Chapter 21

Understand the concept of sustainability and the definition of ecological footprint.
Understand the greenhouse effect and how disruptions in the carbon cycle are creating changes in global climate.
Know the major greenhouse gases and the differences in their lifespans and potencies.
Understand the concept of climate change tipping point and know how close we are to the CO2 tipping point.
Be familiar with strategies that we can use to reduce our ecological footprint and slow the impacts of climate change.

Sustainability: The capacity of the Earth’s natural systems and human cultural systems to survive, flourish, and adapt to changing environmental conditions into the very long future.

Dependence on Solar Energy: Central to sustaining ecosystems as it drives the water cycle, the climate, and photosynthesis in plants.
Biodiversity: The variety of life on Earth, essential for ecosystem resilience and function.
Chemical Cycling: The cycle of elements and compounds through the ecosystem, which provides necessary nutrients to living organisms.

Ecological Footprint: The amount of water and land needed to:
1. Supply a person or area with renewable resources.
2. Absorb and recycle the wastes and pollution produced by resource use.
Per Capita Ecological Footprint: The average ecological footprint of an individual in a given country or area.
Planet Earths Needed: Estimated number of Earths required to indefinitely support current ecological footprints for the present time, projected 2030, and if everyone had the average American footprint.

Over the past 3.5 billion years, Earth’s climate has been altered due to:
- Volcanic emissions
- Changes in solar input
- Shifting tectonic plates
- Impacts of meteors and asteroids
Evidence from the past 900,000 years shows that the atmosphere has alternated between periods of warming and cooling:
- Glacial Periods (Ice Ages): Times when much of the Earth's surface water is frozen.
- Interglacial Periods: Warmer periods where glacial ice melts and retreats towards the poles.

For the past 10,000 years, Earth has been in an interglacial period marked by stable climate conditions, allowing for human population growth.
Rapid changes in atmospheric temperatures have occurred since the mid-20th century due to:
- Industrialization
- Increased burning of fossil fuels
- Deforestation and land-use changes.

Greenhouse Effect: Occurs when some of the solar energy absorbed by Earth is radiated back as infrared radiation (heat) and trapped by greenhouse gases.
- Approximately 1% of the Earth’s lower atmosphere is composed of greenhouse gases.
- Most Abundant Greenhouse Gases:
- Water vapor (H2O)
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)

Between 1860 and 2004, there have been significant increases in the concentrations of greenhouse gases in the troposphere due to:
- Fossil fuel burning
- Deforestation
- Agriculture
The roles each greenhouse gas play in atmospheric warming vary depending on their:
- Atmospheric lifetime
- Global warming potential.

Climate Change Tipping Points: Thresholds beyond which natural systems may change for hundreds or thousands of years with potentially catastrophic effects.
- The CO2 tipping point is estimated to be 450 parts per million (ppm). Currently, we are at 420 ppm and could exceed the tipping point in a few decades without significant changes in activities.
Major Impacts Include:
- Melting of polar ice
- Melting of permafrost
- Rising sea levels
- Ocean acidification
- Increased severe weather events and droughts
- Declines in food production
- Expanded ranges of disease-causing organisms
- Loss of biodiversity.

Good News: We can implement existing and emerging technologies and economic tools to reduce our ecological footprints, potentially allowing for the sustainability of the human population with only one Earth.

Improve energy efficiency to reduce fossil fuel use, particularly coal.
Transition from carbon-based fossil fuels to low-carbon renewable energy resources based on local and regional availability.
Halt deforestation of tropical rainforests and engage in reforestation efforts to absorb CO2 from the atmosphere.
Shift toward more sustainable and climate-friendly agricultural practices.

Renewable Energy Sources:
- Rooftop solar-cell arrays
- Wind farms
- Bioenergy power plants
- Small wind turbines
- Smart electrical and distribution systems.
Residential and Commercial Solutions:
- Microturbines
- Fuel cells
- Small solar-cell power plants.