Chapters in this book 32 Frontmatter. Between the Idea and the Reality. Is Our Planet Fragile or Robust? Light and Air. Why the Peak of a Mountain Is Cold. Capricious Clouds. The Climate Tapestry. Weather, the Music of Our Sphere. Official Partners. Make a Donation.
Donor Memberships. Become a Member. Gift Memberships. Code of Conduct. Gift Certificates. Group Visits. Birthday Parties. Private Events. Special Events. Full Calendar. Public Events. Family Programs. Homeschool Programs. Girl Scout Events. Member Events. I gather you feel that WMGG effects are so small that they will not dominate over other forcing agents for most phenomena of interest even as concentrations continue to grow over the next century.
This is where we part ways if I understand your position correctly. Issac — In terms of very long term effects, the aerosol influence continues even if the emissions were stopped which is not likely to occur, unfortunately. With respect to human land management advertant and inadvertant , land use change will effect climate indefinitely. I agree with you that the effect of added carbon dioxide will also persist indefinitely and it is a significant human climate forcing.
I am actually more concerned about its biogeochemical effects than its radiative forcing, but both are important. Where I see us disagreeing is that you conclude CO2 and a few other greenhouse gases will dominate climate change in the coming decades.
However, as we summarize in. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, Climate change: The need to consider human forcings besides greenhouse gases.
Eos, Vol. Copyright American Geophysical Union. This broader perspective, including the recognition that natural climate variability is larger than simulated by the global models, makes the climate predicition problem much more difficult than suggested in your analogy to the annual cycle. We are too conservative if the focus is just on CO2 and a few other greenhouse gases as the dominate first order climate forcings.
If I am correct, than the proposals to geoengineer away the radiative effect of added greenhouse gases is fraught with risk, as we would be just adding further to the complexity of how humans are altering the climate system. Some climate changes will be dominated by greenhouse gas increases on the time scale of several decades and others will not be due to the higher noise level.
Table I lean on the models a lot, plus I was one of the Lead Authors for this chapter, so this can be taken as a more explicit statement of my starting point for discussing this issue, at least for this subset of variables. Temperature responses emerge in most regions after 20 years — 20 year mean precipitation signals emerge in some regions in 30 years, some not for years if then. Evidence that the model responses, or model internal variability levels, are biased one way or the other can then be brought to bear to criticize these numbers and on a more minor point, one can question how the choice of regions and seasons affects the results — but it helps to have a clear idea of the model results that one is then arguing should be modified.
Issac — Thank you for clearly clarifying our area of disagreement. In my view, the use of the CMIP3 ensemble of models or other global climate models on this time scale does not permit the testing of your hypothesis on the dominance of the added greenhouse gas relative to natural variability over multi-decadal time periods.
While I agree that models are very valuable tools, they are, however, just hypotheses. They must be tested against real world data. This means, for example, they need to show skill at predicting the statistics of large scale circulation features, and the change in these statistics due to human climate forcing. Stephens, G. Forbes, A. Gettlemen, J. Golaz, A. Suzuki, P. Gabriel, and J. Haynes , Dreary state of precipitation in global models, J.
The CMIP3 ensemble of models need to show that they can recreate this observed variability [in fully coupled ocean-atmosphere-land form] given initial conditions for the ocean, atmosphere, and land.
Than the next step is to show they can skillfully predict changes in this variability due to added CO2 and other human climate forcings over the time period for which we have real world observations. This is, in my view, a necessary condition to accept global climate predictions of regional climate in the coming decades. Model quality is one of the things that I hope to discuss, carefully and critically, on this blog. Roger, it seems to me that you and Isaac are focusing on different scales.
I may misunderstand you, but my reading of your argument is that the CMIP3 projections of regional climate statistics such as ENSO are not worth paying attention to because the models do a poor job of simulating them in the current climate. You also seem to be saying that any future local climate changes may be dominated by regional-scale circulation changes, which do not necessarily scale with global-scale changes, and the models do not necessarily do a good job of simulating.
Both of these points seem absolutely valid. My understanding was that modellers actively work to determine whether one can say something significant about the difference A — B between scenario A and scenario B, even if neither corresponds particularly well to the real world. I thought this was done by exploring the parameter space, both directly and using emulations of the simulator, to determine the sensitivity of A — B across a parameter space that is broad, even if it does not completely cover the real world.
There is a narrow meaning which is solely what comes to pass with the unfolding of time. Another important example of tilting the odds is that over recent decades heatwaves have increased in frequency in large parts of Europe, Asia, South America, and Australia.
Marine heat waves are also increasing. Find out about the Royal Society's latest work on energy, environment and climate. Skip to content You currently have JavaScript disabled in your web browser, please enable JavaScript to view our website as intended. If the world is warming, why are some winters and summers still very cold?
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