Quote:
Originally Posted by Peter Ward
Dave, thanks for the link to the paper, which I have just read....and then wondered if you sent me the right link or went beyond the abstract.
Adams et al. constantly refer periods well in excess of a few decades (typically, several thousand years ) and only speculate about changes over periods equivalent to a human lifetime. They candidly admit many, many times the data simply does not have the resolution, is too localized
or both.
But I rather liked this quote:
"If sudden, dramatic climate changes could occur ..... then they could perhaps occur in the future during our present interglacial, especially if we perturb the system by adding greenhouse gases"
Their conclusion (I cut through the waffle):
...sudden shutdowns or intensification (of the gulf stream)..... by the (climate) disturbance caused by rising greenhouse gas levels....is like '...an ill-tempered beast, and we are poking it with sticks"
You have not produced one iota of evidence that current CO2 levels are not man made (its OK, no-one else has) and in light of the above...you've simply made a stronger case we (humans) are in for a rough ride.
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Peter,
Sorry I owe you a reply, I should have got to it sooner.
I don't want to get into a quoting war over a decade old paper, so I'll restrict myself to only the following (unedited) exert:
"From present understanding of the record of the last 150,000 years, at least a few large climate changes certainly occurred on the timescale of individual human lifetimes, the most well-studied and well-established of these being the ending of the Younger Dryas, and various Holocene climate shifts. Many other substantial shifts in climate took at most a few centuries, and they too may have occurred over a few decades. The high time resolution in the climate record, however, is either not available, or records have not yet been studied in enough detail."
I think that summaries the conundrum. On this topic the IPCC said on pg. 465
"If warming continues unabated, the resulting climate change within this century would be extremely unusual in geological terms."
I take that to mean that, if it stops warming now, nothing unusual has happened. And further on:
"Hence, although large climate changes have occurred in the past, there is no evidence that these took place at a faster rate than present warming."
But neither is there evidence that they occurred at a slower rate. Perhaps the onus is on the proponents of AGW to show that the present rate of change is unusual/unprecedented.
Regarding duration of the present warming, I think Fig 6.10 (pg 467) of the IPCC (attached) demonstrates that the present warming commenced around 1600, with a brief (2-3 decade) cooling in the early 1800s. In contrast, prior to 1600 temperatures had fallen since about 1400.
In any case the purpose of my original post was to argue against your suggestion that natural climate change only occurs over millions of years (eg. change has been over *geological* times.....and given geological time scales are in the *millions* that natural change occurs only over millions of years). Since you are now talking of change over thousands of years I'll take that as a win (I'll stop short of suggesting that your understanding has increased by three orders of magnitude
).
I wonder why you introduced the rise in CO2 concentrations? Since it wasn't the topic, I can only assume you wanted to get on to more familiar territory. The reason I didn't mention CO2 is that the facts are not in doubt. Neither is the reason why rising CO2 conc. should warm the planet. I just don't want to fall into the trap that Les described in another thread and think that I have to see everything in black and white and speak in sound-bites. Real science is much more than that. One needs to be able to see the weaknesses in one's own position and see the strengths in the counter-arguments.
For what it's worth, I think that AGW is the most likely scenario. In any case all the measures proposed to stop AGW should be done anyway for other very good reasons. I'm just not willing to paper over shortcomings in our understanding. This forum deserves better.