Since the industrial revolution, human activity has steadily pumped greenhouse gases into the atmosphere. However, the story doesn’t stop there. Fossil fuel energy that drove the rise of modern civilization also emits vast quantities of particulate matter. Greenhouse gases push the plant towards warming, but the particulate pollution pulls us backward towards cooling. Anthropogenic climate change is a balancing act between these two influences.
Emissions are not the only area where opposing processes push and pull simultaneously at global warming. Warmer air holds more moisture, leading to increased cloud cover. Water vapor is a potent greenhouse gas that encourages warming, but the additional clouds created from atmospheric moisture reflect solar radiation and promote cooling.
Much of the pollution contributing to global warming also produces tiny particles of various sorts (aerosols) that hang in the air and float on the wind, creating smog and hazy views.
Aerosols help cool the planet by reflecting solar radiation into space and away from the earth’s surface. The implication is that greenhouse gases are more potent global warming agents than we usually assume. Their full impact hides below the cooling effect of aerosols emitted into the atmosphere along with these gases.
When countries reach their Paris Agreement goals of net-zero emissions, they will also significantly reduce atmospheric aerosols. Ironically, success in controlling fossil fuel emissions will raise global temperatures between a half degree and one degree Celsius as aerosols drop out of the air.
Aerosols are also crucial in cloud formation, and thus they influence weather patterns. But changes in weather due to aerosol removal may be regional as opposed to global. Aerosols don’t stay in the air like greenhouse gases; instead, they fall out relatively quickly.
Water vapor amplification
Greenhouse gases come in two flavors: condensable and non-condensable. Water vapor is a condensable greenhouse gas whose concentration in the atmosphere depends on temperature. Accordingly, the maximum amount of water vapor in a fixed volume of air relates directly to air temperature. Warmer air holds more moisture. When air, fully saturates with water vapor and experiences a temperature drop, the water vapor then condenses into a liquid. In the atmosphere, this condensation effect forms clouds and creates precipitation like rain and snow.
Water vapor differs from non-condensable greenhouse gases like carbon dioxide (CO2) or methane (CH4), whose concentrations hold relatively steady with temperature fluctuations.
Atmospheric warming allows the air to retain more moisture and, since water vapor is a potent greenhouse gas, that extra moisture amplifies the warming trend. But more water vapor also leads to increased cloud cover, and less sunlight reaches the earth’s surface. Hence less solar heat is available for atmospheric warming, and the atmosphere cools.
Global warming is a balancing act, and two sides of the environmental equation play out daily. More water vapor provides increased heat retention, but it also creates clouds that block sunlight and encourage cooling. Additional fossil fuel consumption leads to increases in greenhouse gases and aerosols. The gases work to warm the planet, and the aerosols fight to cool it down.
The battle plays out daily, however, the steady rise in average global surface temperature over the past 100 years attests to the fact that warming is winning out over cooling in this battle.
Water vapor amplification and global warming (Source: ArcheanWeb) – https://archeanweb.com/2020/02/12/water-vapor-amplification-and-global-warming/ Also:
Liquid clouds or ice clouds: Geotagged bacteria genes help to decide (Source: ArcheanWeb) – https://archeanweb.com/2020/06/25/liquid-clouds-or-ice-clouds-geotagged-bacteria-genes-help-to-decide/Also:
Cleaning Up Air Pollution May Strengthen Global Warming (By Chelsea Harvey) – https://www.scientificamerican.com/article/cleaning-up-air-pollution-may-strengthen-global-warming/ Also:
Climate Impacts From a Removal of Anthropogenic Aerosol Emissions (By B. H. Samset, M. Sand, C. J. Smith, S. E. Bauer, P. M. Forster, J. S. Fuglestvedt, S. Osprey, C.‐F. Schleussner; Geophysical Research Letters) – https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079 Also:
Feature Image: Smog in the skies of Delhi (Modified) – By