Climate change is one of the most important and contentious issues facing society. The question of how (or whether) we respond to climate change is ultimately political, but it is a political question intertwined with science. To inform the scientific aspects of the debate, climate scientists at the Jackson School of Geosciences agreed to address eight common myths about climate change. Know will cover these myths in separate installments published over eight days.
Myth No. 1: What global warming? Earth has actually been cooling since 1998.
Some people skeptical of global warming claim that Earth’s global surface temperatures have been falling or have leveled off since 1998. They point to data now several years out of date from U.K. researchers that put 1998 as the warmest year on record. They also point to an unusually cool summer in North America in 2009 followed by an abnormally cold winter across all of the northern hemisphere. People who had to shovel record snows from their driveways or live without power during ferocious snowstorms in the northeastern United States began to doubt decades of scientific evidence on global warming.
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Myth No. 2: Increased carbon dioxide (CO2) can’t contribute to global warming: It’s already maxed out as a factor and besides, water vapor is more consequential.
Some climate skeptics claim that the carbon dioxide (CO2) currently in the atmosphere is already “saturated” in its ability to absorb longwave radiation from Earth and therefore additional CO2 in the air won’t make a difference — won’t, that is, absorb more heat. They also argue that water vapor is a more potent greenhouse gas and therefore increases in CO2 shouldn’t be a concern. These claims have been made in recent years by Hungarian physicist Ferenc Miskoczi and other scientists. They were repeated in the Skeptic Handbook, published in 2009 by science writer Joanne Nova. Yet the seed of the argument actually goes back more than a century.
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Myth No. 3: You can’t trust climate models because they do a lousy job representing clouds and aerosols.
Climate modelers have traditionally had a hard time incorporating clouds because clouds are very complex. On the one hand, by reflecting sunlight, they tend to cool Earth. On the other, they tend to hold in heat from the surface, which is why cloudy nights tend to be warmer than clear nights. The models also divide the atmosphere up into blocks much larger than clouds, so it’s difficult to create realistically sized clouds.
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Myth No. 4: There have been big climate changes in the past, such as the Little Ice Age and the Medieval Warm Period, so why can’t recent climate changes just be explained by natural variability?
People who dispute evidence of recent global warming sometimes point to two episodes in the past 1,000 years called the Little Ice Age and the Medieval Warm Period — times when northern hemisphere temperatures were higher or lower than average for decades or even centuries — as examples of internal variability, a kind of natural randomness in the climate system that can’t be explained by any specific forcing. If true, perhaps internal variability could explain the current rapid global warming, skeptics argue. In other words, maybe our current warming is just an unlucky roll of the dice, a blip rather than a long term trend.
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Myth No. 5: Natural forces such as solar variability, cosmic rays or volcanic eruptions can explain the observed warming.
Nearly all of the heat at the surface of Earth comes from radiation from the sun. Perhaps, as one hypothesis goes, that radiation has become more intense in recent decades and is making the planet warmer. A second, more complicated hypothesis involving the sun proposes that higher solar activity tends to suppress the levels of cosmic rays, high energy particles from space, hitting our atmosphere. Cosmic rays help form water droplets and clouds. Clouds are thought to have an overall cooling effect on the planet. Still with us? So in this view, if the sun is more active, then there are fewer cosmic rays, less cloud cover, and a warmer Earth.
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Myth 6. The urban heat island effect or other land use changes can explain the observed warming.
The urban heat island effect is a well documented phenomenon caused by roads and buildings absorbing more heat than undeveloped land and vegetation. It causes cities to be warmer than surrounding countryside and can even influence rainfall patterns. Perhaps, the argument goes, ground based weather stations have been systematically measuring a rise in temperature not from a global effect but from local land use changes.
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Myth 7. Natural ocean variability can explain the observed warming.
The oceans are the largest single reservoir of heat in the climate system. And they do have internal cycles of variability, such as the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-decadal Oscillation (AMO). These cycles have impacts on the sea surface temperature in specific regions that vary from year to year and even from decade to decade. So perhaps, the argument goes, we just happen to be in a warm period that will last a few decades and the oceans will eventually switch back to a cool period.
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Myth No. 8: In the past, global temperatures rose first and then carbon dioxide levels rose later. Therefore, rising temperatures cause higher CO2 levels, not the other way around.
Ice cores from Dome C in Antarctica record surface temperatures and atmospheric concentrations of CO2 going back over 800,000 years. During that time, several ice ages came and went. After each ice age ended, temperatures rose first and then several centuries later, CO2 concentrations rose. This lag, some skeptics conclude, proves that CO2 increases are caused by global warming, not the other way around.
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You are invited to post comments and follow-up questions on this site. You can also e-mail climate scientists questions. The scientists cannot respond to all questions individually but will address recurring themes with new entries.
