what are some good denier theories to explain current warming?

Well of course we've got a whole bunch listed at SkS. There aren't too many deniers who still blame the Sun - it's pretty hard to do when solar activity hasn't increased in 60 years. Even deniers can't milk that cow forever. Galactic cosmic rays is still reasonably popular amongst the deniers, but that hypothesis is slowly dying too.

http://www.skepticalscience.com/cosmic-rays-and-gl...

There are two clear favorites amongst the deniers now, particularly the denier climate scientists like Lindzen, Christy, and Spencer: internal variability, and internal radiative forcing.

Internal variability is basically your oceanic cycles like ENSO and PDO. They argue that heat is just being moved from the oceans (particularly the deep layers) to the air. Problem is the oceans are warming, and we have new measurements of some parts of the deep oceans, which are also warming. So this hypothesis is basically dead in the water (pun intended).

http://www.skepticalscience.com/lindzen-illusion-5...

Internal radiative forcing is a slightly different concept, and the deniers' last best hope. It's Spencer's pet hypothesis - basically some mechanism (he has no idea what, but thinks it's related to ENSO) causes cloud cover to change, which then changes the amount of sunlight reaching the surface, causing warming and cooling. There are some major fundamental flaws with the argument, but it's the best they've got.

http://www.skepticalscience.com/internal-variabili...

http://www.skepticalscience.com/how-we-know-recent...

There are some other ridiculous ones like underwater volcanoes. And there are deniers like jim who cop out with the logical fallacy "it warmed naturally in the past so the current warming is natural too". These are the deniers who would flunk high school physics, but they're basically arguing for some magical natural cycle. So ultimately most denier arguments boil down to some sort of internal mechanism that they don't understand, so they assume nobody understands it, but whatever it is, it's magically causing the entire planet to warm.

Jim Z gives some more "reasons".

(1) essentially it has to do with the "little ice age"

What caused the warming a thousand years ago? What caused the cooling 500 years ago? What has caused the warming in the last several hundred years? I will give you a hint. It wasn't Exxon Mobil.

(2) Exxon Mobil caused it.

I don't want to comment on how believable or otherwise either of those are.

It's the AMO, it's cloud cover changes (usually decreased cloud cover - related to cosmic ray argument), it's internal variability (which means a whole variety of possible explanations, but mainly they revolve around cyclical changes), it's UHI, it's poor station siting, it's fake, so on. There are many "skeptic" arguments against the enhanced GHE, or for a non-anthropogenic GHE enhancement, but not really as many for other mechanisms for the warming. This lit though combined with yours (and including Jeff's PDO argument) does contain quite a few hypotheses.

Oh yeah, Milankovitch cycles too, thanks to other answerers above for bringing that up.

What caused the warming a thousand years ago? What caused the cooling 500 years ago? What has caused the warming in the last several hundred years? I will give you a hint. It wasn't Exxon Mobil. When you answer my questions, you will have the answers to yours. If only science and facts were what you were after it would be easy to educate you. If it were cooling, you would have the same question and same stupid explanation. Exxon Mobil caused it. That is about the extent of science from an alarmist.

Peace

You can find 163 arguments here

http://www.skepticalscience.com/argument.php

Mr Zedd

<What caused the warming a thousand years ago? What caused the cooling 500 years ago?>

A certain yellow ball in the sky.

http://www.mps.mpg.de/dokumente/publikationen/sola...

<What has caused the warming in the last several hundred years?>

It wasn't warming in the last several hundred years.

http://www.meteo.psu.edu/~mann/shared/research/ONL...

<When you answer my questions, you will have the answers to yours.>

Actually, no. The Earth has been warming while the Sun has been cooling since 1980.

http://www.skepticalscience.com/solar-activity-sun...

<If it were cooling, you would have the same question and same stupid explanation. Exxon Mobil caused it. That is about the extent of science from an alarmist.>

If it were cooling, the explanation would be what ever scientific evidence showed to be the best explanation.

"good" is a relative word I would describe a good theory as one that can not be easily explained away, the ones you have listed don't seem to fit that definition.

-It's volcanoes (Human activity is current 100x that of volcanic Co2 contribution)

http://www.newscientist.com/article/dn11638-climat...

-it's the sun (again solar activity for the last 3 cycles shows the Sun not having increased activity)

http://www.newscientist.com/article/dn11650-climat...

-global expansion (sorry that's a nonsense theory)

-solar expansion (only one I am aware of is the expansion it will go through near the end of it's life, still billions of years away)

-there is no warming because it's not hotter than it was 13 years ago.

"13 years", strange then that the (tied) warmest year is 2010 (last year) and the year it is tied with is 2005 (6 years ago) and that starting point deniers use 1998 set that record because it had the strongest El Nino of the last century (another thing deniers ignore when trying to use this as a theory)

http://www.ncdc.noaa.gov/sotc/global/2010/13#gtemp

If these are the 'good' theories it's not saying much for the rest, all the above theories prove is that we are dealing with deniers not skeptics, that at least they do quite well.

Here are some anti-global warming denier theories I found laughable

http://mediamatters.org/research/201102010025#1

My favorite being their argument that the Earth is actually cooling...and to solve it we need to burn more CO2

There are no more "good" theories for why Magellan's ship Victoria was able to leave Seville in 1519 and return there in 1522 sailing only west (and not back east again), except that the earth is indeed round.

No doubt there are plenty of crap theories, such as

- the sunspots in the eyes of the dragons at the end of the flat earth caused them to blast the Spanish fleet into outer space and back to Spain by way of Elvis's time-traveled UFO

- the flat earth only appears round due to natural cycles

- the Pacific ocean is a hoax invented long ago by Al Gore's masseuse and her California hippie surfer friends, who are actually 500 year old aliens now pretending they are riding west coast ocean waves while secretly plotting to enslave us all with gasoline taxes collected by UN black helicopters

It's the PDO

Edit: Larry Lawrence, solar variation and orbit eccentricity have caused it in the past. they are not causing it currently as solar input has remained relatively stable while tropospheric longwave radiation at specific greenhouse gas wavelengths has increased. On top of that nights are warmign at a faster rate than days and the higher you go in the messphere and thermosphere the cooler it is getting. If you want to state that there is another natural cause you should lay it out and show that it is the cause. As of now all your doing is arguing a fallacy.

Jerry: You'll have to show that the milankovitch cycles, which usually provide the same warming over many thousands of years, is responsible for the current fast warming rate. temperature variations due to milankovitch cycles cause variations in solar input. this is not what is occurring currently as outlined in my response above.

Here's a theory for you, It's getting warmer, oh no, we've got to do something about it, quick someone tax developing countries and make solar ovens to give to underdeveloped countries.