A stark appraisal of the synthesis report of the IPCC 4th assessment (AR4) reveals some disturbing realities.
First, stabilisation scenarios indicate that to have a reasonable chance of avoiding 2 to 2.4°C warming, we will need to achieve global emissions reductions of 50 to 85 percent by 2050, relative to year 2000 output and a levelling off by no later than 2015. On a globally equitable basis, the burden on developed nations will be higher (80 to >95% by 2050) because of their disproportionately high per capita emissions. Second, there is no mitigation scenario proffered for <2°C, yet the model scenarios do take us into the intemperate realm of 4.9 to 6.1°C of planetary heating.
The IPCC, it seems, is not at all confident that global society will be able to implement the sort of wholesale socio-economic restructuring that is likely to be required to stave off substantial global warming this century. It seems, therefore, quite necessary to assess the likely implications of scenarios for a 2 to 6°C warmer Earth. I did this recently in a speech to the Manning Clark House conference ‘Imagining the Real’, and followed this up at the 2008 JD Stewart Address I delivered to the University of Sydney. You can download the slides and listen to the audio here. My Climate Change Q&A seminar #4 on 19 September will cover similar ground, with a slightly different slant.
In brief, analogue climates from deep time may help in this “imagining the real” - when the real is something never before witnessed by humanity, or indeed, at its most extreme, by most species now occupying the planet.
The average lifespan of a species is 1 to 10 million years, and yet to approach conditions 4 to 6°C hotter than today’s climate, we must look back to the world of the Eocene, some 35 to 50 million years ago. The world was then a very different place – there was no permanent ice cap shrouding Antarctica, sea levels were considerably higher than today, and deserts were more widespread. The tundra and boreal forests were limited or non-existent.
The cooling descent into the icehouse conditions of the Quaternary, 1.6 million years ago through to the present, was a slow progression that took place over tens of millions of years – an unimaginably vast stretch of time. Although this slide from a Cretaceous greenhouse world towards a “modern climate” was punctuated by occasional rapid climatic reversals, the globally hot conditions of the deeper past were never again re-visited. Now, through the actions of modern civilisation, we risk returning to the Eocene (or earlier) within the geological wink of an eye – a matter of a mere century or two. How will Earth, and its diaphanous clothing of life, cope?
Simply put, even under the most stringent mitigation scenario proposed by the IPCC AR4 (scenario I, in which CO2 equivalent is limited to 445 – 490 ppm), and more recently by the Garnaut Review, there is a high confidence that a slew of what can only be described as catastrophic impacts (30 percent species loss, major coastal flooding, most corals bleached, significant global water stress), will unfold! Indeed, beyond the mitigation scenarios, the fossil-fuel intensive business-as-usual – right to the bitter end – runs off the chart of possible impacts, with a disturbingly plausible risk of up to 6.8 – 8.6°C heating. This would truly be “game over” for humanity and most other life on this planet.
In this context, I focussed in the JD Stewart Address on describing a range of potential future impact scenarios and tipping elements, under scenarios of 2 to 6°C warming. These include the instability of the large polar ice sheets, which threatens major sea level rise, possible collapse of major carbon sinks in the ocean and on land – exacerbating committed climate change, increased intensification of the hydrological cycle and the related problems of desertification and water stress, severe impacts on biodiversity and ecosystem services – interacting with ongoing stressors such as habitat loss, and erosion of the natural, agricultural and infrastructure capital that is required to support modern civilisation. I also presented an overview of recent scientific research in this area of extreme outcomes, and speculated on some of the more worrying “low risk, high consequence” tipping points that we risk breaching, beyond 1 to 2°C of warming.
One can only consider it a damning indictment on our collective vacillation, inaction and deliberate stalling to date, in facing up to this problem (Australia and the US being two historically prominent curmudgeons), that we are now facing the stark choice between a bad situation, a catastrophic situation, or a civilisation-terminating situation.
The European Union somewhat arbitrarily defined “dangerous anthropogenic interference with the climate system” (what we were supposed to avoid, according to the 1992 UN Framework Convention on Climate Change) as being anything over 2°C warming – and many claim this is already too much for comfort, given the changes we are witnessing already, at 0.8°C warming.
Given what is at stake, there is some dark humour to be had in contemplating that only 6 of 177 AR4 mitigation scenarios actually allow for the possibility of avoiding 2.5°C!
There is good news, however, if policy makers will just take heed. The costs involved in moving fast to address the emissions problem and avoid the catastrophic global scenarios that threaten to “awaken the Balrog” of 2 to 6 degrees of planetary heating, are incredibly small, or perhaps even beneficial overall, and that’s before we count the social and environmental cost of not taking action.