CLEARING UP THE CLIMATE DEBATE: CSIRO’s James Risbey explains why it’s not “alarmist” to describe the threat of climate change to the public and how the climate system will respond to half measures.
With many issues to be considered in setting a climate policy one can end up wondering what the role of climate science is in all this.
After all, climate science doesn’t tell us what to do. It doesn’t tell us whether to have a carbon price or where it should be set. Those decisions ultimately involve a range of normative and deliberative issues which are beyond the scope of climatology.
Climatology can tell us, however, what is likely to happen if we don’t act, or if we don’t act with sufficient speed to keep total emissions within specific carbon allocations.
There is no single threshold above which climate change is dangerous and below which it is safe. There is a spectrum of impacts. But some of the largest impacts are effectively irreversible and the thresholds for them are very near.
In particular, the melting and breakdown of polar ice sheets seems to be in the vicinity of a couple of degrees warming. This expectation is based on current high rates of mass loss from the ice sheets compared to relative stability through the Holocene (the past 10,000 years) and on past ice sheet response in periods such as the Pliocene (a few million years ago) when the Earth was a couple of degrees warmer than preindustrial times (and sea level up to 25m higher).
We have already had about 0.8°C warming globally, with another third of a degree locked in by the inertia of the climate system.
That leaves, somewhat optimistically, perhaps a degree or so of wiggle room. Translating that into carbon emissions, if we wish to keep the total warming below about 2°C (with 50% chance), then we have a total global carbon emission allocation of between about 800 and 1000Gt carbon.
We have already emitted about 550Gt, leaving perhaps another 250–450Gt. Current global emissions are about 10Gt per year, growing at roughly 3% per year.
That leaves a few decades at present rates before having committed to 2°C warming and crossing the expected thresholds for ice sheet disintegration. And that is for a 50% chance of not crossing the 2°C threshold. For more comfortable odds of staying within the threshold, the total carbon allocation drops and so the time to threshold is even shorter.
Surely this estimate is vastly uncertain?
Everything has some uncertainty, but the uncertainty in this case lies mostly in the timing, not in the essential result. Ice sheets are sensitive to warming somewhere in this vicinity of temperature change and the climate system will yield 2°C warming somewhere in the vicinity of 800–1000Gt of carbon emissions.
If the climate is a bit less sensitive than we think then we might have a little bit more wiggle room than the 250–450Gt allotment, but not much, and we’ll exceed that allotment very soon thereafter anyway.
We’re only a few decades away from a major tipping point, plus or minus only about a decade. The rate at which the ice sheets would melt is fairly uncertain, but not the result that says we are very close to a tipping point committing to such melt and breakdown.
If we were to keep remaining emissions inside the 250–450Gt carbon allocation, we would need to take account of the inertia in energy systems and infrastructure, which set some limits on the maximum rate that emissions can be reduced.
To stay within the budget, we can’t hope to emit 10Gt a year (the present emissions rate) for the next thirty years and then reduce emissions suddenly to zero. Rather, net emissions would need to be phased down to zero to stay within the budget.
The longer stringent emissions reductions are delayed, the more drastic they must be to stay within the 250–450Gt budget. With more than a small delay, the reductions needed are faster than can be achieved in turning over the stock of emitting infrastructure.
Thus, if we were to stay within this budget, dramatic emission reductions would have to begin now. Delayed action on stringent emissions reductions almost certainly implies overshooting the thresholds and locking in vast long term impacts.
Is it irresponsible or “alarmist” of climatologists to point this out? The science brief for policy is not to prescribe policies, but to point out the implications of pursuing or not pursuing particular courses of action.
Pointing out that we are close to one of the largest tipping points imaginable in the climate system is well within the remit of science. It’s not alarmist to describe the threat accurately; it’s alarming if the political and social culture can’t absorb this.
Sociologists tell us that it is easier to motivate people for climate policies by focusing on the benefits of acting (the carrot) rather than on the costs of not acting (the stick).
As such, they suggest focusing on a positive vision and the good outcomes associated with addressing climate change. While this may be the right strategy, the appeal to benefit comes with no timetable and no particular sense of urgency.
It is the knowledge of climate thresholds and emission rates that sets the timing issues. Science provides the stick, which is the statement of consequence of not reducing carbon dioxide emissions in rapid order. The carrot might be the best way to get us moving, but the stick sets the beat.
Whatever motivations we use to enact climate policy, the climate will respond to our emissions. Emissions policies must therefore be measured by the effects they will have on the climate (among other things).
Policy measures that do not provide the ability for a stringent draw down of carbon emissions on the short time scales implied by the 250–450Gt carbon budget vastly increase the likelihood of crossing critical climate thresholds.
This is the third part of our series Clearing up the Climate Debate. To read the other instalments, follow the links below:
Part One: Climate change is real: an open letter from the scientific community
Part Four: Our effect on the earth is real: how we’re geo-engineering the planet
Part Five: Who’s your expert? The difference between peer review and rhetoric
Part Six: Climate change denial and the abuse of peer review
Part Seven: When scientists take to the streets it’s time to listen up
Part Eight: Australia’s contribution matters: why we can’t ignore our climate responsibilities
Part Nine: A journey into the weird and wacky world of climate change denial
Part Eleven: Rogues or respectable? How climate change sceptics spread doubt and denial
Part Twelve: Bob Carter’s climate counter-consensus is an alternate reality
Part Thirteen: The false, the confused and the mendacious: how the media gets it wrong on climate change
Ken Sekiya
logged in via Twitter
There are some interesting points in this article that should be expanded on and linked.
Such as the impact spectrum and budget pressure depending on delay with diagrams.
Also considering the wider "Voter" population that should to be attracted to read this...
I don't think many will be able to push themselves to read the whole article.
Let a lone an academic who'd just crawled out of bed.
John Dodds
Retired Engineer
You said"We have already had about 0.8°C warming globally, with another third of a degree locked in by the inertia of the climate system" Just where is this third of a cegree locked in? We have so much water (a GHG) in the ocean that does not undergo greenhouse effect warming that ther is no such thing as reserving or locking in warming. Likewise for CO2.
You fallacy is that you fail to consider that the Earth cycles from above equilibrium to below equilibrium every day. Any excess warning is returned to space by the Stefan Boltzmann law which dictates that a warmer temperature than equilibrium will radiate more energy out. IN other word we are at equilibrium, we return there at least daily if not at the sped of light as any excess heat is radiated out.. There is no such thing as locked in warming.
Michael J. I. Brown
ARC Future Fellow and Senior Lecturer at Monash University
The temperature of the oceans does increase in response to the increased temperature of the atmosphere. Indeed, the increase in the temperature of the oceans is partly responsible for rises in sea levels.
Sea level rise is discussed in the IPCC Synthesis Report and elsewhere. http://en.wikipedia.org/wiki/Current_sea_level_rise provides a nice introduction and has links to many original references.
John Dodds has contributed frequently to "The Conversation" forums on climate change. However, his knowledge of the relevant science is marginal at best and he has "theories" that are worthy of a crank.
Douglas Cotton
B.Sc.(Physics), B.A.(Econ), Dip.Bus.Admin
The only problem is - the temperature of the oceans is now falling since 2003.
The three extracts below warrant careful scutiny because this IS ground-breaking stuff. But firstly, let me point out we have a problem for GH exponents in that the mean temperature at sea surface was slightly lower in the 12 months ending yesterday than in the 12 months ending 31 Dec 2003.
See http://earth-climate.com/2003-2011.jpg
This levelling out (actually a decline below the long-term trend) is in keeping with…
Read moreJohn Dodds
Retired Engineer
The Earth used to be at 5000 ppm of CO2 & we have come back to 290. There is no critical limit or tipping point.. There is only your goal of what you desire the number to be. and I do not agree with your limit. because it will limit the amount of energy that man can produce and peope will die.
The fact that there is excess GHGs water (in the ocean) means that it all has the potential to be used in the GHE IF there is an energy photon available to be absorbed. We aso have the potential for the land to absorb more energy and thus warm up IF the energycoming in increases. So far in billions of years we have not gone to the extreme of making us uninhabitable. Your article is not worth reading.
Kip Hansen
Retired IT Professional, Humanitarian Missionary
'Pointing out that we are close to one of the largest tipping points imaginable in the climate system is well within the remit of science.'
Well, if it were true, it would be. But there is no solid science that indicates any such thing as a 'climate tipping point' even exists and there is double-no science that says 'we are close to one of the largest tipping points imaginable '. I challenge James Risbey to supply a link to the peer-reviewed study or studies that support such a claim. I'd even accept a link to a page in the ever-alarmist IPCC 4th AR.
John Brookes
logged in via Facebook
John Dodds, do you really think that 5000 ppm of CO2 would be ok? Were there humans around when CO2 were at that level? You are aware that the sun has got considerably brighter since then? You do know that the amount of water in the atmosphere increases with increasing temperature, giving a positive feedback to any forcing?
Thomas Brennan
logged in via email @hotmail.com
I have one question in relation to this article:
The author states: "We have already emitted about 550Gt, leaving perhaps another 250–450Gt. Current global emissions are about 10Gt per year, growing at roughly 3% per year."
How do these figures relate to the monitoring of CO2 output by the International Energy Agency, who estimate current output (from energy generation) at 30.6Gt for 2010, an increase of 5% on the record of 29.3Gt in 2008? (See: http://www.iea.org/index_info.asp?id=1959). My understanding is that energy production accounts for approximately 65% of global man-made greenhouse gas emissions, suggesting that annual man-made emissions are in the region of 45 to 49Gt of CO2 equivelent greenhouse gases.
It would be helpful to have the source for the figures you quote, and how they relate to the significantly higher numbers cited by the IEA. Obviously this discrepency will have a significant impact on projections of global warming.
Ian Enting
Honorary Senior Associate, Faculty of Science at University of Melbourne
Both James and I have got back to Thomas directlyon this, but to clarify things for others:
James' figures are for the mass of carbon in the CO2, often written as GtC, while the IEA fugures are for mass of CO2, in GtCO2, which is larger by a factor of about 44/12.
ian hilliar
country gp
Very disappointed by our CSIRO, but unsurprised. Tipping points ? Are you talking about the tipping point in 1975/1976 when the world stopped cooling and started warming, or about the tipping point in 1998 when the rapid warming of 1976 -1998 peaked, with no warming trend over the last 12 years? Or about the tipping point announced today where global alarmist scientists have finally admitted that our latest sun cycle has run out of steam and we MAY well be heading into another Maunder Minimum…
Read moreJohn Coochey
Mr
What the whole debate boils down to is let us assume that AGW is happening and signicant. What precisely has the author of this document done to reduce his carbon footprint? How many cars are in his driveway? How big is his house? When did he get his driving licence, how many jet flights has he ever taken, how many chidren? The list is endless but somehow I think I already know the answer. There is a book that every observer should read. It is called "When Professy Fails" it is what happens to a doomesday cult when the world does not end. Standard reading in sociology courses. But as I have posted elswhere Tim Flannery says if all human activity stops it will take a thousand years for temperatures to decline, we are not talking about a five per cent reduction of going back to 1980 no human activity. However Andy Pittman says 20-30 years. Which is right? But I thought the science is settled.
Douglas Cotton
B.Sc.(Physics), B.A.(Econ), Dip.Bus.Admin
All of this totally ignores long-term temperature cycles that have been observed in the past and will continue into the future. Some cycles are governed by solar activity, others by gravitational forces from the planets which affect ocean currents and then temperatures. There is good evidence for a 900 year cycle going back to Roman times. We are, after all, seeing a long-term upward trend from around 1700 to the present. IMHO temperatures will continue to remain about the same from 2003 to somewhere…
Read moreJohn Dodds
Retired Engineer
I agree almost completely with Douglas Cotton et al on the 60 year cycle theory.
Read moreI even propose (in the paper "John Dodds Wobble Theory,..." & its Summary "Gravity causes Climate Changes" (available in www.scribd.com) that the major causes of the temperature variations is the effects of Gravity and planetary eccentricity on the amount of energy photons rather than CO2. in the greenhouse effect. This theory says that while CO2 and the greenhouse effect interaction with photons may be responsible…
David Arthur
n/a
Thanks Ian.
Post-WW2 cooling is due to global dimming due to industrial pollution (primarily sulfate aerosols, but lead aerosols from leaded petrol played a substantial part) reflecting more sunlight than rising CO2 was trapping.
This was addressed in efforts in the Industrialised West to clean up its act in the last decades of the 20th century; economic collapse of the Soviet also caused substantial decrease in industrial air pollution.
Air pollution has risen in the 21st century due to the industrial takeoff of China.
Another constraint on rises in atmospheric temperatures of late has been accelerated ice melting, plus thermal expansion of sea water. Atmospheric temperature rises will remain modest while there is polar ice to melt.
Barrie Collins
logged in via Facebook
Could one, or more of the scientists in this project tell me whether it is possible to differentiate human produced carbon form natural carbon? And is it possible to measure the amount of human-produced carbon as against natural carbon in the atmosphere.
Andrew McRae
B.InfTech, software developer.
Hello Barrie,
I am not a scientist by qualification, neither am I "in this project", but your question is a good one and is typically asked in such forums and I think I can answer it.
Generally the answer is Yes.
Chemically CO2 is CO2, it's all the same. However you are wondering how anyone can tell what proportion of the atmosphere's CO2 is anthropogenic, and there are two main solutions to this question.
The first solution is carbon accounting. Just add up the oil and coal that has been sold…
Read moreOregon Stream
logged in via Facebook
Wow, some old, widely discredited claims appearing in this thread. But to Barrie's query, there's a fairly good discussion including some other linked references here:
http://www.skepticalscience.com/How-do-we-know-CO2-is-causing-warming.html
http://www.skepticalscience.com/its-not-us-basic.htm
Really, it's more about the cumulative concentration increase resulting from a substantial disruption of the carbon cycle's quasi-equilibrium.
Douglas Cotton
B.Sc.(Physics), B.A.(Econ), Dip.Bus.Admin
So let's be "Speaking Science" ...
The consensus says "we caused climate change" for the simple reason that it takes time for a majority to come to grips with the "New Theory." Some people probably still think that the sun's solar radiation is the Earth's main source of energy. It is not. Its gravity is, with further minor contributions from all the planets, Jupiter, Saturn and Venus having the greatest effect. If we only had solar insolation to warm the Earth the facts are that the Earth would…
Read more