What are some genuine reasons to be skeptical of climate change?

I don't think there is any genuine reason to be skeptical of the existence of man-made global warming. The theory is supported by the well-understood basic physics of the greenhouse effect, and 97% of published climate research agrees on this subject.

There is uncertainty regarding the magnitude of the human contribution, though studies investigating this question almost universally put the human contribution at around 100% of the observed warming over the past 50 years, and greenhouse gases at well over 100% (as anthropogenic aerosols have a cooling effect).

The climate sensitivity to the increased greenhouse effect has a large uncertainty range, between about 2 and 4.5°C mean global surface air warming in response to a doubling of atmospheric CO2. The main sources of uncertainty remain aerosols and the cloud feedback. But sensitivity is certainly not zero, which is what it would have to be if humans weren't causing any global warming.

Really, human-caused global warming is about as settled as science gets. It's also very well settled that we're the main driver of the warming over the past 50-100 years. The magnitude of future warming is an open question, but the main uncertainty there is in how much greenhouse gases we'll end up emitting.

I see two major groups or subject headings for skepticism. One is the sensitivity of the climate to increased CO2 levels and the other is the effect on the physical world of increased temperatures.

The first has several aspects which are all related:

1. Recent global surface temperature data vs. model projections. e.g. http://www.climate-lab-book.ac.uk/2013/updated-com...

2. Recent studies coming up with climate sensitivity lower than the 2007 IPCC AR4 report.

3. Uncertainties in feedback processes like clouds and aerosols.

The second is a collection of predicted changes ranging from the spread of malaria to disrupting bird migratory habits to changes in precipitation patterns. From a skeptical point of view, many are either very weak scientifically or again have a large range of uncertainty. Of the entire lot, I would say that rising sea levels might be the most significant as far as being damaging or need adaptation. Many others are just red herrings to make the AGW argument sound stronger and more urgent.

I'm sure you've heard all of that before so I'll drop one that isn't often talked about. That is, if humans were not burning fossil fuels, what would the natural variation in temperature be? Some say we are in a general cooling trend since the beginning of the interglacial. Well that may be true, but we need to deal with changes in years or decades. What SHOULD temperatures be doing in the next ten or twenty years if it was 100% natural? I don't know, do you?

Climate change has always happened. It is not something that has only just started since the beginning of the human race or since the start of the industrial revolution. The first major pollutant in the atmosphere was O2, for instance. That changed the face of life on earth.

One problem is just semantic. Your question mixes climate change with man-made climate change with global warming. To me they are quite different. You can have one without the others.

Let me pick just one for now: man-made global warming. I suspect that there is some man-made global warming. I think you do too. What we really need to know is how much of the warming is man-made and how much not. We also need to know how much of that is CO2-related and how much not.

If science could tell us that 10% of warming was man-made and only 5% of that was CO2-based with the other 95% being caused by deforestation, land use changes and that the remaining 90% of warming was natural then we could use that as a base. We would then need to know whether the warming was going to cause a serious problem or not. Conflating all those issues does not help to make a case.

If it turned out that 95% of warming was caused by man-made CO2 and that it would be catastrophic then we would arrive at a different conclusion. The fact that we don't seem to know any of these things and that science can't tell us gives me pause for thought.

Proposed theories also disagree with some of my fundamental beliefs. I believe, for instance, that cause must precede effect. So when we see that CO2 increases follow temperature increases I wonder if we are being told the whole truth. (Yes, I have read SkS on the subject but that just ignores what actually causes the initial change i.e. the crucial bit!)

Without the causality link, all correlation says is that A might cause B, or B might cause A, or A and B are both caused by something else, or it is coincidence - all equally likely.)

The fact that climate scientists will not publicly debate sceptics is a bad sign. Surely, if the science is so settled and overwhelming any dissenting views should be put down in moments?

The fact that the IPCC reports are so stage-managed is a bad sign as well. Their charter is to investigate man-made climate change - not all climate change. They cherry-pick suitable papers for inclusion, bend the cut-off rules if a warmist paper arrives late, use grey literature (about 30% in AR4) record input from specialists then ignore any bits the central committee does not like, publish the Summary for Policy Makers a few weeks before the supporting documentation (that must have been finalised first because that is what the summary should have been based on) possibly to prevent immediate fact checking etc etc.

Why are we only given a one-sided view of things. For instance, we are told that CO2 traps heat. Why are we never told that CO2 releases heat? Surely, more CO2 in the atmosphere means that there is more CO2 to release heat to space and thus cool the earth?

Why is there so little in the way of experiments? Saying it is hard or we need a parallel universe is no answer. That is exactly the thing physicists have done in the past e.g. looking into atoms, discovering the Higgs boson, showing that gravity can bend light, predicting eclipses etc. Climate scientists think experiments can all be done with a computer model or with access to Google. The models are still naive - even after 30 years: flat earth, no clouds, no day and night - and they call us "flat-earthers".

We are still lacking the final conclusive experiment that links it all together. Doing an experiment in a brass tube in a lab is not quite the same as doing it in a real atmosphere. Consider, for instance, measuring the temperature at the lab floor and the lab ceiling. Ceiling is hotter than floor therefore heat rises. So why are the tops of mountains colder than the bottoms? You need to carry out the experiment in the proper environment.

Partly because there are no suitable experimental results we have Oxford professors claiming 11° C increases by 2100 one week and then claiming it will only be 3° C the next week - quite a degree of uncertainty.

I could go on but I will spare you any more. Anyway, the blood pressure tablets are wearing off!

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Edit: Talking of 97% surveys. I hear a recent such survey defined its highest category as "... human activity is a dominant influence or has caused most of recent climate change (>50%)." and that only 65 out of 11,944 abstracts were in that category. Is this true? If so, it looks like 99.5% were AGAINST the AGW proposition.

To Maxx: <<1) The Earth has been both much warmer and much colder in the distant past,....>> Could you please explain to me Maxx how on earth (pun intended) you can claim the above while you religiously believe the earth is only 6,000 years old, give or take a few thousand years? It is not that I do not believe that the earth was warmer or colder 'in the distant past' (which in fact it was, several times). It is just that I cannot comprehend how you can keep a straight face argueing a paleoclimatic record (which goes back hundreds of thousands of years) when you do not believe in a paleoclimatic record at all to begin with.

Scepticism is the reasonable default position, it does not mean as denialists would have us believe "ignoring overwhelming evidence to the contrary" but rather examining what evidence there is and coming to a conclusion. As a sceptic I accept the theory of anthropogenic climate change

One scientific group has stated that climate change is only 2-3% man -made.It is up to you to decide what you want to believe.

Fair & Balanced Trevor: "what are some of the genuine reasons to be skeptical of manmade global warming, or to at least to question our current understanding of it."

Today he thinks the science is not precise. A few weeks ago he was telling us precisely what would happen if we stopped adding CO2 to the atmosphere, and he was even able to do so without using differential equations.

1. There are reasons to be skeptical about the pace and severity of anthropogenic long term global climate disruption, and the degree and impact of the negative consequences for the long term global human economy.

2. There are also reasons to be skeptical about efficacy of many proposed remedies.

Neither form of skepticism has any significant presence within the 1990s fossil fuel industry funded, cold war paranoia fed, and slick con artist formulated grab bag of anti-science trickery that is all that most deniers have a clue of.

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

http://www.huffingtonpost.com/bill-mckibben/the-gr...

Uncertainty about timing and seriousness is an argument for insurance (pro-active diversification AWAY from fossil fuels not myopic cornucopian fantasies about them).

http://www.aps.org/publications/apsnews/200602/bac...

http://answers.yahoo.com/question/index?qid=201204...

The dubious viability of many proposed policies (e.g. cap and trade) is an argument for BETTER policies against fossil fuels, NOT no policy against fossil fuels.

http://www.carbontax.org/who-supports/scientists-a...

U.S. National Academy of Sciences, 2010:

http://books.nap.edu/openbook.php?record_id=12782&...

“Climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems.”

http://www8.nationalacademies.org/onpinews/newsite...

“Choices made now about carbon dioxide emissions reductions will affect climate change impacts experienced not just over the next few decades but also in coming centuries and millennia…Because CO2 in the atmosphere is long lived, it can effectively lock the Earth and future generations into a range of impacts, some of which could become very severe.”

http://www.physics.fsu.edu/awards/NAS/

“The Academy membership is composed of approximately 2,100 members and 380 foreign associates, of whom nearly 200 have won Nobel Prizes. Members and foreign associates of the Academy are elected in recognition of their distinguished and continuing achievements in original research; election to the Academy is considered one of the highest honors that can be accorded a scientist or engineer.”

http://www.aip.org/history/climate/timeline.htm

http://ideas.repec.org/p/cwl/cwldpp/615.html

I have no idea what you consider nonsense. I find the certainty of the effects of CO2 to be nonsense, I find it more nonsense to claim that none of you claim certainty, and even more nonsense that we should be even more concerned because there is so much uncertainty. Ambiguity is the best tool you have to convince people of the effects of CO2. I grow tired of seeing the more sensible warmons say there is no evidence that X weather pattern is a result of AGW and turn around ringing the alarm crying this is the kind of weather we warned of. I know when a warmon is talking nonsense when he starts an answer with it may sound counterintuitive.

We do not have a good enough understanding of climate to precisely predict how much a given change in CO2 will change the average temperature of the planet, so we may be overestimating the change.

We do not have much in the way of measurements of deep-ocean conditions, so we can't entirely rule out the possibility that some of our current weather/climate is due to deep-ocean heat that is upwelling for some reason, or the like.

For the most part, paleoclimate reconstructions have fairly low resolution, so we can't be sure that rapid warming events like this haven't happened frequently in the past, for (obviously) non-anthropogenic reasons.