Global Warming

he relationship between humans and the state of the ecosystem is not only

dependent upon how many people there are, but also upon what they do. When there

were few people, the dominant factors controlling ecosystem state were the

natural ones that have operated for millions of years. The human population has

now grown so large that there are concerns that they have become a significant

element in ecosystem dynamics. One of these concerns is the relationship between

human activities and climate, particularly the recent observations and the

predictions of global warming, beginning with the alarm sounded by W. Broecker

(1975).

The relationships among humans, their activities and global temperature can be

assessed by making the appropriate measurements and analyzing the data in a way

that shows the connections and their magnitudes. Human population can be closely

estimated and the consequences of their activities can be measured. For example,

the volume of carbon dioxide, methane and nitrous oxide emissions is an

indicator of human's energy and resource consumption. An examination of

population size, atmospheric concentrations of these gases and global

temperature relative to time and with respect to each other is presented here to

demonstrate the relations among these factors.

POPULATION GROWTH

Many of us have seen linear graphs of human population showing the enormous

growth in the last two centuries. However, significant changes in population

dynamics are lost in the exponential growth and long time scales. If the data

are replotted on a log-population by log-time scale, significant population

dynamics emerge. First, it is apparent that population growth has occurred in

three surges and second, that the time between surges has dramatically shortened

(Deevey, 1960).

Figure 1. Population (Log-population verses log-time since 1 million

years ago). Time values on x-axis, ignoring minus sign, are powers of 10 years

before and after 1975 (at 0). Vertical dashed-line at 1995. Filled circles for

known values are to left of 1995 and open circles on and to right of 1995 are

for projected values. (Data updated from Deevey, 1960). ----------

Deevey's 1960 graph has been brought up to date in Figure 1 to reflect what has

been learned since then. The data have been plotted relative to 1975 with

negative values before 1975 and positive values thereafter. The reason for this

will become clear below. The values of the time scale, ignoring the minus signs,

represent powers of 10 years.

It has been argued that a population crash occurred about 65,000 years ago (-4.8,

Fig. 1), presumably due to the prolonged ice-ages during the preceding 120,000

years (Gibbons, 1993). Humans came close to perishing and Neanderthal became

extinct. However, by 50,000 years ago (-4.6, Fig. 1), humans had generated

population mini-explosions all around the planet. Deevey's data for population

size since 500 years ago have been replaced with more recent estimates taken

from The World Almanac, (1992 - 1995) including population projections out to

2025. A vertical dashed-line has been placed at 1995. Filled symbols for the

known values are to the left of it and open symbols on and to the right of it

are for values projected into the short-term future.

The first surge coincides with the beginning of the cultural revolution about

600,000 years ago, interrupted by the population crash 65,000 years ago.

Population size rebounded 50,000 years ago and then growth slowed considerably.

The second surge began with the agricultural revolution about 10,000 years ago

and was followed by slow growth. Deevey argued that moving down the food chain

was the underlying cause of this large and rapid spurt. The timing of the

present surge matches the rise of the industrial-medical revolution 200 years

ago.

A relation between innovation and population growth is embedded in the log-log

plot. There was rapid growth at the start of each surge. Then, growth rate

slowed as people adapted to the precipitating innovations. Each surge increased

the population more than 10-fold. It appears that we are nearing the end of the

present surge as recent growth rates have declined. After the initial spurt,

subsequent innovations did not perpetuate growth rates. The only significant

innovations were those that produced the next surge. However, accumulated

innovations during the surges may have played a role in the eventual decline in

population growth rates. Starting with high birth and death rates, death rate

declines and longevity increases, but