Archive for the ‘Managing uncertainty’ Category
I gave a seminar yesterday at the ARC Centre of Excellence for Climate System Science at the University of New South Wales. Thanks Alvin Stone and Andrea Taschetto for organising it. It’s the first time I’ve had the opportunity to go through the entire ‘step change’ hypothesis of how the climate changes, the theoretical background, structural models developed from that and how the testing was set up, prior to showing a whole raft of test results.
One of the questions I got at the end, which also comes up quite often in the literature, was about the potential cause of the step changes in temperature data. It came from a question as to whether we had tested the step change model with artificial data that had been ‘reddened’ – that is, made dependent on the previous data. Such time series can have long-term persistence and contain a number of different quasi-periodic timescales, so do not conform to a single statistical model. This line of questioning alludes to whether a step or nonlinear response in a time series needs to be have an underlying cause that can be linked to an external source or whether it’s the result of random variations (see paper by Rodionov for a more more technical description). I gave a somewhat flip answer – because there is real energy in the system we are assessing (the climate system), whether a rapid shift is due to red noise or not matters less than understanding what that means for risk.
‘Wait and see’ on climate? No, the science is clear: act now
When should we act to reduce our greenhouse gas emissions and tackle climate change: now, or later when we know more?
One person who thinks we should wait is New York University theoretical physicist, and former US Under Secretary of Energy for Science, Steven Koonin.
In an article published by the Wall Street Journal, and reproduced in The Australian, Koonin claims that climate models are still too uncertain and that everyone should hold their horses, arguing that:
… because the natural climate changes over decades, it will take many years to get the data needed to confidently isolate and quantify the effects of human influences.
That’s not to say that the issue isn’t pressing. But Koonin says we should urgently do science, rather than urgently cut emissions:
The science is urgent, since we could be caught flat-footed if our understanding does not improve more rapidly than the climate itself changes.
Well, yes. But we’ve been doing this “urgent science” for decades. Read the rest of this entry »
By Roger Jones, Victoria University and Celeste Young, Victoria University
The Intergovernmental Panel on Climate Change (IPCC) is the accepted global authority on climate change. It produces reports that are collectively agreed assessments of the scientific literature by leading researchers. The Fifth Assessment Report (AR5) is being delivered over 2013–2014, starting this weekend.
What an IPCC report is
An Intergovernmental Panel on Climate Change (IPCC) report is an assessment that collects and summarises current knowledge in relation to climate change. This is done using literature from peer reviewed and unreviewed (grey) sources.
It is considered the leading review globally of climate change and is produced by a team of hundreds of scientists and specialists from a diverse range of disciplines.
The following statements are typical of the gradualist adaptation narrative:
- Within limits, the impacts of gradual climate change should be manageable.
- Therefore, climate change adaptation can be understood as: (a) adapting to gradual changes in average temperature, sea level and precipitation.
- Gradual climate change allows for a gradual shift in the mix of crops and to alternative farming systems.
So why are Gauss and Newton in the bath and Ed Lorenz in the hot tub?
Guest post by Roger Bodman, Victoria University and David Karoly, University of Melbourne
Today we released research which reduces the range of uncertainty in future global warming. It does not alter the fact we will never be certain about how, exactly, the climate will change.
We always have to make decisions when there are uncertainties about the future: whether to take an umbrella when we go outside, how much to spend on insurance. International action on climate change is just one more decision that has to be made in an environment of uncertainty.
The most recent assessment of climate change made by the Intergovernmental Panel on Climate Change in 2007 looked at what is known with high confidence about climate change, as well as uncertainties. It included projections of future global warming to the end of this century based on simulations from a group of complex climate models.
These models included a range of uncertainties, coming from natural variability of the climate and the representation of important processes in the models. But the models did not consider uncertainty from interactions with the carbon cycle – the way carbon is absorbed and released by oceans, plant life and soil. In order to allow for these uncertainties, the likely range of temperature change was expanded.
A couple of my recent forays into the media have provoked comment below the articles themselves and in emails sent querying particular points. They are worth unpacking because they reflect on the different between the straight communication of science and framing risk.
One was in reference to a recent op-ed in The Age. In it, I said:
If people accept the 0.0038 and 0.02 degree benefits as valid then they also accept the science behind a 5.3 degrees warming for business as usual (As in the emission scenario created by Treasury for the 2008 Garnaut Review). Who wants to live in a world warming by 5 degrees or more? Major food crops could not be grown in many parts of the world, projected sea level rise would be tens of metres, most of the shelled species in the ocean would not survive, ecosystems would be disrupted as the pace of change outstripped their ability to adapt and millions to billions of people would lose environmental security leading to mass migrations never before seen.
That prompted an email from an earth scientist wanting to know what peer-reviewed reference I was using for the projected tens of metres of sea level rise. I sent back this now famous diagram and a note saying that I wasn’t putting it on a timetable. He then replied suggesting that people could be misled into thinking that the date was 2100 (because that was tied to the two temperature measures) and that I was being alarmist. Because it would take thousands of years to be realised. Read the rest of this entry »
For those who didn’t catch it, during the week an op-ed of mine was Climate Policy will Stay a Mystery until Silent Specialists Join the Debate was published in The Age. It was based on an earlier post where I detailed the benefits of Australia’s climate policy and the tricks used by opponents to make it look more ineffective than it is likely to be. In the op-ed I ask where are the barefoot economists who will challenge untrue statements about climate and the economy? Text reproduced below (with small edits for clarity).