tag:blogger.com,1999:blog-9959776.post114562165796212018..comments2024-02-15T04:42:41.606+00:00Comments on James' Empty Blog: Science on Hegerl et al (and Annan & Hargreaves)James Annanhttp://www.blogger.com/profile/04318741813895533700noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-9959776.post-1147239063896203072006-05-10T06:31:00.000+01:002006-05-10T06:31:00.000+01:00Ah, that makes more sense :-)These sort of estimat...Ah, that makes more sense :-)<BR/><BR/>These sort of estimates are tyically based on observed/estimated past changes in temperature and how they relate to the observed/estimated forcing at the time. For example, if a -1W reduction in solar output (during the maunder minimum) resulted in a 0.7+-0.2C temperature change (at 5-95% confidence), then +4W from doubled CO2 can be expected to give 2.8+-0.8C warming - ie an estimate (in this example) that 2 < S < 3.6 at the 90% level.<BR/><BR/>That's the basic idea, anyway - thermal inertia of the earth system makes it a bit more complex in practice, since it is rarely in a true equilibrium. For the most part, these calculations don't actually depend on complex GCMs at all, but rather simpler energy balance models - and the biggest uncertainties are in how well we can estimate the historical forcings and temperature changes, rather than the modelling itself.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-1147224280232661142006-05-10T02:24:00.000+01:002006-05-10T02:24:00.000+01:00Poor phrasing on my part. Of course temperature es...Poor phrasing on my part. Of course temperature estimates have to be a hard number. My question was in reference to the probability estimates mentioned in the Scientific American review: "In this week's issue of Nature, they report a 5% probability that climate sensitivity is less than 1.5°C and a 95% chance that it's less than 6.2°C." <BR/><BR/>I ask because I've encountered skepticism about GCM forecasts, and not just from the general public, but from working climatologists as well. <BR/><BR/>Can you talk a little about how researchers arrive at those probability numbers? Thanks...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9959776.post-1147146825024614322006-05-09T04:53:00.000+01:002006-05-09T04:53:00.000+01:00Kit,I'm not sure that I understand the question. I...Kit,<BR/><BR/>I'm not sure that I understand the question. It's an estimate of a temperature change, which necessarily means it's a hard number. The uncertainty interval is basically a measure of our confidence.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-1147110874635016812006-05-08T18:54:00.000+01:002006-05-08T18:54:00.000+01:00Wonderful to read some actually reassuring news on...Wonderful to read some actually reassuring news on the climate change front. <BR/><BR/>As a journalist, I have to ask the obvious-but-probably-dumb question:<BR/>how can hard numerical values be put on global temperature estimates with as vastly many variables as future climate change?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9959776.post-1146144230729610682006-04-27T14:23:00.000+01:002006-04-27T14:23:00.000+01:00Thanks for that Chris - I don't think I'll bother ...Thanks for that Chris - I don't think I'll bother starting on another front - at least, not there and not yet :-) There's still plenty of discussion to be had though - and in fact there is a workshop in the UK at the end of June (specifically on uncertainty and climate change) which should be useful.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-1146135940971994692006-04-27T12:05:00.000+01:002006-04-27T12:05:00.000+01:00This CPDN thread seems to have developed into a di...<A HREF="http://www.climateprediction.net/board/viewtopic.php?t=4820" REL="nofollow">This CPDN thread</A> seems to have developed into a discussion about Hegerl et al and Annan & Hargreaves.<BR/><BR/>Dave seems to have avoided answering the question of whether he was waiting for Julia but perhaps this is just because there is more interesting things to discuss.<BR/><BR/>crandlesAnonymousnoreply@blogger.com