What causes climate change?

What causes climate change?

Menu: The causes

(Image: Twitter/ @Rachelhatesit – soot on NZ glaciers from Aus. bushfires )

Other gasses and aerosols

Summary

  • Ozone (O3) in the lower atmosphere (troposphere) absorbs some infrared energy from earth, re-radiating it in the atmosphere. It’s short lived and entirely due to man-made emissions including methane, nitrous oxide, and carbon monoxide, mostly pollution in cities, so its concentration varies enormously in different places and times (Figs. 1 & 2).
  • Sulphur hexafluoride (SF6), has a global warming potential (GWP) 22,200 times that of CO2, and it’s increasing (Fig. 3).
  • CFCs, HCFCs, HFCs, PFCs and others (Fig. 4) are man-made chemicals with a global warming potential many thousands of times that of CO2. Some contribute to the loss of the ozone layer. CFCs have been linked to why the Arctic and Antarctic regions are warming faster than anywhere else on Earth.
  • SF6, CFCs, HCFCs, HFCs, and PFCs collectively contribute 2.4% to New Zealand’s emissions.
  • Dust, black carbon, ash, and other aerosols help cool the atmosphere by reflecting sunlight, but they also lead to increased warming if they fall on ice and snow (Cover image, figs. 2 & 6-9).

Ozone (O3)

“Ozone is present in two different areas of the atmosphere and plays two different roles. It is produced naturally in the outer layers of the atmosphere (the stratosphere) very high above earth. This stratospheric ozone helps protect the planet from the Sun’s ultraviolet rays which can damage our skin and health. This ozone is typically known as the ozone layer.

“Although ozone is vital in the stratosphere, here at the Earth’s surface it is a pollutant which can damage our health and the environment.

“At the Earth’s surface, ozone is not directly emitted but is formed by reactions of other pollutants such as nitrogen oxides and volatile organic compounds (VOCs), and sunlight. This is known as a photochemical reaction and often produces photochemical smog.

“The primary pollutants are produced mainly from motor-vehicle emissions and other combustion sources, and industrial and domestic use of solvents and coatings.

“Auckland, Hamilton and Christchurch have the highest potential for ozone pollution.” – NZ Ministry for the Environment

Fig 1: The protective ‘Ozone Layer’ in the stratosphere 20-30km above the surface of the Earth. When ozone is in the troposphere down near the surface of the Earth, it is a powerful greenhouse gas and pollutant. (Image: UCAR Centre for Science Education)
Fig. 2: Ozone in the lower atmosphere has contributed ~0.18C warming since 1850. In contrast, aerosols in the atmosphere, which reflect sunlight and prevent it reaching the Earth, have led to a slight cooling of ~ -0.46C. However, this highlights the complexity of climate change. Ozone in the upper atmosphere is essential for life on Earth, while aerosols that fall on ice and snow contribute to warming—see below. (Image: Carbon Brief)
Fig. 2: Ozone in the lower atmosphere has contributed ~0.18C warming since 1850. In contrast, aerosols in the atmosphere, which reflect sunlight and prevent it reaching the Earth, have led to a slight cooling of ~ -0.46C. However, this highlights the complexity of climate change. Ozone in the upper atmosphere is essential for life on Earth, while aerosols that fall on ice and snow contribute to warming—see below. (Image: Carbon Brief)

Sulphur hexafluoride (SF6)

Video 1: The greenhouse gas is you’ve never heard of is also the most powerful.

Fig. 3: Sulphur hexafluoride atmospheric concentrations 1994-2000. ‘Zonal’ means or averages are calculated from data taken in four Northern Hemisphere (solid lines) and three Southern Hemisphere (dashed lines) latitude zones. (Image: NOAA Global Monitoring Lab.)

SF6, CFCs, HCFCs, HFCs, PFCs, and others

Fig 4. Other greenhouse gasses that contribute to warming the atmosphere. Click on the image to be taken to the NOAA page to see the latest measurements. (Image: NOAA Global Monitoring Laboratory)

Aerosols

“While most aerosols in the atmosphere scatter incoming solar radiation, resulting in a net cooling effect on the atmosphere, BC [black carbon] absorbs significantly more light than it reflects, resulting in a net warming effect. Light absorbing particles radiate long-wave energy that heats the surrounding air which results in a positive (warming) forcing effect. Additionally, when BC is deposited on, or precipitated with snow, it lowers the albedo (reflective properties) and the absorbed light heats the snow causing it to melt which has important implications for permanent snowpack such as the Himalayan, Arctic and Antarctic regions.”                                                    – GNS Science Consultancy Report 2018

Fig. 5: (image: Climate coalition)
Fig. 6: Smoke plumes from bushfires in southeast Australia on January 4, 2020, as seen by the MODIS imager on NASA’s Aqua satellite. (Image: NASA Earth Observatory)
Fig. 7: Impact of Australian 2019-2020 wildifres over New Zealand (Image: Twitter/ @MetService)
Fig. 8: Franz Josef glacier. The albedo effect increases the melt rate of snow and ice on New Zealand’s glaciers. This in turn has an impact on river flows and water storage. (Image: Twitter/ @Rachelhatesit)

Impact of ash on glaciers is likely to accelerate melting. How one country’s tragedy has spillover effects.”                            – former Prime Minister Helen Clark

Fresh snow has an albedo of about 0.86, meaning it reflects about 86% of the sunlight that hits it. However, when aerosols like black carbon (Fig. 5) and ash from volcanoes and wildfires (Figs. 6, 7, 8 & 9) falls on snow, the albedo declines, sometimes dramatically. Dark ice and snow absorbs a much higher percentage of incoming sunlight, warming the surface faster, which hastens melting.

It will be one of the factors that is accelerating the demise of glaciers in New Zealand overall.”                                             – Prof. Andrew Mackintosh, Monash University

Fig. 9: Greenland. A combination of ash from increasing numbers and intensity of Northern Hemisphere forest fires plus algae growth plus meltwater lakes is collectively reducing the albedo effect of ice. This in turn is causing increased melting and raising sea levels. (Image: Eli Kintisch, 2017).

Explainers

Ozone:

Without ozone in the upper atmosphere (stratosphere), the DNA of plants and animals would be so damaged that life on the surface of the Earth would be unable to exist. Unfortunately, in spite of an international agreement to stop using ozone-depleting gasses, the hole in the ozone layer over the Arctic grew to a record size in 2020.


Global Warming Potential (GWP):

Is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (CO2). This is sometimes written as eCO2 or e-CO2.


 The Arctic:

Is warming at more than twice the average rate of the rest of the globe—a phenomenon known as Arctic amplification—and it is losing sea ice at a staggering pace.


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 (Fig. 10). This feedback effect then leads to more warming, then more melting, and so on.

Fig. 10: The Albedo Effect. Clean ice reflects about 90% of the sunlight that strikes it. Dark ocean water only reflects about 6%. This aerial photo shows a small portion of A-68, the iceberg that broke of Larsen C Ice Shelf in 2017 (Photo: NASA/ Nathan Kurtz)
Fig. 10: The Albedo Effect. Clean ice reflects about 90% of the sunlight that strikes it. Dark ocean water only reflects about 6%. This aerial photo shows a small portion of A-68, the iceberg that broke of Larsen C Ice Shelf in 2017 (Photo: NASA/ Nathan Kurtz)

References and further reading