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There are many factors that affect climate change, making it very difficult to predict exactly how the climate will evolve over the coming decades, though we do have a pretty good idea. On this page I mention some factors that may not have been mentioned in the brief introductions or in Al Gore's documentary film.

Clouds. Do clouds cause warming or cooling? It's a tricky question, for clouds are usually light-colored and therefore reflect sunshine during the day, causing cooling, but at night they act like a blanket, stopping the earth cooling.

Aerosols. In chemistry, an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or anthropogenic (man-made). Examples of natural aerosols are fog, clouds, dust, forest exudates and geyser steam. Examples of anthropogenic aerosols are haze, particulate air pollutants and smoke. Aerosols in the atmosphere reflect about a quarter of the energy coming from the sun, so they have a cooling effect. There was a global drop in temperature from 1940 to 1980 which was caused by aerosols released from the burning of coal. After 1980 we made efforts to clean up the emissions of coal-fired power stations and they released fewer aerosols, causing the temperature to begin rising again. It has been suggested that we could deliberately inject sulfate aerosols into the atmosphere so that they would slow global warming, but such a deliberate intervention would have very unpredictable consequences and could make things worse, or could help one part of the planet while hurting another part. See 1 2 3 4 5

The melting of the tundra or permafrost in northern Canada and Siberia threatens to unleash even more carbon and methane, hastening climate change.

The burning of fossil fuel is in not the only man made source of carbon dioxide. Cement manufacturing is responsible for an estimated 5% of global CO2. Did you know that every two years China produces more concrete than the United States made in the whole of the twentieth century?

How much do volcanic eruptions contribute to climate change? The consensus is that volcanoes don't contribute very much, though aerosols (dust) put into the air by large volcanic eruptions can lower the global temperature by half a degree or so for a couple of years by blocking some of the sunlight.

Why is the Arctic warming much faster than the rest of the planet? One reason is that ice and snow are white and therefore good at reflecting the light and heat from the sun but once the ice starts melting it becomes liquid water which is very good at absorbing the light and heat of the sun, raising the temperature of the water and causing more ice to melt. It is a good example of a 'vicious circle' or 'positive feedback loop'.

Currently the gulf stream and the north Atlantic drift bring warm water towards the UK from the American east coast, causing the climate in the UK to be warmer than it would otherwise be. One worry about climate change is that it could interfere with that mechanism, causing temperatures in the UK to DROP.

Climate change is causing species to become extinct much faster than normal. According to Greta Thumberg, 200 species are going extinct every day, and this is 1000 to 10000 times the normal rate. Therefore Greta speaks of the risks of a mass extinction.

Some people have suggested that the climate change we see happening may be caused by variations in solar activity and that these variations could explain why the Earth cooled slightly from 1940 to 1980. Of course the sun drives the Earth's climate, but the idea that solar activity was responsible for the cooling has been rejected - it is now thought to be due to aerosol emissions from coal-burning power stations. The sulfate aerosols emitted from the power stations had blocked some sunlight, causing the cooling. Sulfate aerosols also cause acid rain, so the emissions were cleaned up beginning around 1980, meaning that acid rain became less of a problem but meaning also that the cooling effect was gone so the temperature began climbing again.

Photosynthesis is the process by which plants use the energy in sunshine to make glucose from water and CO2. The full chemical equation is: 6CO2 + 6H20 + energy → C6H12O6 + 6O2

Half of the world's oxygen is produced via photosynthesis in phytoplankton, single-celled plants that float in the ocean.

Cellular respiration is the process by which cells get energy from glucose - it's the exact opposite of photosynthesis: C6H12O6 + 6O2→ 6CO2 + 6H20 + energy

The same equation, or a similar one, would apply to organisms that die and then rot away.

Many people believe that forests release lots of oxygen into the atmosphere, and absorb CO2. That's only true when the amount of forest is increasing. for a mature, stable forest on a thickness of soil that does not change then the forest absorbs as much oxygen as it emits, due to the rotting of dead trees. Similarly, a mature forest does not absorb any more CO2 than it emits, for just as much CO2 is released by rotting vegetation as is as absorbs by photosynthesis. If the soil is thickening significantly with time however, or if the trees fall into swamps and cannot rot (because swamps contain very little oxygen) then that would mean that photosynthesis is emitting more oxygen and absorbing more CO2 than is being respectively absorbed and emitted due to rotting. You don't believe me? Read this National Geographic article. The value of mature forests, then, is not that they flood the world with oxygen or absorb CO2, it is that they keep lots of CO2 locked away that would otherwise be in the atmosphere. Hence forests are a great 'carbon sink'.

The greening of the Earth. One of the most trustworthy sources for climate change information must be NASA and NASA says that 'A quarter to half of Earth’s vegetated lands has shown significant greening over the last 35 years largely due to rising levels of atmospheric carbon dioxide, according to a new study published in the journal Nature Climate Change on April 25.' Here is the accompanying graphic. Note that the greening effect is not just a couple of percent, it is more than 25% in many areas, and more than 50% in some!