CLIMATE CHANGE

Introduction to Climate Change

·         Definition: Long-term, significant change in average weather patterns (temperature, precipitation, winds) over an extended period (typically 30+ years).

·         Current Trend: The planet is warming faster than at any point in recorded history, with the last decade (2015-2024) being the warmest on record.

·         Key Concept: The warming is unequivocal—a certainty—and primarily driven by human activities (anthropogenic). 

II. Primary Evidence of Global Warming

·         Rising Surface Temperatures: Earth's average surface temperature has risen by about 1°C-1.42°C since the late 19th century. Each of the last four decades has been successively warmer than any preceding decade since 1850.

·         Warming Oceans: The ocean has absorbed over 90% of the excess heat trapped by greenhouse gases in the climate system.

·         Ocean Acidification: The ocean absorbs about 30% of human-emitted, causing increased acidity (lower pH) which threatens marine life.

·         Rising Sea Levels: Global sea levels have risen by about 20 cm (8 inches) since 1901, a rate that is accelerating. Both the melting of land-based ice and thermal expansion (water expanding as it warms) causes this.

·         Shrinking Ice Sheets and Glaciers: Greenland and Antarctica are losing mass, and glaciers are retreating globally (Alps, Himalayas, Andes, etc.).

·         Declining Arctic Sea Ice: Arctic sea ice has thinned and reduced in extent by over 40% since 1978. 

III. Indirect Evidence & Environmental Shifts

·         Decreased Snow Cover: Spring snow cover in the Northern Hemisphere has decreased over the past five decades.

·         Extreme Weather Events: Increased frequency and intensity of heatwaves, heavy precipitation (floods), and drought.

·         Shifting Ecological Zones: Changes in the timing of seasonal activities, such as earlier plant flowering, bird migration, and altered hibernation patterns.

·         Reduced Permafrost: Thawing of frozen ground in Arctic regions. 

IV. Atmospheric and Geological Evidence (Paleoclimate)

·         Atmospheric  Levels: Current  levels are over 420 ppm, the highest in at least 2 million years.

·         Ice Core Data: Air bubbles trapped in ice sheets in Antarctica and Greenland provide a record of atmosphere composition spanning 800,000+ years.

·         Tree Rings and Sediments: Used to reconstruct past climate conditions (dendroclimatology), showing current warming is anomalous. 

V. Key "Fingerprints" of Human Influence

·         Troposphere Warming/Stratosphere Cooling: The lower atmosphere (troposphere) is warming, while the upper atmosphere (stratosphere) is cooling—a signature expected from greenhouse gas trapping of heat.

·         Nighttime Warming: Nights are warming faster than days.

·         Chemical Signature of Carbon: Atmospheric carbon has a "lighter" isotopic signature, indicating it comes from burning fossil fuels rather than natural sources.