Climate Change - Comprehensive Notes

Climate Change

California and southwest wildfires occurred in 2022, 2023, and 2025, following a prolonged drought.
These areas experienced less precipitation and longer, hotter summers.

Upper Colorado Watershed drought conditions as of January 26, 2021:
- None: 0.00%
- D0-D4: 100.00%
- D1-D4: 99.60%
- D2-D4: 92.28%
- D3-D4: 83.67%
- D4: 53.29%
Drought intensity:
- D0: Abnormally Dry
- D1: Moderate Drought
- D2: Severe Drought
- D3: Extreme Drought
- D4: Exceptional Drought
The Drought Monitor focuses on broad-scale conditions, and local conditions may vary.

Lake Mead, Nevada (1983, 2003, 2023) experienced prolonged drought from 2000-2023.
The Colorado River discharge rate has decreased over the past century, while water demand has increased.
Less precipitation and longer, hotter summers result in lower snowpack and recharge to the basin.

Atmospheric rivers are giant streams of water vapor.
Weaker atmospheric rivers bring needed rainfall, while intense ones cause extreme precipitation, flooding, and mudslides.
Strong atmospheric rivers can carry more than twice the volume of the Amazon River.
They average 250-500 miles wide, 1.8 miles deep, and hundreds of miles long.
About 30-50% of the West Coast's annual precipitation comes from atmospheric river events.
Global warming and sea surface temperatures will cause atmospheric rivers to intensify in area, magnitude, and duration.

Global temperature trends since the Industrial Revolution can only be explained by human-induced warming related to fossil fuel energy use (~74% GHG emissions) and livestock (~14.5% GHG emissions).
2024 was the hottest year on record, exceeding the 1.5°C above the 1850-1900 average; the anomaly recorded was +1.55°C (2.7°F).
The top 10 hottest years on record have occurred within the last 10 years.
The Earth’s climate has been relatively stable over the prior 2000 years. Global temperature anomalies relative to 1850-1900 have varied by less than 0.3°C.

Arctic sea ice reached its lowest extent in late summer of 2012 (compared to the average over 30 years).
The Arctic region could be ice-free within 30 years.
Since 1979, 20% of the polar ice cap has melted away.

Methane gas has a greater greenhouse effect than CO2, but its anthropogenic production and overall atmospheric level are lower.

Atmospheric CO2 concentration at Mauna Loa Observatory:
- June 1st, 2025: 429.33 ppm
- June 1st, 2024: 427.43 ppm
- Increase of 1.90 ppm (0.44%)
On May 11th, 2019, we exceeded 415 ppm, a level of atmospheric CO2 not reached since humans evolved on Earth (3 million years ago).

There is a clear correlation between global temperature anomalies and global annual average carbon dioxide levels.

China surpassed the U.S. in carbon dioxide production 17 years ago, and India and Brazil are rapidly increasing their production.

Snow is converted to glacial ice in 1-5 years to century time scales.
Atmospheric gas bubbles are trapped within the ice, preserving a record of atmospheric gas composition.
Ice core records from Greenland and Antarctica can extend back 100,000’s of years.
Ice cores from Greenland and Antarctica provide detailed records of atmospheric gas composition over multiple glacial-interglacial cycles; Antarctic cores extend back beyond 450,000 years.

The relationship between global temperature and atmospheric CO2 concentration is undeniable, as shown by ice core and other paleotemperature proxy data.

Anthropogenic concentrations of CO2, CH4, and N2O over the last 10,000 years and since 1750.
Measurements are shown from ice cores and atmospheric samples. Radiative forcings relative to 1750 are also shown.
Atmospheric concentrations of CO2 and CH4 in 2005 exceed by far the natural range over the past 650,000 years.

Atmosphere-Ocean General Circulation Model projections of surface warming (2020-2029 and 2090-2099).
Equilibrium temperature increases vary based on inferred pre-industrial range of stabilization levels.

The South Cascade glacier, WA, has retreated several kilometers up-valley since 1928.
Most alpine glaciers worldwide have been retreating since the end of the Little Ice Age near the mid-19th century and currently have negative mass balances.
Retreat rates have increased in the last several decades.
Retreat of the Athabasca Glacier (1963-2019), Jasper National Park, Alberta, Canada.

Mt. Kilimanjaro, Tanzania, will lose all its glacial ice possibly within the next 20 years.

Ocean acidification is correlated with increasing atmospheric CO2 concentration. Shell deterioration in pH solution of 7.8

As of 2022, over 50% of Australia’s Great Barrier Reef is dead due to Coral Bleaching related to rising surface ocean temperatures.
Great Barrier reef encompasses 2300 km (1400 miles) of Australia’s eastern coastline.