How to cherry pick your way to Antarctic land ice gain
Posted on 25 April 2009 by John Cook
I've been reflecting on the recent poll that found a record 41% of people now think global warming is exaggerated. Meanwhile, 86% of climate scientists think we won't restrict warming to under 2°C. Why the discrepancy between qualified climate scientists and the general public? I would suggest that scientists are not always completely effective at communicating their science to the average person. Global warming skeptics, on the other hand, have a wide range of rhetorical techniques that are quite successful in sowing doubt.
One of the most common techniques is cherry picking selected pieces of data while ignoring the big picture. A perfect example is the argument that human CO2 emissions is tiny compared to natural CO2 emissions. After all, humans only emit 26 gigatonnes of CO2 per year. Nature, on the other hand, emits a whopping 770 gigatonnes per year, via the ocean, animals and vegetation. Put that way, how could we possibly say mankind is having that much of an impact compared to nature?
But that argument ignores the fact that while nature emits 770 gigatonnes, it also absorbs roughly the same amount through the ocean and land plants. So the net amount that nature contributes to atmospheric CO2 is practically nothing. In fact, it's slightly negative as nature absorbs a fair chunk of the CO2 we emit.
So there you have it - cherry pick a few incriminating factoids, neglect to give the whole picture and bingo, you've constructed a perfectly functional skeptic argument that while thoroughly debunked, continues to make the rounds to this day. Within the last few weeks, I've had the human CO2 is tiny argument told to me twice by two different family members (gotta love those family get-togethers).
An argument that has found new life in recent weeks is Antarctica gaining ice. It even shot its way into the top ten (at least until the next fad pushes it out). This is largely attributable to an article in The Australian, Antarctic ice is growing, not melting away. The article makes its argument simply and effectively in a single sentence:
"East Antarctica is four times the size of west Antarctica and parts of it are cooling."
Both statements are true. However, what the article fails to mention is that while parts of the East Antarctic interior are gaining ice, it's also losing ice around the edges and overall, is in approximate mass balance. So with West Antarctica losing ice and East Antarctica in balance, Antarctica is overall losing ice. But all The Australian does is cite the size of East Antarctica, mention that parts of it are cooling and the inference is East Antarctic ice gain must outweigh West Antarctic ice melt. It's clever persuasion but very misleading.
The article then transitions into a discussion of sea ice so smoothly, you barely even notice they're no longer talking about land ice. Many discussions of Antarctic ice melt fail to distinguish between land ice and sea ice which are two separate phenomenon. Antarctic land ice is falling. Antarctic sea ice, on the other hand, is increasing. This is partly due to less ocean heat rising to melt sea ice and partly due to cyclonic winds caused by the ozone hole (more on this in an upcoming post). It's important to note that sea ice is increasing despite the Southern Ocean showing pronounced warming.
So to properly understand what's happening with climate, you need the full picture, not a selection of conveniently cherry picked factoids. But how do you communicate complex climate issues in a soundbyte? How do scientists give a user-friendly version of climatology science without over-simplifying? It's an issue I wrestle with a lot lately and welcome any discussion on the topic.