Predictions of climate change are uncertain. IPCC do not know if the warming up to 2100 will be as low as 1.1 degrees or as high as 6.4 degrees. They also allow a 30% chance that warming could be lower than 1.1, or higher than 6.4.

That is very uncertain.

Part of this uncertainty is due to the fact we don't know how much Co2 will be emitted, so 1.1 degrees is only expected if climate sensitivity is low, and Co2 emissions are low as well due to slowing population growth, and favourable developments in 'clean' technology.

If we pick a middle scenario and assume this happens to perfectly predict our Co2 future, then the range is reduced to 1.7 to 4.4. And of course a 30% chance that warming will be outside this range. This is the amount of uncertainty due purely to our lack of understanding of climate.

But what does this uncertainty mean? Some like to argue that it means that we should do nothing. However I believe it is a reason to take action, and to take a stronger action than we would if considering only the ‘most likely’ expected case. Our course of action should consider the low possibility of a disastrous outcome.

An illustration of this is the insurance industry. Most of us consider it wise to take action to protect against the highly unlikely chance of a disastrous outcome for a wide variety of possible disasters, such as extreme weather, earthquakes, theft etc.

This is despite the fact that the insurance premium must be significantly higher than the ‘expected loss’. The insurance premium must be high enough not just to cover the expected loss level, it must cover all the administration expenses and profit for the insurance industry, and cover all cases of deliberate fraud, or cases of carelessness on the part of those insured.

Some may argue that ‘uncertainty’ is no reason to act on climate, and that such an argument would work equally well to justify action to protect against the low probability of an attack by the Flying Spaghetti Monster for instance. However I would contrast the ‘uncertain’ level of knowledge in climate science with what I would term ‘complete ignorance’ about the Flying Spaghetti Monster.

While we do not know everything about climate, we are not in complete ignorance, and there are some things we are quite certain about. We are quite certain that Co2 will cause warming due to a change in the radiation balance of the atmosphere. We are quite certain that a warmer atmosphere can hold more water vapour, and that a warmer world contains less ice, and that both of these are positive feedbacks to the Co2 warming. What we are not certain is all the other things that may happen to change this simple picture. Perhaps atmospheric circulation will change so that water vapour is removed more efficiently from our atmosphere to counteract the increased carrying capacity. Perhaps clouds will change to create enough negative feedback to completely cancel out any other positive feedbacks. Perhaps all the methane stored under the Arctic will escape in a few years threatening civilization as we know it. Or perhaps it will escape slowly as most scientists expect and only add a few tenths of a degree to the total warming.

Uncertainty is a mix of certainty about some factors, and ignorance of others. Uncertainty is when we are justified in paying a premium price for insurance. Ignorance is when we know nothing about any factor, and when we are justified in ignoring an issue.

Nope!. Theory only!
We aren't certain at all about the actual practical effects, not the modeled theoretical effects, on the changes in the atmosphere's radiation balance caused by changes in the atmospheric CO2 levels.
For that the climate sensitivity has to be accurately confirmed and there is no agreement yet on that with the latest theoretical estimates of climate sensitivity to the doubling of CO2 are coming ever lower down to the 2C degrees and less.
When that climate sensitivity figure gets down to about 1.3 C degrees, it becomes indistinguishable from natural and normal variations in the climate and that level of climate sensitivity is being claimed as a possibility, repeat just so I don't get verballed again, as a possibility by an increasing number of climate scientists like Roy Spencer for one.

And therein lays the entire downfall of the CAGW theory. The lower the climate sensitivity figure , the more any climate changes are due to just plain natural variations in the global climate.

If the climate sensitivity is as low as 1.3 degrees, it is still a fact that Co2 is causing 1.3 degrees of warming when it doubles.

If it makes you happy Mike. Ok! but I can't stop laughing!.

8.5 C last night.
25.6 C today
17.6 C and heading downhill right now

The wife, parrot and cat seem to handling that 12 hour, 17 C jump OK!

Mike, you made a genuine attempt at contributing so lets leave it at that and just debate it out if necessary.
Time will prove one or the other or both of us wrong or right and neither of us might like the end result much.

We can probably rule out all the values above 3.0C by 2100.

We are at 0.6C now and increasing at around 0.1 to 0.15C per decade (if it is calculated properly taking into account the volcanoes, ocean trends, etc.)

To get to 6.4C by 2100, the trend would have to increase to 0.644C per decade for the remaining 9 decades to 2100 or up to 6 times faster.

Can you guys imagine what would happen , if somehow it got warmer than it is now ? Then Al Gore wish of more hurricans would come true .
First the oceans must get warmer , when they do , they create more hurricans , cyclons etc.
Then they cause this .

http://earthobservatory.nasa.gov/IOTD/view.php?id=3789

I must be wrong , otherwise somebody before would find it first .
Water cycle cant allow temps to rise , proof is tropics hasnt warmed at all . I think , we are lucky we have 71% oceans .
In case 50/50 increasing CO2 would be different story .
If oceans rose somehow by another meter , wouldnt oceans area increase , futher enhancing water cycle ?

I thought I'd chart up Mike's (the IPCC's) numbers for some perspective.

Hadcrut3 observations versus the IPCC forecasts starting at the time they were made over 1900 to 2100. And then the uncertainty range for the year 2100.

I have to say this just lacks coherence.


http://img221.imageshack.us/img221/3473/ipccforecuncertoct11.png

OMG Bill . Do me a favor will you ? When appropriate thread is posted on Reall Climate , post your graph .
I only add , If by certain ppl temps were not artifically lowered till 1980 , your graph would be almost horizontal

I work in the insurance industry Mike. There are some risks you just dont cover because the cost of the premium makes it impractical. One of the principals we use is if we can't accurately measure the risk and can't cant be confident of pricing it properly (in a way that makes economic sense) we don't insure it.

So if I accept your analogy Mike I would hold off pricing the risk of climate change until I can accurately measure its cost.

No offence locke but I would imagine insurers would simply use climate change as a way to try and squirm out of paying up when something happens.

This is only meaningful if you consider that climate is at least somewhat regular, stable and predictable. How predictable do you think climate is, and why?

Many have argued that climate is chaotic and unpredictable, in the same way that our daily weather is unpredictable. If this was the case, then the above approach makes as much sense as drawing a line between the last two locations of a severe tropical cyclone and using this to forecast the future track.

I do not think that climate is that unpredicatble. And I certainly agree that 6.4 degrees by 2100 is unlikely. My gutfeel is that IPCC have overestimated uncertainty and that warming is more likely to be near the middle than either the upper or lower range. But how unlikely is 6.4 degrees warming by 2100? Can we say it is impossible? 99% unlikely?

If the world were to warm up by about 6.4 degrees then this is enough that heatwaves over a significant portion of the world will be strong enough to kill every single person exposed to them without the ability to shelter in airconditioning. And it would get worse in the following century. How comfortable can we be with a 1% chance that this may happen in the future?

You are looking at things from the insurer's point of view. I'm looking at it from the customer's point of view. Often these points of view are opposite. The insurer would prefer a higher premium, and the customer a lower premium.

If the average insurer has the opportunity to take an action that has a definite financial benefit (i.e. receiving insurance premiums), but unknown risk, they quite wisely decide that this is a bad idea. For mankind digging up coal is an action that has a definite financial benefit, and unknown risk. By this argument the smart thing for mankind to do would be to decide this is a bad idea and not dig up the coal in the first place.

Of course we are quite dependant on coal, so simply stopping its use would have some pretty serious risk of its own, both known, and probably unknown.

What do you think the smart practice for an insurance company that has a large and financially lucrative customer paying for an insurance policy with unknown risks?

Mike. I would say there is a higher than 1% chance that you will have a car crash in the future. Do you do everything possible to avoid that. I think not. Even though there is every chance that car crash could kill you.Everyone seems pretty comfortable with those odds.

The main problem with expending immense resources leading to lower living standards and crippled and inefficient energy networks and serious human degradation of life like the hypothermia deaths in the UK as the old and poor can no longer afford to heat their homes adequately, on something the MAY occur in some unknown and unquantifiable time in the future and thats what was happening with the so called global warming, is that IF a real genuine threat of a completely different nature suddenly appears, neither the financial resources, the industrial and business resources or the human resources will be available to counter the new and real threat.
They will have been eaten up in preparing for the threat; ie global warming that had buckley's chance of ever appearing.

A little like the old Soviet empire where the politburo was spending very close to 50% of the Soviet Russia's GDP on their military in a paranoid anticipation that they would, not might, have to fight the west.
The end result was a level of poverty and low living standards except for the elites and low morale and complete loss of belief in the Communist system and in the communist leadership.
I was in Russia a year or so before the collapse.

Reagan broke the Soviet Empire and reshaped history by simply forcing the Russians to try and counter every new threat, scientifically, militarily and industrially that the superior American scientific and industrial establishment could toss up.

Like wise by throwing immense resources into trying to stop the so called and as yet, despite predictions to contrary, unseen global warming which with it's so far $287 billion dollar cost to the europeans alone, a expenditure of wealth that no doubt has led to, at the very least, an acceleration if not a root cause of the slow continuing collapse of the European economy of which is an example of fighting an invisible cause without any visible results except the bankruptcy of a nation both financially, politically and morally.

We are now seeing the political bankruptcy of our Australian political leadership which is hell bent on putting massive national resources into the invisible and still unseen will o wisp global warming to the detriment of us all.

Far better as I think Locke [ ? ] put it, is to increase the real wealth of a nation as fast as possible and to the highest levels and then we would have the resources to actually counter the real threat, what ever it is, if and when it ever appears.

Where the cost of mitigating a risk exceeds the potential damage from that risk your argument falls down Mike. If I have a $500 bomb that I drive around I'm not going to fit a $500 car alarm to prevent it being stolen.

Reminds me of something that happened when I first started in insurance many years ago. A young driver took out a comprehensive policy on an old car and several months later writes the car off. The car is assessed and is such a bomb that the market value is only about 75% of the actual premium. What went wrong? Well the main issue was we didnt have accurate information on the true nature of the risk. Had this person disclosed the true condition of the car (he was asked), it is highly unlikely he would have been sold a Comprehensive policy.

The main thing I take from this is the importance of understanding the risk your trying to address before you make a significant investment to reduce that risk. Incredibly massive sums are riding on the issue of climate change. What we are being asked to invest dwarfs nearly anything from past history. Right now there is insufficient clarity about the nature of risk upon which this expenditure is being based (which some would argue is almost incomprehensible given the sums of money already spent on climate science).

But we all take reasonable steps to reduce those odds. We pay higher prices for safer cars. We put up with licensing standards and speeding fines. Driving would be much cheaper if we didn't care about the risk of killing someone.

If you value the planetary environment at the same price as a bomby car, then yes it would make no sense to take any significant action to reduce the risk of climate change.

What do you think the worst case for climate change is that we should reasonably consider?

The sun going into a deeper funk and major global cooling setting in.
That would be an unmitigated disaster for the human race and our precarious food supplies as food production would probably just fall off a cliff.
A one degree decrease in global temperatures will lead to something like a 400 km retreat southwards of the furtherest north grain growing areas in Canada. Probably something similar in the Russian grain areas as well.

For increasing temperatures please read my post in the AGW news thread where I included quotes on the climate in the Cretaceous, the times of the Dinosaurs.
I'll post them again to show just what much higher CO2 levels and much higher temperatures can do for plant and animal life.



The current average temperature of the global oceans is about 3.9C.
The Cretaceous oceans as above were proxy estimated at 15c to 20c an increase of some 11 to 16C compared to today's oceans.
Land temps were 6c to 12 C higher than today and at a temperature where according to all the global warmers and enviro mobs we would burn up in the fires of a global hell.

As Oceans hold more CO2 the colder the water, an Ocean Temperature of 15 C to 20C would mean the release of colossal amounts of CO2 which would account for the proxy based estimate of Atmospheric CO2 during the Cretaceous being around 1000 to 1500 ppm.
And of course with these "high" CO2 levels there was still no evidence of a runaway global warming from high CO2 levels. Quite the contrary. The Cretaceous climate appears to have been fairly stable for some 80 million years, a time beyond imagination for human kind.
And animal life of a size and complexity far beyond anything we know of in the last 50 million years
Plus the sheer abundance of plant life needed to feed these immense sized animals .

Provide credible evidence that the results of man's co2 emissions will produce a worse result than what is being proposed to mitigate those results Mike and you'll gain my agreement.

That the AGW movement deems it necessary to allow the promotion of extremely unlikely doomsday scenarios to garner continued support for their "cause" I would argue supports my position. They are aware that their is unlikely to be continuing support for the type of mitigation being proposed given the level of risk that is currently understood without trying to continually scare the crap out of people.

Like ROM says, a more certain risk is that sometime within the next 10,000 years temperatures will begin to cool significantly, to a point where a large portion of the planet that we can currently comfortably feed in warmer conditions will die of starvation. I can't see us rushing to spend billions if not trillions to address this risk. It may be further down the track than any impact from AGW but the catastrophic circumstances are far more certain and may be much more difficult to address.