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.


“This is a civic pride for the digital age”: why we should why we should willingly let City Hall have our data

He was the future once: David Cameron discusses smart cities with Angela Merkel and a German technology executive. Image: Getty.

Victorian England. From the shadows of wealth grew poverty. Slums slumped against symbols of civic pride, cowering next to towering town halls funded through rich merchant princes, whose elitist rule was insufficient to deal with too many people in too few houses with too little infrastructure.

Enter municipality. With darkness came electric light; with disease came tunnels to disperse their cause; with time came reform, regulation and the rise of town planning.

It’s over a century since those places which first industrialised became those first urbanised; yet even the wealthiest cities in the world continue to struggle with the complexities of urbanisation. In London, ten thousand die each year from pollution; in New York, six times this amount reside in homeless shelters.On the rush-hour roads of Sydney, cars stand still, and in the ‘burbs or banlieues of Paris slums still stand.

An umbrella bought during a downpour costs more than one bough under blue sky – and the truth is that, for too, long city halls have failed to forecast and so incurred greater costs. It’s a reactive culture summed up by words first head in Jimmy Carter’s budget office: if it ain’t broke, don’t fix it. Disease before sewer, gridlock before investment, collapse before rebuild – visible fix over unseen prevention

But with the world’s urban population growing by 65m every year, this has to change: there is not enough resource to manage cities reactively. Enter technology and the move to smart cities.

From Barcelona to New YorkOxford to Amsterdam, Singapore to Seoul: billions of low-cost devices are being installed into everyday objects to send and receive data: street lights recording pollution, and bridges reporting performance; traffic lights that count, and whose analysis will be counted upon, to ease traffic congestion; health wristbands understanding our heart’s needs, shop ceilings noting our heart’s desires. A web of information woven into the very fabric of cities which, when added to data from sources like mobile phones, is providing a living-breathing picture of how we and our cities operate.

This data is no longer retrospective or historic but live and dynamic. It is of such quantity, and can be analysed at such granular detail, that it can provide certainty where once there was only supposition. It is build-up before the gridlock, illness before epidemic; the crack of an ageing bridge, the first signs of smog. It is diagnostic to preventative. Umbrella under blue sky.

Those promoting the “internet of things”, estimated to be worth $11.1trn a year by 2025, will declare it a panacea – but it is not, at least not entirely. Sure, challenges regarding data quality, privacy, standardisation, and security will be overcome; 4G will become 5G will become 6G. Devices will communicate intelligently with each other – autonomous vehicle to autonomous vehicle, autonomous vehicle to bridge, drone to home. Data will become as fundamental to cities as infrastructure, and will be referred to as such.

Yet city halls in democracies, whilst infinitely better informed, will continue to make their decisions which are restricted by commercialism, framed by political ideology, and driven by short-term electoral or media pressures.

People first

From the mid-sixties to the start of this century a UK television programme called Tomorrow’s World showcased future living. For every correct prediction (mobile phones) came countless incorrect ones: the floating-bicycle, say, or paper underwear. My point is that only a small part of understanding the future of cities is about understanding technology. The majority is about understanding people and society, the people from whom the very word “city” is derived: civitas, the collective of citizens.

Gutenberg did not change the world by inventing the printing press in the 13th century – but he did enable the world to change. The technology was the printing press, the outputs were books filled with knowledge, the outcomes were the actions of the many who used that knowledge. Technology is a tool, a process towards an outcome. 

In much the same way, the Internet of Things will not change the world – but it will enable the world to change. Sensors are the technology, data the outputs, the analysis of this data and subsequent decisions, the outcome.

It is crucial to avoid the Tomorrow’s World approach. That is, racing to implement technology first without consideration of identified social, economic or environmental needs; introducing more complexity when most citizens seek simplicity. As the writer and urbanist Jane Jacobs once said:“First comes the image of what we want, then the machinery is adapted to turn out that image.”

Start with people. Form the image. Think of technology through the Greek origins of the word, techne and logos – a discourse about the way things are gained – and capitalise on collective intelligence to move towards that image.

Since cities first started to appear some millennia ago, they’ve provided incontrovertible evidence that the wisdom of crowds is far greater than the individual; that collective intelligence gained from that trinity of city institutions – citizen, government, industry – surpasses what can be achieved by any one in isolation. Where would Apple, Uber, or Google be without the government-backed inventions like the world-wide-web, touchscreen technology, WiFi or global positioning systems?

A new civic pride

Of course, an app on a smart phone that can ask a thousand questions is meaningless if nobody feels motivated to answer. Increasing urbanisation brings increasing interdependency: lives intrinsically linked, services shared. The challenge for city halls is to turn the increase in what people have in common, into an increase in common purpose, through understanding the three benefits that motivate and lead to action.

Extrinsic benefits, of status and reward, caused merchant princes to fund city halls in Victorian England: such benefits today see the ambitious putting in extra hours. Intrinsic benefits, like competitiveness or fun, that once caused business tycoons to compete to build the tallest skyscrapers, now explain why “hackathons” and “city challenges” are such a success. Then there are the pro-social benefits of altruism or benevolence, that cause millions to volunteer their time to give back and feel part of something bigger than themselves.

These motivations are of greater significance, because there are no longer people with clipboards standing on street corners asking permission to collate our views on services: it is happening automatically through the Internet of Things. Our choices online, movements offline; the travel we take, the pollution we make; our actions and interactions. We are data.

City halls can take a click-box-small-print approach to this, like so many apps. But there is opportunity to do the opposite. They can promote the fact that citizens can knowingly provide their data towards making lives better; visualise and enable citizens to see and understand their input, alongside data provided by others.

They can incentivise interaction with data, so that entrepreneurs can work back from outcomes, solve challenges, and re-localise where appropriate (we should not need a multinational to get a taxi). They can be proudly open, enabling citizens, industry and government to receive pro-social benefit by contributing to something bigger than themselves: their life and the lives of others.

This is a civic pride for the digital age. Not just localism or patriotism based on geography but the strength of connection between people and their ability to direct and determine change through data. Not just pride in the buildings and infrastructure that form our physical world, but in the quality of data that will shape our future world and move us from a diagnostic to preventative society – umbrellas under blue sky.

We should take pride in technology, yes; but that should come second to the pride in those who, enabled by that technology, drive progress. Who, through the wisdom of crowds, form an image of the future and strengthen democracy by motivating society to move towards it. Who embrace openness and help overcome the challenges of urbanisation.

Kevin Keith is a writer, researcher, urbanist, and director of the southern hemisphere’s largest open data competition, GovHack. He tweets as@KevKeith.

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