Chapter 4 : Is the Earth Warming?

The Greenhouse effect

Global warming is a progessive increase in the earth's temperature. Heat from the sun reaches earth, and some is radiated back into space. Greenhouse gases, particularly carbon dioxide, trap this heat like a blanket, so the earth slowly warms up. Worldwide, the global temperature is expected to rise by 1.5 - 3o C (up to 6oF) by 2050.

Carbon dioxide is produced by natural processes including animals and volcanoes. It is absorbed by plants, oceans and the soil. Fossil fuels (coal, oil and natural gas) are the remains for plants from millions of years ago. When fossil fuels are burnt (in cars, factories, power plants) this releases extra carbon dioxide into the air. The level of carbon dioxide in the air is steadily increasing
Ice cores from Antarctica that contain trapped bubbles of air confirm that levels of greenhouses gases are now higher than any time in the last 600,000 tears.

As temperatures rise, glaciers melt and the sea levels rise. A study in 2014 showed that glaciers in Antarctica are melting at an increasing rate, that will ultimately raise sea levels by over 10 - 12ft. 2014 study

Cellular respiration

Cellular respiration is a chemical reaction that releases energy from food. Animals, plants and fungi all carry out respiration. Respiration produces carbon dioxide. In respiration, oxygen is used to break apart food molecules. The energy released by this reaction is stored as the chemical ATP.
When the cell needs energy, it breaks down ATP (adenosine tri-phosphate) to ADP (adenosine di-phosphate). Respiration is used to regenerate ATP.

Aerobic respiration : uses oxygen.
Anaerobic respiration : does not use oxygen.

Aerobic respiration
Glucose + Oxygen produces Carbon dioxide + Water + Energy
C6H12O6 + 6 O2 produces 6 CO2 + 6 H2O.

Energy is stored in the cell as ATP or NADH. Aerobic respiration is divided into three main stages:
Glycolysis, Krebs cycle and Electron transport chain.

Glucose ( 6 carbon atoms) is split into 2 molecules of pyruvic acid (3 carbons each).
This produces 2 ATP and 2 NADH. Glycolysis takes place in the cytoplasm.

Krebs cycle (or Citric acid cycle)
This breaks down the pyruvic acid to carbon dioxide.
This produces 2 ATP and 6 NADH , for every glucose molecule entering glycolysis. The Krebs cycle takes place inside the mitochondria. The Krebs cycle produces the CO2 that you breath out.

Electron transport chain
This stage produces most of the energy ( 34 ATP molecules, compared to only 2 ATP for glycolysis and 2 ATP for Krebs cycle). The electron transport chain takes place in the mitochondria. This stage converts the NADH into ATP.

The electron transport chain works as a proton pump: it pumps hydrogen ions (protons) through the membrane, and only allows them back through a protein (ATP synthase) which makes ATP.
The electron transport chain uses oxygen to accept electrons at the end of the chain (the electrons combine with hydrogen ions and oxygen to produce water molecules).

Anaerobic respiration ( or fermentation)
Anaerobic respiration does not use oxygen. Only glycolysis can occur. Single celled organisms eg bacteria and yeast can survive anaerobically. Large animals (eg humans) build up an oxygen debt when anaerobic.

During anaerobic respiration, pyruvate builds up and is converted to: lactic acid in animals and ethanol ( alcohol ) in plants.
"Beer is proof that God loves us and wants us to be happy". - Benjamin Franklin


Plants, and other photosynthetic organisms remove carbon dioxide from the air in the reactions of photosynthesis. Literally "photo" means "light" and "synthesis" means "building".

Photosynthesis is a series of reactions that form glucose and other carbohydrates.
6 CO2 + 12 H2O ----------> C6H12O6 + 6 H2O + 6 O2

There are two stages of photosynthesis :
1) Light reactions : use light energy to form chemical energy (ATP and NADPH).
2) Calvin cycle : uses NADPH and ATP to form carbohydrate from carbon dioxide.

Chlorophyll reflects ( does not use ) green light; it absorbs ( uses ) red and blue light. One idea to help search for life on other planets is to look for the characteristic wavelengths that photosynthetic organisms reflect.

Light reactions
The light reactions take place in the grana of the chloroplast. The light reactions produce ATP and NADPH, and also split water molecules to produce oxygen.

Calvin cycle
This takes place in the stroma of the chloroplast. It takes in CO2 and produces carbohydrate (glyceraldehyde phosphate or G3P). The Calvin cycle uses the ATP and NADPH that were produced in the light reactions. Photosynthesis therefore absorbs carbon dioxide from the air. So one way to reduce global warming is to plant more trees (or stop cutting down trees).

Artificial photosynthesis could produce hydrogen which can be used as a fuel in cars and generators. Hydrogen can also be produced directly from plants.

Three different types of plants:

1) C3 plants : typical plants that open their stomata during the day, and close their stomata at night.
Common plants in cool areas eg Canada.

2) C4 plants : open their stomata only briefly during the day. They store CO2 as a 4 carbon sugar.
Mainly tropical plants eg sugarcane.

3) CAM plants : only open their stomata at night. These are desert plants like cactus.

Decreasing the effects of global warming

The US has 4% of the world's population, but it produces 25% of all the greenhouse gases. In 2005 the Kyoto treaty came into effect. This was signed by over 160 countries, and requires them to reduce their emissions of carbon dioxide and other greenhouse gases. The US and Canada are the only major countries that have not ratified the treaty.
In 2006 California was the first state to pledge to cut greenhouse gases by 25% by 2020. Other states, including Florida followed over the next two years.

Alternative Energy

Most of our energy at the moment comes from fossil fuels. Chart. There are several alternatives to using fossil fuels for energy:

1) Electricity generation 2) Transportation
Ways of reducing greenhouse gas emissions:
  1. Buy energy efficient appliances
  2. Plant trees
  3. Recyle metal, glass and paper
  4. Switch to a more fuel efficient car
  5. Replace regular lightbulbs with energy efficient compact florescent, or LED bulbs
  6. Buy food grown locally
  7. Install solar panels or a solar water heater.
Last edited January 2022, by David Byres,