Science is not a belief system: it is repeatable, testable experimentation leading to a working theory. The science behind climate change is basic and can be learned during childhood schooling.
That the climate changes is undisputed - ice ages, dinosaurs, coal deposits, oil; all these are evidence of a very different climate in previous years.
The question is whether mankind is now causing another change.
The chief arguments are:
- the burning of fossil fuel releases carbon dioxide that has been stored for millions of years
- deforestation reduces the number of trees whose natural processes re-absorb carbon dioxide
- increasing meat-eating requires more cattle thus producing more methane release
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Methane is 32 times more potent than carbon dioxide in absorbing the sun's heat but carbon dioxide is by far the most abundant greenhouse gas. Methane is calculated as producing approximately 25 percent of measured atmospheric warming but ultimately, over about 10 years, it breaks down in the atmosphere into carbon dioxide and water.
Greenhouse gases do what you think - they act as a greenhouse in trapping the sun's heat.
The more greenhouse gas, the more trapped heat. The current level of carbon dioxide in the atmosphere is measured, on a mountain in Hawaii, as 400 parts per million.
This is higher than at any time in mankind's history. Trapped gas in ice cores gives us the ability to check this and measure historic levels back to 800,000 years.
Why does it matter if greenhouse gases increase?
The Earth's atmosphere and oceans are a linked heat engine. The sun gives it heat, the environment benefits, and we are happy in our greenhouse. If the greenhouse warms up, it becomes less comfortable.
New period in Earth's history
Weather is short-term climate and weather systems are created from the energy within the earth’s atmosphere. If that energy is increased, in other words if the temperature rises, the weather changes.
The most obvious changes are new records for high temperature, increased violence of storms and erratic occurrence of seasonal weather.
The oceans store most of that energy and ocean currents transport it around the world. If the oceans warm, they expand - sea levels rise. Kiribati and Mauritius gradually submerge. If the oceans warm, there is less ice. The Arctic winter ice cover is now decreasing in extent alarmingly quickly.
If the air warms, so does the ground. Siberia's permafrost is melting.
Does that matter? For the local inhabitants, the answer is "yes" - their houses sink and hard ground becomes a swamp.
For the world, the answer is also "yes" - permafrost has trapped within it gigatonnes of methane. Melting permafrost releases methane and, as mentioned earlier, methane is 32 times more effective than carbon dioxide at holding the sun's heat.
The Paris accord seeks to reduce greenhouse gas emissions by all countries within the United Nations. It has set a goal of limiting global warming to below two degrees Celsius. This is unlikely to be achieved because the Earth reacts slowly and we have already emitted enough carbon dioxide to lift the average temperature by more than 2C.
Such is the scientific consensus that mankind has indeed changed the climate, over and above any natural process, that a new period in the Earth's history has been suggested.
The Anthropocene is a proposed epoch dating from the start of significant human impact on the Earth's geology and ecosystems.
