Getting warmer ...

The Intergovernment Panel on Climate Change (IPCC) released the Physical Science Basis: A Summary for Policymakers (PDF 1.25MB), being the first of three reports to be released this year, which together will make up the Fourth Assessment Report (4AR).

The 4AR has been six years in the writing and is based on peer reviewed and published scientific data, with contributions from about 1,500 climate scientists across the world. The final text in the Summary for Policy Makers which was released last Friday had been reviewed word by word by governments and lead authors for four days prior to its release. It is the most scrutinised climate science report available.

As the work of the IPCC is based on consensus, the outcome is general a conservative assessment and analysis of climate change science and, in particular, climate change projections and models. However, the highlights of the 4AR include a very high confidence (9 out of 10 chance) that human activities have resulting in the warming of the climate. This is the highest level of confidence that the IPCC can attribute to any subject, and demonstrates that the climate science community agrees that we have made the planet hotter and climate change is real.

The IPCC continue to assess the rate of warming as greater than at any period in the past 10,000 years, with the rate of change between 1995 to 2005 faster than any period in the previous 200 years. The major cause of anthropogenic climate change (ACC) is combustion of fossil fuels, and carbon fossil fuel emissions which have risen since the 1990s.

One of the major advances of 4AR from the previous Third Assessment Report (TAR) (published in 2001) is the certainty of future climate projections. If greenhouse gas emissions were kept constant at 2000 levels (i.e. a slight decrease to present day greenhouse gas emissions), we would be locked into future warming.

Irrespective of which of the IPCC six emission reduction scenarios we embrace (they differ by how much we reduce our greenhouse emissions and by when) decadal average warming of 0.2 degree is expected until 2030. Sea level rise and anthropogenic warming is projected to continue for centuries.

Current or increased greenhouse gas emissions are estimated to be 90 per cent likely to result in greater climatic change this century than was experienced in the last, with specific mention of sea-ice shrinkage, hot extremes, heatwaves and heavy precipitation.

These unavoidable climate changes are a consequence of positive feedback in the carbon cycle and lag time of greenhouse gas emissions in the atmosphere.

The message from these climate projections is clear: What we do today affects the climate for decades to come. We are now tasked with dealing with the “locked-in” climatic change that is a result of our historical actions, as well as massively reducing our current emissions to avoid over 2C global rise in temperature.

This brings the climate change debate to a new level of maturity. Currently thinking must now rapidly turn to how much we need to reduce our greenhouse gases to avoid a 2C rise in temperature - the threshold at which ecological systems, food security and coastal erosion becomes internationally dangerous. It is also incumbent upon us to recognise that for some regions of the world, a 1C or 1.5C rise in temperature with a consequential rise in sea level, tropical drought and potential increased intensity of extreme weather events is dangerous.

Based on the precautionary principle, principle of intergenerational equity, and responsibility for species survival, it is essential that we map our climate change policy to ensure we remain under 2C warming. All of the IPCC emissions reduction scenarios see potential warming over 2C indicating that the “storylines” of future action to mitigate climate change as influenced by economic growth and population need serious redesign.

Dr Malte Meinshausen of the Potsdam Institute for Climate Impact Research (PIK), Germany assessed a range of trajectories (PDF 1.51MB) for remaining below 2C and found that to remain above a 90 per cent certainty of not hitting 2C rise requires stabilisation of CO2 equivalents (CO2e) at 350 parts per million (ppm).