Half a story

Popular press reporting of global warming issues continues to irritate. The big news this morning: recent sea level rises are higher than the 2001 prediction. From the SMH:

SEA levels are rising faster than the International Panel on Climate Change predicted, showing computer models have tended to underestimate the problem.

Since 1993 sea levels have climbed at a rate of 3.3 millimetres a year, compared with the panel's best estimate for this period of less than 2 millimetres a year.

The only hint of uncertainty in the report is on the pessimistic side. (A CSIRO scientist is quoted as saying that the contribution of melting ice sheets is still not properly quantified.)

However, in their report on the same story in Nature is this:

Rahmstorf and his colleagues calculate that sea-level rise over the past 20 years has been 25% faster than for any other 20-year period for more than a century. But they accept that this could be due simply to natural variations over decadal timescales. "Sea-level rise has been tracking along the uppermost limit for 16 years now, but it could still be decadal variability, so we don't predict that this will continue," Rahmstorf says.

Another study published last month² suggests that sea-level rises during the twentieth century were indeed very variable. According to calculations by Simon Holgate of the Proudman Oceanographic Laboratory in Liverpool, UK, sea levels rose by an average of more than 2 millimetres per year in the first half of the century, but by less than 1.5 millimetres per year on average in the latter half.

The uncertainty could cut both ways, then.

In any event, those who worry about Tuvalu have to remember that the ocean was still rising at 2mm per year in the first half of the 20th century. (In fact, note how the rate dropped in the second half.) Now it is rising at 3 mm per annum. Tuvalu was never a long term proposition even without global warming.

One other point: the SMH article says this:

In a separate study in the same journal, Helen McGregor, of the University of Wollongong, has found global warming has already changed ocean currents in a way that could have a serious impact on fisheries.

Her team's research off the north-west coast of Africa shows it has led to an increase in a phenomenon called ocean upwelling, in which deep, cold water, usually rich in nutrients, moves upwards to replace warmer surface water.

"Our research suggests that upwelling will continue to intensify with future greenhouse warming, potentially impacting the sensitive ecosystems and fisheries in these regions," Dr McGregor said.

Again, note the emphasis on pessimism. Yet only a few days before, we had this story:

The world's oceans are already in a warming trend that could alter fish stocks, perhaps damaging coral reefs that are vital nurseries for tropical species while boosting northern stocks of cod or herring...

In a sign of how higher temperatures might help some fish stocks, a period of warmer waters in the 1920s allowed cod to spawn off Greenland and let a new stock break away from Icelandic waters. In the cooler 1960s, cod were unable to reproduce off Greenland and the stock collapsed.

[I would also have thought that cold water upwellings rich in nutrients would be good for plankton growth, which is a major CO2 sink. It has long been suggested that Ocean Thermal Power Generation would have this as a side benefit.]

So lets get it right people: oceans have been warming and cooling even before current global warming. It had already had major effects on fish populations a century ago. It will continue to affect fish, with some winners and some losers. (Everyone used to bemoan the loss of cod fisheries. Now that global warming may help them, the tragedy will be fewer tropical fish. )

What bugs me most about this is that it is teaching pessimism to our children. Apart from what children read for themselves in the press, there will be lot of school teachers who pass this on, as they often don't show much inclination towards independent thought. (Sorry, they do a hard job, but you know that is true.)

Wait for the wave of pessimism when the entire IPCC report comes out.

UPDATE: just to be clear, I do take CO2 levels seriously, as explained in a few posts last year. It is just that I don't see any benefit in promoting pessimism as the response to the issue. The attitude I want is optimism that effective action can be taken, and an acknowledgement that things were never static and perfect in the global environment anyway. (Just ask the dinosaurs and the Australian megafauna, the latter increasingly looking like an example of very early technology causing havoc. As for aborigines "living in harmony with the land for 50,000 years": well yeah, after they changed the landscape entirely by fire and hunting.)