Pollution Essay: 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

(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.