Misc
Animation: China’s Rapid Transit Boom (1990 – 2020)
After decades of hyper-growth and worsening pollution, China has fully embraced rapid transit as a way to keep cities moving. By 2020, China aims to have 7,000 km (4,300 mi.) of rapid transit lines, more than five times what exists in the U.S. today.
The following animation from Peter Dovak shows this rapid transit revolution playing out by year:
MIND THE GAP
In the above animation, there’s a distinct uptick in the number of projects started after 2004. It was in this year that the government lifted a ban on new metro construction, after worsening congestion and pollution caused the government to rethink their stance. There has been a rapid transit boom in the country ever since.
Soon, minimum population requirements for cities looking to build subway systems will be halved from 3 million to 1.5 million, and this move is expected to set off an even bigger wave of infrastructure investment in cities throughout the country.
RISING RATIOS
Hundreds of kilometers of track are being added each year. As a result of this unparalleled pace of metro construction, China’s ratio of Rapid Transit to Residents (RTR) has risen steeply over the last 15 years.
RTR is a ratio that compares the length of rapid transit lines (measured in kilometers) with the country’s urban population (measured in millions of people). As you can see, China is making great strides in building urban transit networks, though it is still catching up to countries like Germany, which has a RTR of 81.
Chinese cities have a blend of attributes that make constructing metro lines an appealing option: fewer regulatory hurdles, a low cost of labor, and a high-density urban fabric. Also, because transit is treated as an essential public service (i.e. not expected to be profitable), China’s metros provide affordable mobility to its citizens. Even with Beijing’s recent metro fare increase, most rides only cost about ¥3 to ¥8, or $0.45 to $1.45.
Shanghai is now home to the longest metro system by route length, and the Beijing Subway has the highest ridership in the world. Not bad for cities that lacked any substantive transit system until the 1990s.
By 2020, China is expected to have 220+ cities with over a million inhabitants, so as long as the government can continue to provide the resources and funding to expanding transit networks, the building boom will likely continue unabated.
Maps
Mapped: What Did the World Look Like in the Last Ice Age?
A map of the Earth 20,000 years ago, at the peak of the last ice age, when colder temperatures transformed the planet we know so well.

What Did the World Look Like in the Last Ice Age?
What did the world look like during the last ice age? Was it all endless glaciers and frozen ice? The answer is a partial yes—with some interesting caveats.
The Last Glacial Maximum (LGM), colloquially called the last ice age, was a period in Earth’s history that occurred roughly 26,000 to 19,000 years ago.
This map by cartographer Perrin Remonté offers a snapshot of the Earth from that time, using data of past sea levels and glaciers from research published in 2009, 2014, and 2021, alongside modern-day topographical data.
Let’s dive into the differences between the two Earths below.
The Last Ice Age: Low Seas, Exposed Landmasses
During an ice age, sea levels fall as ocean water that evaporates is stored on land on a large scale (ice sheets, ice caps, glaciers) instead of returning to the ocean.
Earth's Ice Cover | 20,000 Years Ago | Today |
---|---|---|
Surface | 8% | 3% |
Land | 25% | 11% |
At the time of the LGM, the climate was cold and dry with temperatures that were 6 °C (11 °F) lower on average. Water levels in the ocean were more than 400 feet below what they are now, exposing large areas of the continental shelf.
In the map above, these areas are represented as the gray, dry land most noticeable in a few big patches in Southeast Asia and between Russia and Alaska. Here are a few examples of regions of dry land from 20,000 years ago that are now under water:
- A “lost continent” called Sundaland, a southeastern extension of Asia which forms the island regions of Indonesia today. Some scholars see a connection with this location and the mythical site of Atlantis, though there are many other theories.
- The Bering land bridge, now a strait, connecting Asia and North America. It is central to the theory explaining how ancient humans crossed between the two continents.
- Another land bridge connected the island of Great Britain with the rest of continental Europe. The island of Ireland is in turn connected to Great Britain by a giant ice sheet.
- In Japan, the low water level made the Sea of Japan a lake, and a land bridge connected the region to the Asian mainland. The Yellow Sea—famous as a modern-day fishing location—was completely dry.
The cold temperatures also caused the polar parts of continents to be covered by massive ice sheets, with glaciers forming in mountainous areas.
Flora and Fauna in the Last Ice Age
The dry climate during the last ice age brought about the expansion of deserts and the disappearance of rivers, but some areas saw increased precipitation from falling temperatures.
Most of Canada and Northern Europe was covered with large ice sheets. The U.S. was a mix of ice sheets, alpine deserts, snow forests, semi-arid scrubland and temperate grasslands. Areas that are deserts today—like the Mojave—were filled with lakes. The Great Salt Lake in Utah is a remnant from this time.
Africa had a mix of grasslands in its southern half and deserts in the north—the Sahara Desert existed then as well—and Asia was a mix of tropical deserts in the west, alpine deserts in China, and grasslands in the Indian subcontinent.
Several large animals like the woolly mammoth, the mastodon, the giant beaver, and the saber-toothed tiger roamed the world in extremely harsh conditions, but sadly all are extinct today.
However, not all megafauna from the LGM disappeared forever; many species are still alive, including the Bactrian camel, the tapir, the musk ox, and the white rhinoceros—though the latter is now an endangered species.
Will There Be Another Ice Age?
In a technical sense, we’re still in an “ice age” called the Quaternary Glaciation, which began about 2.6 million years ago. That’s because a permanent ice sheet has existed for the entire time, the Antarctic, which makes geologists call this entire period an ice age.
We are currently in a relatively warmer part of that ice age, described as an interglacial period, which began 11,700 years ago. This geological epoch is known as the Holocene.
Over billions of years, the Earth has experienced numerous glacial and interglacial periods and has had five major ice ages:
Major Ice Ages | Name | Time Period (Years Ago) |
---|---|---|
1 | Huronian Glaciation | 2.4 billion - 2.1 billion |
2 | Cryogenian Glaciation | 720 million - 635 million |
3 | Andean-Saharan Glaciation | 450 million - 420 million |
4 | Late Paleozoic ice age | 335 million - 260 million |
5 | Quaternary Glaciation | 2.6 million - present |
It is predicted that temperatures will fall again in a few thousand years, leading to expansion of ice sheets. However there are a dizzying array of factors that are still not understood well enough to say comprehensively what causes (or ends) ice ages.
A popular explanation says the degree of the Earth’s axial tilt, its wobble, and its orbital shape, are the main factors heralding the start and end of this phenomenon.
The variations in all three lead to a change in how much prolonged sunlight parts of the world receive, which in turn can cause the creation or melting of ice sheets. But these take thousands of years to coincide and cause a significant change in climate.
Furthermore, current industrial activities have warmed the climate considerably and may in fact delay the next ice age by 50,000-100,000 years.
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