Climate Warming: Natural and humanly induced
Six hundred students entered the Samoa Observer’s essay writing competition on climate change.
Congratulations to all.
You will become the future guardians of Samoa’s environment. And thanks to the Observer organisers, SSAB and Eveni sponsors and the parents and teachers who encouraged the students to participate. Awareness of the present dangers and those that lie ahead should be a compulsory part of every child’s education, not only here in Samoa but globally. There must be a universal understanding of the enormous problem facing future generations and a universal attempt to solve it.
Now here’s essay number 601.
It is from an elderly Australian geologist living in Savaii who attended school and university during the 1940s and the early 1950s – a period long before warming climate was recognised as a global threat.
Today it is on the agenda of every national and international conference and in most countries, including Samoa, there is a drive to replace the atmospheric polluting fossil fuels of oil, gas and coal by the environmentally clean energy sources of water power, wind power, geo-thermal energy and sunlight.
The conversion to clean energy will take time and, in the meantime, industry will continue burning fossil fuels and we, the worst polluters of all, will continue driving to the local store for groceries. We daily add to the problem, a problem which started 170 years ago with the Industrial Revolution and has increased exponentially ever since with expanding industry and growing population.
Many climate scientists predict that by the close of this century average temperature, if not checked, will be several degrees Celsius higher than the pre-industrial level and that sea level will have risen by several feet. Today’s average temperature is already one degree Celsius higher than that of the 19th century and another small increase could be tolerated by most of humanity. But temperature alone is not the main issue. The danger lies in the changed weather patterns of a warmer climate, the droughts, floods and devastating cyclones. It doesn’t need explaining. Everyone who watches TV knows what happened in the Caribbean and southern U.S. states over the past two months. And a two foot sea rise? If this happens, all coastal communities and low-lying islands, particularly atolls, will be at high risk.
The above discussion is about man’s interference in nature. But natural climatic reversals have been occurring throughout the Earth’s entire 4.6 billion year history and are the result of our Earth’s wobbling axis. For the purpose of this article only the last 2.2 million years will be considered. This was the Ice Age or, in geological terms the Pleistocene when the northern land masses from the pole to between latitude 45 degree and 50 degree were covered by a gigantic ice pack up to a mile in thickness.
This long glacial period was interspersed with 13 or 14 much warmer inter-glacial periods with melting ice causing enormous fluctuations in sea level. The final meltdown, shown by the underlying graph, started 21,000 years ago. It was slow for the first 6000 years, rapid from 15000 to 7000 years ago then very slow during the past 7000 years until today. Total sea rise was 400 feet.
Average rise during the rapid 8000 year pulse was slightly over half an inch yearly. This does not sound like much in today’s fast world but it was sufficient to drown out early coral growth with new growth starting about 5000 years ago. Sea rise over the past 7000 years has been about 14 feet, most of which could be from natural causes, some from recent human activities.
Now a few words about coral reefs and Samoa’s coastline. Coral reef usually starts as fringing reef along a shoreline then migrates seawards with rising sea to become a barrier reef enclosing a lagoon. Barrier reefs protect about 60% of Upolu’s shoreline but only 27% of Savaii’s. Elsewhere in Upolu, coastal waters are too deep for coral growth and in Savaii long sections of pre-existing lagoons have been filled with very young lava flows from inland eruptions.
Samoans, since arrival 3000 years ago until today, have preferred to live by the sea, particularly along lagoons - a pleasant setting and an important source of food. Many villages are built on long, flat strips of white coral sand outcropping along most sections of coast protected by reef. It is called Tafagamanu sand after Upolu’s Tafagamanu village and is five to six feet above sea level. This needs explaining. The sand is raised lagoonal detritus and 5000 years or less in age; but present sea level is at its highest since the last glaciation, so how was the sand raised above sea level? The answer is hydro-isostatic rebound.
Hydro-isostatic rebound is attributed to the final glacial meltdown when a 400 foot rise was added to the ocean’s water column. This addition depressed the thin underlying Pacific Plate into the Aesthenosphere, the hot semi-molten to molten uppermost part of the Earth’s Mantle. Magma collected below the islands causing uplift. The fact that the meltdown tapered off 7000 years ago but has lifted much younger lagoonal fill leads to the question ‘is uplift still active?’ Probably yes, but is now being outpaced by rising sea. There are no figures for Savaii but sea rise in Upolu is 3mm yearly.
It might be noted that hydro-isostatic rebound is not restricted to Samoa. Every island located on a thin plate of oceanic basalt has risen. Rising land might temporarily mitigate sea rise now caused by warming climate but if warming is not stopped and sea rise accelerates, all islands and continental coastal areas within the world’s cyclone belts could expect more frequent and more powerful cyclones; and every low-lying coastal settlement worldwide would be vulnerable to sea invasion.
During the writers 34 years in Samoa there have been numerous cyclones ranging in force from category 2 to 5, the most memorable being Ofa and Val of 1990 and 1991 which devastated both Upolu and Savaii and Evan of 2012 which lashed Upolu but caused only minimal damage in Savaii.
Both of the above photographs are of Savaii’s Saleaula lava field. One shows a group of American university students sitting on basalt boulders that were wave-lifted over a 15 foot cliff. This is from the northern part of the field.
The single boulder overhanging the cliff is from the southern part. Basalt is a heavy rock, one cubic metre weighing 3 tons. This huge boulder was estimated to weigh 12 tons. Anyone can walk across the lava field to see the boulders in the north. They are 20 or 30 feet from the cliff edge. But don’t go looking for the block in the south. The underlying cliff has collapsed and it’s back in the sea.
These two photos illustrate the enormous power of the ocean and make one ponder about the fate of villages built on poorly consolidated Tafagamanu sand in the event of another major cyclone. Villages of Savaii’s Falealupo Peninsula were completely washed away during cyclone Ofa.
There are patches of fringing reef around the Falealupo shoreline but no barrier reef. Elsewhere, both islands, there are barrier reefs plus the added protection of basalt blocks placed along the shoreline. But cyclone surge can rise well above reef level and these mostly small blocks could become more of a hazard than a help.
Samoa and most other Pacific Island nations have suffered enormous cyclone damage with loss of life in recent years. The future will be bleak if the ocean keeps warming and rising. Even if today’s efforts to stem rising temperature succeed, cyclones will continue as a major threat; and the problem could continue well into the future until the Earth starts to cool naturally. This may take thousands of years. In the meantime we must contain warming. If temperature rises by a few degrees the present melting of Antarctic and Greenland ice caps will accelerate; and melting Arctic perma-frost will release millions of tons of methane into the atmosphere. This must be stopped. We unwittingly started this crisis in our rush to become industrialised and modern. We now have to remedy the biggest problem ever created by mankind.
To conclude this article let’s compare the past 400’ sea rise and a future hypothetical two foot rise from a historical perspective. Nomadic hunters and gatherers roamed the world during the last glacial meltdown. There were no permanent settlements with the possible exception of the Middle East where the Agricultural Revolution was in its infancy. Rising sea would have had little or no influence on early civilisation and civilisation would have had no impact on climate. The world’s first polluters were the clans that first discovered the art of making fire – they put a smidgen of wood smoke into the atmosphere.
Low sea level throughout most of the Pleistocene opened land passages between Eurasia and North America and between Asia and Australia allowing population to expand into every continent except Antarctica. Oceanic Islands remained uninhabited until much later when navigation became a means of transport.
Now fast forward to year 2100 and assume that we have achieved wonders by converting the world to clean energy, that all land transport has been electrified and all air traffic banned. Also assume that climatic warming and sea rise have been stemmed at levels slightly higher than today. Will that solve our problems? Unfortunately, no.
The damage has already been done and it will take ages for nature to absorb carbon dioxide, the main warming pollutant, out of the atmosphere. And is an emissionless world realistic by 2100? Again, no. Emissions might be reduced but planes, one of the worst polluters, will continue flying. And Samoa? We are a resilient race and will survive but many coastal communities could be relocated inland.
Despite all the past and future conferences to limit humanly induced climatic warming, this writer believes there may be partial success to curb warming but the ultimate solution lies in nature itself.