Bishop Hill Richard B on the two-degree
Oct 29, 2014 Climate: MetOffice Climate: WG3 A reader points me to this long tweet from Richard Betts, which I missed while I was away last week. It's certainly worth of reposting:
I see the '2 degree limit' as rather like a speed limit on a road - both are set by policymakers on the basis of a number of considerations.
On the roads, the main issues are safety, fuel economy and journey time. Regarding safety, driving at 5mph under the speed limit does not automatically make the journey 'safe', and exceeding the limit by 5mph does not automatically make it 'dangerous'. Clearly, all other rings being equal, the faster one travels the greater the danger from an accident - but you also want to go fast enough to get to your destination in a reasonable time. The level of danger at any particular speed depends on many factors, such as the nature of the particular road, the condition of the car and the skill of the driver. It would be too complicated and unworkable to set individual speed limits for individual circumstances taking into account all these factors, so clear and simple general speed limits are set using judgement and experience to try to get an overall balance between advantages and disadvantages of higher speeds for the community of road users as a whole. Basically, a simple limit is practical and workable.
I see the climate policy focus on global mean temperature (eg. 2 degrees C) as playing a similar role - a simple indicator for policy purposes, and as basis for discussing pros and cons of different policy choices, but not to be taken too literally as a real threshold. Despite what we sometimes hear, there is no clear, scientifically-based threshold for 'dangerous anthropogenic climate change'. Clearly the stronger our influence on climate, the greater the risk of exposing ourselves to conditions we are not used to and hence unprepared for (eg. heavier rainfall, higher storm surges, longer or more intense heat waves). Staying below (say) 2 degrees does not mean these things won't happen, and exceeding (say) 2 degrees does not mean they'll suddenly happen all the time. Specific regional climate changes are not strongly linked to any particular level of global warming - there are many factors which affect the relationship between global mean temperature and regional climate and weather. Moreover, the level of 'danger' from such things also depends on how resilient society is - whether adequate flood provision exists, for example. There's so many complex factors that it's impossible to truly say what the 'dangerous' level of global warming is. However, a simplistic indicator based on global mean temperature does at least give some focus for discussion.
Reader Comments (110)
18 years of global warming pause is one hell of a journey time and its not been very economical.
DEEBEE
"now being raised to 70"
But do the speedometers still stop at 85? I love the idea that limiting the range of the dial will somehow affect the behaviour of the driver - although perhaps in America, it does..?
What the author is arguing is that whatever your speed is traveling right now, if you increase your speed by 2 mph, it will increase the danger.
However study after study has shown that this safest speed to drive is not the speed you are currently driving. Rather the safest speed is slightly above the posted speed limit.
So, whether 2 mph increase in speed is dangerous depends on your current speed. Same with a 2 C increase in temps. If you live somewhere cold, it is unlikely it will be harmful.
Since the average temp of the earth at 15C is much less than the optimum 21C we heat our homes to, for almost everyone an increase of up to 6C would be a benefit.
Going back to the first post by John Shade.
John, I had to read the Scot quote several times and I still can't believe what I think I am reading. Are they really saying that they are planning to deliberately raise their regional temp in order to benefit their people and economy ?
No-one on here appears to have noticed. The SNP are promoting windmills like they might run out of stock. This is very strange.
Stephen Richards,
Fanatics and rent seekers will do just about anything to keep their obsession- and money- moving forward.
My car licence allows me to drive my 7.5 tonne truck with my 4 tonne trailer. So, at 30 mph, I am allowed to control a particular energy budget. Using the same energy budget driving my 360 kilo Isetta at what maximum speed could I drive?
AR - is it not a question of stopping distance and controllability, rather than kinetic energy?
Martin A
Yes indeed. Severity of impact etc. My tractor carries a bale spike at the front so I don't drive that on the road at all.
How about " MP says raising HGV speed limit will help reduce road rage for frustrated Fen drivers"?
Stephen Richards (Oct 31, 2014 at 9:10 AM):
Which part of that is so puzzling to you? That a warmer climate in Scotland would be beneficial? That we can move average temperatures up or down, as the IPCC has been telling us for time?