force) and Vanuatu Mobile Force soldiers loading UNICEF aid (below right, photo: Graham Crumb of Humans of Vanuatu). Much more is still needed, of course.

Please help Vanuatu

The island nation of Vanuatu (above, left) has been in the news because of the terrible damage caused by Severe Tropical Cyclone Pam. The capital, Port Vila, was hard hit (see the photo below by Graham Crumb of Humans of Vanuatu), and some islands (such as Erromango and Tanna) were utterly devastated. The right-hand side of the map above shows the track of the cyclone, with the strongest (Category 5) period shown in red.

The people on the devastated islands desperately need water, food, and shelter. The international community is helping out, but donate if you can. Please: there are many donation options.

However, as the cyclone track above suggests, the large island of Espiritu Santo came through the cyclone comparatively unscathed. The people there, strangely enough, need tourists. Tourists are their livelihood, and tourism is also the engine of Vanuatu’s national economy. So you can also support the nation of Vanuatu by taking a holiday there. The beaches and the diving are, they tell me, great, and the brave people of Vanuatu will become more than just faces on the television. To quote a message from one of the locals on Espiritu Santo:

Thank you everyone for your kind thoughts and wishes sent during this very sad time in Vanuatu. Santo has been blessed, Cyclone Pam has passed by the Island of Santo causing only minor damage. We have clean water, power and plenty of food. We also have travelers waiting to return to their countries as soon as possible. ALL RESORTS AND BUSINESSES ARE OPERATING AS NORMAL.

As of today we still have no communications. Turtle Bay Resorts satellite system is being used by the community to send out emails and to keep up with information on Port Vila’s terrible situation. The business community of Santo is terribly concerned of the warnings for travelers to cancel their travel plans to Vanuatu. The media of course is reporting the situation in Vila but this is not Santo. If our Island can keep receiving the visitors, businesses in Santo will survive the crisis situation in the months to come. This in turn will support many local people who will be able to support their families in Port Vila to rebuild their lives. No tourism and our Vanuatu economy will suffer greatly.