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.

 
 
 
 

To see how a city embraces remote work, just look to Helsinki

A deeply rooted culture of trust is crucial to the success of remote work. (Sean Gallup/Getty Images)

When I speak to Anssi Salminen, an account manager who lives an hour outside Helsinki, he’s working from a wooden platform on the edge of a Finnish lake. With a blanket laid out and his laptop set up, the sun low in the sky, Anssi’s remote work arrangement seems blissful. 

“I spend around half of my time working somewhere else other than the office,” he says. “I can work from home, or on the go, and I also travel to the Netherlands once a month and work from there.

“The emphasis in my work has always been that it doesn’t matter when or where I work, as long as I get things done.”

For many people around the world, the shift to remote work was sudden, sparked by the coronavirus pandemic. Finland, however, is finding the transition much less significant. Before Covid-19, the Nordic nation already displayed impressive levels of remote working, with 14.1% of its workforce reporting usually working from home. Only the Netherlands has a comparable percentage of remote workers, while the UK lagged behind at 4.7%, and the US’s remote workforce lingered at around 3.6%

Anssi works for one of many Helsinki-based companies that offers its employees flexible policies around when and where they work. That arrangement is in part due to the Finnish capital’s thriving start-up scene. In spite of being a relatively small city by global standards it is home to over 500 technology start-ups. These companies are leading the way when it comes to keeping employees connected wherever they choose to work.

“Our company has a completely location-free working policy,” says Kasper Pöyry, the CEO of Helsinki-headquartered software company Gapps. “All meetings are made available for online participants and facilitated accordingly. Some employees have worked extensively from abroad on a working holiday, whilst others prefer the comfort and social aspects of the well-stocked office. Whatever works for our employees is what works for the company.”

Like Gapps, many Helsinki-based firms are deeply preoccupied with providing the necessary technology to attract talent in a vast and sparsely populated country. Finland has only 15 inhabitants per square kilometre, and companies understand that in order to compose teams of specialised expertise, they may have to seek talent outside of the city. Local governments take a similarly proactive stance toward technological access, and Helsinki offers free, unrestricted, high-speed Wi-Fi from city-wide hotspots, while the country as a whole boasts some of the best coverage in Europe. 

But encouraging remote work isn’t just about optimising the potential of Finland’s workforce – companies in Helsinki also recognise that flexibility has clear benefits for both staff and employees. 

“The idea of a good work-life balance is ingrained in Finnish culture,” says Johannes Anttila, a consultant at organisational think tank Demos Helsinki. “It goes back to our rich history of social dialogue between labour unions and employers, but also to an interest in delineating the rules of working life and pushing towards people being able to enjoy their private life. Helsinki has been named the best city in the world for work-life balance, and I think that this underlies a lot of the mentality around remote work.” 

For Peter Seenan, the extent to which Helsinki residents value their free time and prioritise a work-life balance prompted his move to the city ten years ago. He now works for Finnair, and points to Finland’s summer cottages as an example of how important taking time to switch off is for people in the country. These rural residences, where city residents regularly uproot to enjoy the Nordic countryside, are so embedded in Finnish life that the country boasts around 1.8 million of them for its 5.5 million residents

“Flexible and remote work are very important to me because it means that I don’t feel like I’m getting stuck in a routine that I can’t control easily,” he says. “When I’m working outside of the office I’ll go down to my local sauna and go ice swimming during the working day, typically at lunchtime or mid-morning, and I’ll feel rejuvenated afterwards… In winter time especially, flexibility is important because it makes it easier to go outside during daylight hours. It’s certainly beneficial for my physical and mental health, and as a result my productivity improves.”

The relaxed attitude to working location seems to pay off – Finland is regularly named the happiest country in the world, scoring highly on measures such as how often its residents exercise and how much leisure time they enjoy. With large swathes of unspoiled countryside and a national obsession with the outdoors, sustainability is at the forefront of its inhabitants’ minds, leading to high levels of support for measures to limit commuting. In January, Finland passed a new Working Hours Act, the goal of which was to help better coordinate employee’s work and leisure time. Central to this is cementing in law that employees can independently decide how, when, and where they work.

Yet enacting the new ruling is not as simple as just sending employees home with their laptops. For Kirsimarja Blomqvist, a professor of knowledge management at LUT University, perhaps the most fundamental feature that remote work relies upon is a deeply rooted culture of trust, which Helsinki’s residents speak of with pride. The anecdotal evidence is backed up by data which suggests that Finland boasts one of the highest levels of trust and social cohesion in Europe, and equality and transparency have always been key cornerstones of political thought in the country.

“Trust is part of a national culture in Finland – it’s important and people value it highly,” she explains. “There’s good job independence, and people are valued in terms of what they do, not how many hours they work for. Organisations tend to be non-hierarchical, and there is a rich history of cooperation between trade unions, employers, and employees to set up innovative working practices and make workers feel trusted and valued. 

“It’s now important that we ensure that this trust can continue to be built over technology, when workers might have been more used to building it face-to-face.”

As companies begin to look hopefully toward a post-Covid future, the complexities of remote work are apparent. Yet amid issues of privacy, presenteeism, and social isolation, the Helsinki model demonstrates the potential benefits of a distanced working world. The adjustment to remote work, if continued after the crisis, offers a chance to improve companies’ geographical diversity and for employers to demonstrate trust in their workforce. On these issues, Blomqvist believes other cities and employers can learn a lot from Helsinki.

“People are now beginning to return to their workplaces, but even as they do they are starting to consider the crisis as a jumping point to an even more remote future,” she says. “The coronavirus pandemic has been an eye-opener, and people are now interested in learning from Finland’s good practices… We are able to see the opportunity, and the rapid transition to remote work will allow other countries to do the same.”