(6) Air Pollution

Air Pollution


Concept 15-3 Evidence indicates that the earth’s atmosphere is warming rapidly, mostly because of human activities, and that this will lead to significant climate change during this century with severe and long-lasting consequences for humans and many other forms of life.

Global Warming and Global Cooling Are Not New

Changes in the earth’s climate are neither new nor unusual. Over the past 4.7 billion years, the planet’s climate has been altered by volcanic emissions (Core Case Study), changes in solar input, continents moving slowly as a result of shifting tectonic plates, impacts by large meteors, and other factors.

Over the past 900,000 years, the atmosphere has experienced prolonged periods of global cooling and global warming. These alternat ing cycles of freezing and thawing are known as glacial and interglacial (between ice ages) periods.

Some analysts hypothesize that climate change after the last ice age ended about 13,000 years ago was an important factor leading nomadic hunter–gatherers to settle down and invent agriculture. For roughly 10,000 years, we have had the good fortune to live in an interglacial period characterized by a fairly stable climate and a steady average global surface temperature, bottom left). These conditions allowed agriculture, and then cities, to flourish. For the past 1,000 years, the average temperature of the atmosphere has remained fairly stable but began rising during the last century when people began clearing more forests and burning fossil fuels. Past temperature changes such as those are estimated by analysis of: radioisotopes in rocks and fossils; plankton and radioisotopes in ocean sediments; tiny bubbles of ancient air found in ice cores from glaciers; temperature measurements taken at different depths from boreholes drilled deep into the earth’s surface; pollen from the bottoms of lakes and bogs; tree rings; historical records; insects, pollen, and minerals in different layers of bat dung deposited in caves over thousands of years; and temperature measurements taken regularly since 1861.

We Are Making the Earth’s Natural Low-Grade Fever Worse

Along with solar energy, a natural process called the greenhouse effect warms the earth’s lower atmosphere and surface. Life on the earth and the world’s economies are totally dependent on the natural greenhouse effect-one of the planet’s most important forms of natural capital. The oceans are another factor shaping the earth’s climate because they remove carbon dioxide and heat from the atmosphere and move stored heat from one place to another in water currents. Swedish chemist Svante Arrhenius first recognized the natural greenhouse effect in 1896. Since then, numerous laboratory experiments and measurements of temperatures at different altitudes have confirmed this effect-now one of the most widely accepted theories in the atmospheric sciences. It occurs primarily because of the presence of four natural greenhouse gases-water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Since the beginning of the Industrial Revolution about 275 years ago, human actions have led to significant increases in the concentration of earth-warming CO2, CH4, and N2O in the lower atmosphere-mainly from agriculture, deforestation, and burning fossil fuels.

There is considerable and growing evidence that these inputs of greenhouse gases from human activities are causing an enhanced greenhouse effect, popularly known as global warming. In 2006, researchers at the British Antarctic Survey analyzed air bubbles in ice cores from Antarctica going back 800,000 years. Their data indicated that current levels of CO2 are higher than at any other time during that period and are now increasing at an unprecedented rate.

In 2007, the largest CO2 emitting countries in order were China, the United States, the European Union, Indonesia, Russia, Japan, and India. Global CO2 emissions are growing exponentially at an increasing rate.

  1. United States has been responsible for 25% of the world’s cumulative CO2 emissions, compared to China’s 5% contribution. But coal-fired power plants provide over 70% of China’s electricity compared to 50% in the United States. And China’s oil consumption and use of coal to produce electricity are soaring.
  2. China’s total CO2 emissions are high and growing rapidly, its per capita emissions are low. For example, the United States emits about seven times more CO2 per person than China does. China points out that current global warming has been caused mostly by the long-term historic emissions by developed countries and their high per capita emissions.

Critics respond that if China does not radically change to more sustainable forms of production, power generation, transport, and building design, its projected economic miracle will turn into an unsustainable econightmare. Because CO2 mixes freely in the atmosphere, every country’s climate is affected by any one country’s actions.

In 1988, the United Nations and the World Meteorological Organization established the Intergovernmental Panel on Climate Change (IPCC) to document past climate changes and project future changes. The IPCC network includes more than 2,500 climate experts from 130 nations. In its 2007 report, based on more than 29,000 sets of data, the IPCC listed a number of findings indicating that it is very likely (a 90-99% probability) that the lower atmosphere is getting warmer (Concept 15-3) and that human activities are the primary cause of the recent warming.

According to the 2007 IPCC report, here is some of the evidence that supports its conclusions.

• Between 1906 and 2005, the average global surface temperature has risen by about 0.74 C° (1.3 F°). Most of this increase has taken place since 1980.

• Actual temperature measurements indicate that the 13 warmest years since 1861 (when temperature measurements began) have occurred since 1990. In order, the five hottest years since 1861 have been 2005, 1998, 2002, 2003, and 2006.

• Over the past 50 years, Arctic temperatures have risen almost twice as fast as temperatures in the rest of the world.

• In some parts of the world, glaciers and floating sea ice are melting and shrinking at increasing rates, rainfall patterns are changing, and extreme drought is increasing.

• During the last century, the world’s average sea level rose by 10-20 centimeters (4-8 inches), mostly because of runoff from melting land-based ice and the expansion of ocean water as its temperature increases.

  Enhanced Global Warming

May Have Severe Consequences:

Some Scary Scenarios

So what is the big deal? Why should we worry about a possible rise of only a few degrees in the earth’s average surface temperature? We often have that much change between May and July, or even between yesterday and today. The key point is that we are talking not about normal swings in local weather, but about a projected global change in climate-weather measurements averaged over decades, centuries, and millennia.

Climate scientists warn that the concern is not just about how much the temperature changes but also about how rapidly it occurs. Most past changes in the temperature of the lower atmosphere took place over thousands to a hundred thousand years, top and bottom left). The next problem we face is a rapid increase in the average temperature of the lower atmosphere during this century.

In other words, according to the IPCC and other climate scientists, the earth’s atmosphere is running a fever that is rising fast, mostly because of human activities. Such rapid change could drastically affect life on earth. Humans have built a civilization adapted to the generally favorable climate we have had for the past 10,000 years. Climate models indicate that within only a few decades, we will have to deal with a rapidly changing climate.

A 2003 U.S. National Academy of Sciences report laid out a nightmarish worst-case scenario in which human activities, alone or in combination with natural factors, trigger new and abrupt changes. At that point, the global climate system would reach a tipping point after which it would be too late to reverse catastrophic change for tens of thousands of years. The report describes ecosystems suddenly collapsing, low-lying cities being flooded, forests being consumed in vast fires, grasslands drying out and turning into dust bowls, premature extinction of up to half of the world’s species, prolonged heat waves and droughts more intense coastal storms and hurricanes, and tropical infectious diseases spreading rapidly beyond their current ranges. Climate change can also threaten peace and security as changing patterns of rainfall increase competition for water and food resources, cause destabilizing migrations of tens of millions of people, and lead to economic and social disruption.

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