Is CO2 a pollutant?
What the science says...
Select a level... |
![]() |
![]() | |||
Although it has some very important and beneficial effects, CO2 meets the legal and encyclopedic definitions of a "pollutant", and human CO2 emissions pose a threat to public health and welfare. |
Climate Myth...
CO2 is not a pollutant
'To suddenly label CO2 as a "pollutant" is a disservice to a gas that has played an enormous role in the development and sustainability of all life on this wonderful Earth. Mother Earth has clearly ruled that CO2 is not a pollutant.' (Robert Balling, as quoted by Popular Technology)
Before assessing whether or not CO2 is a pollutant, we must first define the term.
What is an Air Pollutant?
The US Clean Air Act was incorporated into the United States Code of Federal Regulations, Title 42, Chapter 85. Its Title III, Section 7602(g) defines an air pollutant:
The term “air pollutant” means any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive (including source material, special nuclear material, and byproduct material) substance or matter which is emitted into or otherwise enters the ambient air.
Clearly this is a very broad definition. More importantly, its Title 42, Section 7408 states that the US Environmental Protection Agency (EPA) Administrator must publish a list of certain air pollutants:
"emissions of which, in his judgment, cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare"
In Massachusetts v. Environmental Protection Agency (in 2007), the US Supreme Court held that the Clean Air Act gives the EPA the authority to regulate tailpipe emissions of greenhouse gases. Two years after the Supreme Court ruling, in 2009 the EPA issued an endangerment finding concluding that
"greenhouse gases in the atmosphere may reasonably be anticipated both to endanger public health and to endanger public welfare....The major assessments by the U.S. Global Climate Research Program (USGCRP), the Intergovernmental Panel on Climate Change (IPCC), and the National Research Council (NRC) serve as the primary scientific basis supporting the Administrator’s endangerment finding."Greenhouse gases including CO2 unquestionably fit the Clean Air Act's broad definition of "air pollutants," and must be listed and regulated by the EPA if it can be determined that they endanger public heath and/or welfare.
"the addition of any substance (solid, liquid, or gas) or any form of energy (such as heat, sound, or radioactivity) to the environment at a rate faster than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form."
Is Increasing CO2 Dangerous or Harmless?
Humans are Increasing Atmospheric CO2 Concentrations
Figure 1: CO2 levels (parts per million) over the past 10,000 years. Blue line from Taylor Dome ice cores (NOAA). Green line from Law Dome ice core (CDIAC). Red line from direct measurements at Mauna Loa, Hawaii (NOAA).
We know that the increase in atmospheric CO2 is anthropogenic from a number of lines of evidence. Atmospheric oxygen is decreasing at approximately the same rate as the atmospheric CO2 increase, which tells us that the source of the change is from a release of carbon combining with atmospheric oxygen rather than a natural release of CO2. We also know that the 30 billion tonnes of CO2 released by human activity must go somewhere, and in fact atmospheric CO2 is only increasing by about 16 billion tonnes per year (the rest is going into the oceans). CO2 produced from burning fossil fuels or burning forests also has quite a different isotopic composition from CO2 in the atmosphere, because plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios. And indeed we've observed this ratio decline in the atmosphere.
Figure 2: Atmospheric 13C ratio as measured at Mauna Loa (CDIAC)
The Increasing CO2 is Causing Global Warming
Thus we know that human emissions are increasing the amount of CO2 in the atmosphere, which as a greenhouse gas, in turn increases the greenhouse effect. This increases the amount of energy (in the form of longwave infrared radiation) reaching the Earth's surface. We've observed this increase through spectroscopy, which measures changes in the electromagnetic spectrum. Climate scientists have also quantified the amount of warming we expect to see from the energy imbalance caused by this increased downward radiation, and it matches well with observations. Given the amount of CO2 humans have added to the atmosphere already, once the planet reaches a new equilibrium state, it will have warmed approximately 1.4°C from pre-industrial levels. Additionally, we have observed numerous key 'fingerprints' of anthropogenic global warming which confirm that the warming we've experienced is due to an increased greenhouse effect.
How Much Warming is Dangerous?
There are some positive effects of global warming from increased CO2 emissions. For example, improved agriculture at high latitudes and increased vegetation growth in some circumstances. However, the negatives will far outweigh the positives. Coast-bound communities are threatened by rising sea levels. Melting glaciers threaten the water supplies of hundreds of millions. Species are already becoming extinct at a rate 100 to 1000 times higher than the “background” rate of long spans of geological time, partially due to the effects of global warming and climate change.
Quantifying exactly at what point global warming will become dangerous is a difficult task. However, based on the research and recommendations of climate scientists, more than 100 countries have adopted a global warming limit of 2°C or below (relative to pre-industrial levels) as a guiding principle for mitigation efforts to reduce climate change risks, impacts, and damages. This 2°C warming level is considered the "danger limit". During the last interglacial period when the average global temperature was approximately 2°C hotter than today, sea levels were 6.6 to 9.4 meters higher than current sea levels. Large parts of the Antarctic and Greenland ice sheets melted, with the southern part of Greenland having little or no ice.
As discussed above, the CO2 we've already emitted has committed us to about 1.4°C warming above pre-industrial levels. Given a climate sensitivity to a doubling of atmospheric CO2 of 2-4.5°C and the fact that on our current path we're headed for a CO2 doubling by mid-to-late 21st century, we're fast-approaching the danger limit.
How Soon Will we Reach Dangerous Warming?
Meinshausen et al. (2009) found that if we limit cumulative CO2 emissions from 2000-2050 to 1,000 Gt (approximately an 80% cut in global emissions), there is a 25% probability of warming exceeding the 2°C limit, and 1,440 Gt CO2 over that period (an 80% cut in developed country emissions) yields a 50% chance of 2°C warming by the year 2100. If we maintain current emissions levels, there is an approximately 67% chance that we will exceed 2°C warming by 2100.
Figure 3: Probability of exceeding 2°C warming by 2100 in various emissions scenarios in gigatonnes of carbon (RealClimate)
In short, to avoid the amount of global warming which is considered dangerous based on our understanding of the climate and empirical evidence, we need to achieve major reductions in global CO2 emissions in the next 40 years. Thus it becomes quite clear that not only is CO2 a pollutant, but it also poses a risk to public health and welfare.
Ocean Acidification
Another impact of increasing atmospheric CO2 emissions is ocean acidification. When CO2 dissolves in seawater, it increases the hydrogen ion concentration though the chemical reaction CO2 + CO32- + H2O → 2HCO3-, thus decreasing the pH of the oceans (NOAA 2008). Among other impacts, this decreasing oceanic pH has a damaging effect on corals, which form the habitat of approximately 25% of marine species (Karleskint et al. 2009). A seminal study co-authored by 17 marine scientists (Hoegh-Guldberg et al. 2007) found:
"Many experimental studies have shown that a doubling of pre-industrial [CO2] atm to 560 ppm decreases coral calcification and growth by up to 40% through the inhibition of aragonite formation (the principal crystalline form of calcium carbonate deposited in coral skeletons) as carbonate-ion concentrations decrease"
Thus not only does anthropogenic CO2 act as a dangerous pollutant due to its impacts on global warming and climate change, but it also has a major effect on marine ecosystems through ocean acidification.
CO2 is a Pollutant
When considering the legal definition of "air pollutants" and body of scientific evidence, it becomes clear that CO2 meets the definition and poses a significant threat to public health and welfare.
Advanced rebuttal written by dana1981
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Last updated on 2 July 2017 by pattimer. View Archives
Regarding lag, see "CO2 lags temperature."
Regarding carbon sequestration by agriculture--yes, it has some unrealized potential and most definitely is being considered; see "It’s too hard."
Also, see "It’s ozone."
[DB] Try here:
http://www.skepticalscience.com/global-warming-positives-negatives-intermediate.htm
I need a link to EPA's listing of CO2 as an air pollutant. This blog states "...the US Environmental Protection Agency (EPA) Administrator must publish a list of certain air pollutants....Greenhouse gases including CO2 unquestionably fit the Clean Air Act's broad definition of air pollutants and must be listed and regulated by the EPA if it can be determined that they endanger public heath and/or welfare." However, I cannot find an EPA list of air pollutants that includes CO2, and the links in this blog don't help. They lead to an EPA Endangerment Finding but not a statement that CO2 is an air pollutant. Or is that the same thing? I appreciate it.
fake progress @27... I believe they would be the same thing.
Earthling,
CO2 is poisoness to animals and (especially) marine life at low concentrations. Past mass extinctions have been caused by high CO2 levels. Calling anything that causes mass extinctions a fertilizer is ludicrous.
Traditionally CO2 has not been considered a pollutant because it does not directly cause human harm (from inhaling it, like particulates), nor does it promote harm to human health indirectly by contributing to smog creation (as NOx leads to the creation of ozone, which in turn may trigger athsma), nor does it lead to property or wildlife damage (as SO2 causes acid rain). CO2, like H2O, is an odorless, harmless emission that is beneficial to humans and wildlife. However, since about 2010, the EPA has tried to intentionally conflate CO2 with other pollutants using the new "carbon pollution" moniker. There is a deliberate intent to confuse CO2--the odorless gas--with black carbon soot (particulates). CO2 itself does not cause any direct or indirect human harm or property damage. There is a theoretical link of global warming to more inense adverse weather events, and a theoretical link of increased CO2 to sea level rise, which may necessitate waterfront modification, depending on the magnitude of the sea level rise. However, in practice, CO2 could double or triple in the atmosphere without any temperature change because there is so much H2O in the system that has about the same greenhouse gas effect. So if you want to classify CO2 as a pollutant, then H2O would also fit the definition. Historically, CO2 has not caused warming. Rather, global warming was caused by some other factor (volcanoes, meteors, sun, etc.), and the warming has caused CO2 to rise as tundra melts.
[TD] Provide evidence for your claim of deliberate intent to confuse CO2 with carbon soot. Else do not make such baseless, conspiratorial claims here.
Your claim of CO2's influence being trivial because of the H2O in the atmosphere is completely, factually wrong, because water vapor is a feedback rather than a forcing. Read the post "Explaining How the Water Vapor Greenhouse Effect Works." Read the Basic tabbed pane there, and then the Intermediate tabbed pane. If you want to comment on that topic, do so there rather than here; comments on that topic here will be deleted for being off topic.
Your claim that historically CO2 has not caused warming also is completely, factually incorrect. Read the post "CO2 Is Not the Only Driver of Climate"--the Basic tabbed pane and then the Intermediate one. If you want to comment on that topic, do so there, not here. Then watch climatologist Richard Alley's talk "The Biggest Control Knob: Carbon Dioxide in Earth's Climate History."
[RH] Extended warning snip. It would be worthy to note that the EPA initially rejected the idea of making a ruling on CO2. It was a court case "Massachusetts v. EPA" that went to the Supreme Court where the court ruled that the EPA was required to make a ruling on greenhouse gases under the Clean Air Act (Wiki). The commenter here clearly lacks sufficient understanding of the issue s/he's opining on and would be well advised to fully inform her/himself before continuing commentary.
Sorry, actually, the "carbon pollution" moniker was introduced by the Obama administration in 2013.
[RH] Searching Google Trends for the usage of the phrase "carbon pollution" shows that you are incorrect. Try it out.
Actually aed939, that CO2 was defined as a pollutant dates back to Massachusetts vs EPA in the US Supreme Court in April2007 when SCOTUS ruled that the greenhouse gases are 'air pollutants' as defined under the Clean AIr Act.
President Bush issued an executive order in May 2007, authorising the EPA to regulate GHGs for mobile sources.
If we can define pollution as the contamination of air, water, or soil by substances that are harmful to living organisms, most substances can fill-the-bill, especially when we consider high/low concentrations and temperatures. Plants that grow in areas that we don't want them will be considered as weeds. Carbon Dioxide that becomes too concentrated for our environment certainly should be considered a pollutant, but the question, and I think it is still unanswered scientifically, is what is that level? The dynamic complexity of the Earth's ecosystem suggests that when we begin tinkering with nature we may find ourselves creating additional problems for mankind that are currently unforseen.
I think carbon dioxide is not a pollution. Let talk about definition ,the definition of pollution in Webster’s dictionary is "to make physically impure or unclean: Befoul, dirty." By that definition, carbon dioxide is not pollution. However, Webster's also has the definition: "to contaminate (an environment) esp. with man-made waste." Carbon dioxide is a waste gas produced by fossil fuel combustion, so can be classified as man-made waste.
Aomsin@34,
You provided two definitions of pollution then provided the connection between human created CO2 from burning ancient buried hydrocarbons to the second definition.
Think seriously about why you opened your comment by declaring "I think carbon dioxide is not a pollution."
The interpretation of the definition is a game played by legal-minded people trying to argue against government regulations to limit harmful impacts of human activity. The EPA written legal mandate is to limit 'pollution'. That is the cause of the attempts to legally argue that CO2 from burning fossil fuels is not 'pollution' (an argument has been lost in the courts). Continuing to argue about the definition distracts from the undeniable harmful consequences of the activity. And regulatory bodies like the EPA should act to restrict the creation of harmful consequences, no matter what term is used to describe them.