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about Gavin Schmidt

Gavin Schmidt is a climate modeler, working for NASA and with Columbia University.

The lure of solar forcing

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It’s obvious.

The sun provides 99.998% of the energy to the Earth’s climate (the rest coming from geothermal heat sources). The circulation patterns of the tropical Hadley Cell, the mid latitude storm tracks the polar high and the resulting climate zones are all driven by the gradients of solar heating as a function of latitude. So of course any significant change to solar output is bound to affect the climate, it stands to reason! Since we can see that there are changes in solar activity, it’s therefore just a question of finding the link. Researchers for over a century have therefore taken any climate records they can find and searched for correlations to the sunspots, the solar-cycle length, geomagnetic indices, cosmogenic isotopes or smoothed versions thereof (and there are many ways to do the smoothing, and you don’t even need to confine yourself to one single method per record). At the same time, estimates of solar output in the past are extremely uncertain, and so there is a great deal of scope in blaming any unexplained phenomena on solar changes without fear of contradiction.

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Climate sensitivity and aerosol forcings

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In a new review paper in Nature this week, Andreae, Jones and Cox expand on the idea that uncertainty in climate sensitivity is directly related to uncertainty in present day aerosol forcing (see also this New Scientist commentary). This was discussed here a couple of months back in the Global Dimming and the climateprediction.net posts, and so it is worth revisiting the question in the light of their analysis.

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Some recent updates

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A couple of recent papers in Science this week relate to discussions we have had on RealClimate recently. The first by Curry and Mauritzen relates to the Gulf Stream Slowdown? post and describes the amount of fresh water that has been added to the North Atlantic over the last few decades (calculated from a database of salinity measurements) and what impact that has had on density and overturning circulations. There is a press release available at WHOI which is quite informative (hat tip to Joseph O’Sullivan for the link).

The second is related to the Storms and Climate Change post and is a perspective by Kevin Trenberth on the potential for a hurricanes and global warming link. The NCAR press release is available here.

These will undoubtedly not be the last word on the subject, and so we will probably be revisiting these topics at some point soon…

Planetary energy imbalance?

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The recent paper in Science Express by Hansen et al (on which I am a co-author) has garnered quite a lot of press attention and has been described as the ‘smoking gun’ for anthropogenic climate change. We have discussed many of the relevant issues here before, but it may be useful to go over the arguments again here.

The key points of the paper are that: i) model simulations with 20th century forcings are able to match the surface air temperature record, ii) they also match the measured changes of ocean heat content over the last decade, iii) the implied planetary imbalance (the amount of excess energy the Earth is currently absorbing) which is roughly equal to the ocean heat uptake, is significant and growing, and iv) this implies both that there is significant heating “in the pipeline”, and that there is an important lag in the climate’s full response to changes in the forcing.

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Ozone depletion and global warming

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Translations: (Français) (Türkçe)

One of the most common mistakes that we have observed in discussions of climate and atmospheric change is confusion between the rather separate concepts of ozone depletion and global warming. This isn’t necessarily surprising given the scant information that most people pick up from the media. However, for many years meteorologists have been fighting a rearguard action to persuade people that the globe isn’t warming because there is more sun coming through the ozone hole. There are however important connections between the two issues that complicate potential actions that we might take to alleviate the different problems. This week, for instance, a new IPCC report was released that looked at the greenhouse warming potential of many of the replacement chemicals (HFCs and HCFCs) that were used to replace CFCs in aerosol cans and refrigeration units under the Montreal Protocol (and subsequent amendments).

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Water vapour: feedback or forcing?

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Translations: (Deutsch)

Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists. “Why isn’t water vapour acknowledged as a greenhouse gas?”, “Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?”, “Why isn’t water vapour included in climate models?”, “Why isn’t included on the forcings bar charts?” etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response (see also this other attempt).

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IPCC in action: Part I

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This is the first of two pieces on the recent IPCC workshop in Hawaii, This brought together independent researchers from all over the world to analyse computer model simulations of the last 150 years and to assess whether they are actually any good.

Guest commentary from Natassa Romanou (Columbia University)

During the first 3 days of March 2005, balmy downtown Honolulu in Hawaii was buzzing with agile scientists conversing, chatting, announcing, briefing and informing about IPCC assessment reports, climate models, model evaluations, climate sensitivities and feedbacks. These were the participants of the Climate Model Evaluation Project workshop (CMEP) and came here from most (if not all) the major, most prestigious climate research laboratories of the world, including; The US labs National Center for Atmospheric Research, the Geophysical Fluid Dynamics Laboratory and the Goddard Institute for Space Studies, the British Hadley Centre for Climate Prediction, the German Max Planck Institute for Meteorology, the Canadian Centre for Climate Modelling and Analysis, the French Centre National de Recherches Meteorologiques and the IPSL/LMD/LSCE, the Australian CSIRO Atmospheric Research, the Chinese Institute of Atmospheric Physics, the Russian Institute for Numerical Mathematics and the Japanese Meteorological Research Institute. This meeting was sponsored by the benevolent NSF, NOAA, NASA and DOE.

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Will spring 2005 be a bad one for Arctic ozone?

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Translations: (Français)

Guest Commentary by Drew Shindell (NASA GISS)

The current winter and early spring have been extremely cold in the Arctic stratosphere, leading to the potential for substantial ozone depletion there. This has been alluded to recently in the press (Sitnews, Seattle Post Intelligencer), but what’s the likely outcome, and why is it happening?

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Why looking for global warming in the oceans is a good idea

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Translations: (Français)

A lot of press and commentary came out this week concerning a presentation and press release from Tim Barnett and Scripps colleagues presenting at the AAAS meeting (The Independent, John Fleck ,(and again) David Appell…etc). Why did this get so much attention given that there is no actual paper yet?

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