Global Surface Temperature Change

I really enjoyed reading “Global Surface Temperature Change“, by James Hansen and his team at GISS. Keep in mind that it’s still in the draft stages – they haven’t submitted to a journal yet, but they certainly plan to, and it’s a very credible team of scientists that will almost definitely get it published.

The paper is mostly about the methods of global temperature analysis. It’s more of a review paper than an account of a single experiment. However, their main discussion point was that even by using the same data, problems can be addressed in different ways. The two main problems with temperature analysis are:

  • “incomplete spatial and temporal coverage” (sparse data)
  • “non-climatic influences on measurement station environment” (urban heat island effect).

The authors explain the methods they use and why, and explore the impacts that different methods have on their results.

GISS measures anomalies in the temperatures, largely because they are much smoother and more consistent, geographically, than absolute temperatures. In 1987, they determined that anomalies could be safely extrapolated for a radius of 1200 km from a station and still be accurate. GISS smooths the whole map out by extrapolating everything and averaging the overlapping bits.

Extrapolating is also very useful in areas with very few stations, such as the polar regions and parts of Africa. In this map, grey indicates missing data:

The Arctic is particularly problematic, not only because its data is so sparse, but also because it has the largest anomaly of any region in the world. If you have incomplete coverage of an area that is warming so dramatically, it won’t pull its full weight in the global trend, and your result will almost certainly be too low.

This difficulty with the Arctic is the reason that GISS says 2005 is the warmest year on record, while HadCRUT, the team in England, says that 1998 is. GISS extrapolates from the stations they have, and end up getting pretty good coverage of the Arctic:

They’re assuming that areas with missing data have the same anomaly as whatever temperature stations are within 1200 km, which, as they determined in 1987, is a pretty fair assumption.

However, HadCRUT doesn’t do this extrapolating thing. When they don’t have data for an area, they just leave it out:

This might sound safer, in a way, but this method also makes an assumption. It assumes that the area has the same anomaly as the global average. And as we all know, the Arctic is warming a lot more and a lot faster than the global average. So it’s quite possible that GISS is right on this one.

Another adjustment that NASA makes is for local, anthropogenic, non-climatic effects on temperature data. The most obvious of these is the urban heat island effect. As an area becomes more urban, it gets more pavement, less vegetation, and its albedo goes down – it absorbs more heat. This often makes cities substantially warmer than the surrounding rural areas, which can obviously contaminate the temperature record. However, there are ways of eliminating urban influences from the data so we can see what the real trend is.

The first step is determining what stations are considered urban. The obvious way to do this is through population, but that’s actually not very accurate. Think of somewhere like Africa, where, even if there are thousands of people living in a small area, the urban influences such as concrete, absence of vegetation, or exhaust aren’t usually present. A much better indication is energy use, and a good proxy for energy use, that’s easy to measure, is lights at night-time.

So GISS put a bit of code into their analysis that singles out stations where nightlight brightness is greater than 32 µW/m2/sr/µm, and adjusts their trends to agree with rural stations within 1200 km. If there aren’t enough rural stations within that radius, they’ll just exclude the station from the analysis.

They did an even more rigorous test for this paper, to test just how much urban influences were contaminating the long-term trend, and it was pretty interesting.

There were enough stations considered “pitch-dark” at night, where they couldn’t detect any light, to run a global analysis all by themselves. The trend that came out was <0.01 °C/century smaller than GISS’s normal calculation, an amount of error that they described as “immeasurably small”.

The result of all this temperature analysis is a graph, with one new point every year, that is “eagerly awaited by some members of the public and the media”:

However, this graph isn’t actually as useful as this one – the 12-month running mean:

“From a climate standpoint there is nothing special about the time  of year at which the calendar begins”, so instead of only measuring January-December, you can also do February-January, March-February, and so on. This way, you get a data point every month instead of every year, and more data means more accuracy. It also solves problems with short-term influences, such as El Nino, La Nina, and volcanic eruptions, that the annual graph was having. These fleeting, but fairly substantial, influences can fall completely into one calendar year or be split between two – so their influence on global temperature could be overestimated or underestimated, depending on the starting month of the calendar. The 12-month running mean is much less misleading in this fashion.

As it is, we just set a new record for the 12-month running mean, and unless La Nina really takes off, 2010 will likely set a new record for the annual graph as well. But the authors argue that we need to start moving away from the annual graph, because it isn’t as useful.

The authors also discuss public perception of climate change, and media coverage of the issue. They say, “Our comments here about communication of this climate science to the public are our opinion…[We offer it] because it seems inappropriate to ignore the vast range of claims appearing in the media and in hopes that open discussion of these matters may help people distinguish the reality of global change sooner than would otherwise be the case.”

They make the very good point that “Lay people’s perception tends to be strongly influenced by the latest local fluctuation”, and use this winter as a case study, where a strongly negative Arctic Oscillation index caused significantly cooler-than-normal conditions across the United States and Europe. Consequently, a lot of people, especially in the US, began to doubt the reality of global warming – even though, in the world as a whole, it was the second warmest winter on record:

The authors also talk about data sharing. GISS likes to make everything freely available to the public – temperature station data, computer code, everything. However, putting it out there immediately, so that anyone can help check for flaws, has “a practical disadvantage: it allows any data flaws to be interpreted and misrepresented as machinations.” Multiple times in the past few years, when there have been minor errors that didn’t actually change anything, GISS was widely accused of making these mistakes deliberately, to “intentionally exaggerate the magnitude of global warming”. They realized this wasn’t working, so they changed their system: Before releasing the data to everyone, they first put it up on a private site so that only select scientists can examine it for flaws. And, of course, this “has resulted in the criticism that GISS now “hides” their data”.

Personally, I find the range and prevalence of these accusations against scientists absolutely terrifying. Look at what has become mainstream:

Scientific fraud is a very serious allegation, and it’s one thing for citizens to make it without evidence, but it’s another thing altogether for the media to repeat such claims without first investigating their validity:

I have been disgusted by the media coverage of climate science, especially over the past year, especially in the United States, and I worry what this will mean for our ability to solve the problem.

However, there is still fantastic science going on that is absolutely fascinating and essential to our understanding of global climate change. This paper was a very interesting read, and it helped me to better understand a lot of aspects of global temperature analysis.


14 thoughts on “Global Surface Temperature Change

  1. nice summary and good job putting this new paper in accessible language. I look forward to the release of the final version. It should prove an important contribution. good find!

    — Jim

  2. I believe that the earth is warming. I am not so arrogant as to believe that man is the cause. Am I still a “denier”?

    Lets face it, the debate really centers around WHAT is causing the warming. Is it mankind with our daily living habits? Or can it be part of a long term oscillation of our environment? The demagogues out there on both sides of the fence really muddy the waters, making it tough for the majority of people to “get a grasp”on what is being said, and being able to make decision as to where they stand on the issue.

    On both sides, we have the nit-pickers (this weather site is contaminated so everything is in question), the arrogant intelligentcia saying (ÿou don’t have the education to understand the science so just take my word for it). Both sets have their fanatical believers flooding the airwaves and the internet with CRAP that just makes it worse. I sometimes have to turn my BS sniffer off cause the stench is so bad.

    What I have experienced in my 62 years of learning and experiencing is the we are all HUMAN. that means we can all be “petty”, “mean”, “selfserving”, no matter our education or stated purpose. 62 years of hearing about oncoming ice ages, sea level rising, global warming (fact) etc, 62 years of reading about past prophecies of doom and gloom have all combined to make me cynical.

    So, when anyone tells me to read this or that book, or this or that “peer reviewed” paper, I turn off. I do not have the time nor the inclination to do that. Tell me what it is about this book or that paper that convinces you that your beliefs are the “right” beliefs. Sell me. Show me that you have “followed up”on the other respected (not fanatical) persons paper or book. Point out the things that are supporting your stance. Give me the comparisons and tell me why you are right. I want YOUR opinion.

    Peer reviewed science has proven over and over again that it can be wrong, as well as right. Just ask Leonardo, or countless others.

    Peer review is not perfect, but it has by far the best track record for providing correct answers. I don’t think it takes “arrogance” to believe that human activity is the cause of climate change – I believe it takes far more arrogance for an individual to decide that he or she is more credible than the entire scientific community. Here is the first part of a three-part video I highly recommend on the nature of science.

    I have seen a poster on classroom walls that says, “Courage is what it takes to stand up and speak. Courage is also what it takes to sit down and listen.” The same goes for science. This doesn’t mean we should take everything lying down and stop looking into things. Rather, our underlying assumption should not be that the entire scientific community is out to lunch, but that we, individual laypeople, are far more fallible.

    Re: past predictions of ice ages – that was largely a media circus and relied on exactly one scientific paper that was soon rejected. Peter Sinclair has a nice video citing very credible sources. And yes, I will continue to point you to outside sources. I don’t see the point of discussing my opinion or proving my integrity when it’s a matter of science. This is not an issue that individuals can prove through philosophy and thought experiments. Science is a group activity.

    Please provide a legitimate example of when climate scientists – not advocacy groups like Greenpeace – have thrown around “crap”. As Michael Tobis says, “Environmentalists have exactly zero relationship with the climate science community and their opinions are irrelevant to the discussion of how the climate science community behaves or should behave. The cultural origins of climate science are in deeply conservative communities: physics, meteorology, aviation, military, agriculture. The convergence of interest with ecologists is very recent.”

    I think what we need is not for advocacy groups to stop mud-slinging (because they never will), but for the public to figure out who they really need to listen to. -Kate

  3. Some points raised by winnipegman…

    1. “I am not so arrogant as to believe that man is the cause.”

    This is a common statement that places humans at the centre, often I think based on religious views. eg. God created and controls the earth, humans can do what they like and the earth will be put right.
    But one can easily say that it is arrogant to think we can not damage the planet, probably more arrogant.

    So where does this get us?
    The comment is irrelevant in the context of better understanding.

    2. “Is it mankind with our daily living habits? Or can it be part of a long term oscillation of our environment?”

    All species alter their environment. The other issue is that it is clear some humans do more damage than others, so it isn’t a question of all humanity being wrong. Probably the only humanity wide issue is population growth, carbon footprints are an issue of culture, politics, history etc.

    3. “Peer reviewed science has proven over and over again that it can be wrong, as well as right. Just ask Leonardo, or countless others.”

    You mean Da Vinci?
    He pre-dates the modern definition of science you refer to in your statement (peer review).

    You say science is faulty. That does not stop us today from flying aircraft, drive cars, use the internet or build computer memory based on quantum physics. All of this is based on ‘faulty’ science. Your mistake appears to be that you expect perfection and that knowledge used in this high carbon world is perfect and that is why we use it rather than living in caves.
    I suggest that instead of being cynical, that you accept that the faults in our knowledge do not matter a great deal when the knowledge is applied.
    This applies just as much to climate science as it does anything else. The fact that climate science produces results that don’t appear to help humanity in a positive way is irrelevant, it is no different to the science that produces the technology that allegedly benefits us.

  4. Oh golly, what to say. first, comments by “the ville”

    1. Perhaps I should have said man is the only cause. I wasn’t clear enough. Sorry. But I want to know, am I still a denier?

    2. The point there is that no matter what the cause under discussion, the strident, fundamentalist, hardline believers, muddy the water, destroy the picture and the sound with their “over the top” retoric. That makes it very difficult for anyone with a point of view to be heard. Please re read what I said in those 2 paragraphs.

    3. Leonardo Da Vinci! Yup, that is who I am talking about. He, and a host of others were, in their day, not believed, persecuted for their scientific beliefs and in the long run, proven right. Who do you believe, Darwins theoreums of the respected christian scientists that do their best to disprove them.

    4. [inflammatory]

  5. I see a couple of reference to “the Arctic is not warming” and “it is the coldest year on record in the Arctic” by Gerald Machnee that have been removed due to a lack of citations. The following quote taken from the National Snow and Ice Data Cente (NSIDC) at the University of Colorado website which documents the annual Arctic sea-ice melt and refreeze, with citation (dated August 17, 2010), may be instructive:

    “This year’s early clearing of sea ice probably resulted from record warm temperatures this past spring over the Western Canadian Arctic, as well as the decline in older, multiyear ice in the channel over recent years. Spring 2010 was the warmest in the region since 1948: some regions of the Western Canadian Arctic were more than 6°C (11°F) above normal.”

    Note the statement ‘warmest in the region since 1948 … more than 6°C above normal’.

    Why 1948? That’s because meteorological records for the Western Arctic only started then. But we can use Inuit oral tradition and records of ships that have traversed these waters in the past 150 years to know that we are seeing very unusual conditions in the Arctic, and not just the Western Canadian Arctic.

    The often quoted claim of a cold winter in the Arctic this past year is rooted in some misconceptions: 1) a single year or even a pair of years isn’t really relevent, it is the trend over decades that matters, and this year is on trend for ever warmer conditions and less sea-ice (see same website above); and 2) the apparent ‘recovery’ of Arctic sea-ice over March and April 2010 was erroneously interpreted by climate change deniers as indicating a return to ‘normal conditions’, when it was an anomaly due to cold weather and winds from the north over the Bering and Barents Seas.

    The NSIDC website notes on 2 separate posts:

    1) “Arctic sea ice extent at end of December 2009 remained below normal, primarily in the Atlantic sector of the Arctic. Average air temperatures over the Arctic Ocean were much higher than normal for the month, reflecting unusual atmospheric conditions.”

    2) “temperatures over the central Arctic Ocean remained above normal and the winter ice cover remained young and thin compared to earlier years.”

    Conclusion? The Arctic continues to warm and Arctic sea-ice continues to get smaller at the end of each summer. Right on the trend of the past 30+ years.

    David G.

    Thanks for all these great explanations, David. Here is a great study about Inuit traditional knowledge of the Arctic, from Inuvialuit in this instance. -Kate

  6. I would also like to pick up on some comments by Winnipegman. I think his posts show some thought, and some misconceptions. I respect an opinon that asks the question ‘the debate really centers around WHAT is causing the warming. Is it mankind with our daily living habits? Or can it be part of a long term oscillation of our environment?’

    I have some hesitation with the use of the word ‘debate’ because the ‘debate’ is in the media, not amongst climate scientists. It is true, however, as I have noted elsewhere on climatesight, that there are many geologists who ask the same question (I used to be one of them), in part rooted in their understanding of large scale earth processes that have driven past oscillations of climate; CO2 levels have been much higher than now in the past and climate at these times was sufficiently warmer that forests grew at the North and South poles (see Zachos et al. 2008, Nature 451, 279-283 (17 January 2008), doi:10.1038/nature06588; see also Ballantyne et al. 2010, Geology 38 (7), 603-606, doi: 10.1130/G30815.1 – this is free to read).

    These past ‘greenhouse intervals’ – the Eocene (50 million years ago) and Pliocene epochs (4 million years ago) – were not in any way related to human activity as they predate humans by several million years. So is current climate change, which is due primarily to CO2 and other greenhouse gases increasing in the atmosphere, due to human activity? The answer lies in 2 points:

    1) CO2 and the other GHGs are the main forcing for climate warming (and most climate scientists do – see Dr. Richard Alley’s Dec 2009 AGU talk here:;

    Past episodes of climate change that triggered the deglaciations at the start of each inter-glacial (i.e. the last 2 million years) are generally understood to be as much due to changes in the earth’s orbit around the sun as they are due to rising CO2 levels (see Zachos et al. 2008 citation above) – the Milankovitch model for ice-ages. But prior to then, GHGs, principally CO2 were the primary forcings (see Richard Alley talk, link above).

    2) given point 1), where has the extra CO2 come from? In the geological past, CO2 rose in the atmosphere due to geological processes – massive volcanic eruptions etc. Several studies have shown that all the extra CO2 in the atmosphere comes mainly from burning fossil fuels – it has a different isotopic signature than CO2 from natural processes. Below is a link to RealClimate that explains this. I hesitate to use a secondary source, but the citations of the primary scientific studies that support this understanding are found on that website:

    David G.

  7. [citations needed – data is smoothed too much, climate scientists will get “kicked out” of the academic community if they argue with the consensus]

  8. winnipegman’s comments didn’t pass moderation, but as a scientist actively involved in publishing his research and actively involved in reviewing papers on past climates for scientific journals across the world (including the journals Nature, Nature Geoscience, Geology, Canadian Journal of Earth Sciences, and several Australian and European mainly geological journals), and associate editor of a US paleontology journal (Palaios), I will comment, if I may, on the implication that ‘climate scientists will get “kicked out” of the academic community if they argue with the consensus’.

    I have heard this said and seen it written many times. But this idea misunderstands how science works. We don’t censor. Period. No-one is ever ‘kicked out’ except for fraud, i.e. making stuff up. Data is data. Interpretation is subject to debate.

    All scientific publishers have a code of ethics for both authors and reviewers. Amongst other things, reviewers and authors must declare any conflict of interest; one of the most important COI is do we stand to gain financially if the research is published or not published? As part of this, any funding, whether a govt. research grant or corporate support, must be declared in the published article – so an article on climate change funded by Exxon-Mobil may be judged differently than one funded by say Greenpeace, or one funded from a govt. research grant; the latter is the only one likely to be unbiased, but potentially all 3 are unbiased, or biased – but at least the reader can see the potential biases. Same goes for place of employment; a scientist employed by an oil company vs. a university or an environmental organization – who is potentially biased? Declaration allows the reader to make their own judgement.

    A similar COI solely for reviewers is whether we stand to gain through the advancement of our own research through rejecting an author’s research for publication. The latter is to stop other scientists blocking (or ‘censoring’) other scientists work from being published just because we disagree with their interpretation (e.g. ‘arguing against the consensus’) or because they have ‘scooped’ us (i.e., beat us to press with a similar study).

    In the peer review process, any corrections, changes recommended or advice to accept or reject must follow the criteria set by the publisher for these, and critically MUST be evidence based. In other words, I couldn’t as either an editor or reviewer reject a scientist’s research paper for publication simply because I disagreed with their interpretation, or because they ‘argued against the consensus’. Authors also have an opportunity to challenge any changes or disagreements with reviewers as part of the normal peer review process. Far from a process leading to censorship, in fact, published research disagreeing with your opinion offers an opportunity to publish a rebuttal (usually in the same journal in a later issue), or write a paper presenting counter arguments. I can only recommend ‘reject’ if the manuscript contains fundamental errors of logic, miscalculations that affect the conclusions, or (very rarely) if scientific fraud or other misconduct is detected (usually stealing someone else’s work or plagiarism; fabrication of data is truly rare). Journals wil publish retractions later if the peer review process fails to detect errors or fraud and faulty research gets published (so-called ‘cold fusion’ is an example).

    Most science journals have web pages devoted to explaining their review process and ethical guidelines for both authors and reviewers. Typically, these pages are freely available and do not require a subscription to the journal.

    The ethical guidelines for the science journal ‘Nature’, which frequently publishes climate change papers, can be found here (look under ‘Editorial and publishing policies’):

    The ethical guidelines for publishing in the science journal ‘Geology’, arguably the top journal for earth science research in North America, is found here:

    Most journals use a process where the reviewer remains unknown to the author(s). This rule is relaxed by some journals with the permission of the reviewers. Anonymous review is better as the reviewer then feels free to ‘not risk offense’ and be as critical as needed.

    The reviewing process is mostly a free service that we scientists provide to the science journals. I don’t receive a cent from any journal for my reviews, nor for the ‘associate editor’ work I have done. That is the normal situation. I guess the main reason is economic, but philosophically I suppose this means I have no financial incentive to either recommend ‘reject’ or ‘accept’ for publication. (journal editors, however are usually paid positions) Sometimes I have been paid a small ‘honorarium’ for reviewing a book (typically $100-$200, or a free copy of a book, or a temporary 25% discount on books they publish).

    So, no one is getting ‘kicked out’ and no one is getting censored. Any scientist who claims they are, is probably submitting substandard (i.e. unverifiable or error filled) research (see publishing guidelines on the journal websites). And frankly, the big money would be in ‘proving’ AGW wrong. I’d get the cover of Nature!

    Thanks, David. A very thorough and helpful comment as always! -Kate

  9. Kate, an update on a prior post I have on this page about Arctic warming. The National Snow & Ice Data Center have released the data for the 2010 September Arctic sea ice minimum, and they’ve declared 2010 as having the 3rd lowest minimum on record (1979-2010).

    Yes, its only a 31 year record, but the trend continues and to quote from their article:

    >>All indications are that sea ice will continue to decline over the next several decades,” said NSIDC Director Mark Serreze. “We are still looking at a seasonally ice-free Arctic in twenty to thirty years.”<<

    Translated, an Arctic Ocean ice-free over summer, a condition likely not seen in 4 million years. As NSIDC note in their article, ice reflects sunlight and water absorbs sunlight, so an ice-free summer Arctic is heating the Arctic Ocean waters. This will lead to even more Arctic warming.

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