by Alok Jha
* * *
GLOBAL CROP YIELDS
Would fall by 10–25% after gulf stream shutdown
* * *
In the US, the cold, windy weather would make it more difficult to grow food. In China, the normally reliable monsoon rains would regularly fail, leading to widespread famine.
* * *
Nations with the resources to do so may build virtual fortresses around their countries, preserving resources for themselves. Less fortunate nations, especially those with ancient enmities with their neighbors, may initiate struggles for access to food, clean water, or energy.
* * *
“The changing weather patterns and ocean temperatures affect agriculture, fish and wildlife, water and energy. Crop yields, affected by temperature and water stress as well as length of growing season, fall by 10–25% and are less predictable as key regions shift from a warming to a cooling trend. As some agricultural pests die due to temperature changes, other species spread more readily due to the dryness and windiness—requiring alternative pesticides or treatment regiments. Commercial fishermen that typically have rights to fish in specific areas will be ill equipped for the massive migration of their prey,” continue Schwartz and Randall.
“With only five or six key grain-growing regions in the world (US, Australia, Argentina, Russia, China, and India), there is insufficient surplus in global food supplies to offset severe weather conditions in a few regions at the same time—let alone four or five. The world’s economic interdependence makes the United States increasingly vulnerable to the economic disruption created by local weather shifts in key agricultural and high population areas around the world. Catastrophic shortages of water and energy supply—both of which are stressed around the globe today—cannot be quickly overcome.”
Is it likely?
“The fate of the thermohaline circulation will be decided by Greenland,” the climate scientist Stefan Rahmstorf told Nature. “If that goes quickly it will be bad news for the deep-water formation. But if Greenland is stable, the risk of shutting down the circulation completely is very small.”
In a 2002 paper, scientists found that fresh water had been entering the North Atlantic for the past 40 years, and at an increased rate in the past decade. Since the mid-1960s, they discovered, the seas feeding the North Atlantic had steadily become less salty.
Will this result in a slowdown or a stop to the conveyor belt? “The short answer is: We do not know. Nor have scientists determined the relative contributions of a variety of sources that may be adding fresh water to the North Atlantic. Among the suspects are melting glaciers or Arctic sea ice, or increased precipitation falling directly into the ocean or entering via the great rivers that discharge into the Arctic Ocean. Global warming may be an exacerbating factor,” says Gagosian.
Abrupt regional cooling, he adds, and gradual global warming can unfold simultaneously. “Indeed, greenhouse warming is a destabilizing factor that makes abrupt climate change more probable. A 2002 report by the US National Academy of Sciences said, ‘available evidence suggests that abrupt climate changes are not only possible but likely in the future, potentially with large impacts on ecosystems and societies’.”
Snowball Earth
* * *
Our world was once covered in ice. This was not just any old ice age, but something far more severe: glaciers stretched down from the poles to the equator, and the entire surface of the ocean was solid. Our planet, 700 million years ago, was a cosmic snowball hurtling through space.
* * *
Overhead, the sky bore only the faintest wisps of cloud—frozen carbon dioxide crystals rather than water, which had stopped circulating around the world due to the freezing temperatures.
For the life forms that had been developing at this time, “Snowball Earth” was a disaster. Until then, our planet had been just warm enough, with exactly the right chemical conditions. Multicellular life forms were beginning to emerge, and mitochondria, tiny powerhouses that sit inside our body cells and turn our food into usable energy, had started to develop symbiotic relationships with the simple organisms that would one day evolve into the animals and plants we see today.
In a flash, all of it was gone. Nothing living on or near the surface survived. If the -50°C temperatures did not stop life flourishing, the lack of liquid water would have been a problem. Only the most primitive of life forms—some algae and bacteria—had any chance under the kilometer-thick ice covering, congregating around the hydrothermal vents and the relatively warm water around undersea volcanoes.
Snowball Earth devastated life millions of years ago; if a similar scenario appeared today, it would have far worse effects. Imagine our cities trapped under glaciers, all our infrastructure destroyed or useless, and access to water severely limited. Ice would cover the fields we use to grow crops, our sources of energy would be compromised, and billions of people would die of cold and hunger. For the Earth, it would be just a blip in its climate before some future return to warmer conditions. But that blip would spell the end of our civilization.
The Snowball Earth hypothesis
There have been many ice ages in the Earth’s past, when the overall temperature dropped and large parts of the world were covered in ice. But in the past few decades, scientists have uncovered evidence of a far more extreme version of the freeze, one that puts all other known ice ages into the shade.
The first of these extreme glaciations is thought to have happened around 2.2 billion years ago, when the planet was half its current age. Another series of extreme freezes began around 700 million years ago and ended more than 130 million years later, at the end of the Proterozoic Eon.
At the time of the last Snowball Earth, our planet looked very different from the way it does today. The supercontinent Rodinia had just broken up into a set of land masses that were clustered around the Equator, and the Sun was giving out around six percent less light.
The ice started to grow because the Earth’s natural greenhouse effect failed. Because of their molecular structure, greenhouse gases in the atmosphere absorb some wavelengths of high-energy electromagnetic radiation coming from the Sun, but allow others (mainly visible light) to pass through. They also trap some of the heat that is radiated toward space from the surface of the Earth, making the surface warmer than it would be if there was no atmosphere.
The key greenhouse gas is carbon dioxide. Today we worry about rising levels of CO2, and its potential to cause a gradual warming of the Earth’s climate. Scientists think that the drop in global temperatures before the last Snowball Earth was partly due to a large-scale removal of CO2 from the atmosphere.
* * *
The thaw takes only a few hundred years, but a new problem arises in the meantime: a brutal greenhouse effect. Any creatures that survived the icehouse must now endure a hothouse.
* * *
They explain it like this: areas that had been previously landlocked in Rodinia were now closer to oceans and moisture, thanks to the break-up of the supercontinent. This created more rainfall, which pushed up a natural process called silicate weathering, where rainwater absorbs CO2 from the air to create carbonic acid, which then disintegrates rocks over geological timescales to create soil. As rain increased, more CO2 was absorbed from the air and more rock was slowly dissolved.
Several million years of excessive rain meant that CO2 levels became low enough to compromise the greenhouse effect. The Earth began to freeze. Ice sheets started to stretch out from the poles, and the runaway drop in temperature was exacerbated by the bright white surfaces of the glaciers, which reflected away more of the Sun’s incoming rays than the darker land or water underneath. With less greenhouse gas in the atmosphere to trap that reflected radiation, the energy simply disappeared back into space and was unavailable to keep the Earth warm.
When ice formed at latitudes lower than around 30° north, the fraction of light being reflected back into space rose at an ever faster rate because direct sunlight was striking
a larger surface area of ice per degree of latitude. “The feedback became so strong in this simulation that surface temperatures plummeted and the entire planet froze over,” say Paul Hoffman and Daniel Schrag, geologists at Harvard University and experts in the evolution and impact of Snowball Earth. For the next 30 million years, the perfect storm of bright white glaciers and lack of greenhouse effect continued to keep temperatures on the surface down to—50°C at the poles and—30°C at the tropics.
After the ice
The extreme conditions of Snowball Earth were described in 1992 by Joe Kirschvink, a specialist in paleomagnetism at the California Institute of Technology, though scientists did not rush to support him at the time. It seemed unthinkable to them that the Earth’s climate would allow glaciers to develop at the tropics, and if the process was self-reinforcing, how would it ever end? Why is the Earth not still a snowball today?
Kirschvink answered the second question by pointing out that the Earth’s shifting tectonic plates would continue to build volcanoes and to pump CO2 into the air. At the same time, since the world was covered in ice, the normal chemical cycles that removed the CO2 from the atmosphere (namely, rain) would have stopped.
All of this would mean that the CO2 would start to accumulate during the millions of years of freeze, and at the point when the levels of the gas had increased 1,000-fold, the greenhouse effect would return to melt the ice. “The thaw takes only a few hundred years, but a new problem arises in the meantime: a brutal greenhouse effect,” say Hoffman and Schrag. “Any creatures that survived the icehouse must now endure a hothouse. As improbable as it may sound, we see clear evidence that this striking climate reversal—the most extreme imaginable on this planet—happened as many as four times between 750 million and 580 million years ago.”
As the tropical oceans thawed after the last Snowball Earth, the water would have evaporated and, together with CO2, made the Earth’s greenhouse effect even more intense. Temperatures at the equator would have reached 50°C and rainfall would have been incessant. The hot seas would have supported powerful hurricanes.
* * *
Extreme freezing might well have killed almost all life on Earth, but it also created the conditions for the diversity of living things we see around us today.
* * *
After millions of years in deep freeze, the Earth would have woken up, and as it got back to a normal climate, conditions became perfect for a boom in life, culminating in the so-called Cambrian explosion between 575 and 525 million years ago, when there was a huge upsurge in the number of life forms on Earth.
How did it affect life?
The snowball itself killed almost everything. But the evidence in the geological record shows that once the last extreme freeze had thawed out, the first multicellular animals appeared. How did such an extreme event kick-start the evolution of life on Earth?
Geologists think that the explosion happened because once the snowball was gone, any organism that had clung on to life for the millions of years of the freeze was suddenly presented with vast empty environments in which to expand. As the glaciers advanced during the freeze, they carried the land’s topmost layer of minerals and nutrients (from the soil and rocks) with them. Millions of years later, as the snowball melted and the glaciers retreated, these minerals and nutrients were released back into the oceans, feeding ever-larger numbers of oxygen-producing algae, which in turn created the atmospheric conditions needed for the evolution of animals.
Extreme freezing might well have killed almost all life on Earth, but it also created the conditions for the diversity of living things we see around us today.
Could it happen again?
Today, the world’s continents are spread more evenly around the planet, so there is less chance of the intense evaporation and rainfall needed to clean the air of CO2. In addition, our Sun is shining far brighter and hotter than it was at the start of the last Snowball Earth.
But Hoffman and Schrag say that we should be wary of the planet’s capacity for extreme change. “For the past million years, the earth has been in its coldest state since animals first appeared, but even the greatest advance of glaciers 20,000 years ago was far from the critical threshold needed to plunge the earth into a snowball state.”
We are more than 80,000 years from the peak of the next ice age, but the geologists say it is difficult to predict where the Earth’s climate will drift over millions of years. “If the trend of the past million years continues and if the polar continental safety switch were to fail, we may once again experience a global ice catastrophe that would inevitably jolt life in some new direction.”
Chemical Pollution
* * *
In some ways, it sounds like the start of an apocalypse already: female pseudo-hermaphrodite polar bears with penis-like stumps; panthers with atrophied testicles; male trout and roach with eggs growing in their testes. This is not the line-up for some macabre circus, but the end of a long chain of events that starts with the materials that build modern society.
* * *
The way we grow our food, make the clothes we wear, build and maintain our cities—all of it is poisoning our planet.
Pesticides, radioactive waste, heavy metals, exhaust gases and excess fertilizers are just a few of the copious toxic chemicals that we dump into our rivers, oceans and air. The sheer size of the Earth has allowed us to turn a blind eye to the effects of all this pollution—clouds of gas dissipate into the atmosphere, effluent and industrial sludge blends into rivers, and pesticides leach away into the ground after they have done their job.
Luckily for us (and the planet), most of the things we dump will become diluted beyond danger, while others will degrade naturally into harmless substances. But many toxic chemicals do persist, and they get into the food chain and sources of drinking water. They enter plants, which are eaten by animals, and all the while the chemicals become more concentrated. At some point, plants, fish and birds start dying and ecosystems will begin to collapse. Humans have less to eat and the food we do have will damage our DNA and make us sick. It might be a slow poison, but it is one that can wreak catastrophic effects on life.
What do we put into the Earth?
We treat the world like a dustbin. We fill our city air with the fumes of cars and lorries. Smoke from industrial plants throws out heavy metals and particulates that travel the world thanks to powerful air currents. Our farms use fertilizers and pesticides with abandon, most of which end up soaking into the ground or getting washed into rivers, damaging the balance of life.
All of this is the flip side to a remarkable rise in our standard of living. Humans have designed and manufactured a staggering number of artificial chemicals to help us live our lives—between 1930 and 2000, the annual production of man-made chemicals increased from 1 million to 400 million tons a year. In the past few decades alone, we have invented some 80,000 new chemicals, and although we may encounter them every day, they are mostly invisible.
Take bisphenol A, a suspected hormone mimic: 700,000 tons of this is produced every year in the European Union alone, and used for everything from cleaning metals to producing babies’ bottles. We apply other chemicals to our skin every day—phthalates and parabenes in cosmetic creams, for example. Yet more are in the objects around us, such as brominated flame retardants on our sofas. Once we have made use of them, all these chemicals will eventually find their way into the wider environment.
* * *
ARTIFICIAL CHEMICAL PRODUCTION
1930: 1 million tons
2000: 4,000 million tons
* * *
Their environmental impact pales, however, when compared to the long-term effects of agricultural and industrial compounds. Take DDT, for example, a persistent bioaccumulative chemical that can stay in the environment for long periods and does not break down easily. This type of chemical can build up in animal tissue and pass up the food chain or to successive generations through the placenta or by suckling.
&n
bsp; DDT was introduced as a pesticide around the time of the Second World War, and quickly became a universal weapon in agriculture and public health to fight disease-carrying organisms such as mosquitoes. A few decades later, it was found everywhere in the environment, spread by the natural wind and water currents of the Earth and carried for thousands of miles by migrating birds and fishes. It was detected in the air of cities, in wildlife, even in the Adélie penguins of the Antarctic. It also started to accumulate in the fatty tissues of humans. It is now banned because of its toxic effects on a wide range of living beings all over the world.
Another worrying class of pollutant is the hormone-mimicking endocrine disrupters. “When you look at the structure of a hormone molecule such as testosterone, they have these circular links of carbon and it’s exactly that sort of pattern that’s present on a lot of the pesticides like PCBs,” says Andrew Derocher, a professor of biology at the University of Alberta. Over time, animals have evolved ways of dealing with naturally occurring chemicals invading their bodies. But the speed at which man-made chemicals have been invented and then released into the environment has had devastating effects. “No organism has evolved to deal with these human-produced chemicals,” says Derocher. The result is that they accumulate in top predators such as polar bears and panthers, interfering with their development.