Brent Cornell

    
Many claims have been made regarding the impact of human activities on climate change – not all are supported by evidence

• Many arguments are not backed by reliable scientific data or are made by entities with vested interests (e.g. oil companies)

Below are some of the main claims raised by sceptics of human-induced climate change and the common counter-arguments:

Examples of Data Used to Make Climate Change Claims

   Data:                        Figure 1                    Figure 2                     Figure 3                     Figure 4

Claim 1:  Climate has changed in the past and current trends merely reflect the Earth’s natural climatic cycle

• Data collected from the Vostok ice core shows several changes in climate over the last 400,000 years (Figure 1)
• At several points in history, global average temperatures have been warmer than those currently observed
  

Counter Argument:  

• Climate changes do occur naturally, but usually not as abruptly as what is seen currently
• When global warming occurred abruptly in the past, it was always highly destructive to life (e.g. Permian mass extinction)
• Atmospheric CO₂ levels positively correlate to average global temperatures and are currently at the highest levels ever recorded

Claim 2:  Climate change is being caused by solar activity and the effect of greenhouse gas emissions is negligible

• Temperatures on Earth are influenced by the amount of solar radiation from the sun (more radiation = warmer temperatures)
• Warmer temperatures may be caused by an increase in solar irradiance by the sun (as determined by the number of sunspots) 

Counter Argument:

• Over the last 35 years the sun has shown a slight cooling trend, however average global temperatures have increased (Figure 2)
• There is no evidence to support a correlation between solar irradiance and current global temperature trends

Claim 3:  Certain changes in climate conditions cannot be linked to greenhouse gas emissions

• Global sea levels began to increase before greenhouse gas emissions significantly increased following the industrial revolution
• Therefore climate changes like rising sea levels are unrelated to greenhouse gas emissions (Figure 3)

Counter Argument:

• The overall pattern of change in sea levels will be influenced by the period of time over which the data is collected
• While sea levels did increase preceding the industrial revolution, this rise in sea levels followed a preceding period of decrease
• The rate at which sea levels have risen in the past 30 years is greater than that seen in the last 200 years

Claim 4:  Variability between predicted climate change models means that such models are unreliable

• Three different models of predicted climate change commissioned by the IPCC show variation of more than 5ºC (Figure 4)
• Climate change models are based on assumptions and if those assumptions are false, the predictions will be incorrect

Counter Argument:

• The assumptions made by the different models relate to the extent of human activity predicted over the next 100 years
• Model A1B predicts a continued reliance on fossil fuels while model B1 predicts a reduction in the current use of raw materials
• All three models still predict an increase in average global temperatures over the next 100 years

Claim 5:  Increases in greenhouse gas concentrations in the atmosphere will not be enough to cause significant climate change

• As of 2009, there were only ~39 molecules of carbon dioxide per 100,000 molecules in the atmosphere
• At our current rate of CO₂ emission, it will take mankind another 5 years to raise that level by 1 molecule (to 40 per 100,000)
• While we may double atmospheric CO₂ levels by the end of the century, doubling a small number still produces a small number

Counter Argument:

• The reason why carbon dioxide is so important to the environment is because there is so little of it
• Living things require constant internal environments (homeostasis) – small external changes can have big impacts on viability

Other Common Climate Change Claims

(For a full list of climate change claims, visit skepticalscience.com)