According to the latest evidence the IPCC concludes that there is a 95 per cent probability that changes to the climate seen since 1950 have been caused by humans and this has mostly been caused by burning fossil fuels which release greenhouse gases such as CO2. Scientists are almost unanimous in their agreement that the planet is warming, regardless of whether or not humanity is the cause. Observational evidence shows that global temperatures have gone up by 0.85°C since 1880, with almost every location on the planet experiencing a surface warming. Sea levels have risen by 19cm since 1900, due to the thermal expansion of warmer oceans and melting glaciers and ice caps. The frequency and intensity of extreme weather has increased, with longer heat waves in Europe and Asia and an increase in bouts of heavy rainfall and droughts across the world.

These trends will continue into the future, although the rate and severity of future climate change will depend on the technological, economic and social development that occurs over the next few decades. To this end, a series of four scenarios have been developed by the climate change community to describe future emissions of greenhouse gases. Even the most optimistic, which involves net removal of carbon from the atmosphere before the end of this century, results in an increase in global temperatures of 1°C by 2100, or nearly 2°C against a pre-industrial baseline. Putting this in context, the UN Framework Convention on Climate Change declared in 2009 that global average temperature rise should be limited to 2°C to avoid the most devastating effects of global warming, with several of the most vulnerable developing countries pushing for a maximum of 1.5°C. The least optimistic projection, in which population and economic growth continues along at current trends without a concerted plan to mitigate climate change, causes global average temperatures to rise by between 3.3-4.9°C by the end of the century compared to the 1990s. The scenarios are intended to be representative rather than prescriptive, but encompass the majority of development forecasts in the scientific literature.

Hard science is only part of the story, as climate change will have a large and potentially devastating effect on ecosystems and livelihoods. The two other working groups of the IPCC focus on climate change impacts, adaption and mitigation, and will release their reports in 2014. With CO2 levels in the atmosphere recently peaking above 0.04 per cent  for the first time in recorded history, a co-ordinated global effort to confront climate change is necessary and long overdue.

Chris Smith