Page 368 - Earth's Climate Past and Future

344 PART V • Historical and Future Climate Change

Future Human Impacts on Projected
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Greenhouse Gases

Over the next few centuries, natural factors will con- 8
tinue to affect climate change, but their impacts will 6
remain small (as in recent millennia). The largest driver Population (billions)
of future climate will be emissions of greenhouse gases 4
and aerosols from human activities. 2
19-1 Factors Affecting Future Carbon Emissions 0
1800 1900 2000 2100
In recent decades, atmospheric CO concentrations have Year
2
been rising at a rate of ~2 ppm/year, mainly because of FIGURE 19-1 Future population A United Nations
burning of fossil fuels and secondarily because of defor- projection of human population during the twenty-first
estation. This rise will continue in the future, but the rate century at first continues the explosive increase of the
is impossible to predict. The uncertainties center mainly twentieth century but later levels off at 10 billion people.
~
on the amount of carbon we will emit but also on the way (Modified from F. Press and R. Siever, Understanding Earth, 2d ed.,
the climate system distributes the additional CO among
2 © 1998 by W. H. Freeman and Company.)
its carbon reservoirs.
For as long as fossil fuels remain reasonably abun-
dant, future carbon emissions can be approximated by
multiplying three factors: moving from semiindustrialized to industrialized status.
Forecasting future living standards is difficult, but the
increase in carbon emissions = increase in population Intergovernmental Panel on Climate Change (IPCC)
× change in emissions per person × changes in has estimated a range of possible increases for the next
efficiency of carbon use few centuries. The efficiency with which carbon is used
is especially hard to predict because it reflects many
The number of humans is critical to these projections factors, including the kind of fossil fuel used and the
for obvious reasons: expanding numbers of humans technology used to burn it.
require more fossil fuel for industry, transportation, and The next few decades will see peaks in annual pro-
home heating, and they cut more forest to clear land for duction of oil and then later of natural gas, after which
farming and urban/suburban growth. The number of production will decline. Compared to coal, oil and gas
humans has increased from 1.5 to 6 billion in just over are relatively “clean” fuels that emit smaller amounts of
100 years as medical and agricultural advances have CO per unit of energy produced. When oil and gas use
2
extended life expectancy. declines, coal will gradually become the primary carbon-
Attempts to project future population increases are based fuel until the end of the fossil fuel era. Most acces-
complicated by the tendency of birth rates to fall as per sible high-grade anthracite coal was burned in the early
capita income rises, by centralized efforts by nations years of industrialization, leaving mostly lower-grade
such as China to slow population growth, and by the bituminous coal in the ground. Because bituminous coal
efforts of some organizations to avoid constraints on produces far more CO per unit of usable energy, global
2
reproduction. Global population is projected to rise carbon emissions will increase. If the bulk of the vast car-
rapidly from 6 billion during the year 2000 to more bon reservoirs stored in tar sands and oil shales becomes
than 9 billion near 2050 but with a leveling off of the commercially worth exploiting, CO emissions will go
2
trend after mid-century (Figure 19–1). Slowing of the even higher.
explosive growth that occurred between 1900 and 2000 To this point, the three factors in the future carbon
will result from developing countries reaching higher emissions equation (population, quality of life, efficiency)
levels of wealth and parents in those countries choosing seem likely to drive CO emissions much higher in the
2
to have fewer children. This trend has already been near future. Because their effects are multiplied, the
underway for decades in fully industrialized countries. increase in future emissions seems likely to be very large.
The change in carbon emissions per person is linked The best hope for reducing (or limiting the increase
to the average standard of living and to the efficiency of) future carbon emissions lies in technology, a part of
of use. In most nations, as the standard of living has the “efficiency” term in the equation. Humans are a
increased over time, the process has required more car- uniquely innovative species, and our ingenuity will cer-
bon-based fuel for industrialization, transportation, and tainly make future breakthroughs in improving the effi-
home heating/cooling. In the near term, the largest ciency with which we use fossil carbon sources. Signs of
changes will occur in Southeast Asian nations rapidly this kind of innovation have begun to appear during the