Global Warming

The 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

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.


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

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 birth rates stay high. Some time later,
birth rates decline so that eventually, net births minus deaths produces slow
growth. The result is a spurt in population size. When referring to the
industrial revolution, this phenomenon has been called the "demographic
transition". It appears that this dynamic may have occurred twice before.

The decreases in time between surges suggests that, if past behavior is the best
predictor of future behavior, we are