Here are five common lines of argument climate deniers or skeptics may use. These lines tend to be hierarchical. But first, a note about semantics: I use the term "deniers" to refer to individuals who refuse to accept well-founded scientific evidence and/or logic and/or increasingly, basic reality. "Skeptics" are individuals who accept evidence, but may have some doubts or otherwise would like firm proof. Remember that scientists are skeptics, at least legitimate ones. Skepticism is at the core of the scientific method after all, as the purpose of good science is to try to disprove theories.
- There is no conclusive evidence that climate change is happening. This argument ignores the global body of scientific research demonstrating that climate change is happening. Alternatively, to counterbalance the overwhelming weight of climate science research, it selectively uses the relatively few inconclusive empirical studies conducted by credible scientists or work written by fellow deniers but discredited by mainstream climate scientists.
- The changes in measured temperatures are part of the natural cycle. These deniers are admitting that there is climate change, but not that it is anthropogenic. On the surface, this argument is much more plausible than the first argument. However, climate scientists have gone to great lengths to develop methods that show how anthropogenic climate change rises above the natural signal (the so-called “fingerprinting” of climate change). Moreover, some of the more important natural cycles should be causing global cooling at present.
- Climate change and CO2 are good. Skeptics who take this line of argument are acknowledging that climate change is happening, and that humans may be causing it. Instead, they extoll the virtues of climate change and are skeptical of potential negative impacts. For example, they claim that agriculture will benefit from higher temperatures, increased rainfall, expansion into northern latitudes, and the fertilization effect of CO2. Climate scientists, ecologists, and agronomists have shown that negative impacts far outweigh positive effects of climate change on agriculture. In fact, the weight of evidence suggests that negative impacts will swamp positive impacts in all sectors.
- The scale of climate change is not sufficiently large to take action beyond sensible least-cost measures. This line of reasoning accepts that climate change is likely, that it is human-induced, and that most impacts are negative. Nonetheless, these skeptics do not believe that climate change will be as bad as mainstream science thinks it will be. A time goes by, however, observed climate changes are greater, and observed impacts are worse than originally projected by climate scientists. Although most experts agree that it is prudent to use least-cost measures when possible, they also agree that combating climate change cannot be cheap because the scope is so large.
- The economic impact of making substantial cuts in greenhouse gas emissions on the scale suggested by the IPCC and other groups is too large. This final line of reasoning by skeptics accepts the conclusions of climate scientists, but says that society cannot afford to make the cuts needed to stave off the worst impacts of climate change. Numerous analyses, however, show that the ultimate cost of inaction or limited action to society will be far greater than the cost of robust responses to climate change and delaying action now necessitates more aggressive action in the future, which is likely to be more expensive.