Climate Change and Global Warming

Estimated Actual Global Mean Temperature

• Historical Context: Thermometer records of surface temperature have been maintained for over a century, providing global data.
  • Records include surface air temperatures (land and islands) and sea surface temperatures (oceans).
  • Average global temperatures can be estimated back to the mid-19th century, but earlier data has increasing uncertainties due to sparse records.

Accelerated Warming

• Temperature Increase: The global mean temperature has increased by about 1.0°C (or 1.8°F) since the beginning of the 20th century.
  • Average global warming for the 20th century was slightly less than 0.10°C (or 0.18°F) per decade.
  • Recent decades have shown an increased rate of warming, over 0.15°C (or 0.27°F) per decade.
  • Early 20th century temperatures averaged around 13.5°C (or 56.3°F) and rose to approximately 14.5°C (or 58.1°F).

Trends in Global Average Surface Temperature

• The overall trend shows that global temperatures have risen almost 1.0°C since 1880, with more recent decades experiencing a 50% increase in the rate of warming relative to the longer-term trend.

Urban Heat Bias Concerns

• Trust in Data: Questions arise regarding the urban heat bias in temperature records due to higher temperatures in urban areas.
  • Scientists have accounted for urban heat effects in global assessments, showing that rural measurements reflect similar trends.
  • Additionally, ocean temperatures are warming, indicating an overall increase regardless of urbanization.

Additional Signs of Warming

• Evidence of warming includes multiple datasets, such as melting of snow and ice, rising sea levels, and biological changes in plant and animal behavior.
• The majority of heat from climate change is absorbed by oceans, leading to oceanic warming which influences global climate patterns.

El Niño and La Niña Phenomena

• El Niño: Leads to warm surface temperatures, allowing heat to escape into space, reducing burial of heat beneath the ocean.
• La Niña: Associated with cooler surface temperatures but increases heat burial beneath the ocean.
• Recent prevalence of La Niña conditions has promoted heat penetration into upper ocean layers despite slightly slower surface warming.

Sea Level Rise

• Ocean heat burial contributes to rising sea levels; water expands when it warms, leading to further sea level increases, compounded by ice loss.

Measurement of Atmospheric Warming

• Discrepancies have existed in temperature measurements from satellites versus ground-level data. However, corrections have led to significant agreement indicating warming at the surface and in the troposphere.

Climate Change and Historical Context

• The planet has a long climate history, with warmer periods in the past tied to high CO2 concentrations, indicating a historical precedent for current temperature rise.

Impacts of Droughts and Heat Waves

• The West U.S. drought of 1999 is linked to rising temperatures and changing precipitation patterns.
• Recent heat waves have been linked to broader climatic patterns, suggesting climate change is currently influencing extreme weather frequencies.

Conclusion

• The current climate change pattern, particularly marked warming trends, is unprecedented in human history, warranting urgent attention for mitigating effects and enhancing understanding.