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

RealClimate

Climate science from climate scientists...

  • Home
  • Start here
  • Contributors
  • Archives
You are here: Home / Archives for Gavin

about Gavin Schmidt

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

Michaels misquotes Hansen

2 Dec 2004 by Gavin

Pat Michaels (under the guise of the Greening Earth society) is particularly fond of misquoting Jim Hansen, director of the NASA GISS laboratory (and in the interests of full disclosure, GS’s boss).

Recently he claimed that Dr. Hansen has now come around to the ‘skeptics’ (i.e. Pat Michaels) way of thinking and suggests that they agree on the (small) amount of warming to be expected in the future. Michaels quotes Hansen from a 2001 PNAS paper:

[Read more…] about Michaels misquotes Hansen

Filed Under: Climate modelling, Greenhouse gases

Climate model scenarios

1 Dec 2004 by Gavin

Translations: (Français)

A couple of commentators (Pat Michaels, Roy Spencer) recently raised an issue about the standard scenarios used to compare climate models, in this case related to a study on the potential increase in hurricane activity.

The biggest uncertainty in what will happen to climate in the future (say 30 years or more) is the course that the global economy will take and the changes in technology that may accompany that. Since climate scientists certainly don’t have a crystal ball, we generally take a range of scenarios or projections of future emissions of CO2 and other important forcings such as methane and aerosols.

[Read more…] about Climate model scenarios

Filed Under: Climate modelling, Climate Science, Greenhouse gases, IPCC

Climate sensitivity

28 Nov 2004 by Gavin

Translations: (Français)

Climate sensitivity is a measure of the equilibrium global surface air temperature change for a particular forcing. It is usually given as a °C change per W/m2 forcing. A standard experiment to determine this value in a climate model is to look at the doubled CO2 climate, and so equivalently, the climate sensitivity is sometimes given as the warming for doubled CO2 (i.e. from 280 ppm to 560 ppm). The forcing from doubled CO2 is around 4 W/m2 and so a sensitivity of 3°C for a doubling, is equivalent to a sensitivity of 0.75 °C/W/m2. The principal idea is that if you know the sum of the forcings, you can estimate what the eventual temperature change will be.

We should underscore that the concepts of radiative forcing and climate sensitivity are simply an empirical shorthand that climatologists find useful for estimating how different changes to the planet’s radiative balance will lead to eventual temperature changes. There are however some subtleties which rarely get mentioned. Firstly, there are a number of ways to define the forcings. The easiest is the ‘instantaneous forcing’ – the change is made and the difference in the net radiation at the tropopause is estimated. But it turns out that other definitions such as the ‘adjusted forcing’ actually give a better estimate of the eventual temperature change. These other forcings progressively allow more ‘fast’ feedbacks to operate (stratospheric temperatures are allowed to adjust for instance), but the calculations get progressively more involved.

Secondly, not all forcings are equal. Because of differences in vertical or horizontal distribution of forcings, some changes can have a more than proportional effect on temperatures. This can be described using a relative ‘efficacy’ factor that depends on the individual forcing. For instance, the effect of soot making snow and sea ice darker has a higher efficacy than an equivalent change in CO2 with the same forcing, mainly because there is a more important ice-albedo feedback in the soot case. The ideal metric of course would be a forcing that can be calculated easily and where every perturbation to the radiative balance had an relative efficacy of 1. Unfortunately, that metric has not yet been found!

Filed Under: Glossary

Isotopes

28 Nov 2004 by Gavin

Isotopes can be thought of as different ‘flavours’ of a particular element (such as oxygen or carbon), that are distinguished by the number of neutrons in their nucleus (and hence their atomic mass). Carbon for instance most commonly has a mass of 12 (written as 12C), but there are also a small fraction of carbon atoms with mass 13 and 14 (13C and 14C), similarly oxygen is normally 16O, but with small amounts of 17O and 18O. All of the isotopes of an element behave in similar way chemically. However, because the mass of each isotope is slightly different there are certain physical processes that will discriminate (or ‘fractionate’) between them. For instance, during evaporation of water, it is slightly easier for the lighter isotopes to escape from the liquid, and so water vapour generally has less 18O than the liquid water from which it came. Because of these physical effects, looking at the ratio of one isotope to another can often be very useful in tracing where these atoms came from.

Filed Under: Glossary

  • « Go to Previous Page
  • Go to page 1
  • Interim pages omitted …
  • Go to page 35
  • Go to page 36
  • Go to page 37

Primary Sidebar

Email Notification

get new posts sent to you automatically (free)
Loading

Recent Posts

  • 2022 updates to the temperature records
  • Unforced variations: Jan 2023
  • The water south of Greenland has been cooling, so what causes that?
  • Unforced variations: Dec 2022
  • Serious mistakes found in recent paper by Connolly et al.
  • Unforced variations: Nov 2022

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

  • macias shurly on 2022 updates to the temperature records
  • Victor on 2022 updates to the temperature records
  • Killian on Unforced variations: Jan 2023
  • Carbomontanus on The water south of Greenland has been cooling, so what causes that?
  • Barton Paul Levenson on Unforced variations: Jan 2023
  • Kevin McKinney on 2022 updates to the temperature records
  • Kevin McKinney on 2022 updates to the temperature records
  • Kevin McKinney on The water south of Greenland has been cooling, so what causes that?
  • Ray Ladbury on 2022 updates to the temperature records
  • Carbomontanus on 2022 updates to the temperature records
  • macias shurly on The water south of Greenland has been cooling, so what causes that?
  • nigelj on 2022 updates to the temperature records

Footer

ABOUT

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

DATA

  • Data Sources
  • Climate model projections compared to observations

INDEX

  • Acronym index
  • Index

Realclimate Stats

1,290 posts

8 pages

229,496 comments

Copyright © 2023 · RealClimate is a commentary site on climate science by working climate scientists for the interested public and journalists.