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President's Corner


The global trajectory, take two: What’s changed since 1993?

On 20 June 2007, the Netherlands Environmental Assessment Agency reported that China surpassed the United States as the world's number one emitter of carbon dioxide by 7.5%—a huge jump for a single year (2006). As recently as five years ago, many analysts did not expect China to surpass U.S. emissions until 2020. This reminded me of an essay I wrote in 1993 for the Bulletin of the American Meteorological Society titled "The Global Trajectory." I decided to look back and see what I wrote then and how much of it is relevant today.

In "The Global Trajectory," I argued for scientists to take activist roles to avert the current path of overpopulation, unsustainable economic development, poverty, and environmental degradation—the modern equivalent of the biblical Four Horsemen of the Apocalypse. I made the "relatively safe" prediction that China, with one-fifth the world's population, would soon have enormous impacts on the global economy, security, and environment. The article lists a number of types of global environmental damage: air and water pollution, land degradation, loss of stratospheric ozone, species extinction, and increased vulnerability to floods, droughts, and tropical cyclones as populations grow rapidly in risk-prone areas. However, I qualified the risk associated with "climate change at an unprecedented rate" as only "possible."

population increase

Human population increase (in red) from 10,000 BCE to 2000 CE

In the nearly 15 years since I wrote "The Global Trajectory," what has happened? Let's look at a few metrics.

  • Global population rose from 5.5 to 6.6 billion, an increase of 20%.
  • The U.S. population grew from 258 to 302 million, an increase of 17%.
  • The amount of CO2 in the atmosphere climbed from 355 to 384 parts per million, an increase of 8%.
  • U.S. emissions of CO2 increased 20% from 1990 to 2007.
  • U.S. consumption of oil products grew from 17 to nearly 21 million barrels per day, an increase of 20%.
  • The average global temperature has risen by about 0.3°C (0.5°F), making Earth the warmest it has been in 100,000 years.
  • Global warming has become an accepted fact for me and most scientists, as well as for the public, as observational evidence of all kinds mounts and the world's best climate models agree on the main aspects of climate change.
  • While some species are thriving, many others are in peril. The American bald eagle, threatened with extinction in the 1950s, was recently removed from the list of endangered species—a tribute to the success of environmental regulation. However, the total number of threatened animal species in the world has increased 40%, from 5,200 in 1996 to 7,300 in 2007.

Two heavy hitters: China and the United States

China's booming economy has led to rapid increases in other pollutants besides CO2. In only seven years, China's emissions of sulfur dioxide, mostly from coal burning, have increased by 27%. By some estimates the cost of air pollution in China is approaching 10% of the country's GDP, mostly in health costs.

There is no sign that China's rapid growth in emissions is anywhere close to leveling off. With a population of 1.3 billion, China releases about 4,800 kilograms (10,500 pounds) of CO2 per person each year, less than a quarter of the U.S. rate per capita. And China's population is growing by 0.6% each year. If development and population continue on their present course, then clearly China has the potential to increase its CO2 emissions by several times.

That China is now the greatest emitter of CO2 is a bit ironic, since China signed the 1997 Kyoto Protocol. But China is exempt from the treaty's emissions reductions because it is considered a developing country, a factor often cited by U.S. and Australian lawmakers in rejecting the treaty. I don't defend for a minute U.S. policies toward carbon emissions, energy use, and climate change. However, if the number one emitter is exempt from any restrictions and the number two emitter refuses to even sign the protocol, where does this
leave us?

It is not my intent to point fingers at China or its people, who are simply trying to improve their economic situation. Indeed, much of China's economic growth and emissions is a direct result of the manufacture of products for U.S. and other world markets. And China has been a leader in recognizing the fundamental driver behind these issues: population growth. Through longstanding policies that encourage small families, China is on a path toward an eventual stable population.

The U.S. population growth rate is 1.1% per year. Although a good part of this is driven by immigration, it remains one of the highest growth rates for any developed nation, only slightly below the global average. Given that the United States also has the highest rate of per capita consumption, stabilizing the U.S. population should be a high priority. Other countries have achieved growth rates well below the replacement level of 2.1 children per woman (the current rate for the U.S.). Germany is at 1.4, Italy at 1.3, and China at 1.7. A variety of factors are at work in these birthrate declines, including greater education and employment opportunities for women, availability of contraceptives, and the trend toward urbanization in many countries (which reduces the economic benefit of large families).

Total consumption of resources equals the number of people times the consumption (or impact) per person, so both are important. If each of us decreases our consumption by 1% per year and the population grows by 1% per year, we are not making progress. The treadmill speeds up even as we run faster. In contrast, a decreasing population makes it possible to have constant rates of consumption and still reduce the overall impact. A stable, prosperous society is thus easier for me to imagine with a level population than with a steadily increasing one.

On the positive side, world population growth shows signs of retreating in the coming decades. The growth rate peaked in the early 1960s at around 2.0% per year; it is now around 1.2%. Some projections indicate that the world population may level off between 9 and 11 billion sometime later this century. But even under the present conditions, a century is a long time to wait, and an additional 3 to 5 billion people in a world already stressed by humans and their activities will have serious consequences unless present patterns of consumption, land use, and other behaviors are definitively changed.

It's much more than climate change!

population evolution

Population evolution, 1950–2050, on different continents. The vertical axis is logarithmic. (Image courtesy Donal Reiskoffer/Wikipedia.)

In recognizing the real threat of climate change and responding appropriately, we must not ignore other significant threats facing humanity and other life on Earth. Even if we could wave a magic wand and stabilize greenhouse gas concentrations today, almost all of the factors causing environmental degradation and increasing vulnerabilities to natural disasters would remain. In fact, they will intensify, as more and more people settle in areas susceptible to floods, droughts, wildfires, tropical cyclones, and other natural phenomena.

The present huge rate of species extinction is just one result of human overpopulation that, in my opinion, is even more serious than climate change (which is reversible, at least in theory). Many ecologists believe that the rate of species loss occurring today is between 100 and 1,000 times higher than the background or "normal" extinction rate. Human beings are currently causing the world's sixth great mass extinction—the first caused by a single species and the largest since dinosaurs disappeared 65 million years ago. If present trends continue, one half of all species of life on Earth will be extinct in less than 100 years. Besides climate change, the major threats to ecosystems and biological diversity include

  • habitat loss and fragmentation, the single most important threat;
  • overexploitation (hunting, fishing, etc.);
  • pollution; and
  • invasion of alien species.

Rounding up the usual suspects

At the end of the movie Casablanca, chief of police Captain Renault says to an assistant, "Major Strasser has been shot. Round up the usual suspects." Much of what we read about climate change and how to slow it down reminds me of Captain Renault's advice. We are urged to do many useful things, such as recycling, adjusting thermostats, or driving less to conserve energy and resources. But we are dealing only with the consumption side of the equation and largely neglecting the other and most fundamental part of the equation, the growth in our numbers. For a variety of reasons, population growth is often ignored or only mentioned in passing in even the most enlightened discussions of climate change.

In this age of global satellite observations, communications, and science, it should be clear to everyone that we remain on an unsustainable global trajectory. We now know without a doubt that our actions are contributing to the destruction of our commons and the life it can support, but we are not yet making the tough individual and societal changes that are necessary to really address the problem in meaningful ways and to bring about the necessary compromises and sacrifices. Isn't it time to broaden the dialogue on global warming and have a serious discussion about ways to both stabilize population and reduce consumption per person, difficult as this may be?

Rick Anthes


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