I'd like to open up an in-depth discussion on climate change science. And in particular the present and past theories. Although I'm a pretty hardcore climate sceptic, I actually do believe in anthropogenic climate change.

http://www.youtube.com/watch?v=GUmnuouD0iQ

The first thing I would like to present is this documentary, entitled "Global Dimming". The original air date was 13/01/2005 (this is important), and it can be viewed above. A full transcript is available here. There is a Wikipedia article on global dimming here.

What strikes me most about this documentary is that its information is cherry picked in such a way as to leave the viewer under the impression that we are presently under the ever-increasing effect of anthropogenic global dimming; and that it has had a "global cooling effect" to-date of about 1 degree Celsius! So the theory presented can be summed up as:

"We are presently in a period of global dimming, defined as a long-term trend in increased anthropogenic areoles which are resulting in the long-term trend of declining direct solar irradiance reaching the earth."

And what's even more disturbing is that a documentary that is now 9 years old seems to be the basis for 90% of the Wikipedia article! The issue is that while global dimming is a recognized phenomena, the amount of anthropogenic particulates in the atmosphere has declined since the start of the 1990's.

But this was already well known by scientists, and why most scientists dismissed the theory. Yet the documentary presents its theories as if they're incontrovertible facts.

Consider a 2007 NASA study that shows a long-term decline in areoles.



Little-to-no effort is made to clarify or support the claims made in this documentary, it may as well be "Inconvenient Truth"!!

Consider:

• PROF VEERABHADRAN RAMANATHAN: We saw ten times more particles in the polluted air mass north of the Maldives compared with what we saw south of the Maldives which was a pristine air mass.
  
  NARRATOR: In the polluted air billions of man-made particles provided ten times as many sites around which water droplets could form. So polluted clouds contained many more water droplets, each one far smaller than it would be naturally. Many small droplets reflect more light than fewer big ones. So the polluted clouds were reflecting more light back into space, preventing the heat of the sun getting through. This was the cause of Global Dimming.

What does any of this mean? TEN TIMES more areoles? Surely that means 10% less sunlight, right (note that direct reference to this number is made twice just before where the quote is)? And what exactly are "man-made particles", surely this would mean synthetic molecules - right? And "tiny water droplets are forming" in the clouds making them super reflective - wow, really?

Nope, they're just leaping to conclusions. In 2006 NASA released a peer-review paper on the effects of air pollution on cloud cover - link. The findings were nothing like the conclusions made in the documentary, and in particular the scientists estimated that worldwide the effect was up to a 5% increase in cloud cover worldwide. It does not, however, make the finings that polluted air creates super-reflective clouds, rather it makes the finding that dark aerosols inhibit cloud production, and light aerosols increase cloud production.

What's worth noting though is the fact that the particulate levels are at or around the 1980's level, so for at least the past 3 decades, the net total long-term global dimming effect has not been observed to increase, or decrease. Thus you have to rule it out of participating in any climate trend for the period 1980-present.

Next, I'd invite you to watch this climate debate between Scott Denning and Roy Spencer, two climatologists. Spencer is the climate "sceptic", although Denning actually starts his speech by saying that really any serious scientist is a sceptic. The main point of their divergence in opinion is in radiative forcing/climate sensitivity.

http://www.youtube.com/watch?v=potLQR7-_Tg

Denning presents the case for anthropogenic climate change very well, in fact he presents it better than I have seen anyone present it, and I certainly liked his approach of dispelling disproven or otherwise unreliable theories.

Theories/Hypotheses:

• Climate is complicated ... have to ask experts. FALSE.
  
• Concern about Global Warming is based on recent temperature tends. FALSE
  
• Global warming is a theory based on complicated computer models. FALSE.
  
• If we stop burning coal we'll freeze in the dark. FALSE.
  
• Climate changes very slowly. (Accepted by observational evidence.)
  
• Climate is very predictable. (True because it changes slowly)
  
• O2 and N2 are not greenhouse gasses because they conduct heat less efficiently than molecules with more than two atoms.
  
• CO2 and H2O are greenhouse gasses because they conduct heat more efficiently owing to having three atoms.

I actually do like his simple explanation of the difference between a greenhouse gas and a non-greenhouse gas, the difference is that infrared radiation passes through O2 and N2 molecules without causing interference, but infrared radiation causes the bonds of greenhouse gasses like H2O and CO2 to bend and vibrate, causing absorption and reemission, and this is what causes the greenhouse effect. It's very well understood.

Theories/Hypotheses:

• CO2 doesn't emit heat any more than O2 and N2. FALSE. Why: Thermal emission of CO2 was observed in 1863 by John Tyndall, and has since been measured in thousands of labs across the world.
  
• Doubling CO2 will add 4 Watts/m2 to surface temperature.

This is true, or rather it's a present theory and the estimated effect of 280ppmv of increase CO2 = 3.7 Watts/m2 is a widely accepted figure (why Denning has rounded this number up I'm not sure), as used by the IPCC (reference). Now I don't want to get too technical, but this figure equals 1.2°C of global mean surface temperature (Wikipedia claims it's 1°C, and that'd be why we don't get our facts and figures from Wikipedia!) Off-hand, I think it's about 2050 we expect to get to this level of CO2. We are now about 40% of the way to a doubling in CO2 levels (40% of 280 is 112), and guess what? We've seen a warming of 0.6°C.

That number is almost exactly what we expect to see just from a 112ppmv increase in CO2, without forcing or other factors.

I can't understate that fact enough. So scientifically speaking, all things being equal - if we were in a period of global climate stability, which we weren't, then we would expect to see 0.6°C from CO2 and more from Methane and other anthropogenic GHG's. However, what we've observed is less warming than predicted!

Next theory Denning presents: "The extra heat from industrial CO2 will be cancelled out by something. NOT DISPROVEN YET." Well I'm going to re-word this into three possible theories:

Theories/Hypotheses:

• Climate sensitivity to CO2 is higher (+280ppmv CO2 > 1.2°C).
  
• Climate sensitivity to CO2 is neutral (+280ppmv CO2 = 1.2°C).
  
• Climate sensitivity to CO2 is lower (+280ppmv CO2 < 1.2°C).

Now what we have in front of us is what makes me a sceptic. And this is where Spencer's part of the debate comes in, as he says: depending on how the climate system responds to increased CO2 will depend on how much warming will occur. He presents the formula as WARMING = FORCING - FEEDBACK. And this determines "climate sensitivity". Sceptics think sensitivity is low, and the IPCC and alarmists think it is high. And as Spencer puts it, if sensitivity is low then we have "nothing to worry about".

And it's also where I come in. Unfortunately, I no longer know exactly where my opinion lies. I have never been more uncertain of what has caused climate change. But I do believe that assuming it is entirely attributed to anthropogenic GHG's is a leap of faith, and that naturally climate change has to be allowed to play a role, because our observations of recent climate change in the past centuries show the climate constantly changing up or down. So any model of climate change that does not include natural sources must be incomplete.

Finally, the observed climate change over the past 150 years does not agree with the first two theories. If we have had 0.6°C warming then we have not observed increased climate sensitivity, we have not observed positive feedback. The IPCC tells us that the radioactive forcing for CO2 is 1.66 ± 0.17 W/m2 Well if that's the case it's 0.6+1.0°C = 1.6°C of warming that CO2 alone has contributed since pre-industrial levels. But we've only observed 0.6°C of warming!

There has been, now, a pause in the warming trend since 1997 - 17 years. This is acknowledged by climate scientists - some will say "oh we're cooling now", some will say "oh we're still warming" and others will say "wait and see". But what the majority of catastrophic climate change supports say is: hey it's really not that important, it's just 17 years it's just a "blip", it's so short it doesn't mean anything. Interesting, so they're obsessed about temperatures over a 100 year period - a pretty short time period - but dismiss discerning any information from a 17-year period. Well if that's true, why do we care about the 20-odd years from the 1970's to the 1990's then? Wouldn't that also be too short to discern any long-term climate change information from?



You may wonder why I deliberately started this post with junk science - well I would hope the answer is obvious!

Finally I'd like to leave on this image.

tl;dr

Brevity is the soul of wit. This is a discussion forum, not a virtual lecture hall. What's your point?

(March 14, 2014 at 7:12 am)Aractus Wrote: There has been, now, a pause in the warming trend since 1997 - 17 years. This is acknowledged by climate scientists - some will say "oh we're cooling now", some will say "oh we're still warming" and others will say "wait and see". But what the majority of catastrophic climate change supports say is: hey it's really not that important, it's just 17 years it's just a "blip", it's so short it doesn't mean anything. Interesting, so they're obsessed about temperatures over a 100 year period - a pretty short time period - but dismiss discerning any information from a 17-year period. Well if that's true, why do we care about the 20-odd years from the 1970's to the 1990's then? Wouldn't that also be too short to discern any long-term climate change information from?

I find it interesting that your chart showing a mean of the major temperature records shows no increase for the period in question yet each of the temperature records shows an increase.


UAH


NASA GISS


HadCRUT4


RSS TLT


NOAA

Quote:I find it interesting that your chart showing a mean of the major temperature records shows no increase for the period in question yet each of the temperature records shows an increase.

It's because it's a dishonest or wrong representation of the data. There was warming during the last 17 years, as you show

All proper scientists use the Daily Mail rather than peer reviewed articles.

If you click on the link the article gives, you get will get to the author of the graph you show that has been linked from the Daily Mail:

[UPDATE (17/03/13): David Rose has written an article in the Mail on Sunday which, by eye, seems to use the top left panel from the figure below, but without mention of its original source. In the article David Rose suggests that this figure proves that the forecasts are wrong. This is incorrect - the last decade is interesting and I have discussed these issues previously (as have many others) and I have even co-authored a published article about the most sensitive simulations being less likely. David also incorrectly suggests that the shaded ranges shown are 75% and 95% certainty. As labelled below, they are actually the 25-75% and 5-95% ranges, so 50% and 90% certainty respectively.]

[UPDATE (21/03/13): Mail on Sunday acknowledge that Climate Lab Book figure was used & redrawn and apologise for lack of credit in article update.]

Normally people don't understand the timescale that is being dealt with in Global warming. It's just human nature that we view things in terms of what is happening right now. If it's a heavy hurricane year, it must be global warming! If it's a cold year, global warming is fake! Everything is on a much bigger scale than that.

In that last image, the temperature is has still risen over a period of time no?

Come now popeyespappy, I expected better from you, cherry picking data like that to show a positive trend, tut tut . Why, just look at this graph a nice person compiled for me in a previous argument that shows the temperature going down. (http://atheistforums.org/thread-22955-pa...warming%22)



My unanswered point from that thread still stands, show me significance please

Good stuff, Aractus. I look forward to your next posts on this subject.

I don't really know if all this panic about climate change is right or wrong, but I do know that the climate as always been changing for thousands or millions of years.