• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

RealClimate

Climate science from climate scientists...

  • Start here
  • Model-Observation Comparisons
  • Miscellaneous Climate Graphics
  • Surface temperature graphics
You are here: Home / Archives for Climate Science / Climate modelling

Climate modelling

On attribution

26 May 2010 by Gavin

How do we know what caused climate to change – or even if anything did?

This is a central question with respect to recent temperature trends, but of course it is much more general and applies to a whole range of climate changes over all time scales. Judging from comments we receive here and discussions elsewhere on the web, there is a fair amount of confusion about how this process works and what can (and cannot) be said with confidence. For instance, many people appear to (incorrectly) think that attribution is just based on a naive correlation of the global mean temperature, or that it is impossible to do unless a change is ‘unprecedented’ or that the answers are based on our lack of imagination about other causes.

In fact the process is more sophisticated than these misconceptions imply and I’ll go over the main issues below. But the executive summary is this:

  • You can’t do attribution based only on statistics
  • Attribution has nothing to do with something being “unprecedented”
  • You always need a model of some sort
  • The more distinct the fingerprint of a particular cause is, the easier it is to detect

Note that it helps enormously to think about attribution in contexts that don’t have anything to do with anthropogenic causes. For some reason that allows people to think a little bit more clearly about the problem.
[Read more…] about On attribution

Filed Under: Climate modelling, Climate Science

Ocean heat content increases update

21 May 2010 by Gavin

Translations: (Español) (Italian)

There is a new paper in Nature this week on recent trends in ocean heat content from a large group of oceanographers led by John Lyman at PMEL. Their target is the uncertainty surrounding the various efforts to create a homogenised ocean heat content data set that deals appropriately with the various instrument changes and coverage biases that have plagued previous attempts.

We have discussed this issue a number of times because of its importance in diagnosing the long term radiative imbalance of the atmosphere. Basically, if there has been more energy coming in at the top than is leaving, then it has to have been going somewhere – and that somewhere is mainly the ocean. (Other reservoirs for this energy, like the land surface or melting ice, are much smaller, and can be neglected for the most part).

[Read more…] about Ocean heat content increases update

Filed Under: Climate modelling, Climate Science, Oceans

First published response to Lindzen and Choi

8 Jan 2010 by Gavin

The first published response to Lindzen and Choi (2009) (LC09) has just appeared “in press” (subscription) at GRL. LC09 purported to determine climate sensitivity by examining the response of radiative fluxes at the Top-of-the-Atmosphere (TOA) to ocean temperature changes in the tropics. Their conclusion was that sensitivity was very small, in obvious contradiction to the models.

In their commentary, Trenberth, Fasullo, O’Dell and Wong examine some of the assumptions that were used in LC09’s analysis. In their guest commentary, they go over some of the technical details, and conclude, somewhat forcefully, that the LC09 results were not robust and do not provide any insight into the magnitudes of climate feedbacks.

Coincidentally, there is a related paper (Chung, Yeomans and Soden) also in press (sub. req.) at GRL which also compares the feedbacks in the models to the satellite radiative flux measurements and also comes to the conclusion that the models aren’t doing that badly. They conclude that

In spite of well-known biases of tropospheric temperature and humidity in climate models, comparisons indicate that the intermodel range in the rate of clear-sky radiative damping are small despite large intermodel variability in the mean clear-sky OLR. Moreover, the model-simulated rates of radiative damping are consistent with those obtained from satellite observations and are indicative of a strong positive correlation between temperature and water vapor variations over a broad range of spatiotemporal scales.

It will take a little time to assess the issues that have been raised (and these papers are unlikely to be the last word), but it is worth making a couple of points about the process. First off, LC09 was not a nonsense paper – that is, it didn’t have completely obvious flaws that should have been caught by peer review (unlike say, McLean et al, 2009 or Douglass et al, 2008). Even if it now turns out that the analysis was not robust, it was not that the analysis was not worth trying, and the work being done to re-examine these questions is a useful contributions to the literature – even if the conclusion is that this approach to the analysis is flawed.

More generally, this episode underlines the danger in reading too much into single papers. For papers that appear to go against the mainstream (in either direction), the likelihood is that the conclusions will not stand up for long, but sometimes it takes a while for this to be clear. Research at the cutting edge – where you are pushing the limits of the data or the theory – is like that. If the answers were obvious, we wouldn’t need to do research.

Update: More commentary at DotEarth including a response from Lindzen.

Filed Under: Climate modelling, Climate Science

Lindzen and Choi Unraveled

8 Jan 2010 by group

Guest Commentary by John Fasullo, Kevin Trenberth and Chris O’Dell

A recent paper by Lindzen and Choi in GRL (2009) (LC09) purported to demonstrate that climate had a strong negative feedback and that climate models are quite wrong in their relationships between changes in surface temperature and corresponding changes in outgoing radiation escaping to space. This publication has been subject to a considerable amount of hype, for instance apparently “[LC09] has absolutely, convincingly, and irrefutably proven the theory of Anthropogenic Global Warming to be completely false.” and “we now know that the effect of CO2 on temperature is small, we know why it is small, and we know that it is having very little effect on the climate”. Not surprisingly, LC09 has also been highly publicized in various contrarian circles.
[Read more…] about Lindzen and Choi Unraveled

Filed Under: Climate modelling, Climate Science

Updates to model-data comparisons

28 Dec 2009 by Gavin

Translations: (Italian)

It’s worth going back every so often to see how projections made back in the day are shaping up. As we get to the end of another year, we can update all of the graphs of annual means with another single datapoint. Statistically this isn’t hugely important, but people seem interested, so why not?

[Read more…] about Updates to model-data comparisons

Filed Under: Climate modelling, Climate Science, Instrumental Record, Model-Obs Comparisons

It’s all about me (thane)!

12 Nov 2009 by Gavin

Well, it’s not really all about me. But methane has figured strongly in a couple of stories recently and gets an apparently-larger-than-before shout-out in Al Gore’s new book as well. Since a part of the recent discussion is based on a paper I co-authored in Science, it is probably incumbent on me to provide a little context.

First off, these latest results are being strongly misrepresented in certain quarters. It should be obvious, but still bears emphasizing, that redistributing the historic forcings between various short-lived species and CH4 is mainly an accounting exercise and doesn’t impact the absolute effect attributed to CO2 (except for a tiny impact of fossil-derived CH4 on the fossil-derived CO2). The headlines that stated that our work shows a bigger role for CH4 should have made it clear that this is at the expense of other short-lived species, not CO2. Indeed, the attribution of historical forcings to CO2 that we made back in 2006 is basically the same as it is now.
[Read more…] about It’s all about me (thane)!

Filed Under: Climate modelling, Climate Science, Greenhouse gases

Decadal predictions

28 Sep 2009 by Gavin

There has been a lot of discussion about decadal climate predictions in recent months. It came up as part of the ‘climate services’ discussion and was alluded to in the rather confused New Scientist piece a couple of weeks ago. This is a relatively “hot” topic to be working on, exemplified by two initial high profile papers (Smith et al, 2007 and Keenlyside et al, 2008). Indeed, the specifications for the new simulations being set up for next IPCC report include a whole section for decadal simulations that many of the modelling groups will be responding to.
[Read more…] about Decadal predictions

Filed Under: Climate modelling, Climate Science

Warming, interrupted: Much ado about natural variability

12 Jul 2009 by raypierre

A guest commentary by Kyle Swanson – University of Wisconsin-Milwaukee

I am quite humbled by the interest that has been generated by our paper “Has the climate recently shifted?” (Swanson and Tsonis, 2009), and would like the thank the RealClimate editors for the opportunity to give my perspective on this piece.

Before delving into the paper itself, a few words about the place of our work in the global warming “debate” are in order. A quote from the early 20th century Viennese polymath Egon Friedell (which I ran across in the wonderful book Cultural Amnesia by Clive James) captures the situation better than any words I could ever weave;

Electricity and magnetism are those forces of nature by which people who know nothing about electricity and magnetism can explain everything.

Substitute the words “modes of natural climate variability” for “electricity and magnetism,” and well…, hopefully the point is made.
[Read more…] about Warming, interrupted: Much ado about natural variability

Filed Under: Climate modelling, Climate Science

Winds of change

11 Jun 2009 by group

Gavin Schmidt and Michael Mann

There was an interesting AP story this week about possible changes in wind speed over the continental US. The study (by Pryor et al (sub.)), put together a lot of observational data, reanalyses (from the weather forecasting models) and regional models, and concluded that there was some evidence for a decrease in wind speeds, particularly in the Eastern US. However, although this trend appeared in the observational data, it isn’t seen in all the reanalyses or regional models, leaving open a possibility that the trend is an artifact of some sort (instrumental changes, urbanization etc.). If the effect is real though, one would want to see whether it could be tied to anything else (such as forcing from greenhouse gas or aerosol increases), and indeed, whether it had any implications for wind-generated electricity, water evaporation etc.

Amusingly, both of us were quoted in the story as having ostensibly conflicting views. Mike was quoted as finding the evidence for a trend reasonably convincing, while Gavin was quoted as being unconvinced of the evidence for an anthropogenic climate change signal (note that the two statements are not in fact mutually inconsistent). As one should expect in any news story, these single lines don’t really do justice to the longlonger interviews both of us gave the reporter Seth Borenstein. So what is the bigger context?
[Read more…] about Winds of change

Filed Under: Climate modelling, Climate Science, Instrumental Record

Yet more aerosols: Comment on Shindell and Faluvegi

21 Apr 2009 by group

Guest post from Drew Shindell, NASA GISS

Our recent paper “Climate response to regional radiative forcing during the twentieth century”, has generated some interesting discussion (some of it very ‘interesting’ indeed). So this post is an attempt to give a better context to the methods and implications of the study.

[Read more…] about Yet more aerosols: Comment on Shindell and Faluvegi

Filed Under: Aerosols, Climate modelling, Climate Science, Greenhouse gases, Instrumental Record

  • « Go to Previous Page
  • Page 1
  • Interim pages omitted …
  • Page 14
  • Page 15
  • Page 16
  • Page 17
  • Page 18
  • Interim pages omitted …
  • Page 24
  • Go to Next Page »

Primary Sidebar

Search

Search for:

Email Notification

get new posts sent to you automatically (free)
Loading

Recent Posts

  • Unforced variations: Oct 2025
  • “But you said the ice was going to disappear in 10 years!”
  • Time and Tide Gauges wait for no Voortman
  • Lil’ NAS Express
  • DOE CWG Report “Moot”?
  • Climate Scientists response to DOE report

Our Books

Book covers
This list of books since 2005 (in reverse chronological order) that we have been involved in, accompanied by the publisher’s official description, and some comments of independent reviewers of the work.
All Books >>

Recent Comments

  • Geoff Miell on Unforced variations: Oct 2025
  • Mo Yunus on “But you said the ice was going to disappear in 10 years!”
  • Piotr on “But you said the ice was going to disappear in 10 years!”
  • Piotr on “But you said the ice was going to disappear in 10 years!”
  • Piotr on “But you said the ice was going to disappear in 10 years!”
  • Tomáš Kalisz on Unforced variations: Oct 2025
  • Mo Yunus on “But you said the ice was going to disappear in 10 years!”
  • Mal Adapted on “But you said the ice was going to disappear in 10 years!”
  • Tomáš Kalisz on “But you said the ice was going to disappear in 10 years!”
  • nigelj on Unforced variations: Oct 2025
  • Tomáš Kalisz on Unforced variations: Oct 2025
  • Russell Seitz on “But you said the ice was going to disappear in 10 years!”
  • Kevin McKinney on “But you said the ice was going to disappear in 10 years!”
  • Kevin McKinney on Unforced variations: Oct 2025
  • Kevin McKinney on “But you said the ice was going to disappear in 10 years!”
  • MA Rodger on Unforced variations: Oct 2025
  • MA Rodger on Unforced variations: Oct 2025
  • MA Rodger on Unforced variations: Oct 2025
  • Barton Paul Levenson on Unforced variations: Oct 2025
  • Barton Paul Levenson on “But you said the ice was going to disappear in 10 years!”
  • Silvia Leahu-Aluas on Unforced variations: Oct 2025
  • Pete best on “But you said the ice was going to disappear in 10 years!”
  • Susan Anderson on “But you said the ice was going to disappear in 10 years!”
  • Mo Yunus on Unforced variations: Oct 2025
  • Geoff Miell on Unforced variations: Oct 2025
  • Russell Seitz on “But you said the ice was going to disappear in 10 years!”
  • Mo Yunus on “But you said the ice was going to disappear in 10 years!”
  • Mo Yunus on “But you said the ice was going to disappear in 10 years!”
  • Mo Yunus on “But you said the ice was going to disappear in 10 years!”
  • Piotr on Unforced variations: Oct 2025

Footer

ABOUT

  • About
  • Translations
  • Privacy Policy
  • Contact Page
  • Login

DATA AND GRAPHICS

  • Data Sources
  • Model-Observation Comparisons
  • Surface temperature graphics
  • Miscellaneous Climate Graphics

INDEX

  • Acronym index
  • Index
  • Archives
  • Contributors

Realclimate Stats

1,383 posts

11 pages

247,251 comments

Copyright © 2025 · RealClimate is a commentary site on climate science by working climate scientists for the interested public and journalists.