Dr Aaron Thierry is a quantitative ecologist who recently graduated from The University of Sheffield’s Department of Animal and Plant Sciences. He is extremely concerned about the level of understanding of the urgency of large scale carbon reductions and feels that scientists are morally obliged to raise awareness of the risks we now face. In contrast to some scientists at Cheltenham Science Festival, he believes climate models under-predict change.
On the 16th September last year the Arctic sea ice reached its minimum extent for the year. At just 3.41 million square kilometres it covered an area almost 50% lower than at the end of summer 30 years ago. Arctic experts spoke of their surprise and amazement that this unprecedented record had been reached so soon. Dr Julienne Stroeve, a research scientist with the NSIDC, explained that the collapse in extent “is an indication that the Arctic sea ice cover is fundamentally changing. The trends all show less ice and thinner ice“.
This continued and dramatic decline now means that the ice is melting far faster than had been predicted. “It is a greater change than we could even imagine 20 years ago, even 10 years ago,” says Dr Kim Holmen, Director of the Norwegian Polar Institute.
This is why the current minimum sea ice extent lies far outside of even the most pessimistic models that the Intergovernmental Panel on Climate Change (IPCC) presented in their fourth assessment report in 2007 (as you can see in this figure).
It is not just sea ice in the Arctic that’s disappearing faster than the models predict, there are many other climate impacts that are occurring more rapidly than had been forecast. The speed of the loss of snow cover in the northern hemisphere also has scientists stumped, “even if we’ve become a bit more willing to be aggressive with the scenarios we use to drive these models, it still doesn’t seem to be enough to describe what we’re observing,” says Dr Martin Sharp, a glaciologist at the University of Alberta, “We end up being conservative”.
Similarly, sea levels are rising 60% faster than the last IPCC report predicted in their central projection, and forecasts for the amount of sea level rise by 2100 are now in the range of 1-2m, compared with just 30-50cm in the last IPCC report – here’s a graph.
This discrepancy is in large part due to an earlier than expected onset of the melting from the Greenland and Antarctic ice sheets. Proffessor Richard Alley, a renowned glaciologist from Pennsylvania State University, noted his surprise a few years ago that “we’re now 100 years ahead of schedule” compared to what the IPCC had predicted in their third assessment of 2001.
As the temperature of the planet changes so does the water cycle and new research shows that it is now turning over at double the rate predicted. A further recent study has shown that, as a result, rainfall intensity worldwide has already been observed to have increased by about 23%. The authors note “that the risk of extreme precipitation events due to global warming is substantially greater than that estimated by the climate models”.
Indeed Proffessor John Holdren, former president of the American Academy for the Advancement of Science, and now chief scientific advisor to President Obama has candidly said that across the board “everything that is expected to result from global climate change driven by greenhouse gases is not only happening, but it’s happening faster than anybody expected”.
He’s not at all alone in that sentiment; Proffessor Sir John Houghton, former co-chair of the IPCC, also recently wrote of how “climate change is accelerating more rapidly and dangerously than most of us in the scientific community had expected or that the IPCC 2007 Report presented”.
But not only are the impacts of climate change greater and arriving sooner than expected, but the models for future temperature projections entirely leave out some crucial feedback processes that could dramatically add to the expected warming. The U.N. Environment Programme recently released a report warning that key carbon cycle feedbacks caused by the melting and subsequent decay of organic matter in permafrost (currently ignored by IPCC models) could add an additional 43 to 135 gigatonnes of carbon dioxide equivalent by 2100.
So why is it that scientists have so often understated the risks? The IPCC has been tasked with assessing the evidence that the planet’s temperature is increasing and whether mankind is responsible, and on both these counts it has been able to demonstrate a watertight case that it is heating and that we are the culprits. The level of scientific consensus that has emerged is now overwhelming and is a testament to the procedures and structure of the IPCC.
Yet the very nature of that consensus building exercise, that is so useful at establishing the veracity of key facts, tends to lead to conservatism when it comes to making predictions about future scenarios. This is because even the most reticent parties must agree upon the statements that are made. What is more, the IPCC is a final stage review process and therefore lags behind some of the most recent developments in the scientific literature, which in turn lags behind the cutting edge of the field due to the time it takes for work to be sent out to peer-review.
Another important point to bear in mind is that climate scientists have been embroiled in the vicious public debate over climate science and consequently have tended to be reticent to raise their heads above the parapet. This has led to a tendency to try and appear more than reasonable and avoid making what appear to be alarming statements. A phenomenon that has been dubbed “erring on the side of least drama” by historian of science Keynyn Brysse and her colleagues, who in a recent paper published in the journal “Global Environmental Change”, wrote that:
“In attempting to avoid drama, the scientific community may be biasing its own work – a bias that needs to be appreciated because it could prevent the full recognition, articulation, and acknowledgment of dramatic natural phenomena that may, in fact, be occurring.”
The case supporting this view was given further credence when Sir Robert Watson, another former co-chair of the IPCC, expressed as much at a meeting in San Francisco last December. “We have to be very careful and conservative. If we ever have a strong statement subsequently proved wrong, we would lose all credibility as a scientific community… I think we should always be slightly on the side of being conservative. Otherwise we are going to get ripped apart by climate-deniers even for the simplest mistake.”
Indeed, another recent study describing a survey of recent papers on climate science, found that new scientific reports were twenty times more likely to have results which told of outcomes worse than the consensus compared to outcomes which were better. The authors of the study concluded that:
“…if reporters wish to discuss “both sides” of the climate issue, the scientifically legitimate “other side” is that, if anything, global climate disruption may prove to be significantly worse than has been suggested in scientific consensus estimates to date”.
When we put this all together we get a clear picture that is, as Proffessor Stefan Rahmstorf of the Potsdam Institute for Climate Science points out, that “the IPCC is far from alarmist, but in fact has under-estimated the problem of climate change”.
But rather than abandon the established consensus building structures, which already provide us with a clear and extremely robust basis for concern and the need for action, I would suggest that we need to acknowledge the likelihood that the concerns it raises are likely underestimates, as an additional thought to bare in mind when reading their reports (the next of which is to be published this autumn). Whilst uncertainty in model prediction suggests that the impacts of climate change could be either better or worse than the average, I hope that it is clear from this blog that it is more than plausible that the impacts of climate will be at the high end of these uncertainties rather than the low end.