Page partially upgraded, 04/08/2001

Please note: this document is the opinions of William Connolley, not those of BAS.

This will always be a work in progress, but at the moment it is very incomplete. Be warned.

Comments to wmc@bas.ac.uk

You can see my main web page. If you want to see what I think about various climate-type things, read on here, or search for "wmc@bas.ac.uk" on sci.environment in dejanews.

The Science Behind the News

This page originated in some lectures for the CU Board of CE in the series "The Science Behind the News". But its mutated since.

This page contains useful web links for the talks and other stuff... but before following any links, please read these little thoughts: there are a lot of web pages out there on climate change and related issues and (if you don't already know the answers) it can be very hard to tell which pages are good, accurate, useful, truthful or none of the above. An example of a plausible-looking page which (in my opinion) is wrong or at best seriously misleading is this piece dealing with the MSU temperature record. An example of complete twaddle is provided by Exxon [link now broken. perhaps they are learning...].

If you only have time for one on-line document, I strongly suggest Climate change: some basics by Jan Schloerer. If that is too dry, then you could try http://www.gcrio.org/gwcc/toc.html, or a page by J. Mahlman: Science and non-science concerning human-caused climate warming.

Complexity of the issue
Some quotes:

"To every difficult question there is a simple, straightforward answer - but its wrong" - exact quote and source, anyone? [thanks to TP: Exact quote is: For every difficult question, there is an answer that is clear and simple and wrong, by George Bernard Shaw. See here or here].

"Make things as simple as possible - but no simpler" - I think thats from Einstein, but I could be wrong. Correction welcome. [It is! For example: http://stripe.colorado.edu/~judy/einstein/advice.html, though I got the exact words a bit wrong, but the sentiment right]

Why do I include those quotes? Because sometimes people have a tendency to see the climate change issue in black and white, simple terms. It is or it isn't. A fight between two sides. Soundbites. If it isn't simple, it can't be true. The full science of climate change is very complex, sometimes it seems to me fractally so - anything you look at and thought you really understood looks, on closer examination, to contain a series of further problems.

But, at the same time, one shouldn't over estimate the problems. Some things are known - more on this later.

There is no simplicity - even to estimate the complexity of the problem, and how much is known, requires careful though.

Terminology

Often confusing. Read carefully...

Miscellaneous essay fragments

why do we think there is a problem
[warning: this section is even more incomplete than the others....]

Or, more precisely, why do scientists believe that adding CO2 to the atmosphere will increase the temperature? Whether this is actually a problem is addressed later.

If you read the everyday media, you will have heard all sorts of things (often contradictory) suggested as going to result from climate change. Often, the actual scientific "predictions" are much milder and less controversial. to set the scene, I recommend rather a nice piece by the AGU: Global Change Researchers Assess Projections of Climate Change, which categorises predictions into virtually certain down to uncertain. A very similar list is in Consequences and yet another version. Compare those two documents to what Mobil thinks we know and note how blurred the latter is.

There are several reasons for believing that increasing CO2 will increase the global mean temperature:

  1. Most importantly, there are theoretical reasons (based on radiative transfer, etc)
  2. This is then elaborated into Global Climate Models (GCM's, also General Circulation Models) which aim to provide more detail, eg about ice-albedo feedbacks, which are hard to include in (1).
  3. There is evidence from the far past (ice ages; ice cores) that CO2 and temperature fluctuate together
  4. The globe has warmed recently and CO2 has increased recently.

It is a good idea to remember that the first is the most important reason. The others are secondary. Often, Bau's attack the other reasons, show that they are not convincing, and claim to have rebutted the very idea of AGE.

Note that increasing global temperature does not imply a steady increase, nor an increase in all parts of the globe: some areas could get colder. Under some (not very likely) scenarios, increasing CO2 leads to cooling (after initial warming) via thermohaline shut-down.

GCMs and how they work
A helpful list of GCM groups is provided by S. Baum. An UNEP factsheet on How climate models work.
how has climate changed in the past 100's of Myr; M yr; 100 kyr; 1000 yr (proxies); 100 yr?

A good place for some web links, when I find them. Myr == M yr == Million years before present; kyr == k yr == thousands of years before present.

Some people would suggest that the recent 0.3-0.6 oC increase over the last century is unprecedented. Others would like you to believe that such events are common. Who is right? Again, complexity... Lets look at different time periods. The further we go back the less we know for sure - surprised?

100's of M yr
As far as I know, useful temperature records back this far are very sparse, so this section is rather brief.

From RMG: The current (ca. 360 ppm) CO2 levels were last reached in the Eocene (IIRC), ca. 40 Mya. The drop in CO2 levels from Cretaceous to present is pointed to as the reason for development of the alternate photosynthetic pathway (C3 or C4, I always forget which), which was contemporaneous with the drop.

The Illinois State Museum provides some perspective.

M yr
[Source: IPCC '90] About 2 M yr (3 M yr according to other sources) ago the ice age cycles began. We are now in an interglacial, so the temperature now is warmer than the average over those cycles. Temperature varies globally by about 5-7 oC between the depths of an ice-age and the interglacial and locally by 10-15 oC (where does the global average figure come from?).

The Illonois State Museum has some good (basic) stuff on the ice ages. They have a Graph of Ice Volume on the Earth over the last million years (well actually its plankton delta O-18 proxy, but it will do).

100 k yr
This covers roughly the last glacial-interglacial cycle. The main proxy for temperature here comes from ice core - oxygen isotope variations.

Placeholder link: milankovitch - could do with something better.

Some more random Milankovitch links:

  1. NOAA Paleoclimatology Program Educational Outreach - Milankovitch Theory
  2. Visualization of the Milankovitch Orbital Theory by Hans J. Wolters, John A. Shaffer, R.S. Cerveny & R.E. Barnhill
  3. EXPERIMENTING WITH ICE-AGE CYCLES IN A SPREADSHEET> W. H. Berger
  4. The timing of the Ice Ages
  5. A Breif History of the Quaternary and Problems of Correlation of Quaternary Sequences
  6. Climate Forcing - Orbital Variations - insolation dataset
  7. Paleoclimatology and climate system dynamics Jonathan T. Overpeck
  8. Astronomical Theory Offers New Explanation For Ice Age - perhaps a little dodgy, but does point out that the 100 kyr peak is dominant in the observations but not the forcing.
  9. Ice Sheets Play Important Role in Climate Change
  10. Barry Saltzman and Mikhail Verbitsky - Nature 2/3/94
  11. Imbrie, J., A. Berger et al. - Paleoceanography, 8(6), 699-735
1000 yr
1000 years goes beyond the instrumental temperature range but is within the range of "proxies": tree rings, coral (only goes back a few hundred years), lake levels, ice cores. Proxies have problems: tree-rings mostly reflect changes in growing season temperatures and don't work in the tropics. Corals aren't exactly global either. Resolution can be a problem. In April 1998 a study by Mann and Bradley looked at a reconstruction of the global temperature record over the last 600 years (in March 1999 this was entended to 1000 years, but only for the northern hemisphere). Why 600 only? Read their FAQ. They tried their best to do a global study, but this image shows how sparse that is. (A slightly more useful version is at http://www.ngdc.noaa.gov/paleo/pubs/mann1998/frames.htm).

From that study, it appears that the recent temperature rise is unusual. They say (in the FAQ) "Our study shows that warming this century is unprecedented many centuries back, beyond the beginning of the instrumental climate record. The study also shows that the warming this century has a very close relationship with the emergence of human greenhouse gases over the same time period, and that this relationship is very unlikely to have occurred if the recent warming is to be interpreted as natural climate variability."

Papers to read:

  • "Mann ME, Bradley RS, Hughes MK (1999) Northern Hemisphere Temperatures During The Past Millennium : Inferences , Uncertainties , And Limitations. GEOPHYSICAL RESEARCH LETTERS, v26, #6, 759-762"
  • "Mann ME, Bradley RS, Hughes MK (1998) Global - Scale Temperature Patterns And Climate Forcing Over The Past Six Centuries. NATURE, v392, #6678, 779-787"
    100 yr
    can we trust GCM's?
    A difficult question. Here is one answer, by Eric J. Barron, reviewed by Schlesinger and Flannery. Another comes from the UNEP factsheet series. Some people, however, think that GCMs are rubbish: for example, Douglas V. Hoyt.
    has the Earth warmed in the last century?
    Various sites around the world keep "authoritative" collections of surface temperature measurements. One of the best is CRU and here is a piece from their 1993 annual report about temperatures over the last 140 years, by Phil Jones. You can see a slightly up-to-date graph, and actually download the data to play with, from www.cru.uea.ac.uk/cru/data/temperat.htm. That page also contains references to the scientfic literature. A not-very-different dataset is available from the Hadley Center (see-also).

    Is the Earth warming up yet ? factsheet from UNEP.

    The MSU temperature record over the last 20- years tends to show less warming than the surface, and is often cited by those who dislike AGE. However, the record has been subject to a number of criticisms and corrections, eg Prabhakara et al. or Wentz and Schnabel.

    If so, why?
    Most people think its related to CO2 increase. Some disagree and say its the sun, or natural variability. If we had very long time-series of global temperature, we would have some better hope of exactly attributing causes. But we don't - we have 140-odd years of observational record (see above) and proxies before that. So what we have is: the earth has warmed by about the amount that modern GCMs predict it should given CO2 and aerosol forcing. Pattern detection studies tend to indicate that the pattern of change fits what would be expected from CO2+aerosol better than, say, solar forcing. This is why IPCC '95 decided that "The balance of evidence suggests a discernible human influence on global climate".

    Judith Lean is sometimes cited by those who assert a large role for solar variability, but in this article (co-authored with David Rind) the authors appear to give a lesser role to the sun.

    will global warming be a bad thing?
    Far more effort has been spent on working out what shape AGE is likely to take than on trying to decide if it will be a problem. This is for a number of reasons:
    1. Predicting shifts in, say, temperature or rainfall is considered easier than predicting shifts in, say, species distribution or farmability
    2. Many "greenies" are content to say: AGE is obviously bad; many "bau"'s have been so busy saying that AGE (or any other form of warming) is not occurring that they haven't got round to marshalling arguements for the next phase: its occurring but its not bad.
    3. Fill in others of your own...

    For example, the EPA website talks about impacts, and mostly in negative terms, but in the end it has to admit that at the moment, we don't really know.

    Many people are interested in this, but often their work is at an early stage: for example, EPRI (Electric Power Research Institute) have a promising looking page but they don't seem to have actually done any of the work yet!

    I don't claim to have any particular insight into whether it will be bad or not. My vague answer is "more unexpected things will happen, weather and climate-wise". This section needs more work...

    and if it was bad, would it be better to adapt or prevent?
    Suppose we get to the end of our chain of reasoning: either by saying
    1. Yes, we can predict climate change and it would be a bad idea
    2. Or, we can't be definite about one of the above but we'd like to make plans in case they are both true
    then we still have to face the choice: would it be better to adapt to a changing climate, or act to prevent the change?

    Some people, most notably John McCarthy argue that human ingenuity can solve virtually any problem, and that global warming can be avoided if it is necessary. It is arguable that, if global warming is not too serious, then the costs of emmissions reductions could be larger than the damage avioded. This, of course, assumes that we have some way to measure these costs comparatively - how does one value a piece of land destroyed by sea rise? If (to take an unrealistic possibility) all the costs of AGE were borne by a poor country (say Bangladesh becoming flooded) and all the costs of emmissions reductions by a rich one, then conventional economics could be interpreted as saying: "well, OK, its most (economically) efficient to just flood the country". But few would regard that as just (but since when has justice had anything to do with international politics?).

    These two issues (valuing externalities, and cost/benefit distribution) are known to be problems and no solution is yet apparent.

    I don't want to talk about this too much. Here are some opinions...

    1. White House Predicts Lower Costs for Controlling Emissions.
    2. FORMULATION OF RESPONSE STRATEGIES BY WORKING GROUP III might be worth a read.
    3. Climate Engineering: A critical review of proposals, their scientific and political context, and possible impacts (Ben Matthews).

    Position statements

    Various scientific organisations have put out position statements on climate change. I shall try to collect them.

    Some links, unsorted at present

    There are so many pages out there on the web on global warming. Many are rubbish. I've listed some below - not all of which are correct or accurate - but which are at least interesting.

    Note: Inclusion in this list does not imply that I agree with anything they say, nor that I think they are useful, nor that I've even read them carefully!

    The links below are from the "dark side":

    Technical resources
    Hmm, I wonder what I'll put here.