Physical Address
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CLAIM
It’s not possible for a trace gas, carbon dioxide, to transform & destroy the balance of a global climate infrastructure. 4 molecules in 10,000 could not raise the temperature of the entire atmosphere several degrees.
FACT
False. The rising concentration of CO2 in the earth’s atmosphere and its unique ability, along with some other GHGs, to absorb heat and re-radiate back to the earth’s surface is warming up the atmosphere leading to global warming and climate change.
WHAT THEY SAY
It has been often claimed by climate deniers that carbon dioxide or CO2 being only a trace gas does not have the capability to heat up the entire atmosphere. They also claim that rising CO2 levels is not a point of concern and is not leading to global warming. They use this claim to support other climate-related misinformation like ‘earth has warmed up before as well in the past and CO2 was not the reason for that hence we don’t need to worry about the present rise in global temperatures’. We came across such a viral post on Twitter and decided to do a fact check on the claim.
WHAT WE FOUND
To understand how CO2, being only a trace gas, has the capability to heat up the entire atmosphere, we have to first understand the concept of the molecular structure of the gases constituting the atmosphere and its connection with solar radiation in terms of the rise of atmospheric temperature.
Molecular structure of CO2 and other GHGs helps them trap heat
The atmosphere mostly comprises of nitrogen (78%) and oxygen (21%) whereas CO2 is a trace element occupying just about 0.041 % of it. When solar radiation comes from the sun and passes through the earth’s atmosphere in the form of electromagnetic radiation, mainly as ultraviolet and visible radiation, none of this can be absorbed by any constituent of the atmosphere since it is of high frequency (low wavelength).
A part of this incoming solar radiation is reflected by clouds back to the atmosphere and outer space; another part reaches the earth’s surface of which a certain amount is absorbed by the earth’s surface and another part is reflected back to the atmosphere by materials like ice and snow. Out of the part that the earth (land and ocean) absorbs, the major portion is radiated back to the atmosphere in the form of infrared radiation (IR) or heat having a lower frequency and higher wavelength.
“The compact molecular structures of Nitrogen and Oxygen do not allow them to interact with and absorb the IR emitted by the earth. In contrast, the loose structure of the molecules of CO2 and other GHGs such as methane (CH4) and water vapour (H2O) molecules permit it to absorb IR emitted from the earth,” said climate and environmental scientist, Dr Partha Jyoti Das who is the head of the ‘Water, Climate and Hazard Division’ of Aaranyak, a premier environmental NGO of Northeast India.
“The CO2 and other GHGs have the property of absorbing the IR and re-radiating it back to the earth’s surface and the atmosphere, which is why the atmosphere warms up. This re-radiated component is responsible for keeping the earth’s surface warm. Thus, the GHGs have the capacity to absorb IR and stop or slow down the rate of escaping the IR radiation to outer space,” Dr Das further said.
Natural CO2 acts as a protective blanket
Natural levels of carbon dioxide in the atmosphere act as a protective blanket as the warmth created by the blanket of CO2 and other GHGs around the earth’s surface is beneficial to human beings and the myriad of life forms (flora and fauna). Life can survive on the earth only because of the maintenance of this optimum temperature which varies between 14 to 15 degrees centigrade. Without the natural level of GHGs, the Earth would have been 33°C (60°F) cooler than it is now and largely covered by ice, meaning the Earth’s average surface temperature would be a very chilly -18°C (0°F).
Main role of CO2 emitted by human activities in global warming
What has become a problem is the emission of carbon dioxide from various human activities like the burning of fossil fuels which is ultimately increasing the amount of carbon dioxide naturally available in the atmosphere. Even if it is a small amount in comparison to the atmosphere in general, this small increase is enough to destabilize the natural balance or the amount of naturally occurring carbon dioxide in the atmosphere. Before the industrial revolution, the amount of CO2 in the atmosphere was about 288 ppm.
As of 2016, CO2 accounted for about 74.4 percent of total greenhouse gas emissions. Methane, primarily from agriculture, contributes 17.3 percent of greenhouse gas emissions. The burning of fossil fuels affects the concentration of CO2 in the atmosphere. The concertation of CO2 in the earth’s atmosphere has risen to 421 parts per million (PPM), as of May 2022, which is the highest in the last several million years. Between 1750 and 2020, about 1.5 trillion tonnes of CO2 were pumped into the atmosphere because of human activities.
According to scientists, if CO2 doubles, it could raise the average global temperature of the Earth between two and five degrees Celsius. The IPCC’s major climate science report in 2021 states that CO2’s contribution to that heat change process was more than 60 percent from 1960 to 2019. The report shows how different gases contribute to ‘radiative forcing’, the process in which more heat from the sun enters the Earth’s atmosphere than leaves it.
GWP of CO2
The concept of the Global Warming Potential (GWP) is another factor in this context. The GWP is a measure of how much energy 1 ton of a GHG will absorb over a period of 100 years, relative to the emissions of 1 ton of carbon dioxide (CO2). This term helps in comparing global warming impacts of different GHGs. The larger the GWP, the more that a given gas warms the earth compared to CO2 over a period of 100 years.
“The ability of all GHGs to warm the Earth by absorbing IR energy is not equal and therefore, they have different effects on the Earth’s warming depending on two characteristics. One is the Radiative Efficiency, which determines how much energy they can trap and re-radiate. The other is their lifetime which is how long they exist in the atmosphere,” Dr Das said.
The GWP of methane is 25, expressed as 25 CO2e (CO2 equivalent). Methane, however, produces one-third the amount of global warming of carbon dioxide since it stays in the atmosphere only for a short duration in comparison to carbon dioxide.
“It means that if 1 tonne of methane was released into the atmosphere, it would create the same warming as 25 tonnes of CO2. Although methane has a larger GWP than CO2, its contribution to atmospheric warming is less than that of CO2 since its resident time is about a decade whereas CO2 persists in the atmosphere for about a century,” Das further added.
