Sunday, February 18, 2007

Uncertainty and the impacts of climate change

A good article by Quirin Schiermeier in last week’s Nature (subscription only) discusses a range of areas in climatology where plenty of uncertainty still exists. Such areas are a prime focus of research in the short- to medium-term future. It is important to note that uncertainty doesn’t mean unlikely, it just means that currently there is insufficient data to draw a firm conclusion. It is also equally important to note that uncertainty doesn’t necessarily mean current predictions of climate change and its impacts are overblown. They may be, but there’s an even chance that current predictions underestimate the likelihood and degree of serious climate change impacts. When denialists attack the accuracy of global warming this is the critical piece of the puzzle they always ‘forget’ to mention. It’s also why it’s obvious that the search for scientific accuracy isn’t any where near the top of their agenda.

And these uncertainties are?

According to Schiermeier:

  • Sea-level changes. Ice-flow dynamics leading to changes in sea-level are poorly understood. The expression of uncertainty about ice-flow dynamics in the AR4 summary lead to many observers incorrectly concluding that estimates of sea-level rises had been reduced. They haven’t, though future research may show that this is indeed the case. Conversely, they may show significant increase from the TAR estimates. A recent paper by Rahmstorf in Science predicts a 1.4 m sea-level rise if the correlation between sea-level rise and temperature rise over the past couple of hundred years holds.
  • The relationship between hurricane intensity and warmer sea-surface temperatures. A number of recent papers have shown a correlation between warmer SSTs and an increased frequency of intense (Cat 4 and 5) cyclones. Potentially inaccurate and inconsistent reporting of cyclone intensity over a decent time-frame (say 100 years) means that long-term trends are difficult to determine. Model predictions are a problem too. Schiermeier states:
In the tropics, rising sea-surface temperatures can be linked in a relatively straightforward manner to storm formation, and the case for more intense storms seems more or less settled. But in the mid-latitudes, where atmospheric processes are more complex, some climate models predict more storms whereas others do not.
  • The relative impact of feedbacks, particularly biological ones. On balance, will they be negative or positive? A rather worrying example given by Nature is the possibility of a change of carbon sinks to carbon sources in a warmer world (e.g. the Arctic tundra). Another example is the ability of the more acidic oceans to take up CO2 and lock it away in the shells and exoskeletons of marine organisms. Most organisms may not be significantly affected or there may be sufficient biological diversity that a changing ecological structure will prevent a negative impact on the oceans’ CO2 sink properties. Conversely, lower calcification rates may become the norm and the oceans’ ability to lock away carbon is reduced.
  • The ability for climate models to predict impacts at a regional scale.
For some areas, models predict specific and well understood effects, such as hotter summers in Spain and smaller snowpacks (the accumulation of snow each season) in the Rocky Mountains in the United States. But improved analyses that incorporate clouds, snow and ice into the models must be developed if regional predictions are to become more accurate, says Rasmus Benestad, a climate modeller at the Norwegian Meteorological Institute in Oslo.
It will be interesting to read about Australian regional predictions when the full AR4 WG1 report is released. I suspect small population = small amount of research money = less money spent on modelling = less accurate models = less accurate regional predictions compared to Europe and the US (Maybe modelling is more difficult in the Southern hemisphere too? I dunno). Anyway, we’ll see. From my understanding current modelling of Australian climate has some pretty gloomy predictions as far as rainfall changes in prime agricultural regions are concerned, so hopefully the predictions are wrong.

I’m sure there are other uncertain areas of climatology that have been missed in the brief article. Feel free to add to the above examples in comments.