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FAQ on climate models

3 Nov 2008 by group

Translations: (Svenska)

We discuss climate models a lot, and from the comments here and in other forums it’s clear that there remains a great deal of confusion about what climate models do and how their results should be interpreted. This post is designed to be a FAQ for climate model questions – of which a few are already given. If you have comments or other questions, ask them as concisely as possible in the comment section and if they are of enough interest, we’ll add them to the post so that we can have a resource for future discussions. (We would ask that you please focus on real questions that have real answers and, as always, avoid rhetorical excesses).

Part II is here.

[Read more…] about FAQ on climate models

Filed Under: Climate modelling, Climate Science, FAQ

Comprehensive climate glossary

9 Aug 2008 by rasmus

Glossary cartoon from Marc Roberts 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.

Filed Under: Climate Science, Glossary, Tutorials

Six Degrees

25 Nov 2007 by eric

“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 1o, 2o, 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 1o, 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 2o, 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 4o, 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 5o and 6o, 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?

Filed Under: Climate Science, Reviews

Storm World: A Review

18 Jun 2007 by mike

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.
[Read more…] about Storm World: A Review

Filed Under: Climate Science, Hurricanes, Reviews

Start here

22 May 2007 by group

[Note this is page is updated regularly. Please notify us of any dead links. Last update: 10 May 2022.]

We’re often 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 selection. 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
Center for Climate and Energy Solutions: Climate basics
Wikipedia: Global Warming
NASA: Global Warming
National Academy of Science: America’s Climate Choices (2011)
Encyclopedia of Earth: Climate Change
Global Warming: Man or Myth? (Scott Mandia, SUNY Suffolk)
Open Learn: The Basics of Climate Prediction

There is a booklet on Climate Literacy from multiple agencies (NOAA, NSF, AAAS) available here (pdf).

The UK Govt. had a good site on The Science of Climate Change (archived).

The portal for climate and climate change of the ZAMG (Zentralaanstalt für Meteorologie und Geodynamik, Vienna, Austria). (In German) (added Jan 2011).

Those with some knowledge:

The IPCC Frequently Asked Questions are an excellent start (AR4 version here , updates were provided in the 5th Assessment report (pdf) and again for AR6).

The UK Royal Society and US National Academies of Science produced a joint Q&A on climate change in 2014, and an update in 2017.

RealClimate: Start with our index.

Informed, but in need of more detail:

Science: You can’t do better than the IPCC reports themselves (AR6 2021, AR5 2013, AR4 2007, TAR 2001). Also the Climate Science Special Report for the US National Climate Assessment.

History: Spencer Weart’s “Discovery of Global Warming” (AIP)

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 (archived)
  • UK Met Office: Climate Science
  • Brian Angliss A Thorough Debunking
  • John Cook Skeptical Science
  • The Global Warming Debate (Presentations from around 2010 resurrected)

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

A Slovak translation is available here

Tłumaczenie na polski dostępne jest tutaj
A Bulgarian translation is available here (via Ivan Boreev).

Filed Under: Climate Science, FAQ, IPCC

Does a Global Temperature Exist?

25 Mar 2007 by rasmus

Translations: (Português)

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.

[Read more…] about Does a Global Temperature Exist?

Filed Under: Climate Science, FAQ, RC Forum

Has Pacific Northwest snowpack declined? Yes.

20 Mar 2007 by eric

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.
[Read more…] about Has Pacific Northwest snowpack declined? Yes.

Filed Under: Climate Science, FAQ, Instrumental Record, Reporting on climate

Swindled!

9 Mar 2007 by group

Translations: (Türkçe)

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?
[Read more…] about Swindled!

Filed Under: Climate Science, Extras, Paleoclimate, Reporting on climate, Reviews, Sun-earth connections

Aerosols: The Last Frontier?

21 Feb 2007 by group

Translations: (Português)

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.
[Read more…] about Aerosols: The Last Frontier?

Filed Under: Aerosols, Climate Science, FAQ, IPCC

What triggers ice ages?

16 Feb 2007 by rasmus

Translations: (Português) (Türkçe) (Français)

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.

[Read more…] about What triggers ice ages?

Filed Under: Arctic and Antarctic, Climate modelling, Climate Science, FAQ, Reporting on climate

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