- The scientific consensus is that the recent increase in global temperature is caused by human activity.
- Human activity has caused global warming by enhancing the greenhouse effect - the effect of greenhouse gases absorbing outgoing energy, so that less is lost to space.
- The greenhouse effect is essential to keep the planet warm, but too much greenhouse gas in the atmosphere means the planet warms up.
- Two of the main green house gases are CO2 and methane:
- Atmospheric CO2 concentration has incresed rapidly since the mid-19th century from 280 ppm to nearly 380ppm. The concentration had been stable for the previous 10 000 years.
- CO2 concentration is increasing as more fossil fuels like coal, oil, natural gas and petrol are burnt. Burning fossil fuels releases CO2.
- CO2 concentration is also increased by the destruction of natural sinks. CO2 is released when trees are burnt, or when decomposers break down the organic compounds and respire them.
- Atmospheric methane concentration has increased rapidly since the mid-19th century from 700ppb to 1700ppb in 2000. The level had been stable for the previous 850 years.
- Methane concentration is increasing because more methane is being released into the atmosphere, e.g. more fossil fuels…