While carbon dioxide is non-toxic, its main environmental effect is as a greenhouse gas. Each year an estimated 30 billion tonnes of carbon dioxide are emitted due to human activity, 2% of which originates from the United Kingdom.
To illustrate the scale of the impact of these emissions as a result of human activities, the atmospheric concentration of carbon dioxide (from all sources) has increased by 31% since 1750. The present concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years. Over the last two decades, about three-quarters of the anthropogenic emissions of carbon dioxide have been a result of burning of fossil fuels, the rest being predominantly due to land-use change (eg deforestation).
By enhancing the greenhouse effect, greenhouse gas emissions are leading to increases of the Earth’s atmospheric, land and sea temperatures. During the 20th century the global average surface temperature (the average of near surface air temperature over land and sea surface temperature) increased by 0.6 (+/-0.2)°C. This temperature is predicted to increase by 1.4-5.8°C by 2100 (1990 baseline). Based on palaeo-climate data, the projected rate of warming is very likely to be without precedent during at least the last 10,000 years. The concomitant rises in sea levels and resulting climatic change will be of great (and as yet unknown) significance to all patterns of life on Earth.