As the fervor over global warming continues to permeate the discussions of politicians and the media alike, I’ve noticed a stock set of anecdotal arguments from those who choose to remain unconvinced of anthropogenic global warming. A lot of their arguments remind me of the arguments of those who believe NASA faked the moon landings: “Well, in their pictures you don’t see the stars, so it must have been done in a studio.” Um, have you ever tried taking a picture of the night sky? How many stars do you see? But I digress…

While RealClimate has a solid collection of responses to common contrarian arguments, I have yet to see a concise, simple document targeted at the average reader for debunking the global warming denier crowd. NASA has hardly bothered to produce a response to moon landing deniers, finding it impossible to do so with a straight face at the preposterousness of the claims. Given the gravity of global warming, we similarly must respond seriously to the denialists even if it pains your face to keep from laughing in theirs.

This is my collection of rebuttals for the most prominent arguments put forth by the folks who deny anthropogenic climate change.

1. Mars is undergoing global warming, therefore humans can not be causing it on Earth.

No. Mars is not undergoing global warming. The Mars Global Surveyor detected a decrease in the mass of the South Polar Cap between 1999 and 2005. First, this is a regional (not global) warming localized to the south pole of mars. There is no similar data for any corresponding temperature change at either the north pole or any other part of Mars. Secondly, since a Martian year is 687 days, this represents only 3 data points, which does not equate to the long-term trend we see on Earth. (Indeed, we see dramatic peaks and valleys in the yearly temperature data on Earth.) Lastly, research has shown that Mars’ climate is far more volatile than our own, and is quite sensitive to changes in dust storm activity and orbital variations. If most of the planets and moons in the solar system were exhibiting warming trends, that would be a valid point for argument.

2. Volcanoes release much more carbon dioxide than humans.

No. Volcanic activity is 0.02 to 0.05 Giga-tons/year. [Note: 1 Peta-gram (PgC) = 1 Gigaton (Gt)] Humans produce 8 Gt/yr (and climbing). Volcanoes elicit a far more dominating cooling effect due to atmospheric dispersal of particulates and sulfur dioxide. In addition, there has been no recent increase in volcanic activity – and the volcanic activity we have seen has actually slowed global warming.

3. The Earth (and its carbon cycle) is too big for humans to affect it.

While the Earth exchanges a great deal of carbon between the ocean, atmosphere, soil, and biosphere, it is the net balance which is of greatest concern to us. Without human influence, this regulatory process produces a net carbon increase of 0.0 Gt/year. During 1850-2000, through a combination of fossil fuel burning, cement manufacturing, and land-use changes, humans added a net 174 Gt of carbon. This caused the majority of an increase from 288 ppm (parts per million) to 369.5 ppm of CO2. As mentioned above, we currently add 8 Gt/year to the atmosphere.

4. The sea level has not changed.

Yes, it has. Since 1900, sea level has risen by about 35 cm (13.8 inches). This change in sea level is accelerating.

5. Scientists predicted imminent global cooling in the 1970s.

No, they did not. Some magazines reported it as such, but scientists understood that their preliminary, localized, and uncertain measurements could not be extrapolated to either the world or a long-term trend. They did indicate that the potential for an ice age in the next 20,000 years was possible, but they made no predictions. Climate science has advanced tremendously in the intervening years, as has the data, and the conclusions for our climate are far more certain.

6. Scientists get paid big bucks to skew their data to indicate global warming.

No, they don’t. There is little commercial funding available for research designed to support global warming. It is far more lucrative to produce research denying global warming. With little exception, funding for climate research is provided by governments, which do not attach conditions to the results of the research (OK…maybe some conditions).
Logically, of course, it doesn’t make sense that corporations or governments would want to fund skewed studies that indicate their entire way of living is threatening the planet. And with tens of thousands of scientists producing research indicating human-induced global warming, the task to compromise the ethics of so many esteemed professionals would be, to say the least, challenging.

7. Variations in solar output cause global warming

While global warming could not occur without solar influx, the sun’s output has been relatively stable for as long as we’ve studied it, and has in fact been declining in recent years. Solar variability plays a very small role, if any, in global warming.

8. All temperature data is suspect due to the urban heat island effect.

That argument might be valid if all measurements were taken in the heart of cities. But they aren’t. Thermometers in the middle of the arctic, in barren deserts, in the middle of oceans, on top of mountains, and deep in the wilderness all agree on a global temperature rise. Unless you believe that the urban heat island effect can affect satellites, this claim is clearly wrong.

9. Because it snowed a great deal and got very cold in some areas, global warming is not happening.

First, increased precipitation is predicted by global warming. Increased snowfall events are further evidence of global warming, not proof against it. Second, regional temperature variations occur. It is the global average temperature which is of greatest concern. And third, temperatures vary. Even record cold global temperatures for an entire year would not be out of step with global warming. Global warming is about the long-term average trend.

10. It is not possible to distinguish the effects of human activities from natural processes with regard to CO2.

That is not true. We know >how much CO2 is produced from burning a barrel of oil and we know how many barrels of oil we use. Similarly, we know how much CO2 certain types of plants absorb and we have solid estimates for how many of each type of plant exist. The same goes for volcanoes, the ocean, and the soil. It is a matter of collecting this data, which is the task undertaken by hundreds of scientists. Estimates vary, but they all agree on one point — humans are causing global warming.