Posts Tagged ‘temperature trend’

A warm 2015 and model –data comparisons

August 7, 2015

Guest post by Jos Hagelaars. Dutch version is here.

Discussions on the Internet regarding climate change are sometimes about scientific details, sometimes about the climate sensitivity regarding the equilibrium situation hundreds of years from now, but the most prevalent discussion topic is probably: the global average temperature. Will it get warmer or colder, is there a temporary slowdown or acceleration in the rise in temperature, are the models correct or not, will the eventual warming of our earth in the future be large or small? New numbers are released on a monthly basis and every month megabytes of text are generated about them. My forecast is that 2015 again will lead to a discussion-spike.

The graph above shows the evolution of the global surface temperature anomaly for three datasets, where the average of the period 1981-2010 is defined as 0. For the year 2015 only data are presented up to and including June. So far 2015 exceeds all other years and the evolving El Niño makes it likely that 2015 will set a new world record.
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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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Eric Wolff on areas of agreement and on the public debate about climate science

May 25, 2011

Dr. Eric Wolff is spot on (see also further below): 

as an outsider to the blogosphere, it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

A peculiar line-up of speakers assembled recently at the Conference on the Science and Economics of Climate Change in Cambridge: Phil Jones, Andrew Watson, John Mitchell, Michael Lockwood, Henrik Svensmark, Nils-Axel Morner, Ian Plimer, Vaclav Klaus and Nigel Lawson. Bishop Hill reports that

Dr Eric Wolff of the British Antarctic Survey tried valiantly to find a measure of agreement between the two sides.

This proved an interesting exercise and resulted in a useful list (also reproduced by Judith Curry) on what we can all agree on (perhaps excluding those too far out on the fringes; links added by me):

  1. CO2 does absorb infrared radiation
  2. The greenhouse effect (however badly named) does occur in practice: our planet and the others with an atmosphere are warmer than they would be because of the presence of water vapour and CO2.
  3. The greenhouse effect does not saturate with increasing CO2
  4. The CO2 concentration in the atmosphere has risen significantly over the last 200 years
  5. This is because of anthropogenic emissions (fossil fuels, cement production, forest clearance). [Ian Plimer disagreed, but as Curry stated: “the anthropogenic contribution is (should be) undisputed”]
  6. If we agree all these statements above, we must expect at least some warming. [Bishop Hill noted “broad agreement” with this point]
  7. The climate has warmed over the last 50 years, [as is evident from] land atmospheric temperature, marine atmospheric temperature, sea surface temperature, and (from Prof Svensmark) ocean heat content, all with a rising trend.
  8. We probably don’t agree on what has caused the warming up to now, but it seemed that Prof Lockwood and Svensmark actually agreed it was not due to solar changes, because although they disagreed on how much of the variability in the climate records is solar, they both showed solar records without a rising trend in the late 20th century. [Excellent point and ironically hitting Svensmark with a stick of his own making. Note the distinction between variability and trend.]
  9. On sea level, I said that I had a problem in the context of the day, because this was the first time I had ever been in a room where someone had claimed (as Prof Morner did) that sea level has not been rising in recent decades at all.  I therefore can’t claim we agreed, only that this was a very unusual room.  However, I suggested that we can agree that, IF it warms, sea level will rise, since ice definitely melts on warming, and the density of seawater definitely drops as you warm it.
  10. Finally we come to where the real uncertainties between scientists lie, about the strength of the feedbacks on warming induced by CO2 [i.e. climate sensitivity]

Eric Wolff also chimed in with a substantial comment over at Bishop Hill’s, rebutting some commonly heard arguments and making some very spot-on remarks:

(…)

I should first state the rationale for the summary I made at the Downing event. The meeting was about the science and economics of climate change, and I was asked to lead a discussion that came between the science talks and the two economics talks. I therefore felt the most useful thing I could do was to try to summarise what we had heard, as a basis for the discussion of whether society should do anything in response to that, and if so what. In particular I did hear a surprising number of things on which almost everyone in the room could agree, and it seemed worth emphasising that, rather than rehearsing old arguments.

I notice in the thread here several comments about who sets the “terms of the debate”, and about the “context of the debate”. While such phrasings may make sense in discussing energy policy, it is a strange way to discuss the science. Our context is the laws of physics and our observations of the Earth in action; our aim as scientists is to find out how the Earth works: this is not a matter of debate but of evidence. I think some of the comments on this blog come dangerously close to suggesting that we should first decide our energy policy, and then tell the Earth how to behave in response to it.

Regarding Plimer’s proposal that volcanic emissions were more important than we thought, (…) if volcanoes were “causing” the recent increase, then around 1800 their emissions would have had to rise above their stable long-term rate, and then stayed high. This is however a rather hypothetical discussion because the change in the isotopic composition of CO2 in the atmosphere over the industrial period is not consistent with an increased volcanic source anyway.

Regarding the idea that the “temperature increase stopped in 2000”: my point is that we know there are natural variations (due eg to El Nino) that cause runs of a few years of temperature colder than the average or a few years warmer. Look on the record at the decade around 1910 for example when there was a long run of cold years on a flat background.

Such a period superimposed on a trend would look like the last decade (but more so). The point of my analogy is that you can’t determine the trend over several months by measuring the gradient in a run of a few days. Similarly, you simply can’t determine a multidecadal trend by measuring the gradient over a few years because all you get is the “noise” of natural variability.

Professor Morner claims that globally sea level has not risen at all; he dismisses the evidence, from both satellites and the global tide gauge network, that it has. (…) There are numerous reasons why a single site can show a sea level signal, either real or apparent, that departs from the global mean.

I am not the best person to discuss models and feedbacks in detail (see comment on expertise below). However, I could not let two issues pass. Firstly, when models are run out for a century into the future, they do indeed show runs of years with flat temperatures amidst a trend (…) (because of El Nino and other natural factors). I am therefore not clear why this is evidence that something is missing. Regarding positive feedbacks: a positive feedback implies amplification, but not a system out of control; this is only the case if the sum of the gain factors is greater than 1.

Finally, a few specific issues that interested or worried me.

(…) CO2 emits infrared as well as absorbing it. (…) indeed, this property is precisely why its effects do not saturate (but fall logarithmically), because it allows the height from which the emitted radiation finally escapes to rise into regions with less and less air.

Geckko accidentally made an important point. S/he did not like the statement: “We can agree that if it warms the sea level will rise”, because it was too simplistic. Well, as a scientist I always like to boil things down to a statement that my brain can grasp, but that contains the essential explanation of an observation or process. And this one does, for example being demonstrably what was observed in going from a cold ice age world, with sea level 120 metres below the present level, to the present. However, you are right: there are factors that could make this statement false, such as increased snowfall when it warms, adding more ice into ice sheets. As soon as several such competing processes have to be taken into account, our brains cannot predict the outcome, and so we have to resort to putting all the “millions of assumptions” into a numerical model and seeing which of them “win”. An argument for models?

Coldish made a good point about expertise, and this is where I am going to go into a slightly more challenging area. I freely admit that I am not an expert on all, or even most, aspects of climate. When I reach a topic that I have not previously studied, I go to those who are experts, either in person or by reading their work. I maintain scepticism about some of their conclusions, but my working assumption is that they are intelligent and that they have probably thought of most of the issues that I will come up with. Can I observe as an outsider to the blogosphere, that it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

and more so, convinced that they are right and almost all of the experts are wrong. That must be the height of hubris.

However, Coldish specifically mentioned IPCC, and I think there is also an interesting point to make about that. At the Downing event, there seemed to be two IPCCs in the room. To some it was a huge plot, masterminded by some mysterious power that manipulates troublesome scientists. To me and the scientists in the room, it is (at least in WG1) simply a set of well-researched review papers, describing the present state of the peer-reviewed literature. I mention this only because I think the former view is a type of groupthink where, because people form an extreme opinion in their private space, they think it is widely held, or even true.

Alas, Wolff’s forray into the blogosphere was short, as is evident from a short comment a while later:

Just in case anyone thinks they are addressing me with their remarks:

I thought this might indeed be a chance for a civilised discussion, and some of the respondents seem happy to have that. However there are also a lot of remarks on here that are frankly rude and aggressive, and I won’t be returning. Now I remember why I hate the blogosphere.

CO2 and temperature both increasing: D’Aleo’s attempt at falsification of AGW debunked

March 17, 2010

Below are two graphs of global average temperature and CO2 concentration. First I show the temperature anomaly from the three major datasets of surface temperature together with the CO2 concentration as measured at Mauna Loa since 1958:

The CO2 concentrations are plotted on a logarithmic axis because the temperature effect of CO2 is logarithmic. The 11 year running mean through the yearly temperature anomalies is given by the thick colored lines.

Before the 1970’s, the temperature trend was more or less flat for a few decades (see also the graphs in this earlier post). The strong increase in cooling aerosols (resulting from e.g. SO2 emissions) counteracted much of the greenhouse warming over that period. Since that time however, greenhouse forcing has been dominant, resulting in the temperature and CO2 trends following a similar pattern (at least over the multi-decadal timescale; short term variability is heavily influenced by e.g. El Nino/La Nina, major volcanic eruptions and other natural phenomena). A graph of the time evolution of relevant known climate forcings over the past 130 years can be found here.

A very popular graph that purportedly falsifies the whole “AGW dogma” is the following, showing unrelated trends of temperature and CO2 for a recent 11 year period. It’s been carefully crafted to create a certain impression:

However, this graph is entirely misleading:

There are more factors than only CO2 that influence global average temperature.

The expected trend in temperature does not necessarily rise above the expected level of yearly variability over the course of a decade.

– The graph purposefully starts at a record high temperature (1998) to maximize the visual impression of “falling temperatures”. It also strongly depends on the specific datasets used. This is a clear example of cherrypicking.

Using the same logic as this graph is based on, one could also falsify the theory of gravity by pointing to a bird in the sky (conveniently forgetting that there are more forces than gravity and that the bird has wings).


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