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Update Paper 5: The science of climate change
Summary of key points
- Observations and research outcomes since 2008 have confirmed and strengthened the position that the mainstream science then held with a high level of certainty, that the Earth is warming and that human emissions of greenhouse gases are the primary cause.
- By mainstream science I mean the overwhelming weight of authoritative opinion in the relevant disciplines, as expressed in peer reviewed publications.
- The statistically significant warming trend has been confirmed by observations over recent years:
- global temperatures continue to rise around the midpoints of the range of the projections of the Intergovernmental Panel on Climate Change (IPCC) and the presence of a warming trend has been confirmed;
- the rate of sea level rise has accelerated and is tracking above the range suggested by the IPCC; and
- rates of change in most observable responses of the physical and biological environment to global warming lie at or above expectations from the mainstream science.
- It is an awful reality that no major developments in the science hold out realistic hope that the judgements of the 2008 Review erred in the direction of overestimating the risks of climate change.?
- The judgement of the Review?that the greater risks of severe consequences under a scenario of 550 ppm concentrations of greenhouse gases make the extra mitigation cost to achieve a 450 ppm outcome worthwhile?has been confirmed.
- There is increasing discussion in the legitimate scientific literature of the possibility that large damage will occur at smaller increases in global average temperature than the IPCC focus and United Nations (Copenhagen and Cancun) agreement on holding temperature increase to 2?C or less above pre-industrial level. ?
- There is a case in managing the risks of climate change for seeking to reduce emissions concentrations below 450 ppm carbon dioxide equivalent, but that would first require a credible programme to get to 450 ppm.
- Despite the increased scientific understanding of climate change, and confidence in the science’s conclusions about climate change, public confidence in the science seems to have weakened somewhat in Australia and some other countries since 2008.
- The scientific community has given greater attention to the ‘emissions budget’ approach that was introduced in the 2008 Review to the global and national task of reducing emissions. This approach warns us that we are rapidly utilising the atmosphere’s remaining capacity to absorb greenhouse gases without generating high risks of dangerous climate change?and now face the challenge of absorbing more carbon dioxide from the atmosphere than we are adding from human activity.?
- The immediate implication is that avoiding high risks will require large changes in trajectories at an early date.