Well, it’s here, the long awaited IPCC Fifth Assessment Report. It is led by the Summary for Policy Makers as the document that is most quoted by news outlets and has more influence over public understanding of climate science than any other single text. It represents a distillation of the work of thousands of climate scientists around the world, summarising 9200 scientific publications on the physical science, impacts, vulnerabilities, adaptation and mitigation options, with 7000 of these being published since Assessment Report 4, aka AR4.
With 259 authors and over 54,000 comments spanning 39 countries, the fact of this report achieving more than 97 per cent consensus is itself remarkable.
That this consensus has held its ground in the midst of the competing pseudo-science and tabloid hostility toward climate change science is even more impressive. The summary points out that the certainty of AR5 has bettered that of AR4 because the climate models have improved, and have reproduced observed surface temperature patterns.
But will AR5 make any difference to public understanding and, more importantly, action on climate change?
Well, let’s go first to the certainty. The really big item that quality press outlets will be reporting in the morning is the 95 per cent (that’s 95 per cent) confidence that most global warming is caused by humans. That much certainly is astonishing for a report like this, from a body that is renowned for its restraint.
While the 2013 report is far less uncommittal than the 2007 report, some climate science communicators have already suggested it does not go far enough. For example, Abraham and Nutticelli, point to evidence that natural external factors had no net influence on global temperatures in the last 60 years, and that therefore the summary should spell out that the 95 per cent confidence relates to humans causing 100 per cent of global warming.
But part of the reason for the restraint here may be the masking effect of human-made aerosols which the full report on the physical science should explain today. That is, humans may be causing 100 per cent of the warming, but human activity also offsets this warming with sulphur aerosols that reduce the rate of warming by up to 30 per cent.
Another resolute but sobering item that the IPCC summary communicates is that “climate change will persist for many centuries even if emissions of CO2 are stopped”. In other words, what climate scientists call “committed warming” is now being talked about not just as fixed global average temperature that we would be committed to, but a commitment to temperature rise that will continue to increase even if mitigation of C02 dropped to zero. This is because the residence time of current CO2 concentrations in the atmosphere is potentially hundreds of years.
Overall, other trends identified in AR4 will continue, sea ice retreat, glacial melt, ocean warming, warming of surface air temperature. And these trends have now been tied to the observation that the last three decades were the warmest in the past 1400 years. These observable trends fly in the face of so many attempts by tabloid news outlets, both print and their echo-media in radio and television bulletins, to spike uncertainty and misinformation ahead of the release of the report. The standout here was the great 'global cooling' swindle inaugurated by the Daily Mail, and scandalously parroted by press outlets that have deemed themselves unaccountable to journalistic codes.
While the summary does not communicate the science in terms of regions of the globe, it forecasts that heatwaves are projected to occur more frequently and last longer, which is likely to be bad news for Australia, in particular. There seems to be a lot more certainty about more of those “angry summers” than there is of the severity of floods and storms.
As an exercise in public communication, the summary is much more confident, resolute and useful for policy makers, as its “likelihood terminology” has been ramped up by the improvement in the modelling. How the tabloid assisted denier industry is going to respond to it, or whether is will be effective in dismantling the manufactured 'debate' remains to be seen. But with this much certainty and this much consensus, the consequences of not taking any action to stop dangerous climate change are far too great to entertain a debate.
David Holmes is senior lecturer in communications and media studies at Monash University
David Holmes does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.