Climate impacts and emission targets

Abstract

Based on the latest available science from groups such as CSIRO and the scientific experts commissioned by the Garnaut Climate Change Review, this policy brief summarises the implications of different carbon pollution reduction targets and projected global, national and state-level impacts. The main conclusions that can be drawn from this analysis are: • On current emission trends, unmitigated climate change is likely to have catastrophic global impacts. Under this scenario current estimates suggest that the world’s coral reefs would be lost and irreversible melting of the world’s great ice sheets would lock in several metres of sea level rise. There is also a very high risk that many forests, grasslands and other natural ‘sinks’ (or stores) of carbon pollution will, through stress, fire and desertification, become big new sources of emissions. In Australia, irrigated agricultural production in Murray-Darling Basin would all but disappear, 2,700 additional temperature related deaths are projected annually and the Great Barrier Reef would suffer “catastrophic” impacts. • Stabilising greenhouse gas concentrations at or below 450 ppm-e needs a global response, where industrialised countries as a group need to reduce emissions by 25-40% below 1990 levels by 2020. A 440 ppm-e target would substantially reduces the risk of large scale global and Australian impacts. For example, only 1-5% of species are at risk of extinction and there is only a 1-5% risk of initiating irreversible melt of the Greenland Ice Sheet. Stabilising at 450 ppm-e and not below would be risky in that it is only a 50/50 chance of avoiding a 2 degree increase. • If we choose to stabilise greenhouse gases at concentrations of 550 ppm-e we would leave future generations a legacy of very high climate risks. Greenhouse gas concentrations at this level would mean about an 80% chance of exceeding a 2 degree increase in global temperatures. The world’s coral reefs would be unable carry out important functions such as maintaining biodiversity and protecting coastlines, and there would be up to a 40% chance of initiating irreversible melt of the Greenland Ice Sheet. There would be a 50-95% chance of exceeding the estimated lower threshold above which land based carbon sinks could become carbon sources and push climate change out of control. For example this could mean the temperatures rising to a point high enough to cause the collapse of the Amazon rainforest, traditionally a carbon sink, which would then unleash billions of tonnes of carbon into the atmosphere, speeding up global warming.