GES 110 - Earth's Climate

Announcements

• Exam 2 grades are posted.
  • Average: 79 (with the study guide extra credit) - Good job everyone!
  • Several scores of 100 (before the study guide extra credit) - Congrats!
  • The exam will not be distributed. Students can review missed questions during office hours or by appointment.
  • Most missed questions will be reviewed in the next class on Thursday, April 17th.
  • Reminder: The lowest exam grade (out of 4) will be dropped.

Class Topics

• Time Travel: Last Class Recap
• NOVA Video (4/3)
• Exam 2 (4/8)
• Class Canceled (4/10)
• Today’s Class:
  • Section 3: Earth’s Climate
  • Present-Day Climate
  • Climate Normals
  • Types of Climates on Earth
  • Human Impact on Local and Regional Climate
  • Book Units: 14–17

Course Outline

• Section 1. Earth and its Atmosphere
  • Earth properties
  • How we view the Earth
  • Atmospheric composition and circulation
  • Temperature and winds
  • Weather
• Section 2. Surface and Interior
  • The ocean
  • Plate tectonics, volcanism
  • Interior
  • The biosphere
• Section 3. Earth’s Climate (the whole system)
  • Present-day climate
  • Natural climate change
  • Global warming and human impact

Tying it all together: The Earth as an Integrated System

• Earth system science studies how data from various fields (atmosphere, oceans, land ice, etc.) form a picture of our planet, including its changing climate.
• Earth’s climate results from interconnected dynamics across the globe.

Main topics of the Climate section

1. Earth’s present-day climate
2. Earth’s past global climate
3. Earth’s future climate
   • The feedback loops and factors that drive climate change
   • The influence of humanity

Weather vs. Climate

• Weather: short-term atmospheric conditions.
• Climate: weather of a specific region averaged over a long period.
• Climate change: long-term change in average weather patterns defining Earth's climates (local, regional, global).
• Climate can be local, regional, and global.

Earth’s Present-Day Climates

• Climate Normal (or climactic normal): 30-year average for climate variables (temperature, precipitation).
• It provides a baseline for comparing current weather to average expectations.
  • For example, whether a particular day is cooler or warmer than usual, or if a month is wetter or dryer than normal.
• Normals are critical for:
  • Characterizing current weather and climate
  • Assessing drought conditions, freeze warnings, energy usage, operations planning (e.g., snowfall), and travel
• New "Normals" are calculated and updated every 10 years.
• Climate Normals are complex statistical calculations of weather observations.
• U.S. climate normals are calculated by NOAA, using approximately 15,000 federal weather stations across the U.S.

Changes in Climate Normals

• Comparison of the change in contiguous U.S. annual mean temperatures (°F) and precipitation totals (% change) between the new set of Climate Normals, 1991-2020, and the previous set of Normals, 1981-2010 (NOAA NCEI).

Temperature Changes

• Comparing 1991-2020 annual temperature Normals to the 20th-century average: warming is seen everywhere across the map.
• No region in the U.S. is cooler than it was during the 20th century; the West and Northeast are one to two degrees warmer.

Köppen Climate Classification System

• The Köppen Climate Classification System: divides climates into six main climate groups, based on local vegetation. Subgroups are divided based on temperature and precipitation.
• Major Groups:
  • A (tropical)
  • B (dry/arid)
  • C (temperate/mid-latitude)
  • D (continental/severe mid-latitude)
  • E (polar)
  • H (highland/mountain)

Köppen Climate Classification System Explained

• First Letter:
  • A: Tropical. Coolest month greater than $18°C$ ($64.4°F$).
  • C: Mild Midlatitude. At least one month greater than $10°C$ ($50°F$). Coldest month between $18°C$ ($64.4°F$) and $0°C$ ($32°F$).
  • D: Severe Midlatitude. At least one month greater than $10°C$ ($50°F$). Coldest month less than $0°C$ ($32°F$).
  • E: Polar. No month above $10°C$ ($50°F$).
  • B: Dry. Potential evapotranspiration exceeds precipitation on average throughout the year.
  • H: Highland. Climates of great variability due to altitude and aspect variation.
• Second Letter:
  • f: Constantly moist. Driest month has at least $6 cm$ ($2.4 in$) precipitation.
  • m: A moist climate with a dry season.
  • w: Dry in winter, wet in summer.
  • s: Dry season in summer.
  • T: Warmest month between $10°C$ ($50°F$) and $0°C$ ($32°F$).
  • F: Warmest month below $0°C$ ($32°F$).
  • S: Semiarid.
  • W: Arid.
• Third Letter:
  • a: Warmest month above $22°C$ ($71.6°F$).
  • b: Warmest month below $22°C$ ($71.6°F$) but with 4 months above $10°C$ ($50°F$).
  • c: Warmest month below $22°C$ ($71.6°F$) but with 1 to 3 months above $10°C$ ($50°F$).
  • d: As for c but with coldest month below $-38°C$ ($-36.4°F$).
  • h: Mean annual temperature greater than $18°C$ ($64.4°F$).
  • k: Mean annual temperature below $18°C$ ($64.4°F$).

ITCZ (Intertropical Convergence Zone)

• ITCZ matches abundant wildlife and forests
• Location of ITCZ in July and January
• Maximum North ~ $25°$
• Maximum South < ~ $20°$

Pressure Systems and Climate

• High pressure is associated with deserts.
  • Examples: Sonoran, Sahara, Namib, Kalahari, Great Australian.
• Descending cold, dry air.
• Rising warm, moist air.

A and B Climates

• Tropical Climates:
  • Af: Tropical wet
  • Am: Monsoonal
  • Aw: Tropical wet and dry
• Dry Climates:
  • BWh: Subtropical desert
  • BSh: Subtropical steppe
  • BWk: Midlatitude desert
  • BSk: Midlatitude steppe

Tropical Rainforest Climate (Af) Example

• Sao Gabriel da Cachoeira, Brazil.
• Warm, consistent temperatures.
• Consistently high rainfall.

Tropical Savanna Climate (Aw)

• Nkhata Bay, Malawi
• Warm, consistent temperatures.
• Variable rainfall.

Desert Climate (BWh)

• Yuma, Arizona
• Seasonal temperature fluctuations
• Low rainfall

C Climates

• Humid Subtropical: Cfa
• Marine West Coast: Cfb, Cfc
• Dry-Summer: Csa, Csb, Csc
• Dry-Winter: Cwa, Cwb, Cwc

Humid Subtropical Climate (Cfa)

• Charleston, South Carolina.
• Seasonal temperature fluctuations.
• Moderate rainfall.
• The D.C. area also falls into this climate category!

Mediterranean Climate (Csb)

• San Francisco, California.
• Consistent temperature
• Rainfall fluctuations throughout the year, though generally sunny
• Considered the most pleasant climate

D, E, H Climates

• D: Humid continental, Subarctic
  • Dfa, Dfb, Dsa, Dsb, Dwa, Dwb, Dwc
  • Dfc, Dfd, Dsc, Dsd, Dwd
• E: Tundra, Ice cap
• H: Highland

Taiga Climate (Dwd)

• Verkhoyansk, Russia
• Extreme temperature fluctuations
• Low rainfall
• Average temp: $5°F$
• Average precipitation: 6 inches

Tundra Climate (ET)

• Barrow, Alaska
• Extreme temperature fluctuations
• Low rainfall
• Average temp: $10°F$
• Average precipitation: 6 inches

Present-Day Climate Influencers

• Atmospheric Circulation: Permanent high- and low-pressure systems influence present-day climate (deserts under high pressure, rainforests under low pressure).
• Ocean: Water retains heat better than land (higher heat capacity), making the climate more moderate near the coast with less annual and daily temperature fluctuations.
• Topography: Can influence climate; mountain ranges can cause orographic lifting, resulting in deserts on the leeward side.

Poll Everywhere Questions

1. What is the difference between weather and climate?
   • a. Weather is short-term, climate is long-term
2. Which climate has the largest annual temperature fluctuation?
   • c. tundra/taiga

Human Impact on Local & Regional Climate

1. Deforestation
   • Deforestation: purposeful clearing of forested land.
   • Forests cleared for agriculture, grazing, fuel, manufacturing, and construction.
   • Deforestation has greatly altered landscapes.
   • Examples:
     • Western Europe: 2,000 years ago, 80% forested; today 34%.
     • Eastern North America: About half of the forests were cut down from the 1600s to the 1870s for timber and agriculture.
     • Today, the greatest amount of deforestation is occurring in tropical rainforests.

Deforestation Impact

• Deforestation can result in more carbon dioxide being released into the atmosphere – Carbon cycle!
• Deforestation threatens the world’s biodiversity.
• Loss of trees from a forest can leave soil more prone to erosion.
• Deforestation can disrupt the water cycle and changing the overall climate of the area.

Human impact on the climate regimes

2. Desertification
   • Desertification is the process by which once fertile land becomes desert
   • Causes:
     • Erosion
     • Drought
     • Deforestation
     • Inappropriate agriculture
     • Overgrazing
   • Typically, more than one of these above occurs
   • Example: Dust bowl, the great plains, USA.

Acid Rain

• Acid rain: precipitation that contains high levels of nitric and sulfuric acids (e.g., rain, snow).
• Normal rain is slightly acidic (pH of ~5.6); acid rain generally has a lower pH (4.2 – 4.4).
• Acid rain is primarily caused by human activities.
  • Biggest sources are coal-burning power plants, factories, and automobiles.
• Process:
  • Burning of fossil fuels → sulfur dioxide $(SO<em>2)$ and nitrogen oxides $(NO</em>x)$ into the atmosphere
  • Pollutants react with water, oxygen → sulfuric and nitric acid
  • Winds spread these acidic compounds through the atmosphere
  • When acid rain reaches the Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil.

Next Class

• Climate Feedback Loops
• Climate Forcings
• Variation in Climate
• Read Units for next class:
  • 1, 5, 18
  • 10 (El Nino section)