The reasons for raising doubts about the human causes of global warming, explains Skeptical Science's John Cook, are often political rather than scientific. Cook hears from climate change skeptics that '"it's all a liberal plot to spread socialism and destroy capitalism.' ... However, what is causing global warming is a purely scientific question." Cook tries to remove the politics from the debate by concentrating on the science.
Below is Cook's list of the most-used arguments of climate change skeptics, compared to what the science actually says.
"It's the sun."
Fact: In the last 35 years of global warming, the energy from the sun has been decreasing while the earth’s temperature has been increasing.
"The climate's changed before."
Fact: The climate reacts to whatever forces it to change. Humans are now the dominant force causing change.
“There is no scientific consensus on climate change."
Fact: More than 95 percent of scientists working in the disciplines contributing to climate studies accept that climate change is almost certainly being caused by human activities.
"Global warming has stopped and a cooling is beginning."
Fact: Empirical measurements of the Earth’s heat content show the planet is still accumulating heat and global warming is still happening.
"Climate models are unreliable."
Fact: While there are uncertainties with climate models, they successfully reproduce the past and have made predictions that have been subsequently confirmed by observations.
"The surface temperature record is unreliable, and affected by artificial heat sources."
Fact: The warming trend is the same in rural and urban areas, measured by thermometers and satellites. Confidence in climate science depends on the correlation of many sets of these data from many different sources in order to produce conclusive evidence of a global trend.
"For the years 1998 to 2005, the Earth’s temperature hasn't increased."
Fact: Globally, 2010 was the hottest year on record, tied with 2005. Surface temperatures show much internal variability due to heat exchange between the ocean and atmosphere. Due to a strong El Niño climate pattern, 1998 was an unusually hot year.
"An ice age was predicted in the 1970s."
Fact: Ice age predictions during the 1970s were predominantly media-based. The majority of peer reviewed research at the time predicted global warming due to increasing CO2.
"Antarctica is gaining ice."
Fact: Overall, Antarctica is losing land ice at an accelerating rate while Antarctic sea ice is growing -- despite a strongly warming southern ocean.
"A rise in carbon dioxide doesn’t precede a rise in temperatures, but lags behind it."
Fact: In the case of warming, the lag between temperature and CO2 is explained as follows: As ocean temperatures rise, oceans release CO2 into the atmosphere. In turn, this release amplifies the warming trend, leading to yet more CO2 being released. In other words, increasing CO2 levels become both the cause and effect of further warming.
John Cook, author of "The Scientific Guide to Global Warming Skepticism," lives in Queensland, Australia, and maintains the Skeptical Science website (skepticalscience.com), from which this is adapted.