Do we trust climate models or observations?

In the VRT news section (in Dutch) I found this topic: the assumed impacts of climate change on Flemish agriculture in 2050. It was about the doctoral dissertation of Eline Vanuytrecht: Crop Responses to Climate Change: Impact on Agricultural Production and the Soil Water Balance in the Flemish Region of Belgium. It basically says that on the one hand the agricultural production could potentially rise (because of the increase in CO₂), but on the other hand the stability of the harvest is in great danger (because of droughts in summer and water supplies will come under increased pressure). The latter means harvests will reduce significantly.

The solution was a bit of an anticlimax. After first explaining how bad it all would be, the most plausible solutions seem to be planting our crops earlier in the year (which was admitted farmers already do intuitively), things like planting other varieties and possible irrigation (less plausible due to high cost). It seems adapting to that “great danger” would be rather simple and farmers already are capable of doing this.

Productivity impact studies on Belgian crops had been done before, but this study included also the effects of increasing CO₂ concentrations.

This is how the study was done:

• 24 climate models were studied (15 global and 9 regional). All the models gave a temperature rise as result, but not all in the same seasons (global models showed higher increase in summer than in winter, regional models the reverse). In precipitation large differences existed between different models, not all models even agreed on the sign of the change.
• Then the response of crops to CO₂ was measured in the field. The results were as expected: more yield, less evaporation (because of reduction of the number of stomata), increased development of the canopy (less soil evaporation), higher root to shoot ratio, shorter cycle from seed to harvest, but a dependence on nitrogen availability.
• The AquaCrop model (a water driven model that simulates the development and production of crops) was calibrated to the Flemish situation.
• Finally, the results of the 24 climate models and the measured response of the crops to CO₂ were fed into AquaCrop model. In a good year (meaning without droughts) this could result in 10-15% more yield for winter wheat. Other crops like potatoes and sugar beet could benefit also. But not corn.

All very nice of course, but there is an Achilles heal: the conclusion of the study relies heavily on models (and their underlying assumptions). Not only the crop growth model, but also climate models, which are not well known for their accuracy, nor for their correct results. The study tried to counter this by combining a bunch climate models. Sound a bit strange, the output of climate models offer hypotheses. Combining lots of them is throwing many hypotheses on a pile and calling the result more accurate. Sure, one will see the direction (or not) in which the results go, but if those depend on similar assumptions, then it doesn’t prove much. Feeding the results of models into another model will create even more uncertainties.

To be fair, the many uncertainties of the models are discussed in several places in the dissertation. But in the media this is completely ignored, as expected. The results are treated as the reality 37 years from now, probably even as a further proof of the effects of climate change, but not being said that the results depend on the many ifs and buts of the models used.

How well do these climate models? According to a paper by Hans Van Storch:

However, for the 15-year trend interval corresponding to the latest observation period 1998-2012, only 2% of the 62 CMIP5 and less than 1% of the 189 CMIP3 trend computations are as low as or lower than the observed trend. Applying the standard 5% statistical critical value, we conclude that the model projections are inconsistent with the recent observed global warming over the period 1998- 2012.

This doesn’t necessarily invalidates the models, but it shows there some important processes that are not included and/or some minor things are overemphasized. In the dissertation CMIP3 models are used as General Circulation Models (GCMs). Meaning the temperature increase forecasted by this models would probably way too high and are fed as such into the AquaCrop model.

Now back to reality. The basis of the predicted problems in 2050 are droughts coupled with higher temperatures. After several decades of increasing CO₂, is this a trend we see in observational data? MIRA Indicator report 2012 (MIRA is the State of the Environment Report of the Flemish region). What do they say about temperatures and precipitation trends?

Temperature. In our country, we see a incredibly large increase in temperature since the start of the measurements in 1833: 2.3 °C. This is much more than the world average and the average of our neighbor countries. The big question is of course why. Is CO₂ working in overdrive in our little country? Of course not. The reason is probably the place where temperatures are measured (Uccle). It is close to the ever expanding city of Brussels. Uccle was a rural village a century ago and underwent a population explosion since then. Although KMI doesn’t acknowledges it, there is a known Urban Heat Island effect. Nevertheless, this station is used in the GISS dataset as a “rural” station.
It got warmer the last century, but one can only speculate by how much.

What about precipitation? Drought in summer is said to be the main culprit of the disruption. In Belgium there is a significant increase in precipitation since the beginning of the 20th century. A significant part of it in winter, but there is also a slight increase in precipitation in spring and also in summer (from the 1970s). That means more precipitation in three seasons! In about 40 years of ever increasing CO₂ levels it gets wetter and wetter. In a way that makes sense. Yet the model data seems much more attractive than decades of observations.

Advertisement

The carbon dioxide trap

It is a statement that I heard many times before: “What’s wrong with cleaning up CO₂ emissions? Even if science of CO₂ is not correct, we will end up with a cleaner environment”. I have to admit that is also what I thought until some years before, but I came back from it.

Let me first say I am not against cleaning up pollution, on the contrary. But I think CO₂ is not necessary a “pollutant” in the way we think of harmful substances. CO₂ is an essential part of life. Plants need it for photosynthesis and if they would have a vote, they would go for more emissions. On the other hand we, as humans, don’t have to fear toxic effects of it. It becomes only toxic for us in very high concentrations. If we would burn all fossil fuel we would not even come close.

The reason why a rising CO₂ concentration is feared is because it is a greenhouse gas. But as a greenhouse gas it is not particularly powerful, also not the most abundant. More, its effects are logarithmic, so the effects are decreasing with higher concentrations. Even the IPCC, after overstating it for many years, had to downgrade the warming effects of CO₂ (they didn’t tell it with that many words).

But these are not the reasons why I came back from the statement cleaning up CO₂ from the atmosphere. Yes, I think its effects on the climate are much overstated as more scientists seem to come to this conclusion, but there are deeper issues. If we declare a problem and it is in fact not (much of) the problem, then people will get creative to try solving it even if it doesn’t need solving. It can prevent us from looking at the real problems and find a real solution.

An example that I have recently read on the Climate Etc blog (on the paper of John Pethick and Julian Orford): the World Bank stated in a press release that human caused global warming will cause significant sea level rise and Bangladesh will be affected. But according to Judith Curry this line of thinking may spell danger to the population of Bangladesh because its sea level rise problem is not really driven by climate change, but by land subsidence.

Policies targeted at trying to help this situation through emissions reductions seem futile. But of even greater concern are WorldBank and other adaptation strategies for Bangladesh will not be adequate if they are targeted only at the global warming piece of the problem. This is a very large geo-political issue with regards to the substantial international (UN, WorldBank) funds targeted at climate change adaptation. Bangladesh’s sea level rise problem is not really driven by climate change – the risks here are that UN/WB adaptation solutions will be inadequate to help them deal with their sea level rise problem, or that Bangladesh will find itself ineligible for international climate adaptation funds.

Might Bangladesh become a tragic victim of the UNFCCC/IPCC oversimplification of the climate change problem and its solutions?

Another example is the Kiribati/Tuvalu story from last post. If their problem is attributed to rising sea level caused by increasing CO₂ levels, then there is no need to find a solution for actual problems like increasing pressure on the fresh water lenses because of overpopulation and increasing tourism, destruction of the protective reef for building material, more paving,… This attitude makes them basically powerless. Therefor hoping for the funds of those countries that feel guilty and are eager to compensate.

That’s the real danger: that we will not necessarily have a cleaner environment after dealing with a non-problem, how altruistic the intention might be, and that the problem still exists. Leaving us with less resources to face it. CO₂ being very expensive to tackle, that might not leave much.

Taking sea level rise in Kiribati for granted

This week I read a story about a Kiribati man that seeks asylum because of sea level rise. This is how it goes: a man from Kiribati came to New Zealand in 2007, had 3 children born there and asked asylum. He was fleeing “rising seas and environmental risks caused by global warming”. There was no land he could safely return to because of the sea level rise. Asylum was refused on the grounds his claim fell short of the legal criteria, such as fear of persecution or threats to his life. He then appealed the decision.

What struck me in the article was the obviousness with which sea level rise in Kiribati was taken for granted. A lawyer said that what’s happening to Kiribati in the next 30 years is a catastrophe. Does he have some kind of crystal ball? Also the “New Zealand’s Immigration and Protection Tribunal accepted the genuineness of Ioane Teitiota’s [the asylum seeker] claims”. Sure, but did they check the background of this claim somehow? Neither of them considered doing a basic check to find how much the sea level actually had risen in Kiribati. They just took it for granted that it increased, even dangerously increased.

Luckily, sea level data is available online. When looking for Kiribati, I found four sets with recent data:

Source: psmsl

Sea level stayed basically the same in all four data sets. In one of these, the sea level was somewhat higher at the end, in another somewhat lower. Compared to European or American sea level rise, all these Kiribati graphs are remarkably stable. Is this a surprise? Well, yes … and no, depending how deep I think about it.

Yes, because this is not what the mainstream media is telling us for many years now. They are telling us that Kiribati (and also the more known Tuvalu) are a bunch of “islands” that are under threat of being flooded by the sea because of the rising sea level caused by global warming/climate change. This is even how their president stated it:

More recently, President Tong has spoken of climate-change induced sea level rise as “inevitable”. “For our people to survive, then they will have to migrate. Either we can wait for the time when we have to move people en masse or we can prepare them-beginning from now …”

All quite dramatic. If you only listen to what the media tells us about it, you would think this is a island group that is going to be flooded soon. Until one looks at the data. But very few do.

But in a way it shouldn’t be a surprise because these are not “islands”, but atolls. There is a huge difference between the two, both have different properties. An island is a static piece of land in a sea or an ocean. When sea level rises the island will be flooded.

An atoll is of a different kind. They are not made of solid material, but of sand and coral rubble. There is an interaction between building up sand and removing it by the tides. This means there is a dynamics going on: atolls rise and fall with it. When the sea level falls, more of the atoll is exposed to wind. Because of the erosion the atoll lowers. When sea level rises, the flow of sandy material will increase and the atoll will grow.

In the last decades Kiribati indeed grew. Even according to the Kiribati wiki:

However, sea-level rise may not necessarily inundate Kiribati. Paul Kench at the University of Auckland in New Zealand and Arthur Webb at the South Pacific Applied Geoscience Commission in Fiji released a study in 2010 on the dynamic response of reef islands to sea level rise in the central Pacific. Kiribati was mentioned in the study, and Webb and Kench found that the three major urbanized islands in Kiribati -Betio, Bairiki and Nanikai- increased by 30% (36 hectares), 16.3% (5.8 hectares) and 12.5% (0.8 hectares), respectively

But if the sea level is not rising, how come they have these problems with contaminated fresh water, lost crops and floodings? The ability to grow and fall according to sea level is not unlimited. The problem arises when the natural dynamics get disturbed. An atoll is a delicate ecosystem that can not sustain an unlimited population. Increasing population and tourism will put more stress on the the fresh water lenses and these will be contaminated with salt water. Also, paving a part of the atoll will end up with rainwater not flowing into the soil and the fresh water lens.

Using coral as a local building material is a nice thing, but with a larger population this could mean a breach in the natural protection of the atoll. With flooding of those areas as a result. Both are definitely caused by humans, but they have nothing to do with “global warming” or “climate change”. Fighting global warming/climate change will not help with any of these.
But it can help if you are hoping for money from the Western countries that are admitting being the cause of “global warming” and are very eager to pay for it. Or when applying for asylum due to global warming…

This is how the momentum is kept being build. The mainstream media only one-sidedly reports that Pacific “islands” are in danger of flooding by global warming and subsequent sea level rise because that is the most dramatic story. People read it and without checking pass the message. More of it will be communicated in flyers, magazines, newspapers, TV,… unchecked. People will start to believe that this is true, because the message is being repeated…one-sided and unchecked…over and over again.

The need to compensate for hurricane damages caused by imaginary increasing temperatures

Last week this tweet caught my attention.

It goes back to the article: You Break It, You Fix It: Why Carbon Polluters Should Pay for Hurricane Damage.

On the one hand I can image what they are talking about, but on the other hand I think it is not as simple as they show it.

This is what I can understand: if I go to a china shop and break a vase, then I will have to dig up my wallet and pay for the damage. The price tag of the vase at that time is the amount of money that will go off my bank account. If I bump into the vase and it falls down there is no doubt that I was the culprit. Action and reaction. Action and direct reaction. But in the real world this is not as sharply aligned as in above example. With hurricanes things are a lot less clear. This direct action/reaction is absent.

This is how the article puts it: the emission of CO₂ drives the temperature rise (they call it with its name: “global warming”) which raises sea level rise and this makes hurricanes stronger (because of a higher surge).

There are some problems with this. Although CO₂ is increasing and at the highest point in the last century, there is a pause in global temperature of a decade and a half. So much for CO₂ causing global warming. Also hurricanes seem to be declining. Sandy and Irene were hyped big time and no attention that they became rare examples. Compare that with the end of last century when CO₂ levels were much lower.

The sea level is rising, at least in most places, but it was already rising before CO₂ got traction in the 1950s-1960s. What part is natural and what part is anthropogenic?

Even the IPCC was not really confident about attribution of hurricanes and climate sensitivity. Although they didn’t say it with that many words, they lowered the climate sensitivity (the warming we could expect for a doubling of CO₂ levels). If this is much lower then previously assumed and no warming was observed in the last 1.5 decade and hurricanes are on the decrease, how can this CO₂ then be the main culprit of those hurricane damages?

The example of the china chop was not really a good one. It would be a good analogy when man is causing hurricanes. Even the article doesn’t say that. They say man makes it worse. So, suppose the vases in that shops fall to smithereens on a regular basis for whatever reason. If the person now comes into the shop and a specific vase drops to the ground, how much was the person responsible for the falling of that specific vase?

Now more philosophically: assume that CO₂ is really linked with hurricane damages and carbon emitters have to pay for the damages. What if there are less (stronger) hurricanes. Do they get a, ahem, refund?

When thinking about it more deeper, the link between CO₂ and hurricanes is not clear as the writers of the tweet and the article want us to believe. It involves lots of assumptions and ignoring observational data. Saying “carbon polluters” should pay for the damages of hurricanes implies a clear connection which just is not there. But it sure sounds nice and powerful. Let’s say this is more a political message rather than a scientific one.

Trees need the Government to grow big

This week a controversy flared up about the area of woods are taking in Belgium. The Minister of Environment, Nature and Culture declared that according to a survey this year 185,686 hectares of woods was counted (Dutch). This is 8,262 hectares more than the baseline measurement two years ago.

Two environmental organizations, Bos+ (translatable as Woods+) and umbrella organization BBL (translatable as Federation Better Environment), were not amused. They didn’t believe the results of the survey, saying it is strange that so many extra woods were created with no extra funds. It would be by far the fastest growth of woods in Belgium or even our neighbor countries. They also had criticism on the way of measuring. They didn’t like that the survey also counted trees along the motorways, fallow land and private properties.

Groen (the Flemish green party) added to this saying there was even a decrease in area (Dutch), not the increase that the Minister claimed.

This seems confusing. The Minister said there was an increase, environmental organizations said there was not much of a change and a political organization said there was a decrease. First let’s look at the methodology to be classified as “wood” in the report:

• a collection of trees
• in an area of at least 0.5 hectare
• trees should be higher than 3 meters.

Reading more about the history of the survey, it seemed that Bos+ and the Minister didn’t get along well. Bos+ has a competing measurement system, based on the information of licenses and subsidies. Obviously less accurate and not comparable with the more objective measurements. They also knew about the methodology of the survey and that it is much more objective than their own.

Who was right? Well, they were all right, at least according to their own definitions. They understand “wood” in a different way and don’t necessarily take the same time frame:

• the governmental report said there was an increase because it measured tree collections of at least 0.5 hectare with trees of more than 3 meters high. Doing that they found about 8,262 hectares more than 2011. And yes, it included all trees regardless they were “natural”, planted by man or regardless their function. Every collection of trees with those properties was counted
• Bos+ said there is not much difference because of their focus on the “official” numbers of areas that were newly converted to wood or existing woods that lost their purpose. There weren’t many new projects in the last two years, so they concluded that there would not be much improvement in those two years.
• the decrease that Groen was talking about was a 600 hectares increase during 2008-2011 and logging licenses for 1,000 hectares in the same period. When adding this together it indeed means a decrease. But I think this is beside the point as the survey covered the period from 2011-2013, not from 2008-2011.

Those green organizations seem to have a nanny mentality towards woods. As if trees don’t grow in absence of action by man. They also seemed not really happy with the news that there is now more area with large trees in Belgium without the intervention of our Government. Even the “unofficial” woods will have specific functions like for example generating oxygen, breaking winds, preventing soil erosion,… They don’t need to be licensed or subsidized to do that. In their attack they looked disconnected from the reality of real nature. In a small (30,500 km²) and densely populated country like Belgium, new trees will have an impact. At least I was happy to hear that there was an almost 5% increase in areas with large trees in our country, even without the need of action by the Government.

On the other hand, I agree that the statement of the Minister (that this result shows that the Ministry makes an effort in forest policy) is stretching it a bit. This survey proves there are more areas with large trees than two year ago, but this doesn’t necessarily prove better forest policy.

But more importantly, it indicates that definitions are very important. That does make climate communication with their very vague definitions even more hard. But more about that in a next post.

Update 1:
The count in the governmental report seem to have quite a wide error margin: between -14,163 hectares and +1,803 hectares. Depending on the error margin of the baseline measurement, an addition of 8,262 hectares might not be significant.

Update 2:
Go to the follow-up post about definitions.

Closing the gap or influencing others to jump off the cliff?

A couple days ahead of the IPCC AR5 report release I found this video in which 20 climate scientists were interviewed about the “gap between science and public opinion”.

It starts rather innocent telling that public perception of climate change (I believe they use in the meaning of “global warming”) is hard to perceive. The reason given is the flow of the seasons which makes it difficult to experience climate change conscientiously. I could agree with that. After this the admission that climate science is really difficult field. It is complex and spans over different disciplines.

Then “climate communication” comes up and things become more slippery.

We need to find a way to take the science that we produce and make it digestible to the general public. And then we will see people generally asking government and really forcing the government go out and do something.

At first it seems plausible. There is nothing wrong with making science digestible to the general public. But the intention of this is not to let the public gain knowledge, but to put pressure on politicians. Is that what climate science is about? And it continues:

Recently we started to realize that the problem with us taking action now is not with we perhaps don’t have enough research, but it is constantly a fight to make the research that we do have gets heard properly outside of the scientific circles. And it is a fight that we are not winning at the moment.

A fight they are not winning? Really? They got the mainstream media in their pocket. Climate scientists only have to make a press conference and whatever information they want to give will be printed in the mainstream media. Some journalists will even crank up the volume. And now he is telling us they are losing the fight?

What’s that all about fighting a battle? Since when does science need to fight a battle about the perception of the public? But it get even weirder:

The most important is to communicate the science, accurately. The climate science community is being doing it for 50 years. In the 1960s the first science came out spelling the warnings of ongoing greenhouse gases emissions. President Carter commissioned a report on the dangers of ongoing carbon emissions. And he was told at the time this is a problem we need to urgently move away from fossil fuels in terms of a source of electricity and for power and transport.

As far as I know Carter was worried about energy independence, not greenhouse gases. It was the time of the oil crisis and prices of oil skyrocketed. The frightening word back then was OPEC. By the way, it was at the end of the ice age scare and warming by greenhouse gases would be more a desired thing than something that urgently need as solution. It was the beginning of climate science and back then climate scientists (at that time probably only Lamb and Bryson) acknowledged both greenhouse gases and cooling. But, at least in the media, their bet was on cooling, not on warming.

The most interesting statement was this:

They say the reason why we should believe the climate scientists is there is a consensus because of the globe warming because of humans etcetera. I think people then think that somehow the science works by consensus or that someone is deciding this is the way is going to be and then everyone says That’s cool, let’s do that. The truth is the complete opposite. The scientists are so argumentative, so hate to be wrong and so like to argue with their peers. It is like a constant battle amongst everyone. Then there is one viewpoint that is coming out of this constant battling. Then this viewpoint is extremely, extremely valid. And we know it gonna be very close to the truth. So if you understood it more how argumentative scientists were in the field they might have more respect for these mayor viewpoints that coming out of their research.

That’s a strange reasoning. “No, (climate) science doesn’t work by consensus, but climate scientists are so argumentative, so when many of them agree that is really, really valid”. That’s like a consensus in disguise. It still means the debate is over because there is … a consensus. “They just looooove the debate”. Therefor they exclude other scientists that think differently. By calling them deniers, which is the case even in this video. Words like “Denier of climate science” and “anti science” start flying around. Calling people who have another viewpoint “denier” or worse, is not exactly a good example of being “argumentative”. Or are they only “argumentative” with the like-minded?

The science is clouded by these messages from the anti science community. So people left with a confused message and they decide, well, who to believe? That guy in a suit or that guy in a suit. It has been a very difficult communication message

Science is not particular well suited to communicating all this stuff and it is unfortunate because in the last 10-15 years there has been such concerted campaign to distort what the scientific community actually found.

My heart is going weak, those poor little climate scientists. They really think that the science or the debate is hindered by people who have another opinion. Just a couple years ago I had the same misconception. I thought “progress” in climate understanding was hindered by “deniers”. But I didn’t have a clue what the arguments of those deniers were. I wasn’t aware the skeptics’ arguments were only brought by the climate scientists themselves and a lot of things went lost in translation.

Then of course the road we will have to go:

I think that it is clear that it is not hard to do, that it is not changing the economy, that it is not impacting all of your life. I think that would be a start.

That seems unbelievable. We have to wean off fossil fuel energy (and probably other reliable energy sources) and replace it with intermittent and expensive energy sources. Hey, that’s going to be really easy! 😉

Then the “misconception” that climate scientists have diverse political views and that politics doesn’t drive the science. Well, looking at this clip gives me another impression. Sure, scientists have different political views, as have most other fields in our society, but that is not the issue. At issue is not that these scientists have political views, but that they want to influence the public towards one view. Confirmed in depth by the scientists in this clip. When they themselves know the subject is a very complex matter, yet pretending to have the answers and dismissing other viewpoints in the process.

Low confidence in trend and attribution of droughts and hurricanes, doh!

In climate change communication droughts and hurricanes are two constants. We hear there is an increase in droughts, of course due to global warming. Also, more hurricanes are the fingerprint of a warming world. It looks strange because nor droughts nor hurricanes are on the increase, but it has been told so many time that a lot of people believe it.

Therefor it was a surprise to see the extreme weather table in SPM AR5 (table SPM.1 on page 23) and even more when comparing it with the similar table in SPM AR4 (table SPM.2 on page 8).

This is the comparison table:

			Likelihood of future trends
Phenomenon and direction of trend	Likelihood that trend occurred in late 20th century (typically post-1960)	Likelihood of a human contribution to observed trend	Early 21st century	Late 21st century
	AR4 → AR5	AR4 → AR5	AR4 → AR5	AR4 → AR5
Area affected by droughts increases	Likely in many regions since 1970 → Low confidence on global scale/Likely changes in some regions	More likely than not → Low confidence	Likely → Low confidence	Likely → Likely (medium confidence ) on a regional to global scale
Intense tropical cyclone activity increases	Likely in many regions since 1970 → Low confidence in long term (centennial) changes. Virtually certain in North Atlantic since 1970	More likely than not → Low confidence	Likely → Low confidence	Likely → More likely than not in the Western North Pacific and North Atlantic

Droughts

Likelihood of the trend occurred since late 20th century went from “likely in many regions since 1970” to “Low confidence on global scale/likely changes in some regions”. Rather odd that they had to adjust their assessment for a trend that supposedly was there, “clear” to see. Some areas were likely to change, but globally there is not much confidence.

The same with human attribution: this went from “More likely” in AR4 to “Low confidence” in AR5. Nice to hear.

Likelihood of future trend went from “Likely” to “Low confidence” in the early 21th century and “Likely” on a regional to global scale. After hearing so many horror stories about droughts this seems serious backpedaling.

Tropical cyclone activity

Like droughts the trend occurred since the late 20th century went from “likely in many regions since 1970” to “Low confidence on a global scale”, but “Virtually certain in North Atlantic”.

The likelihood of human attribution went from “More likely than not” in AR4 to “Low confidence” in AR5.

Also the future likelihood short term went from “Likely” to “Low confidence” and on long term the confidence is assigned to “More likely than not”. Not that much confidence anymore.

Well, low confidence of human attribution and short term increases in droughts and hurricanes. That’s good news! Until now we were bombarded with loads of doom stories. Now those seems to to be based on nothing much. Pity this was not in the press release. Wouldn’t it be great when the public got to know such things? 😉

95% certainty or 95% opinion?

On September 27, 2013 the IPCC declared that the “human influence on the climate system is clear” in the AR5 Summary for Policymakers. In the current report they declared more than 95% certainty (extremely likely) that greenhouse gases account for more than half of the increased global average surface temperatures, while they declared only 90% (very likely) for something similar in the previous report.

For us, the great unwashed, this seems really impressive. We assume it is a accurate picture of reality and the science made quite some progress in the last six years and hey, 95% certainty isn’t that more than enough for action?

It made me wonder what this “certainty” exactly means and how it is determined. This is what the AR Summary for Policymakers says about it (page 2):

The degree of certainty in key findings in this assessment is based on the author teams’ evaluations of underlying scientific understanding and is expressed as a qualitative level of confidence (from very low to very high) and, when possible, probabilistically with a quantified likelihood (from exceptionally unlikely to virtually certain).

That seems more like the subjective interpretation of a certain group of scientists (that probably are selected for having these opinions in the first place).

But look at reality. The “pause” was not foreseen and unexplained. We were told many times (also in this report) that human produced CO₂ drives temperatures. If this really is the case then a more than a decade long standstill in temperature increase, together with a record amount of CO₂ in the atmosphere, must tell us something: there is at least one forcing or feedback with at least the (combined) strength of CO₂ that is not accounted for.

That alone should have humbled the scientists and adjust their certainty DOWNwards in stead of upwards. Self declaring more certainty in the face of a glaring gap in their understanding of the climate system doesn’t make much sense.

95% certainty or 90% certainty, what does it even matter? It is both as impossible to evaluate anyway.

Climate sensitivity? What climate sensitivity?

After looking at the attribution certainty differences between AR4 and AR5, this time the differences of the equilibrium climate sensitivity. This is how AR5 defines it:

The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales. It is defined as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration.

Basically, the warming we would expect for a doubling of CO₂, in most cases determined as doubling of pre-industrial concentration of 280 ppm to 560 ppm (when we continue emissions like this, we will maybe get there, dependent on how much fossil fuels stay available). This is how they were assessed in both reports:

AR4 (SPM p. 12)
Progress since the TAR enables an assessment that climate sensitivity is likely to be in the range of 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.

AR5 (SPM p. 11)
Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).

That’s a step back in sensitivity and no mention anymore of the best estimate (3 °C in AR4). Maybe it is still too high. The pause tells us that something doesn’t add up: the climate sensitivity could be even smaller than presented and/or there are other forces or feedbacks that are not represented in the models. Therefor the big surprise about the declaration of “even more certainty” in AR5, despite the known discrepancy between the observations and the outcome of the climate models.

It is strange that the certainty range is getting larger. The lower limit is 1.5 °C, but the higher limit stays at 4.5 °C and a best estimate can not be given anymore. Really? After 6 years the settled science is even less clear about sensitivity?

Nevertheless, if climate sensitivity could be lower than expected, then less warming could be expected. That’s good news. But no mention of the lowered limit in the press release. To be fair, it is mentioned in the Summary for the Policymakers, also that it is lower than the value in AR4, but because the media doesn’t read the Summary report, it is not communicated to the public. It almost didn’t get in the Summary report. According to the minutes of the IPCC plenary session:

Quantification of Climate System Responses: On equilibrium climate sensitivity, several delegations, including Australia, the Netherlands and others, noted that the message that the lower limit of the assessed “likely” range of climate sensitivity is less than the 2°C in the AR4 can be confusing to policy makers and suggested noting it is the same as in previous assessments. The CLAs explained that comparison to each of the previous IPCC assessments would be difficult, and new language was developed adding that the upper limit of the assessed range is the same as in AR4.

Some representatives in the plenary session found the lower sensitivity to be “confusing” and suggested to note it is the same as previous assessment (it is not). I can imagine vividly why this lower value would be confusing for policymakers.

Finally, when looking at how this lower sensitivity limit is communicated to the public…Nothing…Nada…Niente… only skeptical sites/blogs seem to report on it.