Causes: Cooling effect of carbon emissions
Image: Peggy Anke
Causes
- A brief history of climate change: who knew what, when
- What causes climate change?
- Would the climate be warming without humans?
- Is it just a cycle? (Earth’s wobbly orbit)
- Sunspots & solar activity
- Land use: agriculture & cities
- Volcanoes
- Ocean currents
- Black carbon & ash
- Blue hydrogen
- Greenhouse gases & how they work
- – Carbon dioxide & the carbon cycle
- – Methane (biogenic & ‘natural’ gas)
- – Nitrous oxide
- – Clouds & water vapour
- – Ozone
- – Man-made industrial chemicals
- – Aerosol pollution
- How to start an Ice Age!
- What’s in a name?
Other sections
Home > Climate wiki > What causes climate change? > Greenhouse gases > Emissions pollution
The cooling effect of carbon emissions
Summary
- Burning fossil fuels emits both long-lived greenhouse gases and short-lived aerosols such as sulfur dioxide (SO2) and nitrogen oxides (NO). Along with an increasing number of wildfires globally, these contribute to the formation of smog and acid rain, and are directly linked to the deaths of millions:
“More than 8 million people died in 2018 from fossil fuel pollution, significantly higher than previous research suggested, according to new research from Harvard University.” – Harvard School of Engineering
- When these pollutants interact with clouds, they make them brighter and more reflective. The resulting albedo effect results in cooling that masks around 1°C of warming. A sudden reduction in emissions would, perversely, result in the abrupt rise of temperatures beyond 2°C.
- The effects are more pronounced over the localised regions that emit the most greenhouse gases; that is, heavily industrialised areas such as China, and large fossil-fuel uses such as India.
- The cooling effect lasts for hours to months, but as emissions are continuous, the cooling is ongoing. The exception was when global industries and international travel largely shut down due to Covid in 2020-2021. This led to an abrupt spike in temperatures and heat-related impacts (Videos 1 &2).
- Pollutants include hydroxyl radicals, which are present in tiny quantities and have a lifetime of less than a second. However, they remove about 85% of methane from the atmosphere. The abrupt reduction in these during Covid has been attributed to the sudden, abrupt rise of atmospheric methane 2021-2022 (Video 2). Due to feedback effects and a possible tipping point being breached, methane now continues to rise at an alarming pace.
- Figures used in the IPCC Sixth Assessment Report WG1 estimate the impact of pollutants is less than 1°C. Others (Video 1) suggest this is a dangerously conservative under-estimate (the research supporting this is more recent than IPCC AR6 WGI).
- Volcanoes also emit sulfates. Eruptions have masked some warming over the last few hundred years, causing global temperatures to drop slightly for short periods.
- See also ‘water vapour and clouds‘ and ‘ozone‘, as both influence the amount of warming or cooling depending on the type of cloud and where they are in the atmosphere.
Causes
- A brief history of climate change: who knew what, when
- What causes climate change?
- Would the climate be warming without humans?
- Is it just a cycle? (Earth’s wobbly orbit)
- Sunspots & solar activity
- Land use: agriculture & cities
- Volcanoes
- Ocean currents
- Black carbon & ash
- Blue hydrogen
- Greenhouse gases & how they work
- – Carbon dioxide & the carbon cycle
- – Methane (biogenic & ‘natural’ gas)
- – Nitrous oxide
- – Clouds & water vapour
- – Ozone
- – Man-made industrial chemicals
- – Aerosol pollution
- How to start an Ice Age!
- What’s in a name?
Other sections
Home > Climate wiki > What causes climate change? > Greenhouse gases > Emissions pollution
Summary
- Burning fossil fuels emits both long-lived greenhouse gases and short-lived aerosols such as sulfur dioxide (SO2) and nitrogen oxides (NO). Along with an increasing number of wildfires globally, these contribute to the formation of smog and acid rain, and are directly linked to the deaths of millions:
“More than 8 million people died in 2018 from fossil fuel pollution, significantly higher than previous research suggested, according to new research from Harvard University.” – Harvard School of Engineering
- When these pollutants interact with clouds, they make them brighter and more reflective. The resulting albedo effect results in cooling that masks around 1°C of warming. A sudden reduction in emissions would, perversely, result in the abrupt rise of temperatures beyond 2°C.
- The effects are more pronounced over the localised regions that emit the most greenhouse gases; that is, heavily industrialised areas such as China, and large fossil-fuel uses such as India.
- The cooling effect lasts for hours to months, but as emissions are continuous, the cooling is ongoing. The exception was when global industries and international travel largely shut down due to Covid in 2020-2021. This led to an abrupt spike in temperatures and heat-related impacts (Videos 1 &2).
- Pollutants include hydroxyl radicals, which are present in tiny quantities and have a lifetime of less than a second. However, they remove about 85% of methane from the atmosphere. The abrupt reduction in these during Covid has been attributed to the sudden, abrupt rise of atmospheric methane 2021-2022 (Video 2). Due to feedback effects and a possible tipping point being breached, methane now continues to rise at an alarming pace.
- Figures used in the IPCC Sixth Assessment Report WG1 estimate the impact of pollutants is less than 1°C. Others (Video 1) suggest this is a dangerously conservative under-estimate (the research supporting this is more recent than IPCC AR6 WGI).
- Volcanoes also emit sulfates. Eruptions have masked some warming over the last few hundred years, causing global temperatures to drop slightly for short periods.
- See also ‘water vapour and clouds‘ and ‘ozone‘, as both influence the amount of warming or cooling depending on the type of cloud and where they are in the atmosphere.
Video 1: November 2022 at COP27, Dr. Ye Tao covers some of the latest research, with a critique of the IPCC 6th Assessment Report (2021) use of the lowest estimate of 0.7C, when the range is much higher. As the IPCC has consistently underestimated the speed and impacts of climate change, Tao argues that it would be prudent to prepare for a higher figure.
Video 2: Methane comes from production and transport of fossil fuels, but instead of tumbling during the global COVID lockdowns, they spiked upwards.
More information
-
The Albedo Effect: Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it much faster than the snow and ice. This feedback effect then leads to more warming, then more melting, and so on.
The effect also happens on any white surface. This explains why painting a roof black in cold regions helps the building absorb more warmth. Conversely, painting it white in tropics and desert areas, reflects more sunlight, helping to cool the building.
Image: Nathan Kurtz / NASA - The Albedo Effect: Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it much faster than the snow and ice. This feedback effect then leads to more warming, then more melting, and so on.
-
The term ‘climate forcing’ comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy reaching Earth’s atmosphere and the amount that escapes. If more solar energy escapes than arrives, the planet cools. Conversely, if less energy escapes than gets in, the planet warms.
Click here to learn about the main forcings and how they work (links to a page on this site).
-
- 2022: Peng et al; Wetland emission and atmospheric sink changes explain methane growth in 2020, Nature 612, pp477–482 (2022)
- 2022: Macnamara, Study explains surprise surge in methane during pandemic lockdown, Physics.org article explaining the above research in plain English
- 2022: Manshausen et al; Invisible ship tracks show large cloud sensitivity to aerosol, Nature 610, pp101–106 (open access)
- 2022: Watson-Parris & Smith: Large uncertainty in future warming due to aerosol forcing, Nature Climate Change 12 pp1111-1113
- 2021: IPCC Sixth Assessment Report WG1, Chapter 6 & 7
- 2019: Shindell & Smith: Climate and air-quality benefits of a realistic phase-out of fossil fuels, Nature 573 pp408-411
- 2019: Samset et al; Emerging Asian aerosol patterns, Nature Geoscience 12 pp582-584