There is broad scientific consensus that global warming is occurring and that human activity has been the predominant cause, principally through greenhouse gas emissions, since the mid-20th century. Since 1880 the planet’s mean surface temperature has increased by about 0.8° C, with about two-thirds of the increase occurring since 1980. The planet’s ice caps are melting, glaciers are (mostly) retreating, sea levels are rising and extreme weather events are becoming more frequent and severe. These trends are likely to continue, resulting in widespread disruptions that could affect the food and water supplies of billions of people and displace millions.
The main source of greenhouse gases is the burning of fossil fuels for industry, transport and energy generation, particularly in industrialised countries. Deforestation, land clearance and agriculture are contributing to the problem. China has become the world’s largest greenhouse emitter, but in terms of emissions per person the United States, Australia, Saudi Arabia and Canada are the worst offenders.
It is too late to prevent climate change but it is not too late to take action that will significantly limit its severity, its effects and the rate at which it occurs. Just over half a trillion tonnes of carbon have been burned since the beginning of the Industrial Revolution. According to the 2013 report of the Intergovernmental Panel on Climate Change, no more than a trillion tonnes can be burnt if the average global temperature is to be kept under 2°C above the level of preindustrial times: the level above which the most dangerous effects of climate change would begin to occur. Achieving this limit will require reducing carbon emissions by 50-85% of 2000 levels by 2050.