due to the observed increase in anthropogenic greenhouse
gas concentrations. Discernable human influences now
extend to other aspects of climate, including ocean
warming, continental average temperatures, temperature
extremes and wind patterns.
CO2 concentrations have risen from 280 parts per million
(ppm) in the period before 1750 to levels now approaching 390
ppm with the annual concentration growth rate greater in the
past 10 years. Based on ice-core samples, the natural range of
CO2 concentration over the past 650,000 years was from 180
ppm to 300 ppm. There is even evidence that the current CO2
forcings only) and including (anthropogenic and natural forcings) human influence. The observations cannot be explained
without considering the human influence.
Anthropogenic and natural forcings
Temperature Change, Centigrade
For anyone attempting to move through the informational confusion on climate-change issues, the proliferation of counterfactual information makes the task daunting. Though the vast
majority of climatologists support the global-warming theory,
much of the media coverage gives approximately equal weight
to the proponents of each side of the debate. The following addresses some of the more common counterarguments.
■ The greenhouse effect
is just a theory. Yes, it is, but a
theory in science means considerably more than speculation. It means that the theory
is based on a coherent body of
understanding supported by diverse evidence and a conceptual
framework. The greenhouse effect accurately describes the
fundamental principles that
determine planetary climates.
Other examples of scientific
theories include the theory of
relativity in physics and plate
tectonics in geology.
■ Addressing global
warming keeps us from addressing other important
issues. Examples of issues
threatened by overattention
to global warming range from
emerging diseases to the resurgence of malaria, health
care, drought, the economy,
crime, energy, infrastructure, and political instability. But
this is a false choice. While these issues are important, they
don’t diminish the need to address climate change. Further,
this argument ignores the interrelationships among issues.
Because of the interconnections, addressing climate change
can help address many of these other issues.
■ Climate change is an excuse for government to grow even
bigger. Arguments of this type combine several different issues
and treat them as a single package. Climate change and big government are not the same issue. If big government is the concern, then
address that issue. Big government or small government doesn’t
change the legitimate science underlying climate change.
■ Scientists are still arguing about the causes of climate change
and the current warming trend. Most scientists agree about the
causes of climate change today. While most of the current increase
in warming isn’t due solely to human activity, we are contributing
enough to upset a precariously balanced system. Even as little as a
1900 1920 1940 1960 1980 2000
ADAPTED FROM “COMBINATIONS OF NATURAL AND ANTHROPOGENIC FORCINGS IN TWENTIETH-CENTURY CLIMATE,”
JOURNAL OF CLIMATE
17, NO. 19 (2004): 3723. REPRINTED WITH PERMISSION.
concentrations are higher than at any time in the last 20 million
years. This is significant because the operation of the carbon
cycle ensures that carbon remains in the system for hundreds to
thousands of years. Even the addition of relatively small amounts
will accumulate over time and exacerbate the warming trend.
The human “fingerprints” visible on these increases in carbon
dioxide levels come from at least three sources. First, scientists can
accurately calculate the increase in carbon dioxide that has entered
the atmosphere from the fossil fuels that have been burned. This
increase tracks with the observations. Second, the mix of carbon
isotopes in the atmosphere has shifted in a manner expected if the
cause were burning fossil fuels. Third, while we aren’t in danger
of running out of breathable oxygen, its atmospheric content is
decreasing in a way consistent with burning fossil fuels.
Further reinforcing the human factor in climate change, the
above chart highlights the significant relationship between temperature observations and climate modeling, excluding (natural