Archive for the ‘Climate science’ Category

Tropospheric hot spot

August 19, 2013

The current topic under discussion at ClimateDialogue is the tropospheric hot spot: Is it there, and if not, so what? Invited discussant are Steven Sherwood of the University of New South Wales in Sydney, Carl Mears of Remote Sensing Systems (working on the RSS satellite product) and John Christy of the University of Alabama in Huntsville (working on the UAH satellite product).

I’ll provide a short overview here (loosely based on the intro over at CD), interspersed with my own and other people’s commentary.

Based on theoretical considerations and simulations with General Circulation Models (GCMs), it is expected that any warming at the surface will be amplified in the upper troposphere. The reason for this is as follows: More warming at the surface means more evaporation and more convection. Higher in the troposphere the (extra) water vapour condenses and heat is released. Calculations with GCMs show that the lower troposphere warms about 1.2 times faster than the surface. For the tropics, where most of the moist is, the amplification is larger, about 1.4.

This means that, contrary to what some people claim, the hot spot is not specific to the enhanced greenhouse effect: Any surface warming (or cooling) would be expected to be magnified higher aloft, at least in the tropics. Lindzen says it as follows:

We know that the models are correct in this respect since the hot spot is simply a consequence of the fact that tropical temperatures approximately follow what is known as the moist adiabat. This is simply a consequence of the dominant role of moist convection in the tropics.

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EGU General Assembly: The Arctic, Models, and Data

June 7, 2013

Guest post by Heleen van Soest

In April, the annual European Geosciences Union conference was held in Vienna, Austria. Heleen van Soest, MSc student Climate Studies at Wageningen University, attended the conference, and shares some thoughts and tweets (@Hel1vs).

The opening reception, April 7, reveals that geoscientists are fond of beer. I get to talk to some nice people and hand out my first business cards. Yay! I talk with Walter Schmidt,  President of the Division on Geosciences Instrumentation and Data Systems, about observations and data. Lesson learned: data are important, but never take them for granted. Especially from satellites: they basically measure counts and voltages. To interpret the numbers and get something useful, we already need models, i.e. algorithms. Usually, model skill is tested against data. Disagreement between them is often blamed on model errors, assumptions, etc. Keep in mind that data might be wrong, too. Fortunately, raw data is increasingly archived as such, together with the algorithms used to interpret them. In that way, data can still be used if the algorithms are updated. I dedicate my first #egu2013 tweet to this conversation and go home. I am happy to find a Va Piano (Italian restaurant) in ‘my’ street. Together with Sherlock Holmes (the book, that is), I eat my pasta.

Tweet At #egu2013 opening reception, interesting conversation about models and data: “important, but never take them for granted” (Walter Schmidt)

Monday, 8 April

Permafrost day. An important issue, as permafrost contains about half of the world’s soil carbon. If permafrost thaws, the organic carbon becomes available for microbes to degrade. Greenhouse gas (methane) emissions are a result, further increasing temperatures. This positive feedback is sometimes compared to a time bomb. Modelling studies of permafrost do show it will degrade under further warming. For example, Greenland permafrost south of 76°N will disintegrate this century. However, see RealClimate before you start to worry that this bomb is about to explode.

But today is not only permafrost; I’ve also got something on ice observations.

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Long term persistence and internal climate variability

April 30, 2013

After a long hiatus, Climate Dialogue has just opened a second discussion. This time it’s about the presence of long term persistence in timeseries of global average temperature, and its implications (if any) for internal variability of the climate system and for trend significance. This discussion is strongly related to the question of whether global warming could just be a random walk, a question vigorously debated on this blog (incl my classic  april fool’s day post three years ago).

Invited expert participants in the discussion include Rasmus Benestad (of RealClimate fame), Demetris Koutsoyiannis and Armin Bunde. The introduction text here slightly differs from that posted on ClimateDialogue.org

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The two epochs of Marcott

March 19, 2013

Guest post by Jos Hagelaars. Dutch version is here.

The big picture (or as some call it: the Wheelchair): Global average temperature since the last ice age (20,000 BC) up to the not-too distant future (2100) under a middle-of-the-road emission scenario.

Shakun_Marcott_HadCRUT4_A1B_Eng

Figure 1: The temperature reconstruction of Shakun et al (green – shifted manually by 0.25 degrees), of Marcott et al (blue), combined with the instrumental period data from HadCRUT4 (red) and the model average of IPCC projections for the A1B scenario up to 2100 (orange).

Earlier this month an article was published in Science about a temperature reconstruction regarding the past 11,000 years. The lead author is Shaun Marcott from Oregon State University and the second author Jeremy Shakun, who may be familiar from the interesting study that was published last year on the relationship between CO2 and temperature during the last deglaciation. The temperature reconstruction of Marcott is the first one that covers the entire period of the Holocene. Naturally this reconstruction is not  perfect, and some details will probably change in the future. A normal part of the scientific process.

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Klotzbach Revisited

March 1, 2013

Guest blog by Jos Hagelaars. Dutch version here.

The average surface temperature of the earth, measured by ‘thermometers’, are released by a number of institutes, the most well-known of these datasets are GISTEMP, HadCRUT and NCDC. Since 1979 temperature data for the lower troposphere are released by the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS), which are measured by satellites.
The temperatures of these two methods of measurement show differences, for instance: the NCDC data indicate a trend over land of 0.27 °C/decade for the period 1979 up to and including 2012, while over the same period, the trend based upon the satellite data by UAH over land is significantly lower at 0.18 °C/decade. In contrast, the trends for global temperatures indicate much smaller differences, for NCDC and UAH these are respectively 0.15 °C/decade and 0.14 °C/decade for the same period.

Big deal? Almost everything related to climate is a ‘big deal’, so it is of no surprise that the same applies to these trend differences. In a warming world it is expected that the temperatures of the upper troposphere increase at a higher rate than at the surface, regardless of the cause of the warming. The satellite data (UAH and RSS) do not reflect this. Why is the upper troposphere expected to warm at a higher rate and what is the cause of these trend differences between the surface  and satellite temperatures?

The temperature gradient in the troposphere / the ‘lapse rate’

When you go up in the troposphere it gets colder. This is caused by the fact that rising air will cool down with increasing altitude due to a decrease in pressure with altitude, by means of so-called adiabatic processes. This temperature gradient is called the lapse rate, a concept one will frequently encounter in papers regarding the atmosphere in relation to climate. When the air is dry, this temperature drop is about 10 °C per km. When the air contains water vapor, this vapor will condense to water upon cooling as a result of the rising of the air, which releases heat of condensation. So in this way, heat is transported to higher altitudes and the temperature drop with height will decrease. For air saturated with water vapor, this vertical temperature drop is approximately 6 °C per km.

When the earth gets warmer, air can contain more water vapor. This also has an impact on the lapse rate, since more water vapor means more heat transfer to higher altitudes. This effect on the lapse rate is called the lapse rate feedback. More heat at higher altitudes implies that there will be more emission of infrared light, a negative feedback. This effect is particularly important in the tropics. At higher latitudes, the increase in temperature at the surface is dominant, therefore the change in the lapse rate will turn into a positive feedback. See figure 1 (adapted from the climate dynamics webpage of the University of Leuven).

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Launching ClimateDialogue.org

November 14, 2012

Guestpost by ClimateDialogue editors Rob van Dorland, Bart Strengers and Marcel Crok

ClimateDialogue.org
Exploring different views on climate change

Goal of ClimateDialogue.org
ClimateDialogue.org offers a platform for discussions between invited climate scientists on important climate topics that have been subject to scientific and public debate. The goal of the platform is to explore the full range of views currently held by scientists by inviting experts with different views on the topic of discussion. We encourage the invited scientists to formulate their own personal scientific views; they are not asked to act as representatives for any particular group in the climate debate.

Obviously, there are many excellent blogs that facilitate discussions between climate experts, but as the climate debate is highly polarized and politicized, blog discussions between experts with opposing views are rare.

Background
The discovery, early 2010, of a number of errors in the Fourth IPCC Assessment Report on climate impacts (Working Group II), led to a review of the processes and procedures of the IPCC by the InterAcademy Council (IAC). The IAC-report triggered a debate in the Dutch Parliament about the reliability of climate science in general. Based on the IAC-recommendation that ‘the full range of views’ should be covered in the IPCC-reports, Parliament asked the Dutch government ‘to also involve climate skeptics in future studies on climate change’.

In response, the Ministry of Infrastructure and the Environment announced a number of projects that are aimed to increase this involvement. Climate Dialogue is one of these projects.

Topics
We are starting Climate Dialogue with a discussion on the causes of the decline of the Arctic Sea Ice, and the question to what extent this decline can be explained by global warming. Also, the projected timing of the first year that the Arctic will be ice free will be discussed. With respect to the latter, in its Fourth Assessment Report in 2007, IPCC anticipated that (near) ice free conditions might occur by the end of this century. Since then, several studies have indicated this could be between 2030-2050, or even earlier.

We invited three experts to take part in the discussion: Judith Curry, chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology; Walt Meier, research scientist at the National Snow & Ice Data Center (NSIDC) in Boulder, Colorado; and Ron Lindsay, Senior Principal Physicist at the Polar Science Center of the University of Washington in Seattle.

Future topics that will be discussed  include: climate sensitivity, sea level rise, urban heat island-effects, the value of comprehensive climate models, ocean heat storage, and the warming trend over the past few decades.

Our format
Each discussion will be kicked off by a short introduction written by the editorial staff, followed by a guest blog by two or more invited scientists. The scientists will start the discussion by responding to each other’s arguments. It is not the goal of Climate Dialogue to reach a consensus, but to stimulate the discussion and to make clear what the discussants agree or disagree on and why.
To round off the discussion on a particular topic, the Climate Dialogue editor will write a summary, describing the areas of agreement and disagreement between the discussants. The participants will be asked to approve this final article, the discussion between the experts on that topic will then be closed and the editorial board will open a new discussion on a different topic.

The public (including other climate scientists) is also free to comment, but for practical reasons these comments will be shown separately.

The project organization consists of an editorial staff of three people and an advisory board of seven people, all of whom are based in the Netherlands. The editorial staff is concerned with the day-to-day operation of researching topics, finding participants for the discussion and moderating the discussions between the experts. The main task of the advisory board is to guard the neutrality of the platform and to advise the editorial staff about its activities

Editorial Staff
Project leader is Rob van Dorland of the Royal Netherlands Meteorological Institute (KNMI). Van Dorland is a senior scientist and climate advisor in the Climate Services section and is often operating at the interface between science and society.

The second member is Bart Strengers. He is a climate policy analyst and modeler in the IMAGE-project at the PBL Netherlands Environmental Assessment Agency (PBL) and has been involved in the discussion with climate skeptics for many years.

The third member is Marcel Crok, an investigative science writer, who published a critical book (in Dutch) about the climate debate.

Questions
We welcome comments on this blog and are happy to answer any questions regarding this project. You can send an email to info [at] climatedialogue [dot] org.

Postscript (Bart V):

(Disclaimer: I am involved in this initiative as a member of the advisory board)

I think ClimateDialogue is a unique project in both its organization (people with wildly different views are involved) and in its aim: Facilitating a public discussion between scientists with strongly differing opinions.

Discussion topics are chosen to be relevant and interesting to the general public as well as receiving scientific attention. Discussants are chosen to reflect different stances in the spectrum of scientific opinion, explicitly including ‘sceptical’ voices. Naturally, the ensuing discussion is not necessarily representative of the full spectrum of scientific discussion (painting it as such would likely lead to a ‘false balance’).

The idea is that the discussion can alleviate the polarization between ‘sceptics’ and ‘mainstreamers’ and provide some clarity in background of the (dis)agreements. Moreover, having scientists discuss their scientific disagreements in a public setting can go a long way to increase the public trust in science, which has suffered from the (imho incorrect) impression of being closed-minded. All in all, I think that ClimateDialogue provides a valuable service to both the public and the scientific debate. That doesn’t mean that it’s free of risks, but these are more in the framing and the perception than in the discussions itself. Naturally, the participation of good scientists is a necessary condition to make this experiment a success. Don’t hesitate to contact the editors (or me) if you fit the bill and are not afraid of a public debate!

Climate Science Survey – the questions

October 8, 2012

In the spring of 2012, a large scale climate science survey was held amongst 6500 scientists studying various aspects of global warming. The survey was spearheaded by the Netherlands Environmental Assessment Agency (PBL), where I was responsible for the execution and analysis during the first half of 2012.

The objective of this study is to gain insight into how climate scientists perceive the public debate on the physical scientific aspects of climate change. More info about the survey was posted on the PBL website at the time, which has recently been updated to include a link to the survey questionnaire. Please note that the survey is no longer active.

Some confusion has arisen over the status of this survey. I responded at WUWT in an attempt to clarify:

We undertook a survey in March/April of this year (which, as Hans Labohm mentioned in a comment on WUWT, had been previewed by a variety of people with different viewpoints). Some respondents, e.g. Timothy Ball, asked to see the questions again. After internal consultation, we decided to publish the survey questions on the institute’s website, so that they are viewable to all. We contacted the survey respondents to inform them of the questions being available to view. I informed Dr Ball of this as well, to follow-up on my earlier email to him.

Our email to all respondents, informing them of the fact that the survey questions are available on the web, was apparently misunderstood to mean that we were again soliciting responses to a survey; this is however not the case. Roger Pielke Sr had already put a notice about the survey on his blog, which he has since updated after an email clarifying that this is an inactive survey, to which he had previously responded.

Below we (Bart Verheggen and Bart Strengers) reply to some of the more substantive questions regarding the survey questions raised on WUWT. However, we will not discuss results or the survey sample at this point in time. We will do so when our manuscript has been accepted.

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Comment on EER interview with Fritz Vahrenholt

June 11, 2012

Also published in European Energy Review (EER).

Greenhouse gases are responsible for warming, not the sun

Scientists working on climate on a daily basis must have been rather astonished by the interview with Professor Fritz Vahrenholt (European Energy Review, May 2, free registration required). Vahrenholt, chief of RWE Innogy, self-proclaimed climate expert and author of the book Die Kalte Sonne (The Cold Sun), claims that “the contribution of CO2 to global warming is being exaggerated”. These claims, however, do not stand up to scientific scrutiny. We assess his ideas in the light of the scientific literature on the role of the sun versus other climate forcing factors. The dominant influence of greenhouse gases follows not only from their basic physical properties, but also from their “fingerprint” in the observed warming. The sun, in contrast, has not exhibited any warming trend over the past 50 years. The sun is thus not responsible for the warming seen during this period. Greenhouse gases in all likelihood are.

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What are the pros and cons of reducing CO2 vs other warming agents?

December 15, 2011

That is the question I’ve been pondering earlier this year and which’ pontifications you can now read on Planet3.

The difference is mainly in the timescale: CO2 lasts a lot longer in the atmosphere than most of the other warming agents (e.g. black carbon, ozone, methane). This means that the temperature will decrease faster when the emission of shortlived compounds is decreased, as compared to that of a longlived compound such as CO2.

The other side of the coin is that for long term warming, the cumulative emissions of CO2 are dominant, even if in the short term changes in its emission are relatively ineffectual. Other important aspects in this discussion are health effects from air pollution (e.g. soot and ozone) and political practicability (gridlock in global climate negotiations).

So the question is: Are you more concerned about the short term or the long term effects of climate change? Which is a similar question that is often implicitly present in climate debates: Weighing the right of this generation to economic wellbeing (through cheap fossil energy) with the right of future generations to a pleasant planet to live on (through us not using too much cheap fossil energy). Strangely enough, that central and deeply ethical question is usually embodied in the discount rate (as used in economics when comparing investments with the expected rate of return).

My conclusion:

It’s clear that for long term climate stabilization, cumulative CO2 reductions are paramount, and that for the short term, reducing other forcings can offer faster results and offer other benefits as well. So the answer to the question “what should we focus on” is “all of the above”. I would applaud more attention to the non-CO2 forcings in the International policy arena. However, let’s not forget that there’s a hefty price and/or climate tag to pay in the end for delaying CO2 emission reductions.

You can read the whole thing over at P3.

 
Planet3 is a community new(s) blog, aptly described by main driving force Michael Tobis (in an interview with Andy Revkin) as
opinionated yet skeptical, informed yet passionate
 
Conflict of interest statement: I live on the planet in question.
(via Elmar Veerman)

Ocean Heat Content: Can we monitor the transfer of heat through the top 700 metres?

October 12, 2011

At RC, Gavin Schmidt and Roger Pielke Sr are discussing how Ocean Heat Content (OHC) has changed in the recent past. The disagreement seems to be on how the apparent slowdown in heat uptake of the top 700 metres can be reconciled with apparent warming of the deeper ocean. It’s very informative to witness two experts debate this in public (even though the discussion is hampered by frequent misunderstandings and other derailing issues). I’ve found this a puzzling issue for a while and am still not sure if I fully grasp it, but here goes: 

On his blog, RPSr writes:

If heat is being sequested in the deeper ocean, it must transfer through the upper ocean. In the real world, this has not been seen that I am aware of. In the models, this heat clearly must be transferred (upwards and downwards) through this layer. The Argo network is spatially dense enough that this should have been seen.

Gavin responds to this statement at RC:

Obviously heat going below 700 m must have passed through the upper ocean. However, the notion that Argo could see this is odd. Argo measures temperature, not flux. The net flux into a layer is calculated by looking at the change in temperature. It cannot tell you how much came in at the top and left at the bottom, only how much remained.

Both arguments make intuitive sense. Whether indeed temperature measurements should have seen a transfer of heat depends on the precision and on the (spatial and temporal) density of the Argo network. Besides that, it also depends on the mode of heat transfer (episodic or continuous). Or perhaps better put: the extent to which the influx and outflux of heat balance each other.

Gavin does not agree with Roger’s last statement (that it should have been see), but argues instead that the signal would not likely be observable amidst the variability (response to 140): 

I have no confidence that the observations will be sufficient to distinguish the anomalous heat flux from the climatological mean with sufficient precision to be helpful.

Roger concedes that the observation network’s precision is an important precondition for heat transfer to have been observed, when he writes in response to my little summary over there: (Roger)

(…) we should still see a slight elevation in the temperature anomalies IF the Argo data precision is good enough. I do not know the precision of the temperature data measurements, and hope someone else can answer that.

And in 193 Roger writes:

First, I stated that the Argo data density was fine enough to see the movement of the heat downward, but am now unclear on this, and look forward to an Argo specialist to give us an overview of capability in this regards.

There is however a second if-statement to make, about the mode of transfer. In response to 2, Gavin wrote:

Most heat transport into the deep ocean will occur in the down-welling branches of the overturning circulation, centered in theNorth Atlanticand the Southern Oceans. Diffusive fluxes in the rest of the ocean will be much smaller.

Roger (140) says more or less the same, but arrives at a conclusion that is not shared by Gavin:

if this transfer occurs in globs associated with mesoscale and larger ocean circulation features (as suggested in the ECMWF data), we should clearly see this movement of heat.

About the mode of heat transfer Gavin writes in response to 155:

Heat transfer will be mainly continuous, not episodic.

I.e. the heat transfer is strongest in specific locations (agreed on by both), but continuous in time (which prompted a question from Roger “how do you know?”).

In a continuous case, for a while the same amount of heat may enter the top 700 m from above, as leaves it from below. As a result, no warming signal in this layer will be observed, whereas heat is being transferred through it. In an episodic case, it would in principle be observable (though still dependent on the precision and signal to noise ratio of the measurements).

In contrast to what I wrote in my little summary at RC (175), the disagreement is not so much on whether the heat transfer is concentrated in space (both seem to agree that it is), but rather on whether the heat transfer is continuous or episodic in time (Gavin thinks it’s the former; Roger doesn’t say) and on whether the data precision is sufficient (Gavin thinks it isn’t; Roger doesn’t say).

Figure 9b from Hansen et al., ACPD 2011, “Earth’s Energy Balance and Implications”. Note that this Fig gives the heat uptake, which is the slope of a figure of heat content (in Joules): A positive heat uptake means that the heat content is increasing.

Figure caption: Six year trends of ocean heat uptake estimated by Levitus et al. (2009) and Lyman et al. (2010) for upper 700 m of the ocean, and estimates based on Argo float data for the upper 2000 m for 2003–2008 and 2005–2010.

I’ll probably update this post as the discussion progresses. Over at SkS, there have also been informative discussions between Roger and the regulars over there.


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