What causes ice ages – and when is the next one?

What remains of the ice age: Antarctica. Image: Getty.

Over the last 2.5m years the Earth has undergone more than 50 major ice ages, each having a profound effect on our planet’s climate. But what causes them and how do we predict when the next big ice age will hit?

About 40 years ago, scientists realised that ice ages were driven by changes in the Earth’s orbit. But, as I recently argued in Nature, it’s not that simple. Scientists are still trying to understand how such wobbles interact with the climate system, particularly greenhouse gases, to push the planet in to or out of an ice age.

During the last ice age, only 21,000 years ago, there was nearly continuous ice across North America from the Pacific to the Atlantic Ocean. At its deepest over the Hudson Bay, it was over two miles thick and reached as far south as what would now be New York and Cincinnati. In Europe, there were two major ice sheets: the British ice sheet, which reached as far south as what would now be Norfolk, and the Scandinavian ice sheet that extended all the way from Norway to the Ural mountains in Russia.

In the Southern Hemisphere there were significant ice sheets on Patagonia, South Africa, southern Australia and New Zealand. So much water was locked up in these ice sheets that the global sea level dropped by over 125 metres – around ten metres lower than the height of the London Eye. In comparison if all the ice on Antarctica and Greenland melted today it would only raise sea level by 70 metres.

So what caused these great ice ages? In 1941, Milutin Milankovitch suggested that wobbles in the Earth’s orbit changed the distribution of solar energy on the planet’s surface, driving the ice age cycles. He believed that the amount of incoming solar radiation (insolation) just south of the Arctic Circle, at a latitude of 65°N, was essential. Here, insolation can vary by as much as 25 per cent. When there was less insolation during the summer months, the average temperature would be slightly lower and some of the ice in this region could survive and build up – eventually producing an ice sheet.

But it wasn’t until 30 years later that three scientists used long-term climate records from analysing marine sediments to put this to the test. Jim Hays used fossil assemblages to estimate past sea surface temperatures. Nick Shackleton calculated changes in past global ice volume by measuring oxygen isotopes (atoms with different numbers of neutrons in the nuclues) in calcium carbon fossil in marine sediments. John Imbrie used time-series analysis to statistically compare the timing and cycles in the sea surface temperature and global ice volume records with patterns of the Earth’s orbit.

In December 1976 they published a landmark climate paper in Science, showing that climate records contained the same cycles as the three parameters that vary the Earth’s orbit: eccentricity, obliquity and precession (shown in Figure 1). Eccentricity describes the shape of the Earth’s orbit around the sun, varying from nearly a circle to an ellipse with a period of about 96,000 years. Obliquity is the tilt of the Earth’s axis of rotation with respect to the plane of its orbit, which changes with a period of about 41,000 years. Precession refers to the fact that both Earth’s rotational axis and orbital path precess (rotate) over time – the combined effects of these two components and the eccentricity produce an approximately 21,000-year cycle.

Image: author provided.

The researchers also found that these parameters have different effects at different places on our globe. Obliquity has a strong influence at high latitudes, whereas precession has a notable impact on tropical seasons. For example precession has been linked to the rise and fall of the African rift valley lakes and so may have even influenced the evolution of our ancestors. Evidence for such “orbital forcing” of climate has now been found as far back as 1.4bn years ago.


Beyond wobbles

However, the scientists realised that there were limitations and challenges of their research – many of which remain today. In particular, they recognised that variations in the Earth’s orbit did not cause the ice age cycles per se – they rather paced them. A certain orbit of the Earth can be associated with many different climates. The one we have today is in fact similar to the one we had during the most intense part of the last ice age.

Small changes in insolation driven by changes in the Earth’s orbit can push the planet into or out of an ice age through the planet’s “climate feedback” mechanisms. For example when summer solar radiation in reduced it allows some ice to remain after the winter. This white ice reflects more sunlight, which cools the area further and allows more ice to build up, which reflects even more sunlight and so forth. Therefore, the researchers’ next step was to understand the relative importance of ice sheet, ocean and atmospheric feedbacks. They discovered that greenhouse gases had an important role in controlling climate. In particular atmospheric carbon dioxide had to be low enough for the planet to start cooling before it could tip into an ice age.

So how can all this help us understand future climate? One idea is that small increases in greenhouse gases due to the expansion of agriculture that started 8,000 years ago have in fact delayed the next ice age. What’s more, if we continue emitting greenhouse gases at the same rate, we might have put off the next ice age for at least 500,000 years.

If we have merely delayed the next ice age, we will still be in the Quaternary Period – the last 2.58m years defined by the ice age cycles. But if we have stopped the ice ages, humans will have caused a much greater change and so have entered the Anthropocene period as some argue. If I had to put money on it, I’d say the Earth has experienced its last ice age for a very, very long time.The Conversation

Mark Maslin is professor of palaeoclimatology at UCL.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

A nation that doesn’t officially exist: on Somaliland’s campaign to build a national library in Hargeisa

The Somaliland National Library, Hargeisa. Image: Ahmed Elmi.

For seven years now, there’s been a fundraising campaign underway to build a new national library in a nation that doesn’t officially exist. 

Since 2010, the Somali diaspora have been sending money, to pay for construction of the new building in the capital, Hargeisa. In a video promoting the project, the British journalist Rageeh Omar, who was born in Mogadishu to a Hargeisa family, said it would be... 

“...one of the most important institutions and reference points for all Somalilanders. I hope it sets a benchmark in terms of when a country decides to do something for itself, for the greater good, for learning and for progress – that anything can be achieved.”

Now the first storey of the Somaliland National Library is largely complete. The next step is to fill it with books. The diaspora has been sending those, too.

****

Some background is necessary here to explain the “country that doesn’t exist” part. During the Scramble for Africa of the 1880s, at the height of European imperialism, several different empires established protectorates in the Somali territories on the Horn of Africa. In 1883, the French took the port of Djibouti; the following year, the British grabbed the north coast, which looks out onto the Gulf of Aden. Five years after that, the Italians took the east coast, which faces the Indian Ocean.

And, excepting some uproar during World War II, so things remained for the next 70 years or so.

The Somali territories in 1890. Image: Ingoman/Wikimedia Commons.

When the winds of change arrived in 1960, the British and Italian portions agreed to unite as the Somali Republic: a hair-pin shaped territory, hugging the coast and surrounding Ethiopia on two sides. But British Somaliland gained its independence first: for just five days, at the end of June 1960, it was effectively an independent country. This will become important later.

(In case you are wondering what happened to the French bit, it voted to remain with France in a distinctly dodgy referendum. It later became independent as Djibouti in 1977.)

The new country, informally known as Somalia, had a difficult history: nine years of democracy ended in a coup, and were followed by the 22 year military dictatorship under the presidency of General Siad Barre. In 1991, under pressure from rebel groups including the Hargeisa-based Somali National Movement (SNM), Barre fled, and his government finally collapsed. So, in effect, did the country.

For one thing, it split in two, along the old colonial boundaries: the local authorities in the British portion, backed by the SNM, made a unilateral declaration of independence. In the formerly Italian south, though, things collapsed in a rather more literal sense: the territory centred on Mogadishu was devastated by the Somali civil war, which has killed around 500,000, displaced more than twice that, and is still officially going on.

Somalia (blue) and Somaliland (yellow) in 2016. Image: Nicolay Sidorov/Wikimedia Commons.

The north, meanwhile, got off relatively lightly: today it’s the democratic and moderately prosperous Republic of Somaliland. It claims to be the successor to the independent state of Somaliland, which existed for those five days in June 1960.

This hasn’t persuaded anybody, though, and today it’s the only de facto sovereign state that has never been recognised by a single UN member. Reading about it, one gets the distinct sense that this is because it’s basically doing okay, so its lack of diplomatic recognition has never risen up anyone’s priority list.

Neither has its library.

****
Rageeh Omar described the site of the new library in his fundraising video. It occupies 6,000m2 in the middle of Hargeisa, two minutes from the city’s main hospital, 10 from the presidential palace. In one sequence he stands on the half-completed building’s roof and points out the neighbours: the city’s main high street, with the country’s largest shopping mall; the Ministry of Telecoms that lies right next door.

This spiel, in a video produced by the project’s promoters, suggests something about the new library: that part of its job is to be another in this list of landmarks, more evidence that Hargeisa, a city of 1.5m, should be recognised as the proper capital of a real country.

But it isn’t just that: the description of the library’s function, in the government’s Strategic Plan 2013-2023, makes clear it’s also meant to be a real educational facility. NGOS, the report notes, have focused their resources on primary schools first, secondary schools second and other educational facilities not at all. (This makes sense, given that they want most bang for their buck.)

And so, the new building will provide “the normal functions of public library, but also... additional services that are intentionally aimed at solving the unique education problems of a post conflict society”. It’ll provide books for a network of library trucks, providing “book services” to the regions outside Hargeisa, and a “book dispersal and exchange system”, to provide books for schools and other educational facilities. There’ll even be a “Camel Library Caravan that will specifically aim at accessing the nomadic pastoralists in remote areas”.

All this, it’s hoped, will raise literacy levels, in English as well as the local languages of Arabic and Somali, and so boost the economy too.

As described. Image courtesy of Nimko Ali.

Ahmed Elmi, the London-based Somali who’s founder and director of the library campaign, says that the Somaliland government has invested $192,000 in the library. A further $97,000 came from individual and business donors in both Hargeisa and in the disaspora. “We had higher ambitions,” Elmi tells me, “but we had to humble our approach, since the last three years the country has been suffering from a large drought.”

Now the scheme is moving to its second phase: books, computers and printers, plus landscaping the gardens. This will cost another $175,000. “We are also open to donations of books, furniture and technology,” Emli says. “Or even someone with technical expertise who can help up set-up the librarian system instead of a contemporary donation of a cash sum.” The Czech government, in fact, has helped with the latter: it’s not offered financial support, but has offered to spend four weeks training two librarians.  

Inside the library.

On internet forums frequented by the Somali diaspora, a number of people have left comments about the best way to do this. One said he’d “donated all my old science and maths schoolbooks last year”. And then there’s this:

“At least 16 thousand landers get back to home every year, if everyone bring one book our children will have plenty of books to read. But we should make sure to not bring useless books such celebrity biography books or romantic novels. the kids should have plenty of science,maths and vocational books.”

Which is good advice for all of us, really.


Perhaps the pithiest description of the project comes from its Facebook page: “Africa always suffers food shortage, diseases, civil wars, corruption etc. – but the Somaliland people need a modern library to build a better place for the generations to come.”

The building doesn’t look like much: a squat concrete block, one storey-high. But there’s something about the idea of a country coming together like this to build something that’s rather moving. Books are better than sovereignty anyway.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

Want more of this stuff? Follow CityMetric on Twitter or Facebook.