by Joseph Powell

Earth, our home, owes its habitability to greenhouse gases, which trap heat from the sun (Figure 1). According to NASA, without the 400 parts per million carbon dioxide (CO2) in the atmosphere, the Earth’s surface would be 60 degrees cooler. But when we combust fossil fuels to power our lives, we release prehistoric carbon into the atmosphere as carbon dioxide, which increases the average temperature due to its known infrared absorption of heat.

The Earth’s average temperature has fluctuated over time due to periodic variations in the Earth’s orbit, precession, and tilt relative to the sun (Figure 2). This gives rise to ice ages followed by interglacial periods approximately every 100,000 years (Figure 3). These periods correlate with carbon dioxide concentrations in the atmosphere. Humans have thrived only during the interglacial period following the last ice age.

To prevent damage to the Earth’s ecosystems, the International Panel on Climate Change (IPCC) seeks to limit temperature increases due to human-induced carbon dioxide emissions since the industrial revolution (circa 1850) to less than 2 degrees Celsius, and preferably less than 1.5 degrees Celsius. As observed in the past, temperature rise can disrupt weather patterns and induce melting of polar ice caps. As a consequence, sea levels can rise, and food production becomes more difficult, impacting our ability to feed a growing population.

Our reliance on stored fossil energy is disrupting the natural balance of our dynamic planet. In future episodes, we will explore solutions and ideas that may help.

More episodes available at Houston Public Media-dot-org-slash- UH Energy

Figure 1: CO2 as a Greenhouse Gas

The greenhouse effect traps heat from the sun and allows the Earth to be inhabitable. Carbon dioxide is a primary greenhouse gas that impacts global temperatures. Combusting fossil fuels to provide energy releases stored carbon from prehistoric times as CO2, increasing concentrations and leading to an increase in temperature.
Source: US EPA Climate Change Basics

Figure 2: Illustration of the Three Milankovitch Cycles
From the COMET Program at the University Center for Atmospheric Research

Periodic variations in the Earth’s orbit (eccentricity), tilt, and precession cause approximately 100,000-year cycles of ice ages followed by interglacial periods, with a pronounced impact on the habitability of the planet. Control of fossil CO2 emissions over and above natural fluxes is sought to ensure that the Earth’s ecosystem will not be subject to adverse human-induced changes in temperature due to the heat-trapping characteristics of carbon dioxide.
Source: Carbon Brief

Figure 3: Antarctic Temperature (via Ice Cores) and CO2 Concentrations Over the Past 800,000 Years

Average temperatures correlate with CO2 concentrations over the 100,000-year cycles of glacial and interglacial periods.

References:

 ¹ US EPA, Climate Change Basics https://www.epa.gov/climatechange-science/basics-climate-change

 ² Carbonbrief,  https://www.carbonbrief.org/explainer-how-the-rise-and-fall-of-co2-levels-influenced-the-ice-ages/

 ³ Carbonbrief,  https://www.carbonbrief.org/explainer-how-the-rise-and-fall-of-co2-levels-influenced-the-ice-ages/ , op cit.

 ⁴ International Panel on Climate Change:  Special Report Global Warming of 1.5°C.  https://www.ipcc.ch/sr15/