Incorrect Beliefs about the CO₂ impact on Global Warming: A Summary
Even today, a significant number of people are convinced that the CO₂ emitted by humans is not warming our planet. Several incorrect beliefs fuel this conviction.
1. Some believe that the observed warming is the result of an increase in solar energy received by earth.
2. Some point to the very low content of CO₂ and the high content of water vapor in the atmosphere.
3. Some believe that the temperature rise is because of the urban heat island effect.
4. Some suggest that CO₂ cannot be a problem because plants require CO₂.
We will review the shortcomings of these beliefs in this article.
Is global warming a result of the change in the solar energy received by earth?
If this was true, the change in global temperature would correlate with the change in solar energy over time. Figure 1 compares the change in solar activity over time with the change in global temperature.
Figure 1 Comparison between the changes in the global surface temperature and sun’s energy (solar irradiance) received by earth. Data Source¹: NASA-JPL/Caltech
The solar energy information is presented in terms of solar activity or total solar irradiation. The figure shows that the global temperature has increased markedly since the year 1960. But there has been no concurrent increase in the solar energy received by earth. In fact, there has been a slight decrease in the solar energy received by earth. This shows that an increase in solar energy is not responsible for the warming.
What about the role of CO₂ and water vapor?
As a start, let us review some basic science about greenhouse gases. Atmospheric greenhouse gases such as water vapor and CO₂, provide a blanketing effect over earth because of their ability to trap heat. If our atmosphere did not have greenhouse gases, more heat energy would have escaped back into space. This would have resulted in a hostile temperature of -18ᵒC on earth². The temperature is 33ᵒC higher because of the greenhouse gases. Thus, greenhouse gases are responsible for the comfortable temperature on earth.
Earth’s heat balance depends on the greenhouse gas content of the atmosphere. Human activities can disturb our planet’s delicate heat balance by increasing the greenhouse gas content³. The average temperature of earth has increased by over 1.1ᵒC since the industrial revolution. This increase is consistent with the basic science of greenhouse gases⁴.
But there is an important difference between the impact of water vapor and CO₂.
Water vapor is the major greenhouse gas component in the atmosphere. Yet it only plays an indirect role in the earth’s temperature rise⁵. CO₂ on the other hand plays a primary role. Let us examine the reasons below.
CO₂ is a non-condensable, long-lived gas. For example, some of the CO₂ can remain in the atmosphere for over a hundred years⁶. Unlike CO₂, water vapor is a condensable gas that can easily convert back to water. The temperature of the air determines how much water vapor it can hold. Specifically, air at higher temperature can hold a higher water vapor content. So, the impact of water vapor depends on the temperature.
Human activities release CO₂ from activities such as burning fossil fuels. As CO₂ is long-lived, it accumulates in the atmosphere. This increases its atmospheric content and blanketing effect. This, in turn, increases the earth’s temperature.
The rise in earth’s temperature because of the additional CO₂ results in extra water vapor in the atmosphere. The greenhouse effect from this extra water vapor further increases earth’s temperature⁷. In other words, the extra impact of water vapor is a result of the accumulation of long-lived greenhouse gases in the atmosphere. The extra impact would not exist if the content of the long-lived gases such as CO₂ did not increase in the atmosphere.
Let me summarize. The accumulation of CO₂ increases the temperature. This, in turn, increases the water vapor content. The extra water vapor content further increases the temperature. So, the impact of the extra water vapor only exists because of the increase in CO₂ and the other long-lived gases⁸. That is why the focus is on the long-lived greenhouse gases such as CO₂, methane, nitrous oxide and fluorinated gases.
The CO₂ content in the atmosphere is 0.04%⁹. How does such a small amount have such a large impact? Because the impact of a substance does not depend only on its quantity. It also depends on its properties. For example, the legal blood alcohol content for vehicle drivers in most countries is between 0.01 to 0.08%¹⁰. This is because of the properties of alcohol. Even levels of blood alcohol as low as 0.05% can impair human abilities¹¹. Similarly, the large impact from greenhouse gases-at very low levels-is because of their powerful ability to trap heat. Recall, CO₂ is also responsible for increasing the greenhouse gas effect from water vapor.
What about the urban heat island effect?
Is it the cause for the observed warming trend as opposed to CO₂? We will review why that is not the case below.
An urban area is warmer than the adjacent rural areas. This urban heat island effect is because of some specific features¹². An urban area has fewer natural landscapes such as vegetation and water bodies that can cool the surroundings. Urban materials such as pavements, roads, and rooftops add to the heat effect because they absorb and emit more of the sun’s heat. The large concentration of human activities in an urban area also contributes to the heat effect.
But the urban heat island effect is not the cause for the global warming trend¹³. How do we know that? Because scientists can separate these local effects from the long-term global warming trends. Scientists have known about the urban island heat effect for a long time. They account for the effect in their analysis¹⁴. The scientific community has concluded that the urban heat island effect has a negligible effect on the average global temperature rise¹⁵.
What about plants and the levels of CO₂?
Plants require CO₂ for photosynthesis. Humans have emitted over 2000 billion tons of CO₂ over the past few centuries¹⁶𝄒¹⁷. The current CO₂ levels are higher than any time in the past eight hundred thousand years¹⁸.
Studies show that the increase in CO₂ is having a fertilization effect on plants¹⁹. But plants and oceans can only absorb half of the extra CO₂ emissions²⁰. The other half accumulates in the atmosphere. This accumulation is upsetting the heat balance of our planet. It is causing a long-term increase in temperature and shift in weather patterns. Over time, the increase in heat waves and unusual precipitation is expected to have a strong negative impact on agriculture²¹. Scientists have weighed the benefits and negative effects from the rise in CO₂ levels. They have concluded with high confidence the excess CO₂ in the atmosphere, overall, is having an overwhelmingly negative impact on our ecosystems²².
Note: This is a modified excerpt from my book “The Climate Misinformation Crisis: How to move past the mistruths to a smarter energy future. “
References & Notes
[1] NASA Global Climate change. Graphic temperature vs solar activity. https://climate.nasa.gov/climate_resources/189/graphic-temperature-vs-solar-activity/
[2] NASA global climate change. What is the greenhouse effect? https://climate.nasa.gov/faq/19/what-is-the-greenhouse-effect/
[3] U.S. Department of Energy (DOE): DOE explains the carbon cycle. https://www.energy.gov/science/doe-explainsthe-carbon-cycle
[4] IPCC: AR6. Climate Change 2021: The Physical Science Basis. Figure SPM1.b: Change in global surface temperature relative to 1850–1900. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM_final.pdf
[5] American Chemical Society. Myth: Its water vapor not the CO₂. https://www.acs.org/content/acs/en/climatescience/climatesciencenarratives/its-water-vapor-not-the-CO2.html
[6] US EPA: Climate change indicators- Greenhouse gases. https://www.epa.gov/climate-indicators/greenhouse-gases
[7] Such an effect is described as positive feedback, i.e., a response that increases the temperature.
[8] This is another way of looking at this issue. Removal of the long-lived gases contributed by the human society will decrease the earth’s temperature. This will decrease the water vapor content, which will further decrease the earth’s temperature.
[9] NOAA Climate.gov. Climate change: Atmospheric carbon dioxide. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide The CO2 content of the atmosphere is 420 ppm currently.
[10] World health organization (WHO). Legal BAC limits by country. https://apps.who.int/gho/data/view.main.54600
[11] National Safety Council. https://www.nsc.org/getmedia/9f523dba-b7ec-4c66-9f7c-f360e4ea45dd/low-alcohol-risk.pdf.aspx Centers for disease control and prevention (CDC). Impaired driving. https://www.cdc.gov/transportationsafety/impaired_driving/states.html
[12] U.S. EPA. Learn about heat islands. https://www.epa.gov/heatislands/learn-about-heat-islands
[13] NASA. Global climate change. Can you explain the urban heat island effect? https://climate.nasa.gov/faq/44/can-you-explain-the-urban-heat-island-effect/
[14] IPCC Sixth Assessment Report (2021). Working Group I. The Physical science basis. https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_10.pdf
[15] IPCC Sixth Assessment Report (2021). Working Group I. The Physical science basis. Regional Fact sheets. Urban areas. https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC_AR6_WGI_Regional_Fact_Sheet_Urban_areas.pdf AR4(2007): https://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch3s3-2-2-2.html
[16] Earth system science data. Global carbon budget 2020. Vol. 12, Page 3269, Year 2020. https://essd.copernicus.org/articles/12/3269/2020/
[17] IPCC Special Report: Global warming of 1.5 oC. Chapter 2. Figure 2.3 https://www.ipcc.ch/sr15/chapter/chapter-2/
[18] NASA Global climate change. Graphic: the relentless rise of CO₂. Data: Data: Luthi, D., et al. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record. https://climate.nasa.gov/climate_resources/24/graphic-the-relentless-rise-of-carbon-dioxide/
[19] NASA. Carbon dioxide fertilization green earth: Study funds. https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth
[20] NOAA. Science on a sphere. Ocean-atmosphere CO2 exchange. https://sos.noaa.gov/catalog/datasets/ocean-atmosphere-CO2-exchange/
[21] IPCC Special Report on Climate change and land. Chapter 5. Food security. https://www.ipcc.ch/srccl/chapter/chapter-5/
[22] IPCC AR6 Synthesis Report Climate change 2023. https://www.ipcc.ch/report/sixth-assessment-report-cycle/
