Global Climate Change Notes

Ozone ( $O_3$ ) in the stratosphere (about 20 km altitude) absorbs 99% of UV radiation from the sun.
Most ozone forms over the tropics and moves toward the poles via air currents.
The ozone layer's thickness varies across Earth.

Good Ozone (Stratospheric):
- The ozone layer filters out UV radiation, acting as a global sunscreen.
- Formation: 3O2 + uv leftrightarrows 2O3
Bad Ozone (Tropospheric):
- A secondary air pollutant at ground level.
- Causes asthma, bronchitis, harms lung function, irritates the respiratory system, causes heart attacks, and suppresses the immune system.
- Produced through burning of fossil fuels.
- Formation: $NO2 + uv \rightarrow NO + O$ , $O + O2 \rightarrow O3$ , or $NOx + VOCs \rightarrow PANs + O_3$

Stratospheric ozone is crucial for life's evolution and survival on Earth.
It filters out 99% of UV radiation, acting as a global sunscreen.
Ultraviolet radiation is part of the electromagnetic radiation emitted by the sun.

UVA:
- Closest to blue light; birds, reptiles, and bees can see it.
- Usually causes skin tanning.
UVB:
- Causes sunburns and is responsible for skin cancer.
UVC:
- Found in the stratosphere and is largely responsible for ozone formation.
A decrease in stratospheric ozone increases UV rays reaching Earth's surface, leading to skin cancer and cataracts in humans.

Ozone layer thinning occurs naturally (e.g., melting of ice crystals in the Antarctic spring).
In 1984-1986, scientists discovered man-made thinning above Antarctica, traced to chlorofluorocarbons (CFCs).

CFCs are very stable compounds that reach the stratosphere.
In the stratosphere, they react with UV radiation and ozone.
Their stability results in low reactivity, low toxicity, and low flammability.
They were used in refrigeration (air conditioning and refrigerators) and as propellants in aerosols/hairspray.
Banned in 1987 by the Montreal Protocol (but are still produced/sold on the black market).
Ozone depletion can be mitigated by replacing ozone-depleting chemicals with substitutes like hydrofluorocarbons (HFCs), though some HFCs are strong greenhouse gases.

Sunlight strikes Earth's surface, some is reflected back as infrared radiation (heat).
Greenhouse gases absorb this infrared radiation, trapping heat in the atmosphere.
The greenhouse effect results in a surface temperature necessary for life on Earth.
Principal greenhouse gases: carbon dioxide ( $CO2$ ), methane ( $CH4$ ), water vapor, nitrous oxide ( $N_2O$ ), and chlorofluorocarbons (CFCs).
Water vapor has a short residence time, so it doesn’t contribute significantly to global climate change.
Carbon dioxide (GWP = 1) is the reference point for comparing greenhouse gases.
Chlorofluorocarbons (CFCs) have the highest GWP, followed by nitrous oxide, then methane.

Earth’s carbon cycle regulates carbon dioxide levels through photosynthesis and ocean absorption.
The carbon cycle cannot absorb all carbon dioxide added by human activities like burning fossil fuels.
Humans add carbon dioxide faster than it can be absorbed naturally.
Only half of the carbon dioxide emissions are absorbed each year through natural processes.

Climate change has occurred throughout geologic time with shifts in global temperatures recorded with CO2 data and ice cores.
The current rate of climate change is faster than before.
Past climate change was caused by natural causes; now it is primarily due to increased greenhouse gases.

Carbon dioxide:
- Pre-Industrial (1750): 280 ppm
- Post-Industrial (2020): 411 ppm
- GWP: 1
- Atmospheric lifetime: 120 years
Methane:
- Pre-Industrial (1750): 700 ppb
- Post-Industrial (2020): 1834 ppb
- GWP: 25
- Atmospheric lifetime: 12 years
Nitrous oxide:
- Pre-Industrial (1750): 270 ppb
- Post-Industrial (2020): 328 ppb
- GWP: 310
- Atmospheric lifetime: 120 years
CFCs:
- Pre-Industrial (1750): 0 ppt
- Post-Industrial (2020): 232 ppt
- GWP: 4000+
- Atmospheric lifetime: 50-100 years
HFCs:
- Pre-Industrial (1750): 0 ppt
- Post-Industrial (2020): 84 ppt
- GWP: 1430
- Atmospheric lifetime: 14 years
Tropospheric ozone:
- Pre-Industrial (1750): 25 ppb
- Post-Industrial (2020): 34 ppb
- GWP: 17
- Atmospheric lifetime: hours
Sulfur hexafluoride:
- Pre-Industrial (1750): 0 ppt
- Post-Industrial (2020): 8.6 ppt
- GWP: 23500
- Atmospheric lifetime: 3200 years

Greenhouse effect: the warming effect of Earth’s atmosphere.
Global warming: the steady measured increase in Earth’s surface temperature.
Climate change: the long-term climatic effects of the greenhouse effect and global warming.
Global climate change can lead to:
- rising sea levels from melting ice sheets and ocean water expansion
- decreased ability of ocean waters to absorb carbon dioxide (solubility of gases decreases in increased temperatures)
- disease vectors spreading from the tropics toward the poles
These issues can lead to changes in human population dynamics, emigration, animal and plant migration and extinction.

Rising temperatures, melting permafrost and sea ice, rising sea levels, and displacement of coastal populations.
Marine ecosystems affected by sea-level changes: new habitats on flooded continental shelves and deeper communities may no longer be in the photic zone.
Climate change may change atmospheric circulation patterns, impacting Hadley cells and the jet stream.
Oceanic currents carry heat throughout the world; changes can impact global climate in coastal regions.
Climate change can affect soil viability and potentially increase erosion.
Polar regions show faster response times due to ice and snow reflecting energy, leading to a positive feedback loop.
Melting ice and snow means less solar energy is radiated back into space, causing more warming of the polar regions.
Global climate change response time in the Arctic is due to positive feedback loops involving melting sea ice and thawing tundra, and the subsequent release of greenhouse gases like methane.
Loss of ice and snow in polar regions affects species that depend on the ice for habitat and food.

Ocean warming is caused by the increase in greenhouse gases in the atmosphere.
Ocean warming can affect marine species in a variety of ways, including loss of habitat, and metabolic and reproductive changes.
Ocean warming is causing coral bleaching, which occurs when the loss of algae within corals cause the corals to bleach white.
Some corals recover and some die.

Ocean acidification is the decrease in pH of the oceans, primarily due to increased $CO_2$ concentrations in the atmosphere.
As more $CO_2$ is released into the atmosphere, the oceans become more acidic.
Anthropogenic activities that contribute to ocean acidification are those that lead to increased $CO_2$ concentrations in the atmosphere: burning of fossil fuels, vehicle emissions, and deforestation.
Ocean acidification damages coral because acidification makes it difficult for them to form shells, due to the loss of calcium carbonate.

Coral reefs have been suffering damage due to a variety of factors, including increasing ocean temperature, sediment runoff, and destructive fishing practices.