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MYTH #18: Carbon dioxide only causes 35% of global warming


Some scientists say that CO2 doesn’t even account for half of the warming we’ve seen recently.


What's the biggest cause of global warming today? Man-made pollution from carbon dioxide.

A 2010 study found that methane, ground-level ozone, and black carbon (i.e., soot) increase the global warming effect of carbon dioxide by 65 percent. Some people misread this as a suggestion that carbon dioxide was only responsible for 35 percent as much global warming as previously believed. What it actually says is that these short-term pollutants cause warming IN ADDITION to carbon dioxide. Nothing in the study changes the fact that carbon dioxide is the main cause of the warming we’re seeing today.

Additional info from the Union of Concerned Scientists

CO2 has caused most of the warming and its influence is expected to continue.

CO2, more than any other driver, has contributed the most to climate change between 1750 and 2005. The Intergovernmental Panel on Climate Change (IPCC) issued a global climate assessment in 2007 that compared the relative influence exerted by key heat-trapping gases, tiny particles known as aerosols, and land use change of human origin on our climate between 1750 and 2005. By measuring the abundance of heat-trapping gases in ice cores, the atmosphere, and other climate drivers along with models, the IPCC calculated the “radiative forcing” of each climate driver — in other words, the net increase (or decrease) in the amount of energy reaching Earth’s surface attributable to that climate driver. Positive radiative forcing values represent average surface warming and negative values represent average surface cooling. CO2 has the highest positive radiative forcing (Figure 1) of all the human-influenced climate drivers compared by the IPCC. Other gases have more potent heat-trapping ability molecule per molecule than CO2 (e.g., methane), but are simply far less abundant in the atmosphere and being added more slowly.

Figure 1: Carbon dioxide (CO2), more than any other climate driver, has contributed the most to climate change between 1750 and 2005.

CO2 sticks around.

CO2 remains in the atmosphere longer than the other major heat-trapping gases emitted as a result of human activities. It takes about a decade for methane (CH4) emissions to leave the atmosphere (it converts into CO2) and about a century for nitrous oxide (N2O). In the case of CO2, much of today’s emissions will be gone in a century, but about 20 percent will still exist in the atmosphere approximately 800 years from now. This means that the heat-trapping emissions we release today from our cars and power plants are setting the climate our children and grandchildren will inherit. CO2’s long life in the atmosphere provides a clear rationale for reducing our CO2 emissions without delay.