Recently we received a request for setting up a glossary-only search mechanism, or perhaps one web page with a long list of glossary entries with hot links to full explanations. The glossary that we already have is a good start, but we are all busy and it's hard to find the time for extending this.

But there are also a number of external web pages which provide climate-related glossaries, such as the NOAA (they also have a seperate page for paleo-stuff), the Bureau of Meteorology (Australia, and there is even one by the Australian EPA), the Environmental Protection Agency (EPA, the U.S.), and the Western Regional Climate Center (WRCC, the U.S.). Wikipedia also has a glossary for climatological terms.

For those who seek the explanation for more bureaucratic terms, both the EU and the UNFCCC provide glossaries that may be useful.

Furthermore, there are some nice resources available, such as the Encyclopedia of Earth.

"Alarmism" is a term that gets bandied about a lot. It is often said that one should not call out "fire" in a crowded building. But it really depends, one might say, on whether the "calling out" is done in such a way as to simultaneously prevent a stampede and prevent anyone getting burned.

This riddle was very much on my mind as I sat down to write my thoughts on Mark Lynas's book, Six Degrees: Our Future on a Hotter Planet (London: Fourth Estate, 2007). I don't read much popular science literature, and I doubt I would have read this book if I hadn't made the mistake of referring to it (in a negative manner) in the comments section of a RealClimate post. I don't think my error was very grave. What I actually said was that if what I had heard about the book from the press materials were true, then the book was probably alarmist and not worth reading. But I don't blame the author for asking me to read the book and see for myself. He said that the press (in this case Sunday Times (London)) had misconstrued what he says in the book, and he assured me that is was all based on very careful review of the scientific literature. I was thus both curious and obligated to read the book.

Mark Lynas will no doubt be pleased that I very much like the book. To be sure, it is alarming, but the question of whether it is alarmist is a more difficult one, and I don't think the answer lies in debating the book. Rather, it lies in looking closely at the underlying science the book builds on. I don't intend to do that here, but I do think that all climate scientists (particularly those that talk to the public) ought to read this book, and ask themselves a question. I'll get to that question at the end, after saying a bit more about the book.

Six Degrees, as the title suggests, is comprised of six main chapters (plus an introduction and a conclusion). Each of the main chapters examine what the earth might look like as we raise the planet's temperature by 1^o, 2^o, etc. degrees Celsius, based on what the scientific literature has to say about it. Laying out the book this way makes for a good logical progression of ideas, and a fair bit of suspense. Very few people, Lynas says, have got "the slightest idea what two, four or six degrees of average warming actually means in reality, and I'm sure he is right.

In Chapter 1, at 1^o, we have predictions of, for example, an annually ice free Arctic ocean. Yes, quite plausible and supported by the literature, and perhaps occurring a little sooner than expected. At 2^o, we have, "so whilst southern China can expect more flooding as the two-degree line is approached, the oceanic time lag means that it may take much longer for the rain-bearing summer monsoon to reach the drought-stricken north." Yes, certainly plausible based on the studies Lynas cites. At 4^o, we have "with global sea levels half a meter or more above current levels, [the Egyptian city of] Alexandria's long lifespan will be drawing to a close. Even in today's climate, a substantial part of the city lies below sea level, and by the latter part of this century a terminal inundation will have begun. … a rise in sea levels of 50 cm would displace 1.5 million people and cause $35 billion of damage." Alarmist? Hardly. A 50 cm rise in sea level, is well within the conservative IPCC projections, even for temperature rises less than four degrees.

At 5^o and 6^o, the book really does start to sound alarmist, with the analogy to Dante's Inferno – used to good literary effect throughout the book – coming very much to the fore. At five degrees, we have "an entirely new planet is coming into being – one largely unrecognizable from the Earth we know today. At six degrees, "… the pump is primed … not for flourishing palm trees in Alaska, but for the worst of all earthly outcomes: mass extinction."

Aha, say the skeptics! It is alarmist after all. But is it? Lynas's reference to the "entirely different planet" actually refers to the fact that at five degrees, the "remaining ice sheets are eventually eliminated from both poles." That's entirely true. And unlike in Gore's discussion of sea level in Inconvenient Truth Lynas does emphasize the long timescales (thousands of years) in this case. Furthermore, there is published research that raises the likelihood of the significant loss of ice sheets at lower temperatures, and Lynas could have claimed certainty of a disappearing Greenland ice sheet in an earlier chapter. That he doesn't do that is characteristic of the book: it doesn't tend to go beyond the published literature. This is what Lynas claims at the outset — "all of the material in the book comes from the peer-reviewed scientific literature" – and I think he does an admirable job.

And that brings us back to the question I promised to raise at the beginning, which is this:

If a reading of the published scientific literature paints such a frightening picture of the future as Six Degrees suggests – even while it honestly represents that literature – then are we being too provocative in the way we write our scientific papers? Or are we being too cautious in the way we talk about the implications of the results?

If you are a RealClimate regular, you are undoubtedly aware of our ongoing interest in the developments in the scientific understanding of potential hurricane-climate change linkages. This is an area of the science where a substantial body of significant new research has emerged even since RealClimate's inception in late 2004. The scientific research in this area, and the media frenzy and political theatrics that have inescapably followed it, are thoughtfully placed in a broader historical context in a fascinating new book by Chris Mooney entitled Storm World: Hurricanes, Politics, and the Battle over Global Warming. Anyone who is at all interested in the scientific history that has led to our current understanding of Hurricanes and their potential linkages with climate change, will find this book a page turner. The book is a nice complement to Kerry Emanuel's recent book Divine Wind: The History and Science of Hurricanes (which too is so readable that it lies on our coffee table). Mooney in a sense picks up where Emanuel's left off. Like Emanuel, he explores the history of the science. But he uses this historical context, and his studies of the personalities of key actors, to explore how the current scientific debate can be traced back to a rift that has emerged over many decades between distinct communities of atmospheric scientists.
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We've often been asked to provide a one stop link for resources that people can use to get up to speed on the issue of climate change, and so here is a first cut. Unlike our other postings, we'll amend this as we discover or are pointed to new resources. Different people have different needs and so we will group resources according to the level people start at.

For complete beginners:

NCAR: Weather and climate basics
Oxford University: The basics of climate prediction
Pew Center: Global Warming basics
Wikipedia: Global Warming
NASA: Global Warming update
National Academy of Science: Understanding and Responding to Climate Change
Encyclopedia of Earth: Climate Change Collection
Global Warming FAQ (Tom Rees)

Those with some knowledge:

The IPCC AR4 Frequently Asked Questions (here) is an excellent start. That covers:

• What Factors Determine Earth's Climate?
• What is the Relationship between Climate Change and Weather?
• What is the Greenhouse Effect?
• How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences?
• How are Temperatures on Earth Changing?
• How is Precipitation Changing?
• Has there been a Change in Extreme Events like Heat Waves, Droughts, Floods and Hurricanes?
• Is the Amount of Snow and Ice on the Earth Decreasing?
• Is Sea Level Rising?
• What Caused the Ice Ages and Other Important Climate Changes Before the Industrial Era?
• Is the Current Climate Change Unusual Compared to Earlier Changes in Earth's History?
• Are the Increases in Atmospheric Carbon Dioxide and Other Greenhouse Gases During the Industrial Era Caused by Human Activities?
• How Reliable Are the Models Used to Make Projections of Future Climate Change?
• Can Individual Extreme Events be Explained by Greenhouse Warming?
• Can the Warming of the 20th Century be Explained by Natural Variability?
• Are Extreme Events, Like Heat Waves, Droughts or Floods, Expected to Change as the Earth's Climate Changes?
• How Likely are Major or Abrupt Climate Changes, such as Loss of Ice Sheets or Changes in Global Ocean Circulation?
• If Emissions of Greenhouse Gases are Reduced, How Quickly do Their Concentrations in the Atmosphere Decrease?
• Do Projected Changes in Climate Vary from Region to Region?

We'll link to the individual pages once the report is available in html.

RealClimate: Start with our index

Informed, but in need of more detail:

Science: You can't do better than the IPCC reports themselves (AR4 2007, TAR 2001).

History: Spencer Weart's "Discovery of Global Warming" (AIP)

Art: Robert Rohde's "Global Warming Art'

Informed, but seeking serious discussion of common contrarian talking points:

All of the below links have indexed debunks of most of the common points of confusion:

• Coby Beck's How to talk to Global Warming Skeptic
• New Scientist: Climate Change: A guide for the perplexed
• RealClimate: Response to common contrarian arguments
• NERC (UK): Climate change debate summary
• UK Met Office: Climate Change Myths
• Brian Angliss A Thorough Debunking
• John Cross Skeptical Science

Please feel free to suggest other suitable resources, particularly in different languages, and we'll try to keep this list up to date.

Does a global temperature exist? This is the question asked in a recently published article in Journal of Non-Equilibrium Thermodynamics by Christopher Essex, Ross McKitrick, and Bjarne Andresen. The paper argues that the global mean temperature is not physical, and that there may be many other ways of computing a mean which will give different trends.

The common arithmetic mean is just an estimate that provides a measure of the centre value of a batch of measurements (centre of a cloud of data points, and can be written more formally as the integral of x f(x) dx. The whole paper is irrelevant in the context of a climate change because it missed a very central point. CO₂ affects all surface temperatures on Earth, and in order to improve the signal-to-noise ratio, an ordinary arithmetic mean will enhance the common signal in all the measurements and suppress the internal variations which are spatially incoherent (e.g. not caused by CO₂ or other external forcings). Thus the choice may not need a physical justification, but is part of a scientific test which enables us to get a clearer 'yes' or 'no'. One could choose to look at the global mean sea level instead, which does have a physical meaning because it represents an estimate for the volume of the water in the oceans, but the choice is not crucial as long as the indicator used really responds to the conditions under investigation. And the global mean temperature is indeed a function of the temperature over the whole planetary surface.

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There has been a bit of a flap here at the University of Washington over the state of the snowpack in United States Pacific Northwest region. The Seattle city mayor, Greg Nickels (a well known advocate for city-based CO₂ reduction initiatives) wrote in an Op-Ed piece in the Seattle Times that

The average snowpack in the Cascades has declined 50 percent since 1950 and will be cut in half again in 30 years if we don't start addressing the problems of climate change now. That snow not only provides our drinking water, it powers the hydroelectric dams that keep our lights on.
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By William and Gavin

On Thursday March 8th, the UK TV Channel 4 aired a programme titled "The Great Global Warming Swindle". We were hoping for important revelations and final proof that we have all been hornswoggled by the climate Illuminati, but it just repeated the usual specious claims we hear all the time. We feel swindled. Indeed we are not the only ones: Carl Wunsch (who was a surprise addition to the cast) was apparently misled into thinking this was going to be a balanced look at the issues (the producers have a history of doing this), but who found himself put into a very different context indeed [Update: a full letter from Wunsch appears as comment 109 on this post]

So what did they have to say for themselves?
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Guest commentary from Juliane Fry, UC Berkeley

The recently released IPCC 2007 Fourth Assessment Report Summary for Policymakers reminds us that aerosols remain the least understood component of the climate system. Aerosols are solid or liquid particles suspended in the atmosphere, consisting of (in rough order of abundance): sea salt, mineral dust, inorganic salts such as ammonium sulfate (which has natural as well as anthropogenic sources from e.g. coal burning), and carbonaceous aerosol such as soot, plant emissions, and incompletely combusted fossil fuel. As should be apparent from this list, there are many natural sources of aerosol, but changes have been observed in particular, in the atmospheric loading of carbonaceous aerosol and sulphates, which originate in part from fossil fuel burning. While a relatively minor part of the overall aerosol mass, changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged net radiative forcing of roughly -1.2 W/m², in comparison to the overall average CO₂ forcing of +1.66 W/m².
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by Rasmus Benestad, with contributions from Caspar & Eric

In a recent article in Climatic Change, D.G. Martinson and W.C. Pitman III discuss a new hypothesis explaining how the climate could change abruptly between ice ages and inter-glacial (warm) periods. They argue that the changes in Earth's orbit around the Sun in isolation is not sufficient to explain the estimated high rate of change, and that there must be an amplifying feedback process kicking in. The necessity for a feedback is not new, as the Swedish Nobel Prize winner (Chemistry), Svante Arrhenius, suggested already in 1896 that CO2 could act as an amplification mechanism. In addition, there is the albedo feedback, where the amount of solar radiation that is reflected back into space, scales with the area of the ice- and snow-cover. And are clouds as well as other aspects playing a role.

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New addition: Download an annotated pdf of the Fraser report. An interactive pdf file, to be read on the screen, is here, and a printable version is here. Suggestions for further commenting are welcome. Additions to the pdf have to be short, and tied to particular pieces of text or figures. And of course we will only incorporate comments that we deem to be scientifically sound and cogent.

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While most of the world's climate scientists were following the IPCC fest last week, a few contrarians left out in the cold were trying to to organize their own party.

An unofficial, "Independent Summary for Policymakers" (ISPM) of the IPCC Fourth Assessment report has been delivered by the Fraser Institute. It's a long, imposing-looking document, resembling, come to think of it, the formatting of the real Summary for Policymakers (SPM) document that was released on Friday after final negotiations of the IPCC in Paris last week. The Fraser Institute has assembled an awesome team of 10 authors, including such RC favorites as tilter-against-windmills-and-hockey-sticks Ross McKitrick, and other luminaries such as William Kininmonth, MSc, M.Admin — whose most recent paper is "Don't be Gored into Going Along" in the Oct-Nov issue of Power Engineer. To be fair, he did publish a paper on weather forecasting, back in 1973. According to the press release, the London kickoff event will be graced by the presence of "noted environmentalist" David Bellamy. It's true he's "noted," but what he's noted for is his blatant fabrication of numbers purporting to show that the world's glaciers are advancing rather retreating, as reported here.

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