Archive for the ‘Modelling’ Category
After promising to have our flagship paper on reconciling the signal and noise of global warming on decadal timescales subject to open review, it is finally on. The paper has been submitted and accepted for open review at Earth System Dynamics.
Reconciling the signal and noise of atmospheric warming on decadal timescales
Roger N. Jones and James H. Ricketts
Victoria Institute of Strategic Economic Studies, Victoria University, Melbourne, Victoria 8001, Australia
Received: 13 Aug 2016 – Accepted: 22 Aug 2016 – Published: 23 Aug 2016
Interactions between externally-forced and internally-generated climate variations on decadal timescales is a major determinant of changing climate risk. Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal-to-noise model, or whether they interact, resulting in steplike warming. The multi-step bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to show strong differences between the two statistical hypotheses, hstep and htrend: (1) Since the mid-20th century, most of the observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the northern hemisphere and 1968/70 in the southern hemisphere. Temperature is more steplike than trend-like on a regional basis. Satellite temperature is more steplike than surface temperature. Warming from internal trends is less than 40 % of the total for four of five global records tested (1880–2013/14). (2) Correlations between step-change frequency in models and observations (1880–2005), are 0.32 (CMIP3) and 0.34 (CMIP5). For the period 1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98), correlation increases to 0.78. (3) Steps and shifts (steps minus internal trends) from a 107-member climate model ensemble 2006–2095 explain total warming and equilibrium climate sensitivity better than internal trends. (4) In three regions tested, the change between stationary and non-stationary temperatures is steplike and attributable to external forcing. (5) Steplike changes are also present in tide gauge observations, rainfall, ocean heat content, forest fire danger index and related variables. (6) Across a selection of tests, a simple stepladder model better represents the internal structures of warming than a simple trend – strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store-and-release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of steplike – rather than gradual – warming is important information for characterising and managing future climate risk.
Comments welcome: here or there. Deadline October 4.
Imagine you didn’t know anything about climate change and the greenhouse effect but were interested and you know a bit about general science. Would you accept the following story?
“Earth’s climate is a large, complex system, affected by forces that produce both linear and nonlinear responses. Shortwave radiation – basically UV – from the sun comes in and heats up the planet, producing infrared radiation. Some UV gets reflected straight back out by clouds, snow and ice and stuff. The land can heat up quite a lot, but it cools back down again and doesn’t store much. If a forest is cleared and replaced by buildings, it will warm up a bit but the effect is only local.”
“But the ocean – that’s another story. It absorbs a lot of radiation, so is taking up heat all the time. Huge streams of energy are entering and leaving the ocean store each year. Some is ‘dry’ or sensible heat, which is ordinary warmth. Some is ‘wet heat’ or evaporated moisture. Energy gets taken up when the moisture is evaporated and it will be released again when the moisture cools, condenses and then gets rained out. In this way, the oceans provide a lot of heat to the land every year, largely as rainfall and a bit of snow.”
CSIRO (the Commonwealth Scientific and Industrial Research Organisation) is facing another round of job losses to basic public research, with the news that the organisation is making deep staffing cuts to areas such as Oceans and Atmosphere and Land and Water. Internally, there are signals that Oceans and Atmosphere will be cut substantially, amid 350 job losses over two years across the organisation.
In a letter to staff, CSIRO chief executive Larry Marshall said:
CSIRO pioneered climate research … But we cannot rest on our laurels as that is the path to mediocrity. Our climate models are among the best in the world and our measurements honed those models to prove global climate change. That question has been answered, and the new question is what do we do about it, and how can we find solutions for the climate we will be living with?
Fairfax journo Gareth Hutchens has an article in today’s Herald with the headline:
Well, it is April the first.
Hutchens has a go at the recent Chief Scientist and Australian Academy report: The importance of advanced physical and mathematical sciences to the Australian economy (pdf). They engaged the Centre of International Economics to conduct an economic analysis that used the MMRF-NRA computable general equilibrium model to estimate the impacts of a number of input assumptions on the contribution of the physical and mathematical sciences to the economy. The report estimates that the direct contribution of the advanced physical and mathematical sciences is
equal to 11% of the Australian economy (about $145 billion per year). Along with the direct contribution, the report estimates additional and flow-on benefits of another 11%, bringing total benefits to just over 22% (around $292 billion per year).
I felt I had to defend the report, which is not perfect but necessary (I think I also agree with the headline). In doing so I find myself in defence of CGE economic models (which I can’t quite believe I’m doing). Basically, Hutchens reckons that by engaging with an economic consultancy and an economic model, the Chief Scientist and Australian Academy of Science have prostituted themselves (my words) to the same economic lobbying that everyone else in Canberra uses to argue for government support. Here’s my response posted to the comments of the article (slightly edited – doesn’t seem to have made it through, either):
‘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 »
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.
This posts looks at how climate shifts affect extremes using the example of heat extremes in SE Australia. We had another burst of hot weather this week, which led to rolling power blackouts in South Australia. These are becoming more common, as our electricity bills rise to pay for network infrastructure. In every year but one since 1997, the Laverton, Victoria climate record has registered at least 1 day above 40°C. For those of you interested in how the science of detecting and projecting extremes is carried out, there is a comprehensive background on methods. For those who are just interested in results, page down to the results section. Read the rest of this entry »