Your thoughts?

If you stood in a cornfield in Kansas, common sense would tell you the earth is flat.

Just watching the sun and moon, common sense would make you SWEAR they revolved around the earth.

Good thing, instead of using common sense, we are using good scientific principles which often go against our better judgment. And those scientific principles tell us that, while the earth IS warming naturally, humans are also contributing to that warming.

JACQUELYN – That’s a good place to get you info from, consists of the world’s leading scientists, is completely impartial, independent and even has the Royal seal of approval.

DANA – There’s a lot of invented data around, that’s why many skeptics find it impossible to back it up with anything.

TOMCAT – I notice you opted not to answer my question – why? I’ve responded previously with regard to troposheric warming / cooling, there’s no need for me to respond again (it would be about the 5th time if I did). With all due respect, you seem to be getting somewhat confused about the role of the causes and effects of global warming in respect of the troposhere and vice versa. Might I suggest further studying in order to obtain a clearer understanding (you may then want to revisit the graph you linked to and correctly interpret it).
VLADOVIKING: I think that’s more of a legal definition of the world ‘evidence’. A more realistic use would be that based on the literal definition ‘see-cause’ and in this respect we can quite clearly see what the causes of global warming and climate change are.

G_U_C: Whilst those claiming that global warming exists have a reponsibility to validate their claims so too do the skeptics when they make statements, you can’t have it just one way.

E-NESS: Thanks for the informative answer, I hope people read it and follow your link. I didn’t know about Northern Sweden, went to Siberia and studied the melting permafrost there, very strange seeing trees leaning at strange angles and buildings half sunk into the soft ground.

MADNOELLE: I think you might be onto something there. There’s certain people on here who invent their own science then attempt to pass it off as fact, could this be coming from voices in their heads?
BOB: It’s not hard to find the evidence to back up statements relating to anthropogenic global warming is it? So why do some skeptics have so much trouble, it could almost make you think they didn’t have any.

SOPHIEB: All of that is true but please remember, sometimes the media go overboard and make things out to be worse than they really are, they also have a habit sometimes of apportioning blame to global warming even if it hasn’t yet been established as a fact. It’s bad but it’s not the end of the world.

PERMACULTURE BELLA: A good mix of links there and some of them do present seemingly credible arguments against manmade global warming. Interesting that it’s a GW beleiver who is the first person to provide any ‘evidence’ against manmade GW.
JABLOB: Your answer has disappeared, it can happen if you post a really long answer.

ALFRATTA437: If you source your data from unreliable sources it’s going to get questioned / dismissed. Exxon etc are quite clearly biased, they make claims that fall at the fist hurdle because they have no substance to them. There are genuine scientific concerns that have been raised regarding global warming and our greater understanding of the climate, if skeptics were to use these sources their arguments would have much greater credibility.

JBTASCAM: The AGW advocates have produced the evidence you mention and have been doing so for 100+ years, the best scientists in the world can’t refute it or provide alternative explanations, e.g. increasing atmospheric greenhouse gas concentrations leads to increased retention of thermal radiation – that’s indisputable, so too is the fact that we’re emiting ever increasing amounts of greenhouse gases into the atmosphere.
You’re illustrating the point of my question pefectly in that you’re making claims but not validating them. For example, you state positive feedbacks required…aren’t happening in the real world. Positive feedbacks don’t cause global warming – they compound or accelerate it, the feedbacks we expected to see are happening (as has been mentioned in earlier answers) and the rate of warming is in fact faster than previously thought (as will be stated in the next IPCC report due next month).

FYZER: It’s a good point you make and yes, both sides are guilty. I can understand ‘challengers’ not jumping into line too quickly – as a scientist myself I don’t form opinions or take sides without a thorough examination of all the evidence. However, remove the dogma of the greenies and those with a vested interest and there’s still the hard science and evidence remaining.
LARRY: The only answer to include a valid reason to question certain aspects of our understanding of historical climate (not AGW).

The solar contribution argument isn’t really valid, we can measure to 6 decimal places the energy from the Sun, there may have been under / over estimations in the past but today it’s down to a fine art. The arguments about clouds is outdated and distorted and may stem from the that early climate models that didn’t acccount for clouds. More recent ones do and the most recent ones include very complex cloud simulations; be a bit wary of co2science.org and check out the people behind the site.

The last point has some validity to it in that there isn’t an ideal correlation between historical CO2 level and temperatures. There is some correlation and when other factors are taken into account there is a good correlation for much of the 542 million years for which we have climate data but there are some as yet unexplained anomalies.
However, these are events spanning thousands and millions of years and are not related to the circumstances giving rise to the current warming trend.

FINAL COMMENT – Thanks to all for the answers. A couple of people mentioned sources that have some credibility although they’re not related to the claims that skeptics have been making, I guess we’ll never get to find out where they got their information from.

Any ideas on what the best arguments to include would be/ones that sound the stupidest?

There have been plenty saying unequivocally it’s not (mostly) the Sun. For example:

Recent oppositely directed trends in solar
climate forcings and the global mean surface
air temperature, Lockwood, Frohlich (2007), Proc. R. Soc. A, doi:10.1098/rspa.2007.1880

"Our results show that the observed rapid rise in
global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified."

So I’m looking for a paper that says unequivocally 51% or more of the warming in the last 20 years or so is due to the Sun. There have been a few, but they’ve all been conclusively refuted.

People keep saying "It’s the Sun" with no proof. Show me some unequivocal proof.
Nathan – That’s not a scientific paper, that’s simply someone flapping their gums on the Internet. Proves absolutely nothing. Their stuff is loaded with scientific errors, let’s just take one of the more silly.

"Scientific research through U.S. Government satellite and balloon measurements shows that the temperature is actually cooling – very slightly – .037 degrees Celsius."

No serious skeptics make that claim anymore. This graph is pretty much undisputed (except for some small details):

http://data.giss.nasa.gov/gistemp/graphs/new_Fig.A.lrg.gif

=^_^= – The article you cite says:

"Abdussamatov’s work, however, has not been well received by other climate scientists."

"His views are completely at odds with the mainstream scientific opinion," said Colin Wilson, a planetary physicist at England’s Oxford University.

"He claims that carbon dioxide has only a small influence on Earth’s climate"

Once again, no serious skeptic says that today.

"The solar irradiance began to drop in the 1990s, and a minimum will be reached by approximately 2040," Abdussamatov said"

That one is completely at odds with the measured data.

http://www.giss.nasa.gov/research/news/20030320/sun4m_tn.jpg

New ideas – great. Nonsense – not so much.

The Mars deal has been discussed here over and over. The reasons for warming on Mars are giant dust storms.

http://www.nasa.gov/centers/ames/research/2007/marswarming.html

Other planets are not warming, so it’s definitely not the Sun that’s causing it on Mars.
Marc G – I need to research your papers. I won’t reflexively respond. Take me a day or two. But thanks for answering in the spirit of the question.
$ – You and I agree 100% on this. The Max Planck Institute does really good scientific work.

And this quote from one of their papers is absolutely typical of their results:

"We show that at least in the most recent past (since about 1970) the solar influence on climate cannot have been significant."

Solar variability and global warming: a statistical comparison since 1850, N. A. Krivova and S. K. Solanki, Adv. Space Res. 34, 361-364 (2004)

That’s not cherry picking, it’s absolutely typical of their results. Look at the graph on their home page, showing temperature taking off while the Sun is relatively constant.

Also see their paper:

Can solar variability explain global warming since 1970?

Their answer is no.

Press release from their site:

"…the Earth’s temperature has risen dramatically in the last 30 years while the solar brightness has not appreciably increased in this time."

Great answer – for my argument.
Correction to the above – The graph is not on their home page, it’s on $’s link.
Marc G – I’m not going to do it any better than Trevor. Here’s the rebuttal reference he alluded to, but didn’t give. It seems to dispose of the paper.

http://schwinger.harvard.edu/~motl/usc-rebuttal.html

I note that some of the studies seem to be more mathematical exercises than anything else.

Clearly you win Best Answer. You did it, you enlightened me, and you (at first) reduced Trevor to a philosophical reply rather than a factual one.

My bottom line is that I find the mainstream science on this far better. Better documented, more thorough, less biased in looking at the data. I suspect you agree, but have more doubts than I that the contrarians could be right.

I find this attribution of global warming to the various factors quite persuasive:

Meehl, G.A., et al(2004). "Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Cliate 17: 3721-3727

Pretty decent fit to the data.

Leaving this open for a bit, just in case.