global warming, fact or fiction? — Julia Slingo

intro slide


Last week, I attended a very informative talk by Julia Slingo, the chief scientist of the UK Meteorological Office , one of the top research institutions in weather forecasting and climate research. When i’m not inside a concert hall or playing with my nephews/nieces or hiking up the mountains somewhere, this is my passion, doing research related to the polar region in particular and climate change in general.

Quite a few years ago, while in transit at an airport somewhere in the middle of the US, a woman asked me what I do for a living.  At the time, i was a graduate student just getting started in looking at melting of the ice sheets in response to global warming, so I told her as such.  Her response: “well, i’m not sure if i believe in global warming.”  My first reaction was that it’s not a religion, not like you believe in God or not.  It’s a scientific question, and there are evidences to back up conclusions about global warming.  She didn’t seem to care for reading up, and I was also stuck because as such a beginner, I didn’t know enough to give her concrete evidence.

Fast forward to now, of course there are plenty of evidences, it’s just a matter of taking the time to read and analyze them yourself.  As I can not be the expert in every field related to this complex problem, it would have taken me a long time to pull all the evidences together from this 997-page report of the intergovernmental panel on climate change (IPCC) titled “2007 IPCC report: the physical scientific basis“.

That’s what Dr. Slingo’s talk offers: a very good overview of global warming, climate change, human impact, consequences and mitigations.  Specifically, what she gave in her talk are concrete numbers.  This is my attempt to make these numbers available to everyone, as well as pointing you to where to find answers for how scientists arrive at those numbers and error bars.  Someone in the audience asked Dr. Slingo at the end of her talk what the scientific community’s response should be to questions regarding “climate change”.  Her (rough, i can’t remember word-for-word) response is that we need to be honest and provide all the available numbers.  “Climate change” is a very complex problem, and we don’t know yet all the answers.  However, what we begin to have now are actual numbers to support evidences for global warming and human impact.  There will always be doubters regardless of whether we provide them with details or not.  However, for our own goods, everything should be transparent.

So, (if you have read it this far, which makes me happy 🙂 ), I hope you will follow the trail of evidence below and make decision for yourself. The rest of this post is a very brief attempt to provide some answers / references (from Dr Slingo’s talk and IPCC-2007 report) to the following questions:

1) Is global warming happening?  What are the evidences?
2) Is human responsible for the warming?  What are the evidences?
3) What are the consequences?  What is needed now?


1) Is global warming happening? What are the evidences?


Yes.  the net increase in temperature over the last 100-yr (1906-2005) is 0.74°C ± 0.18°C (p36).  Going back further in time, the latest study by Mann et al. [2008] concluded that “Nominally, the recent observed decadal warmth recorded in the instrumental observations exceeds the uncertainty range of the reconstructions over at least the past 1,600 years for Northern hemisphere land temperatures as reconstructed by CPS (Fig. S5) and the past 1,700 years for Northern Hemisphere land plus ocean temperatures as reconstructed by EIV.”  In other word, the “recent Northern Hemisphere warmth exceeds that of at least the past 1,300 years with 66%-95% certainty.” (Mann et al., 2008, IPCC-2007, pg 56-57, see figure below.)


1b) A related question is: Is the current warming part of the Earth’s cycle of warming and cooling? Is it due to sun-spots? due to earth’s orbital variations?
I will address (1b) later when I have more time.  However, you can read up the IPCC-2007 FAQ pages here and answers to Questions 6.1 and 6.2.

2) Is human responsible for the warming? What are the evidences? (FAQ pages, Question 2.1, 7.1)
The conclusion from the IPCC-2007 report is (p60):

anthropogenic greenhouse gas increases caused most of the observed increase in global average temperatures  since the mid-20th century with > 90% probability.and thatIt is extremely unlikely (<5%) that the global pattern of warming observed during the past half century can be explained without external forcing (i.e., without man-made greenhouse gas)”

2a) So, the first sub-question here is: has anthropogenic (man-made) greenhouse gas increased since the mid-20th century?  
Yes.  see the figure below for the increase (See also Figure TS.1 and Figure TS.2 on page 24-25 of the Technical Summary report).  The 1995-2005 average rate of increase in CO2 gas in the atmosphere is 1.9 part-per-million/yr. The rate over the 8000 year prior to the industrial period was 80ppm/8000yr = 0.01ppm/yr (p25).

Julia Slingo's talk, slide #21


2b) How can we tell it’s man-made CO2 and not CO2 from some other natural processes that have been pumped into the atmosphere?

The most compelling evidence that the increase in CO2 is due to fossil fuel buring comes from the accurate measurement of decrease in O2 in the atmosphere; for material to burn O2 is needed, such as in this simple equation for burning coal: C + O2 –> CO2Here‘s the starting point (slide 40) of evidence (and the person responsible for most of the accurate O2 measurements and analyses).

Julia Slingo's talk, slide #24


2c) OK, CO2 is rising.  Where is the evidence that this rise causes global warming?

The answers to this question are of 2 types: physics (what is happening now) and numerical model results (what can happen in the future).  Here’s the simple 2-page explanation (p98-99) of what the green house effect is.  This is physics.  Once physics are accounted for in a numerical model for the ocean + atmosphere, we can attempt to quantify how high temperature can rise as a function of how much we put in to the atmosphere.  The key result here is that when man-made CO2 increase is omitted, the models CAN NOT reproduce the observed increase in global temperature (which leads to the conclusion to (2) above):

Julia Slingo's talk, slide #25

The subfigure on the left shows the predicted temperature rise matching the observed one when man-made CO2 and naturally occurring green-house gases were used in the model.  On the right, only naturally occurring green-house gases are used to drive the model, and the observed temperature rise can not be reproduced (see p62 in Technical Summary for full description).


3) What are the consequences? What is needed now?

Regardless of question #2, we’re still faced with the fact that global temperature is rising and there are consequences. Some examples are sea level rise (at rates of 1.8 ± 0.5 mm/yr for 1961-2003 and 3.1 ± 0.7 mm/yr for 1993-2003, p48-49) and increase in extreme weather conditions (p52, Table 3.7-3.8 on page 314-315).

Julia Slingo's talk, slide #39


Since the majority of human beings live near coast-lines, sea-level rise is an immediate issue (as opposed to what our children will face). So what is needed now is a strategy to curb the rise in global temperature.  The slide below (and Figure TS.27 on p71) shows the various scenarios to keep the increase in temperature in 2090-2099 relative to 1980-1999 to within 2°C:

Julia Slingo's talk, slide #47

There are two sets of curves above. The set which shoots UP are the cases if we go on with current business as usual. The second set called “early and rapid decline” shows the predicted temperature rise if we start curbing the CO2 emission.


OK, this post is quite long already, let’s wrap it up. What I’ve shown above is only a brief overview of the current research on climate change.  I encourage everyone to take a look at the IPCC-2007 report for more accurate assessment and references.  I also leave Julia Slingo’s Presentation here (she said it’s available to the public).


About thả diều
writing-challenged opera-addict

9 Responses to global warming, fact or fiction? — Julia Slingo

  1. Smorg says:

    Great post, An. Thanks for doing the hard work of compiling the evidence and putting them into easy to follow format for us. The facts are as they are regardless of some folks’ tendency to just want to ignore them and keep trying to justify their lack of concern for what sort of environmental condition they will be leaving for their grandchildren to have to survive in. I’m so tweeting this essay! 😉

  2. Eyesometric says:

    Thank you for literally bringing me down to earth and reminding me of the important things in life. I second Smorgy’s thoughts on the importance of this and how grateful we are for your work in making this accessible to the non-expert. Well done!

  3. Gina M says:

    cool. the co2 was confusing at first because it was a reverse timeline and i couldn’t at first see where the small chart fit in. I am not understanding the last chart on irreversability. There are 6 curves and the legend has 3 explanations for 3 of those curves with 2 curves having the same color and are indistinguishable to me.

  4. jtg says:

    Re: Is Geo-engineering an option?

    Many thanks for an excellent presentation.

    In my opinion it is dangerous for the science community, especially those with a deep understanding of global warming, to advocate these technical solutions known collectively as “geo-engineering”.

    1) As I see it, undertaking such “fixes” far-ahead enough in time to do any good will necessarily mean much uncertainty in the long-term benefits and risks of such projects, for the same reasons and limitations that currently prevent accurate predictions of the “do nothing” option.

    2) Putting these inherently risky proposals forward will inevitably be seen as “solutions” by many (perhaps most) of our citizens. Worse, such notions will be encouraged by those with a vested interest in the continued use of fossil fuels: It’s OK to drive a 400 horsepower SUV (it’s good for the economy) because the cloud ships will take care of it. How could it be otherwise? It is these same forces that are fighting now to prevent even the most tentative and timorous proposals from being implemented.

    3) While the physics types among the science elites will advocate physics-centered projects, the biologists and their industrial backers will advocate biological fixes. “Geo-engineering” will be joined by “genetic engineering” and we will be told that all our problems can be solved if we just re-plant much of the world’s forests with carbon-eating trees. What could possibly go wrong with such a plan? And if not this scheme, then some other, the key feature of which will always be deployment of patented, genetically modified organisms in order to save the planet.

    4) The real, permanent fix is obvious, but difficult: emit less greenhouse gases. Accomplishing this in a manner that allows a meaningful standard of living for the world’s population is the goal toward which the world’s science, engineering, economic, and especially political resources urgently need to be directed — immediately. Cloud-ships, even if feasible and however exciting for those involved, are a distraction. Carbon-eating trees and their ilk strike me as likely to pose an eventual threat greater even than global warming.

    5) The “real” challenge is finding the political will and leadership required to galvanize enough of the planet’s people and organize the multinational players to work together to take the necessary and probably at-first painful steps needed to do what we know must be done. Those whose training and profession have afforded special insight into the problem should strongly demand and endorse the political efforts to deal with this unfolding global catastrophe, and refrain from suggesting purely technical steps that will inevitably be portrayed by the clueless and unscrupulous as solutions sufficient unto themselves.

    6) In elementary school we sang a song that neatly characterizes the problems and dangers associated with engineering our way out of this kind of global, systemic problem.

    There was an old woman who swallowed a fly,
    I don’t know why she swallowed a fly,
    Perhaps she’ll die.

    There was an old woman who swallowed a spider,
    that wiggled and jiggled and tickled inside her.
    She swallowed the spider to catch the fly,
    But I don’t know why she swallowed the fly.
    Perhaps she’ll die.

    [The old woman took increasingly radical steps to solve her initial problem of insect ingestion, As described in the song, she successively swallowed a bird, a cat, and a dog. The song then continues…]

    I know an old woman who swallowed a goat —
    just opened her throat and swallowed a goat.
    She swallowed the goat to catch the dog.
    She swallowed the dog to catch the cat.
    She swallowed the cat to catch the spider,
    that wiggled and jiggled and tickled insider.
    She swallowed the spider to catch the fly.
    But I don’t know why she swallowed the fly.
    Perhaps he’ll die.

    [At this juncture, the old woman took a fatal step…]

    I know an old woman who swallowed a horse —
    She’s dead, of course!
    She swallowed the horse to catch the goat.
    She swallowed the goat…

    Well, you get the picture. The only question in my mind is whether geo(genetic)-engineering represents the goat or horse phase of the effort to fix global warming.

    • thả diều says:

      Dear jtg,

      thank you very much for stopping by and providing us with your insights. and I love very much the song, can you point to me where I can get the melody and the song? I can teach to my many young nephews and nieces :-).

      Song aside, I agree with you. In fact, Dr. Slingo skipped all slides re geo-engineering EXCEPT pointing out one important thing: We don’t know enough to interfere. The key example is the emission of greenhouse gas into the atmosphere: that’s already geo-engineering, and clearly we don’t have yet full capabilities at the moment to predict its full effect in the future (as expressed in the error bars for future climate scenarios). She warned against using geo-engineering in her talk.

      I also agree that the best solution is curbing the emission. The key lesson for the future should be conservation: “use less, emit less, trash less” rather than “use more and fix”.

  5. Eyesometric says:

    There’s a version of the song by Burl Ives

    or if you prefer I could write out the melody and send it as pdf

    I’m sure the nieces and nephews will love it!

    • thả diều says:

      thanks eyesometric for the link! it’s quite a long song, i’ll have to write it down indeed, then learn a bit of the melody, or i can just show the clip to my nephews and nieces (there’s another one that looks like cartoon, that might draw their attention better 🙂 )

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s