2. Global Warming

Likely consequences of global warming

If current emissions of carbon dioxide and other greenhouse gases go unchecked, temperatures should continue to rise and the climate will inevitably change. A significant warming ought to occur by the end of the 21st century, but the predicted consequences range from an ominous, catastrophic future to a mildly uncomfortable one. Two extreme arguments have therefore been advanced. One side, supported by environmentalists, warns of an imminent apocalypse and global catastrophe caused by our own tinkering with nature. In their perspective, belching smokestacks, gasoline-powered automobiles, power-generating stations and the voracious destruction of forests are turning up the heat on an overburdened environment, pushing it over the edge with raging storms, flooded cities and poisoned air. The alternate view, championed by some industrialists, is that doomsday predictions are exaggerated and hopelessly uncertain. And if the world does get a little warmer, they say, it won’t be that bad. After all, most people like a warmer climate and many of us could use a little more heat in our lives.

There are both positive and negative aspects to even the worst-case forecasts of global warming. Not everyone and every place will be affected the same. Some regions will benefit, and others may suffer unbearable damage. Many aspects of a temperature increase would probably be welcome at high northern latitudes that are now too cold over much of the year. Regions that are near the equator are already hot, and a further increase in heat could be devastating. So there is bound to be a mixed verdict, and the outcome of the debate depends upon which kind of evidence you focus on.

Who should we believe? It is probably unwise to lapse into apocalyptic think, especially in view of the scientific uncertainty and long-time scales, but ostrich-like denial is also imprudent since a lot is at stake, from the wealth of nations to the future of the planet. The best we can do is to examine the full spectrum of potential, long-range consequences, from good to bad.

In the best-case projection, at the low end of the predictions, global warming will, by itself and independently of other influences, raise the average temperature of the world by 1.4 degrees Celsius (2.5 degrees Fahrenheit) over the next 100 years. If the warming takes this gradual, modest course, some parts of the world will benefit, and the normal resilience of society ought to accommodate the climatic change.

The modest increase in temperatures at mid-northern latitudes, where most people live, will be welcome. There will be longer summers, shorter winters and warmer nights. Residents of cities like Boston will suffer fewer colds, experience fewer heart attacks from shoveling snow, and spend less on heating, snowplowing and road salting. On the other hand, summer air conditioning will cost more, the winter ski slopes may turn to slush, and the colorful fall foliage could disappear as trees move away from the heat to the north.

If global warming is at the upper end of the prediction, at 5.8 degrees Celsius (10.4 degrees Fahrenheit) in 100 years, many humans should also be able to adapt without much difficulty. After all, this rise in temperature is less than the average daily temperature difference between New York City and Atlanta, Georgia, or between Paris and Naples, and there is little evidence of greater risk to people who now live in the warmer southern climate. And those who live in the colder, northern locals are already used to a seasonal temperature increase between winter and summer that can be three times greater than the largest predicted heating over the next 100 years.

So, the good thing is that humans are adaptable. But the bad thing is also that humans are adaptable. As long as the climate changes occur slowly, we can adapt without realizing what is happening, but some very uncomfortable things can happen at the top part of the expected warming in 100 years.

There is an applicable proverb about frogs. If you put a frog in boiling water, it will jump out and save itself. But if you gradually increase the heat, with the frog in the water, it will die.

Very hot will be decidedly unwelcome in many places. Within deserts, entire cities will be immobilized under the heat. The wealthy will move out of Palm Springs, and Las Vegas could become a ghost town. Residents in many other large cities should experience severe heat waves, making them feel like the world is melting down in a pool of sweat. As the climate becomes hotter and drier, drought will probably become more severe in areas prone to it, and supplies of freshwater will dwindle. More frequent bouts of extreme weather will also be expected, with widespread flooding and intense hurricanes.

Agriculture in some regions will be better than other regions. The longer growing season and increasing carbon dioxide will foster plant growth, making much of the developed world greener. Agriculture will likely become more productive in Canada, northern Europe, Russia and the northern United States. As droughts turn some mid-American farms to dust, both agricultural production and population centers in the United States will shift north, and the same thing will probably happen in Europe.

The world’s poorest countries are, on the other hand, highly vulnerable to agricultural disaster, for they are already located in arid and semi-arid regions. A further rise in temperature will almost certainly reduce crop yield in south Asia and sub-Sahara Africa, where expending deserts will additionally claim more land.

As environmental conditions change over time, plants and animals will migrate, as they have throughout geological history – moving up and down in latitude as the globe warms and cools. The recent increase in temperatures has already caused some species to move north, and the accelerated heating could wipe out many of them in the future. Some plants and animals might not be able to move fast enough to keep pace with the rapid rate of temperature change, and climate-sensitive habits could be destroyed altogether, hastening the extinction of some species.

No one can see much advantage in the rising seas, which are one of the most certain effects of the warming projected during the coming decades. There is just one indirect advantage – the meltdown of polar ice, that contributes to the sea rising, could result in permanent ice-free passage in the Arctic Ocean, providing a new shipping route between Europe and Asia.

The climate experts predict a rise in sea level of between 0.09 and 0.9 meters (3 inches to 3 feet) over the next 100 years if nothing is done to curtail the emission of greenhouse gases. The resultant flooding will seriously disrupt coastal areas where more than a quarter of the world’s population now lives. In the worst-case increase, Venice and Alexandria will be inundated, as will many cities on the Atlantic and Gulf coasts of the United States, including Boston and New York City. Residents in South Florida will not have to worry about the sweltering heat; their homes will be flooded with seawater.

As with agriculture, the developing nations will get the short end of the stick. Thirty million people in Bangladesh could be displaced by a 0.9-meter increase in sea level, and the rising waters would most likely force the evacuation of 70 million Chinese. Salt water could move several thousand meters inland at the mouths of rivers, invading coastal drinking water systems. The Nile, Yangtse, Mekong and Mississippi deltas are all at risk. Island nations will suffer severe flooding or completely disappear under the rising waters; they include the Bahamas, many of the Caribbean islands, Cyprus and Malta in the Mediterranean, and several Archipelagos around the Pacific Ocean.

Even a modest rise in sea level will wipe many of the world’s beaches out of existence. Flooding isn’t the problem; it’s the removal of sand by waves. Even a 0.3-meter (1-foot) rise in sea level creates wave action that erodes away up to 5 meters (200 feet) of some beaches. So, people who live by the seashore had better sell their homes, and you can forget winter vacations in parts of Florida and the Caribbean islands.

The last factor in our catalog of likely consequences of severe global warming is increased health risk – a topic close to the hearts of most people and nearly every politician. Many diseases might spread dramatically as the temperatures head upward, especially those born by mosquitoes. As the world warms, mosquitoes will move north, into regions where the winter cold used to kill them, carrying malaria, dengue fever, yellow fever and encephalitis with them. Extremely hot weather may also directly terminate the lives of a lot of people, particularly the very old and the very young living in cities.

The list of possible consequences of global warming looks pretty grim, especially if the worst forecasts come true. Some of the threats are immediate and inevitable; others are remote and uncertain. Only time will tell for sure.

But that doesn’t justify inaction. Even if worldwide emission of heat-trapping gases were capped at today’s amounts, their concentrations in the atmosphere would continue to increase. And if we stopped burning fossil fuels altogether, the atmosphere would not immediately recover. The carbon dioxide already released in the air would stay there for at least a century, keeping the planet warm and the global temperatures high. So, its time we acted to correct the problem – we may have waited too long already.

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Copyright 2010, Professor Kenneth R. Lang, Tufts University