Leyland on global warming

Bryan Leland writes in the Dom Post on global warming:

Although the world did warm by about 0.7C between 1975 and 1988, there has been no significant warming since then. All the major temperature records show that global warming has flattened off.

I think Bryan means 1998. In 1975 the average temperature was 0.17c below the norm. In 1988 it was 0.18c above the norm and in 1998 it was 0.55c above the norm – the highest year on record.

I wouldn’t quite say there has been no significant warming since then. 1998 was an exceptional high. A significant warming trend did continue until the early 2000s. However as one can see it has tapered off in recent years.

There is a divergence of views about the leveling off. Many factors affect the global temperature. I think it is premature to conclude it disproves global warming, but certainly the longer the “flat” period continues the more the prediction models will come under scrutiny.

Regarding sea levels, the highly accurate sea-level gauges installed around Australia and on the Pacific Islands (including Tuvalu) in the early 1990s showed that sea level rise is small – less than 3mm a year – and that, in recent years, it has levelled off. The 3mm a year is consistent with the sea-level rise that we have experienced since the end of the Little Ice Age. So the only strange thing that is happening is that we cannot explain why the sea level is no longer rising.

The increase is only around 3 mm a year, but this is up from 1.8 mm a year for the previous century. It is not dramatic end of the world Al Gore type hysteria rises, but it is an increase. The graph shows:

On the basis of that data, I wouldn’t say the sea level is no longer rising. It is. An increase of 3 mm a year is not the end of the world, but if it acclerates, then it does post significant challenges.

The climate models predict that an increase in carbon dioxide causes dangerous global warming purely because they have been programmed to do just that. The science tells us that if we double carbon dioxide from the present level it might cause a warming of about 1C. The climate modellers escalate this 1-to-3C, with little supporting evidence, and then, quite predictably, the models show a much higher rate of warming. But if you talk to the modellers, they will tell you that the big unknown is the effect of clouds because they cannot model them with any accuracy. There is more and more evidence that an increase in temperature brings an increase in clouds and this has a cooling effect.

This is the area of most uncertainty, as I see it. As Bryan says there is no dispute about the direct impact of increased greenhouses gases being around 1 to 1.5 degrees (off memory). What is disputed is whether the indirect effects will magnify that warming, reduce it, or not affect it. Most climate scientists say it will magnify it, but this is based on models. I bow towards the majority view, but with the caution that if the data does not fit the models, then the models need to be re-evaluated.

One good thing about the decision to try and have a post-Kyoto agreement be completed by 2015, to start in 2020, is that several more years of data should help us understand how significant a problem the level of greenhouse gases in our atmosphere is. It definitely is a problem, but the magnitude of the problem will ultimately depend on the data of the next few years, and beyond.