BBD,

I don't think that mainstream thinking claims that the science around climate is settled, except for some obvious areas of basic physics. You can see this very clearly in the current version of the RS summary. It also follows from this, that mainstream thinking does not propose "science first, then politics", because otherwise there would be little point in discussing the political mechanisms for mitigation and adaptation to occur. I'd add that IMO the papers in this discussion although from 2004 still provide an insightful commentary into the whys and wherefores of the sad state of climate politics.

matthu

That is the stage we are still at, because there is simply not enough evidence to show that some unconsidered natural factor may be causing warming - just as it may have done in the past. Why is this the case? because scientists admit that the undertainty is too great to assume anything else.

There is no evidence for any natural mechanism causing modern warming. This is the last, desperate flailing of those who simply refuse to accept the facts:

RF from CO2 is heating the climate system.

Which scientists 'admit that the uncertainty is too great to assume anything else'? This is news to me.

Are they the same 'substantial body of scientists' that say it's going to cool? You know, the substantial body of scientists that doesn't exist.

Or do you expect me to take the likes of Ball, Michaels, Singer & co seriously? Despite their absolute lack of credibility? I mean, why would any rational person take the views of a bunch of deeply compromised non-climate scientists and three credentialled contrarians over those of the entire expert consensus? It makes no sense at all.

Why are you so profoundly illogical?

AR4 Synthesis Report SPM (emphasis as original):

There is very high confidence that the net effect of human activities since 1750 has been one of warming.

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations. It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica).

There is no evidence for any natural mechanism causing modern warming. This is the last, desperate flailing of those who simply refuse to accept the facts:

Now, did the IPCC report consider any solar mechanism other than total solar irradiance? No? Then that would be one reason they failed to find any evidence.

And most climate scientists agree that there is a lot of uncertainty elsewhere as well - far too much to reject the null hypothesis (which you have yet to state).

Unfortunately, most climate change scientists simply don't understand the concept of a null hypothesis at all.

matthu

And your evidence for any non-TSI effect is...?

And most climate scientists agree that there is a lot of uncertainty elsewhere as well - far too much to reject the null hypothesis (which you have yet to state).

I ask again - who is this majority of climate scientists that claims there is far too much 'uncertainty elsewhere' (eh?) to reject the null?

And why is this majority view not reflected in AR4? Which states the opposite?

The null hypothesis is that human activities play no role in climate change.

I think we can refute that pretty easily.

BBD - At LAST you have come up with a null hypoithesis:

The null hypothesis is that human activities play no role in climate change.
Nov 18, 2011 at 9:26 PM - BBD

I have already agreed that this null hypithesis has been rejected by a consensus of scientists, because I have stated what the consensus is.

This is my understanding of the consensus as I outlined to Richard Betts (who agreed with it)
1) global warming is real (whatever that means)
2) man is having an impact
3) at least some of the impact is likely caused by CO2 emissions

I can live with that (and argue about the meaning of the first point),

Anything further than that e.g. increasing rate of warming, increasingly important factor, catastrophic consequences etc. remain to be proved.

Nov 10, 2011 at 10:57 PM | matthu

matthu

I don't care about your self-contradictory waffle.

I ask again - who is this majority of climate scientists that claims there is far too much 'uncertainty elsewhere' (eh?) to reject the null?

And why is this majority view not reflected in AR4? Which states the opposite?

BBD - please try to understand.

Depending on what alternate hypothesis you pose, the null may change.

I have agreed that the particular alternate hypothesis that you posed above is not contentious. There is no uncertainty about it.

You could even strengthen the alternate hypothesis and say that
H1: CO2 is having at least some effect on global temperatures.
H0: CO2 is not having any effect (this becomes the NULL hypothesis)

Again, the null hypothesis is rejected because the alternate hypothesis is no longer contentious.

@ BBD

Who would it take (from your preferred list of experts) to refute the CO2 argument for you to change your mind? One person in particular? ALL of them? A given percentage?

I only enquire as, for most people, it takes only a given amount of [contradictory] 'evidence' for them to alter their position and I would be interested to know your 'strength' of opinion/feeling.

Latest definition of Climate Change from the IPCC:

Climate Change: A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.

http://www.ipcc-wg2.gov/SREX/images/uploads/SREX-SPM_Approved-HiRes_opt.pdf

So it appears that (unspecified) natural causes and/or changes in land use are both right up there with other potential causes. The alternate hypothesis is being rewritten even as we speak. this can only be a good thing and is likely to widen the consensus.

No doubt though that there will be some factions who will disagree with this definition and try to re-impose the previous definition. Lawyers may even get involved (it will be harder to try to prove liability for climate change in court).

Null Hypothesis: The changes in the global temperature of the earth that have been measured over the last 100 years are within the range of the planets natural variation.

Alternative Hypothesis: The changes in the global temperature of the earth that have been measured over the last 100 years are caused either partially (Alternative Hypothesis 1) or entirely (Alternative Hypothesis 2) by RF from anthropogenically derived CO2.

matthu

I don't care about your self-contradictory waffle.

I ask again - who is this majority of climate scientists that claims there is far too much 'uncertainty elsewhere' (eh?) to reject the null?

And why is this majority view not reflected in AR4? Which states the opposite?

Anon

Who would it take (from your preferred list of experts) to refute the CO2 argument for you to change your mind? One person in particular? ALL of them? A given percentage?

I only enquire as, for most people, it takes only a given amount of [contradictory] 'evidence' for them to alter their position and I would be interested to know your 'strength' of opinion/feeling.

I do not base my views on a 'preferred list of experts'.

You would have to overturn the laws of physics to get rid of the radiative forcing from CO2.

Then, maybe, I would change my position ;-)

Now, what about you?

How many 'sceptic' claims have to be debunked before you accept that CO2 is heating the climate system?

matthu

May I ask if English is not your first language?

It's just that occasionally you misinterpret things so badly it makes me wonder what's going on.

For example:

The uncontrovertial IPCC definition of CC:

Climate Change: A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.

In other words, climate change can be caused by natural internal processes or external forcings or anthropogenic alteration of atmospheric composition/surface albedo.

This is not equivalent to your interpretation (emphasis added):

So it appears that (unspecified) natural causes and/or changes in land use are both right up there with other potential causes. The alternate hypothesis is being rewritten even as we speak. this can only be a good thing and is likely to widen the consensus.

But please, don't forget, I also need to know all about this majority of climate scientists that holds that there is too much 'uncertainty elsewhere' (Nov 18, 2011 at 8:53 PM) to reject the null hypothesis that human activities play no role in climate change:

And most climate scientists agree that there is a lot of uncertainty elsewhere as well - far too much to reject the null hypothesis

BBD - you need to say exactly what null hypothesis you are talking about. You do not seem to appreciate that depending on how you frame your alternate hypothesis (i.e. the hypithesis you are trying to prove) the null hypothesis can be either rejected or not.

The null hypothesis and the altenate hypothesis need to be mututally exclusive and exhaustive events.

What this means is that whatever alternate hypothesis you choose, the only other possibility should be the null hypothesis (and vice versa) so that if you find evidence to reject the null hypothesis then the alternate hypothesis is necessarily true (and vice versa).

Example: If you frame your alternate hypothesis as
H1 "human activities have at least some impact on climate"
then the null hypothesis is
H0 "human activities have no impact on climate".

This particular null hypothesis (i.e. the one you proposed higher up) is already rejected by a vast majority of scientists and there is almost no uncertainty about this. I am in agreement with that.

However, it is possible to frame many different and more controversial alternate hypotheses which make it very much harder to reject the null hypothesis because of the curent level of uncertainty.

Example: If we frame the alternate hypothesis as
H1 "Human activities are by far the dominant factor in climate change"
then the null hypothesis may possibly be framed as
H0 "Factors other than human activities (including factors not yet identified or fully understood) may play a much bigger role in climate change than any we have yet measured from human activities".

In this case it become very much harder to reject the null hypothesis simply because you are not yet in a position even to ennumerate all the possible factors which may be playing a part.

So (many scientists would say) the level of uncertainty is too much to be able to reject the null hypothesis at a 95% level, which is the minimum standard usually required for a statistical test. This means that there is no consensus on this particular alternate hypothesis.

BBD you claim

There is no evidence for any natural mechanism causing modern warming.

However, this is insufficient argument to reject the possibility that such evidence exists if we know where to look. The null hypothesis needs to be rejected with a lot of certainty, not simply a lack of evidence.

matthu

I don't care about this null hypothesis red herring.

Please respond to:

- Nov 19, 2011 at 4:06 PM

- Nov 19, 2011 at 4:38 PM

If you don't specify which "null" you are talking about, then it is hard to give you an answer.

But it is already very obvious that hypothesis testing is very foreign to you so I am not sure it is worthwhile proceeding with this discussion.

Which is a pity, because the latest definition of climate change does now include a reference to statistical testing, the very essence of which relies on formulating an alternate hypothesis and a null hypothesis.

Meanwhile you are rude enough to ask me whether English might be my second language.

"How many 'sceptic' claims have to be debunked before you accept that CO2 is heating the climate system?

CO2 may indeed be heating the climate system - I don't see any evidence that it's man-made CO2 that's the problem though. Given the recent rise in CO2 levels there hasn't been a corresponding significant rise in temperature. There are too many variables to pick out CO2 as the main cause consequently my scepticism remains.

matthu

If you don't specify which "null" you are talking about, then it is hard to give you an answer.

Where is this majority of climate scientists that you refer to in your comment at Nov 18, 2011 at 8:53 PM?

And most climate scientists agree that there is a lot of uncertainty elsewhere as well - far too much to reject the null hypothesis

Presumably you know which null hypothesis you are referring to. So let's have an end to the evasions.

Your answer please. Now.

The earlier hypothesis relating to climate change was as advoicated in AR4.
The fact that the definition of climate change has changed should give you a clue: the original hypothesis no longer attracts a consensus.

Scientists no longer accept the view that C02 is the only important and dominant factor affecting climate. Hence the change of definition to include references to other natural factors (unspecified because there is as yet uncertainty as to exactly what mechanism is involved) and land use change.

This is not complicated.

matthu

You have not answered my question. For the sixth time in a row.

So, once again, your claim that your 'sceptical' ideas are supported by a 'substantial body' of mainstream climatologists proves false. And you haven't got the intellectual integrity to admit that you have yet again been caught out making a false claim.

Have you no sense of shame at all?

Scientists no longer accept the view that C02 is the only important and dominant factor affecting climate.

Climatologists never made such a claim. Look at the comparison of forcings from AR4 WG1 that I keep linking to for a very good reason.

Do we see only CO2? Well, no, we don't.

But... which is the dominant forcing? CO2.

This is why I wonder if there's some sort of fundamental comprehension problem here. You thought I was being rude ascribing it to language. I could just as easily have questioned your honesty or your intelligence.

This new definition differs from that in the United Nations Framework Convention on Climate Change (UNFCCC), where climate change was defined as: “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.”

New definition: Climate Change: A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.

Now most readers of this blog will appreciate a significant change of emphasis here.
(Not you.)

No need to keep responding (because you will only get ruder).
The argument you always resort to when you are losing is ad hominem.
That's when I realise the argument is won.
The consensus has changed - and you have been left behind.

matthu

No need to keep responding (because you will only get ruder).
The argument you always resort to when you are losing is ad hominem.
That's when I realise the argument is won.

You are delusional. See above.

There is certainly one delusional person posting regularly in this thread but I do not think it is Matthu.