What causes climate change?
(Image: Twitter/ @Rachelhatesit – soot on NZ glaciers from Aus. bushfires )
Other gasses and aerosols
- 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 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
Sulphur hexafluoride (SF6)
Video 1: The greenhouse gas is you’ve never heard of is also the most powerful.
“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
“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
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.
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.
References and further reading
- Ministry for the Environment: New Zealand’s Greenhouse Gas Inventory 1990–2017 Vol 1; Chapters 1-15
- Ministry for the Environment: New Zealand’s Greenhouse Gas Inventory 1990–2017: graphic
- Ministry for the Environment: 2019 Measuring Emissions: A Guide for Organisations
- Ministry for the Environment: 2019 Measuring Emissions: A Guide for Organisations. 2019 Summary of Emission Factors
- Ministry for the Environment: New Zealand’s Greenhouse Gas Inventory
- NOAA: Global Monitoring Laboratory Earth System Research Laboratories
- UCAR Center for Science Education: The troposhere
- 2020 Polvani et al; Substantial twentieth-century Arctic warming caused by ozone-depleting substances Nature Climate Change 10, 130-133
- 2020 WMO (World Meteorological Organization): Arctic ozone depletion reached record level
- 2019 IPCC: Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories
- 2019: The Guardian New Zealand glaciers turn brown from Australian bushfires’ smoke, ash and dust
- 2018 IPCC: Chapter 4, Atmospheric Chemistry and Greenhouse Gases
- 2018: Davy & Trompetter; Black Carbon on New Zealand, GNS Report 2017-122
- 2018: Climate and Clean Air Coalition: Annual Science Update – Black Carbon Briefing Report
- 2013 IPPC: Chapter 8: Anthropogenic and Natural Radiative Forcing in: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change