Climate change

May 21, 2009

More ice, flat temperatures – what does it all mean?

Filed under: Global Warming — Barry Brook @ 1:59 pm

Simple messages, which make headlines and create doubt amongst the laity, are an easy sell in the pseudo-sceptical world of climate science contrarianism. Many sound (kind of) plausible, and so gain an undue amount of traction among the general public and non-science decision-makers.  Ian Plimer’s recent book capitalises on these themes to full advantage, and, as Tim Lambert has patiently detailed over the past year or so, some media outlets such as The Australian also give such unscientific messages an extended and unbalanced run.

One that never seems to go away is that ‘1998 was the hottest year and every year since has been cooler‘ meme, or similar such variants. This little gem preys upon most people’s lack of appreciation of statistical inference, just like the ‘climate models didn’t predict recent variability‘ exploit a lack of understanding of the difference between a mean model output and any single realisation of a stochastic model run. Another one that’s come up quite a bit recently — including a number of editorials and reports in The Oz (I’m quoted in one of them) — is the claim that Antarctica (and worldwide) ice extent is growing. It’s a great one for climate contrarianism, because it immediately raises people’s suspicion levels — ‘How can the Earth be warming if the ice is growing?‘. You get the picture. Doubt is their product.

Now it would be nice to give people a simple explanation to these — ideally, some analogy that is easily visualised in the mind. Alas, the scientific explanations for these will always be, by necessity, somewhat technical and therefore easily glazed over by 95% of readers. Recently, the Australian Science Media Centre asked some scientists for an explanation, in simple terms, as to why ice in Antarctica might be growing. You can find their answers here. Ian Allison gave the most technically comprehensive and scientifically satisfactory reply, but I don’t imagine it meant much to most folks. I had a stab at a simpler explanation, which I reproduce below, but I also struggled, I think, to really make it clear.

Question: With confusion in the media this week over whether ice is decreasing or increasing in the Antarctic, here experts clarify the apparent anomaly.

Answer: This is a common source of confusion among climate change sceptics. As the world warms, the atmosphere’s ability to hold water vapour increases. Think of how humid it is in the tropics, and how dry the Arctic air is. The largest desert on Earth is the continent of Antarctica — it receives very little annual precipitation. In a warming world, more water vapour allows for more snowfall in Antarctica, which accumulates particularly in East Antarctica where the temperature never rises above freezing point. So, ice accumulates on that side of the continent. In the Antarctic Peninsula and West Antarctica, this extra accumulation of snow is more than offset by summer surface melt.

Also, as the sea warms around the continent, especially in the most northerly parts of the continent (Antarctic Peninsula) large ice shelves are eroded from beneath, and the frequency with which they break up starts to accelerate. This melting of buttressing ice shelves unplugs the land-based glaciers, and they begin to flow into the sea more rapidly. As such, there is a large net loss of ice from the western half of the continent, and a slight gain in the eastern half. More sea ice builds up around the continent because as the surface waters warm, the ocean becomes more stratified (it ‘turns over’ less readily). Less ocean heat is brought up from below. So it’s a battle between the negative effect of increased surface melt of sea ice, and the positive effect of more snowfall and decreased in melting from below, both of which reinforce sea ice formation. The result — a steady state or slight increase in the amount of floating ice around the great southern continent.

Better explanations than this exist. The main point of this blog entry is to alert my readers to two sites that I consider to be outstanding in this respect. They are ‘Skeptical Science (examining the science of global warming skepticism’ and ‘The Global Warming Debate (a layman’s guide to the science and controversy)’. I’d recommend these two sites as the first ‘go to’ point for anyone with doubts or simple curiosity about what the whole ‘climate change debate’ is about — even above Real Climate (which is technically superior to all other climate science blogs, but is generally pitched at a sufficiently advanced level that the casual layperson may often feel overwhelmed by the content and technical jargon).

John Cook, who runs Skeptical Science, took a break for a few months but is now up and running with three excellent new posts — one on the ‘cooled since 1998′ malarky and the other two on Antarctic ice spread. All three offer superb explanations. This site also has a list of the 50 ‘Hottest Skeptic Arguments‘ (in rank order) and regular specific posts which add further commentary to key points or things that are currently in the news. It is worth spending a day reading through the whole site, and sending links to your friends and family when they raise questions.

The Global Warming Debate is a wealth of interesting information. It includes 14 ‘chapters’ (extended web-based postings with pictures, hyperlinks and scientific references), supported by flash-driven video presentations presented by the author. It is simply superb. Here is the ‘About‘ description from the website, which gives you a broader idea of the motivation and content:

I created this presentation in response to persistent arguments that I’d read throughout the Internet (see introduction). “The Global Warming Debate” is my attempt to document the controversy as it is presented to the general public. Legitimate scientific questions remain, but the question of whether or not humans are capable of significantly altering the climate has been resolved.

If you are wondering “why should I believe you?” my advice is: don’t take my word for it. I have no special expertise in climate science. I call it a “Layman’s Guide” because it is by and for the layman. What I do suggest is to investigate the citations that I provide and weigh both the credibility of the argument and those making it. This is covered in much more detail in section 2 (”The Scientific Consensus“), but the world’s scientific societies, from which we draw virtually all of our scientific knowledge of the Earth, have all endorsed the science of anthropogenic global warming (AGW).

Skeptics call this an “appeal to authority” but it is really an appeal to credibility. There is a very small group of active climate scientists who doubt the consensus position on climate change, and their alternative theories will be examined in this presentation. The “debate” that you read about in newspaper editorials or watch on political talk shows overwhelmingly originates from Libertarian-leaning think tanks who see anthropogenic global warming as a conspiracy of greedy scientists and a danger to free market ideals.

In reality, a very good case for global warming has been made by the world’s scientists, and the consequences of not acting are grave. I will present a mainstream view of global warming based on my best effort to understand the various issues, from measurements of past temperatures and atmosphere, to modeling the climate of the future, to policies and technologies intended to mitigate the problem. This remains a work in progress, and comments are always welcome.

If you are truly sceptical (i.e., unsure of the case but willing to be convinced, if sufficient, logical and rational explanations are presented), about whether humans are having an impact on the climate system, how valid past temperature reconstructions and present measurements are, what the models really say, and how climate change attribution works, then you have a duty to read this site. All of it. Then we can talk, here or on other climate science sites (many linked in my left sidebar), about the points you still don’t understand or are unconvinced about.

Over to you, John Cook and cce. I tip my hat at your efforts.

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