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On climate blogs I've been visiting lately, discussions have formed around three main themes - cold weather, Antarctic temperatures, and the respective values of caution and catastrophism in climate discourse.

I'd never presume to have definitive words on any of these topics, if indeed definitive words exist.

But all three have raised a few thoughts in my mind that I'd like to share and discuss a bit further.

Cooling down

At least in my part of North London, it has certainly than we've been used to (I'll not call it "bad weather", because the sight on our first white morning of two youngsters building what was presumably the first snowman of their young lives was far too uplifting for that description).

Turn the globe upside down, though, and the picture looks very different.

have raised questions about the [pdf link] in creating conditions that make fires more frequent or more rampant. The issue there isn't what cold conditions have to do with a supposed warming trend, but whether the warming trend has anything to do with the tinderbox conditions.

Those questions aren't answered yet. But it's clear that if you're looking to seasonal weather as an indicator of how the climate is changing globally, the global picture you paint depends very much on where you are in the world; and it's equally clear that all such pictures will be unreliable.

In earlier years of reporting climate change, news media were regularly accused of attributing any unusual or extreme weather events to climate change - and often the accusations were justified.

I hope that on the whole, professional journalists and broadcasters do not make the same mistake these days; but it seems to me that in the blogosphere, the two are still often confused. One cold winter, or even five consecutive cold winters, do not tell you anything about a longer-term global trend, and no-one's interests are served by pretending otherwise.

This was one of the points made by Vicky Pope of the UK Met Office, one of the country's most prominent climate scientists, in a .

There are several themes to Dr Pope's article, which is well worth a read.

Some scientists overplay the "threat" of climate change, she argues. Media organisations ignore studies that go against the "it's all getting worse" narrative, such as that a recent acceleration in the flow of Greenland glaciers had ceased; and the discourse around the issue errs in asking whether scientists "believe" in climate change, when scientists actually take positions based on evidence.

That someone in Dr Pope's position would write along such lines created a major stir in some circles, though quite why it should have done I'm not sure, given that many other equally eminent climate researchers have taken a similarly cautionary position down the years (including Mike Hulme, former head of the Tyndall Centre, just over two years ago).

But the points she raises are all, I suggest, worth a mull.

Yes, some scientists have on occasion gone beyond the data in arguing that climate change will bring global catastrophe; not least in the US, where there was a feeling in some quarters that only extremely graphic projections of future doom could shake the Bush administration into curbing greenhouse emissions.

Yes, news organisations are prone to reporting studies that paint a more extreme picture - and not just in climate change. That partly stems from the assumed link between lurid headlines and audience interest (and hence income), and partly because issues develop narratives, and stories that fit the narrative are more likely to make the cut.

Neither situation is ideal, but both are understandable given that scientists and editors are all human beings with human emotions.

Where I do part company with Vicky Pope to some extent is in her argument that it is not a question of scientists "believing" or "not believing" in climate change.

Instead, she writes: "Our concerns about climate change arise from the scientific evidence that humanity's activities are leading to changes in our climate. The scientific evidence is overwhelming."

I understand where she is coming from. In a previous life I worked for publications dealing with fairly advanced medical research, and one of the standard questions we asked was "what does this study tell you about how drug x or drug y should be used?".

On one occasion I received a memorable but not very helpful reply from an eminent cardiologist: "The data tells you what the data tells you" - which is basically Dr Pope's position.

But clearly, highly intelligent, highly educated people can look at the same set of scientific evidence and come to radically different conclusions - not, perhaps, on the basic issue of whether climate change is or isn't happening, but certainly on what the pace is likely to be and what threat it poses.

Which brings me to the by US scientist Chris Field to the effect that the pace of climate change had been seriously underestimated, and impacts would in fact "be beyond anything that we've considered seriously in climate policy".

As a recently elected co-chair of the on impacts and adaptation, Dr Field's analyses are likely in coming years to reverberate along the corridors of power, and not just in Washington DC.

There is some evidence to back his contention that things are moving faster than the IPCC projected in its major 2007 report.

, have been rising faster than anticipated to absorb carbon dioxide from the atmosphere, there are hints that the more potent greenhouse gases and are being released from Arctic regions, and several projections indicate that by 2100 than the IPCC projected. (More evidence to back Dr Field's case will be published early next week, by the way).

But equally you can find reasons for suggesting the situation is less calamitous than the IPCC painted. One is the research on Greenland glaciers mentioned above. Another is that the Amazon basin may be less vulnerable to temperature rise than previously believed; and there are that the economic downturn is slowing the rise in carbon dioxide emissions.

These are all disparate elements of a complex picture. How do you rate them? Which do you regard as more or less important?

We are back to what you believe; and if Chris Field sees catastrophe in the picture before him, he is entitled to say so, just as Vicky Pope or Mike Hulme are entitled to urge restraint.

Warming up

Another element in this vast and disparate research landscape was a few weeks ago indicating that Antarctica is, on average, warming up.

There's been a bitter spat between some of the paper's authors, who also maintain the , and some of the more "climate sceptical" denizens of cyberspace, with explosive terms such as "fraud" and "libel" being thrown around.

It's not the first time that such spats have arisen, of course, and it's not the first time that I've wondered if you could become the next dot.com billionaire by inventing the electronic version of a scary Victorian nanny who would make the errant climate offspring stand in opposite corners of their cyberworld balancing servers on their heads until they learned to be civil to each other.

There are used in the Antarctic paper, and although accounts vary as to who pointed them out, we should be grateful that they were pointed out.

Importantly, however, the scientists involved in the study by these issues, and I have not seen any analysis categorically claiming the opposite - though I doubt we have heard of the last of it.

Caution or catastophe?

Another general point we can pull out of this episode is that single scientific papers rarely prove or disprove anything - they simply add to the mass of evidence we have on a given issue, and should be seen in that light.

Once they're out there, they can be pored over and pulled apart and criticised, any novel methods replicated and perhaps cast aside or improved - and through that process the whole field of research moves on.

Another is to guard against false assumptions of what "we know". Many reports of the Antarctic paper suggested that before it came out, "we knew" that Antarctica was cooling; but that isn't actually the case.

The [pdf llink] concluded that "Antarctica has insufficient observational coverage to make an assessment"; but the the IPCC prepared for land south of 65 degrees South (which includes virtually all of Antarctica) contained hints of an upwards trend.

So the argument I have seen often that "the paper must be wrong because we know the Antarctic is cooling" just doesn't make it.

The climate blogosphere is full of straw men; and as always, the only sure-fire way to burn them is to go back to the original, authoritative sources.

So here's my brief take on it all. Science is a repetitive process, and often it's only when we come to something as weighty as an IPCC report that the various bits of evidence are brought together and assessed. Only then can there be some reasonably definitive exposition of what we "know" - or as researcher John Christy , "At our present level of ignorance, (what) we think we know" .

Individual pieces of research rarely prove anything by themselves, though they're a lot more valuable than opening the window, seeing what the weather's like and making a "commonsense" leap to what's happening with the climate globally.

In the meantime, scientists, politicians and Joe and Joanna Bloggs down the pub are all entitled to give their own assessments, and often there is a fair amount of belief involved, even for the scientists.

To me, there's little wrong with that. It's what we do with politics and football and music and film, and I don't see why climate discourse should be different.

There are facts out there, and we should recognise them as such, just as we should with medicine and social issues and economics; but there is freedom to believe too, and that, the last time I looked, was supposed to be a universal human right.

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