Global Warming As A Trigger

According to Dr. Richard B. Alley, a professor of geosciences at Pennsylvania State University and an associate at Earth System Science Center at Pennsylvania State University, in an article in Scientific American, "Humans are pushing certain aspects of climate closer to the thresholds that could unleash sudden changes [in climate]." If global warming triggers climate change, humans will be presented with many challenges. Although it is true that some regions will become more habitable with warmer temperatures, such as at higher latitudes, where it is expected that farming may be possible (if the right type of soil exists for agriculture), other regions will become so warm that heat waves will wreak havoc, threatening agriculture, the availability of water resources, and the health of humans and ecosystems. Likewise, climate changes to cold climates could threaten the health of humans and ecosystems and disrupt transportation and economic systems.

The discoveries that scientists made while studying ice cores from Greenland in the early 1990s are what gave scientists an appreciation for the concept of abrupt climate change. It also made them realize that because of Earth's ability to shift climates within a decade or less, global warming needs to be taken very seriously. It could be a critical factor pushing Earth's climate even faster toward a sudden shift than what would normally be expected.

Scientists studied cores of ice that are up to 1.9 miles (3 km) long to obtain a climate history spanning 110,000 years. What they discovered was startling: There was evidence locked in the ice core revealing a detailed history of many wild fluctuations in climate. There were many long cold periods when the temperature dropped 10°F (6°C) in just a few years, interspersed with brief warm periods. They also found that since the Ice Age 11,500 years ago, the climate gained half of its heat—more than 17°F (10°C)—in just 10 years. This episode correlates with an increase in precipitation in other areas of the world. Because

There will be impacts to ecosystems in the event of abrupt climate changes. If the ice caps were to melt in the Antarctic, it would have a negative impact on penguin habitat. (NOAA)

of this, large amounts of methane were released into the atmosphere as wetlands flooded the Tropics and thawed in the warming northern latitudes.

They found that there were more than 20 intense, abrupt warming episodes, followed by cold periods, only to be repeated again by another warming that only took a few years to occur. Through proxy data, they were also able to determine that the cold, wet episodes in Greenland correlated with cold, dry, windy conditions in North America and Europe. Conditions in the South Atlantic and Antarctica, however, were extremely warm. Also through the analysis of proxy data, they discovered that 5,000 years ago a sudden dry spell converted the Sahara from a lush, green landscape to the dry, hostile environment it is today.

Climate scientists give us a warning as a result of their research on abrupt climate change. According to Alley, crossing a climate threshold is similar to tipping a canoe. In a canoe, a passenger can tip it and be safe initially, but as the leaning progresses to a certain point, it hits a critical threshold that flips the canoe over to the point of no return. Just as with the canoe, the climate system is robust but also has its limits. Once pushed too far, there comes a point where a climatic shift is inevitable and unstoppable. The key is to recognize what pushes the climate to that point and avoid creating situations that trigger them. The following table illustrates what can cause a climate to cross a particular threshold and trigger a climate change.

Alley and most climate experts feel that humans today are tempting abrupt climate change by interfering with so many aspects of the natural world, in particular, the human-induced increases in atmospheric concentrations of greenhouse gases, put there by the excessive burning of fossil fuels. Because of the human influence, the IPCC has predicted that global temperatures will rise 2.5-7.5°F (1.5-4.5°C) in the next 100 years. This warming is what could add freshwater to the North Atlantic, causing the North Atlantic conveyor to slow down or halt, cooling Europe and the eastern United States.

Abrupt climate change is considered an issue of national security. A report was prepared for the Pentagon on the implications of abrupt climate change toward national security and the possibility of human-caused global warming leading to the collapse of U.S. national security specifically. The Pentagon predicts a near-term collapse of the "Atlantic Ocean conveyor belt." If it were to completely shut down it could change precipitation amounts and negatively impact agriculture and populations. The rapid cooling in Europe, diminished rainfall amounts in many key agricultural and urban areas, along with the negative impacts to urban areas and the consequent disruptions in food and water supply pose enormous security issues. This, in turn, would cause significant geopolitical and security issues for countries to deal with, including the possibility of war.

This situation is serious enough that the U.S. Department of Defense created a think tank called the Global Business Network to assess the national security implications of a total shutdown of the North Atlantic conveyor. The think tank considers the situation very serious. In its report, the Global Business Network states: "Tensions could mount

Crossing Climatic Thresholds

climate driver

threshold crossing

resulting climate shift

social consequences

The North Atlantic conveyor current carries warmth northward from the Tropics to Europe.

The addition of freshwater in the north Atlantic slows or stops the conveyor current.

Temperatures fall in Europe and the eastern United States.

It becomes difficult to produce agriculture, and transportation is interrupted.

Evapotranspiration from plants provides the moisture for much of the rain received in farming areas.

A dry spell stresses and kills many plants, decreasing available moisture in the air and causing the area to become continually drier and unproductive.

A mild dry spell can be turned into a severe, long-term drought.

Land cannot be farmed, people cannot grow food and go hungry, health issues become critical, and the economy is negatively impacted.

Currents in the Pacific Ocean control temperature and weather.

natural phenomena, such as El niño, change sea-surface temperatures.

Weather patterns on land shift, causing either unplanned violent storms or drought.

Croplands can dry up, while other areas can be flooded.

(Source: Richard B. Alley. "Abrupt Climate Change." Scientific American November 2004, pp. 62-69.)

around the world. Nations with the resources to do so may build virtual fortresses around their countries, preserving resources for themselves. Less fortunate nations may initiate in struggles for access to food, clean water, or energy."

One thing to keep in mind, according to Alley, is that rapid changes in climate are not easily predictable. No one currently knows what the exact critical threshold is that can flip the climate to change abruptly. Instead, it can be better compared to conducting a large-scale science experiment in which humans are experimenting on Earth in a real-time laboratory experiment. The best scientists can do right now is study the past, observe the present, and develop models that fit both time intervals so that they can project them toward future scenarios.

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