kulu

I don’t believe any rational sceptic would argue the toss over whether or not human activity has affected climate. It’s a question of degree. Sceptical scientists argue that GHGs do increase warming, but it’s very small – around 0.2°C over the 20th Century – and that the rest of the 0.7°C rise is due to natural fluctuations.

One important issue concerns the surface-based weather stations, because surveys have shown that many are poorly maintained or have disappeared (mostly when USSR dissolved), and many have been warmed by urban development. So the historical temperature record is somewhat questionable. Balloon and satellite sensors are the most reliable, but they have only been employed since about 1978. Strangely, James Hansen reportedly still relies on surface-based instruments for his GISS graphs.

Of course anthropogenic GHGs released by burning fossil fuels and other sequestered sources enter the atmosphere. No argument. However, despite the billions of tonnes of CO2 that have been emitted, the change in atmospheric CO2 content is small. Since industrialisation began the level of CO2 has risen from only 0.0285% (IPCC estimate) to 0.0385%. It is that tiny difference of 0.01% that the IPCC’s experts reckon is leading the world to catastrophe.

The IPCC’s hypothesis is that the 0.01% causes water vapour to increase, causing temperature to increase, and so on (i.e. positive feedback). Now, kulu, do you really accept that 0.01% added to the air over 200 years – i.e. one molecule in every 10,000 molecules of air – can cause catastrophic warming and climate change? You would never pick the effect of 0.01% extra CO2 from background climate “noise”. GHG water vapour itself is more potent than CO2, and consider how much "noise" it creates from place to place, day to day.

Re your final paragraphs. AGW temperature, yes, but only slightly, and, yes, AGW is likely to result from our activities, but insignificantly – evidence in the historical record shows that the MWP, and the earlier Roman WP, were warmer than now. How can the IPCC be right when AGW is still an untestable hypothesis? GCMs are only tools.

JohnH,

A .285% to a .385% increase in CO2 is a rather large 35% jump in the amount of CO2 in the atmosphere since the industrial revolution. And if a mere .285% of the stuff played a significant role in providing the earth with a climate that has allowed 6.5 billion humans, there domesticated animals and plants plus a multitude of other complicated living things to exist then that set-up must surely be threatened by the rapid addition of so much more of it.

The fact that more GHG's have been pumped into the atmosphere than appears to have been absorbed by it is reason for concern as obviously the excess has been taken up elsewhere including the sea which itself has a finite capacity to safely sequester CO2. It is now showing signs of becoming more acidic as a result of its own CO2 burden and that is not good for the crustaceans etc who (I think- correct me if I'm wrong) are also long-term sequesters of CO2 and are essential for much of marine life.

On top of all this, once the sea and the other natural sequesters are themselves bloated with CO2 than, presumably the atmosphere will retain the full load of our emissions and there levels will rise even faster than they have done to date.

Lastly, if non-anthropogenic sources are to blame for climate change (as obviously they have been in the past) then what are the precise causes of this happening so rapidly, sun spots, wobbling earth, tilting earth's axis or changes to its orbit around the sun? What body of science is there to back these claims up and to provide credible evidence of it?

Sorry, one more thing - tiny amounts of substances emitted into the atmosphere (far less then our CO2 emissions) have had very profound effects on it. It didn't take huge amounts of CFCs to create a hole in the ozone layer with all the consequences that could, and has flowed from that

JohnH, your random and inexact use of evidence suggests that you have an ideological rather than scientific objection to AGW.

For example, you say "You would never pick the effect of 0.01% extra CO2 from background climate “noise”". On what scientific basis do you make this silly claim? You seek to emphasise that this is only 1 extra CO2 in 10,000 molecules, as if this can make no possible difference. Yet if we remove 4 CO2 molecules per 10,000 (i.e. all the atmospheric CO2) then the world's trees, grasses and crops would quickly die. kulu gives CFCs as an excellent example, but there are plenty of others where extremely low concentrations have major effects. Mercaptan is used to give household gas its smell: in fact, we can smell butyl mercaptan at concentrations as low as one molecule in 10 billion. At the same concentration as current CO2, butyl mercaptan is an overpowering stench; at only 0.01% stronger, it becomes life-threatening.

John, you ask "do you really accept that 0.01% added to the air over 200 years – i.e. one molecule in every 10,000 molecules of air – can cause catastrophic warming and climate change?" Yes, clearly we do - and in fact, that very climate change is already upon us. Melting of glacial and polar ice is beyond doubt. Increased frequency and severity of extreme weather events is beyond doubt. Rising global temperatures is beyong doubt. Rising sea levels is beyond doubt.

What hasn't been established is the cause. But whether it's sunspots, industrial activity or the flatulence of flat-earthers is irrelevant: increased concentrations of atmospheric CO2 are potentially catastrophic, and it would be criminally negligent not to take urgent action for mitigation and adaption.

My last comment on the subject is that we should take heed of global insurance companies. These transnationals make unseemly amounts of money from accurately assessing risk. In 2000 the global insurance council announced that the cost of damage resulting from global warming would, by 2050, exceed the world's capacity to insure against. I think I'll put my money on them being right.

Hi kulu

Yes, a 35% hike does seem large, but it is misleading. If you compare 285% to 385%, or 0.000285% to 0.000385% the hike is 35%. So the figure of 35% really means nothing. What does matter is the change in absolute terms of 0.01%, which is small. (Btw, you quoted 0.285% and 0.385% … you omitted a zero … should have been 0.0285% and 0.0385%.) Wrt your assessment of the 0.0285% having contributed to the warmth of the planet, water vapour is and has been by far the greatest contributor. The percentage of atmospheric water vapour varies between about 2% and 4%, depending on location. Now, that means that the amount of water vapour, which is a more potent GHG than CO2, is from 500 to 1000 times more abundant than the current level of CO2. No prizes for which has the greatest influence on global warmth.

Planet Earth has had much higher levels of both CO2 and temperature, but not always concurrently, in the past. See, for instance, http://www.junkscience.com/images/paleocarbon.gif , but, if you don’t wish to believe the diagram, there are similar references elsewhere.

You mention absorption by the sea – yes, it has increased the “acidity” of the sea. The pH of the ocean is around 8.3, which means that seawater is slightly alkaline. According to a Scientific American article a couple of years back, the pH was reckoned to have fallen to 8.2 (pH 7.0 is neutral). Seems that the sea is handling the absorption pretty well, although marine scientists argue that “acidified” seawater affects CaCO3 shell formation. Maybe, because, like most alarms over anthropogenic climate change, the so-called evidence is highly controversial. In any case, why don’t alarmists say “seas are becoming slightly less alkaline”? The answer is that “more acidic” is more emotive.

The atmosphere can hold a lot more CO2 than currently (see the link above). Sceptical scientists are confident (they could be wrong of course) that there is an upper limit of CO2 (about 700 ppm or 0.07%, if I remember correctly) where CO2 will cease to have further influence.

Chappo

Silly as it may seem, global temperatures do vary enormously, constantly, so how can one isolate the contribution due to anthropogenic GHGs from fluctuations due to other sources? (Obviously, I misjudged your ability to interpret the meaning of “noise”.) Could be that some IPCC experts can do so on paper, but that’s not the same as actually measuring it with instruments.

I appreciate your admission that CO2 is plant food – alarmists usually call it “pollutant”.

All well and good to provide several analogies, but they are false, because they don’t compare with the GHG-AGW situation. (Btw, you forgot Ebola virus and malaria parasites.) However, all of them are good examples of proven cause-and-effect. But with anthropogenic GHGs, cause-and-effect has never been convincingly established – even the circumstantial evidence is disputed.

For instance, according to IPCC experts, the signature of increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics. It's not there.

You quote examples due to global warming (glaciers etc) but there is no proof that anthropogenic GHGs are the cause of global warming. As I’ve said before, there is greater correlation between sunspot activity and GW than between rising CO2 and GW. Sunspot counts have been done for umpteen centuries and it is pertinent that sunspot numbers were very low during much of the Little Ice Age, especially during the Maunder (1645-1715) and Dalton (1790-1830) Minima.

Btw, if you check, you will find that since at least 2004, average global temperatures have declined (markedly over 2007-2008), glaciers have stabilised and sea levels have hardly moved – contrary to IPCC projections. Coincidentally, the sun has been exceptionally quiet for almost a year – zero sunspots.

Unbelievably, you say “rising global temperatures [are] beyond doubt” (but are they?), followed by “what hasn’t been established is the cause” and “increased concentrations of atmospheric CO2 are potentially catastrophic, and it would be criminally negligent not to take urgent action …”. You don’t know the cause, but you want action … now that is like a blind man driving he knows not where, panic-stricken

JohnH,

Sunspots.

In the context of our concerns about climate change as it might effect us and the next couple of generations (people alive today or who will be born during my lifetime) sunspots may indeed contribute a little to climate variability but stellar physicists generally believe - on the basis of an, as yet, fairly limited understanding of the relationship between sun activity and climate - that that contribution is a small part only of the warming trend we are seeing. Sunspots have an 11 year cycle so they will tend to lower average temperatures when activity is lowest and vice-versa. We cannot in any case do anything about sunspots but we can (but won't) do something about GHG's.

Water vapour.

Water vapour is indeed the a potent GHG and again its role in the feedback loop is not fully understood but it reacts to climate change rather than being a primary "forcer" of it.

2008 coolest year?

Indeed as is constantly brought up by the skeptics 2008 was the coolest year... but wait for it... since 2000. I can't remember if you brought this one up or not. But we are talking about trends not about specific years. I understand too that it is still amongst the 10 hottest years since recordings began 100 years ago.