The global scientific consensus is that there is evidence that global warming is occurring due to the impact of human activities, which now imperils the long-term sustainability of human civilisation as we know it.
The use of fossil fuels (coal, oil and gas) started with the industrial revolution about 250 years ago, with major acceleration during the 20th century for energy, transport and industrial use. The combustion of these fuels leads to the production of carbon dioxide (CO2), which then rises to the higher levels of the earth’s atmosphere where it acts as an insulation blanket or “greenhouse gas.” This layer lets in heat from the sun, but retains more of that warmth, giving rise to the phenomena known as “global warming.” There are other greenhouses gases, notably methane (CH4) – arising particularly from the large populations of ruminants (cattle and sheep) raised by man to produce meat. At the same time deforestation and other human impacts on land use have reduced the amount of CO2 that is absorbed from the atmosphere.
Rising temperatures have several adverse impacts. Glacial and polar ice is melting leading to a progressive rise in sea level, threatening millions in coastal communities around the world. Rising temperatures also directly causes water stress and desertification and increases chance of forest fires. In Siberia, melting permafrost releases underground methane further accelerating global warming.
The increased temperatures also lead to migration of tropical diseases further north and south from the equator. The rising temperatures also lead to an increases of disruptive weather extremes, with more storms, heavy rains or droughts.
All such effects then have a human impact, as communities are disrupted by climates change, increasing migration or conflict, due to competition for scarce resources.
It is the ambition of the international community, in general, to keep the increase below 1.5C. An increase in excess of 2C being thought to pose much increased risk of further acceleration of the rate of change, and the onslaught of the adverse impacts.
Further information on the science of climate change can be obtained from the Intergovernmental Panel on Climate Change.