Climate Change

• Weather


  • Temporary behavior of atmosphere (what's going on at any certain time)
  • Small geographic area
  • Can change rapidly
• Climate


  • More than "the average state of the atmosphere" because a complete climate description should also include variations and extremes to accurately portray the total character of an area
  • The most important elements are temperature and precipitation since they have the greatest influence on people and their activities and also have as important impact on the distribution of vegetation and the development of soils
• "Warming of the climate system is unequivocal, human influence on the climate system is clear ..."
• Global warming


  The increase of the Earth's average surface temperature due to a build-up of greenhouse gases in the atmosphere
• Climate change


  A broader term that refers to long-term changes in climate, including average temperature and precipitation
• • September 2023 ranked as the warmest September in NOAA's 174-year global climate record
  • 2020 2nd warmest
  • 17 of the top 18 warmest years on record have all been since 2001 (except 1998)
  • Average global temperatures have increased by about 1.09°C (1.9°F) since 1880
• Climate trends


  • The diurnal temperature range decreased. (Tmin (=night) increasing twice as fast as Tmax (=day))
  • Precipitation trend = + 5–10% for 30–85°N since 1900
  • Sea level rise = +18.5 cm since 1900
  • Snow cover extent has generally decreased

  
• Sea level rise

  • Global average sea level has risen 8–9 inches (21–24 centimeters) since 1880

  
• Glacier retreat


  • Muir Glacier retreated more than 7 miles and thinned more than 2600 feet from 1941 to 2004
• Arctic sea ice


  • September extent has decreased
• • If all permafrost thaws: 3–10 cm (1–4 in) sea level rise
  • If all the (freshwater) sea ice would melt: 4 cm (1.5 in) sea level rise
  • If all of Greenland's ice sheet melted: 6.5 m (21 ft) sea level rise
  • If all of the Antarctic ice sheet melted: ~60 m (197 ft) sea level rise
  • If the entire cryosphere thawed/melted: 67 m (220 ft) sea level rise
  • Substantial areas of coastal plains would be flooded worldwide

  
• Causes of climate change

  • Natural mechanisms: solar output, earth-sun relationships, movement of continents, atmosphere/ocean variability, volcanic activity
  • Human mechanisms: land use/land cover change, changing atmospheric chemistry
• Radiative forcing


  Measure of the climatic impact of a greenhouse gas or other forcing agent
• Major types of radiative forcings

  • Changes in greenhouse gases
  • Changes in aerosols (particles)
  • Changes in surface albedo
  • Changes in contrails
  • Changes in solar variability
  • Changes in volcanic activity
• Radiative forcing gives a first-order estimate of the relative climatic forcing of anthropogenic gases, aerosols, land-use change
• Feedbacks


  • Ice-albedo feedback: positive
  • Cloud feedbacks: positive or negative
  • Land surface feedback: positive (deforestation and hydrological cycle)
  • Water vapor feedback: positive
• General Circulation Models (GCMs)


  Numerical climate model that simulates Earth's circulation, physical processes in the atmosphere, ocean, cryosphere and on land surface, to project future climate, understand past climate, and identify causes and effects
• Data for climate models comes from weather balloons, satellites, airplanes, radar and other ground-based instruments measuring wind, precipitation, temperature, humidity, etc. Reliable records have been kept since the 1800s.
• Climate scenario


  A coherent, internally consistent and plausible description of a possible future state of the world, not a forecast
• Climate models can correctly replicate recent warming only if they include human influences
• Projected changes


  • Maximum warming in high northern latitudes
  • Warming is largest in cold season
  • Precipitation will likely increase (decrease) in some regions 10 to 20%
  • Decrease in snow cover, and sea-ice thickness + extent
  • More frequent and intense heat waves, droughts, and heavy precipitation
  • Tropical cyclones may be more intense
• Projected temperature rise: 1.0–3.7°C by 2100
• How climate change will affect people

  • Sea-level rise
  • Ecosystem change, effect on species and farming
  • Melting of polar ice, effect on shipping and wildlife
  • Coral death
  • Increase in intensity of hurricanes
  • Increase in droughts in some places
  • Increase in intense rain in some places
  • How will humans react
  • Surprise changes