Was the 1990 1st assessment report accurate?

Tom Hunt at Stuff reports:

The roughest storms are set to get rougher under predictions that already have two decades of proven reliability. …

It was possible events such as the floods in Nelson and Golden Bay last December could become more common, said New Zealand Climate Change Research Institute director David Frame.

Professor Frame is co-author of a report published in the latest edition of Nature Climate Change.

Along with Daithi Stone, from the Lawrence Berkeley National Laboratory in California, Prof Frame has compared predictions from the first Intergovernmental Panel on Climate Change (IPCC) assessment report in 1990 with actual data from the past 20 years.

The comparison showed global climate change was happening as predicted in 1990. “Things are changing pretty much the way we thought – surprisingly so,” Prof Frame said.

Since 1990 the average global surface temperature rose by between 0.35 degrees Celsius and 0.39C, in line with 1990 predictions. This was in spite of unforeseen climate-altering events, such as the eruption of Mt Pinatubo in 1991, the collapse of Soviet bloc industries in the 1990s, and the recent fossil fuel-intensive growth in economies such as Asia.

“What we’ve found is that these early predictions seem pretty good, and this is likely due to the climate responding to concentrations of greenhouse gases in the Earth’s atmosphere at a rate broadly in line with what scientists in 1990 expected.”

The 1990 predictions looked ahead as far as 2030, and forecast that average temperatures would continue to rise by about 0.2C a decade.

You have to pay to see the full article, so I can only go on what is reported. There is no doubt the average global temperature today is significantly hotter than in 1990. But what did the 1st assessment report predict:

An average rate of increase of global mean temperature during the next century of about 0.3°C per decade (with an uncertainty range of 0.2—0.5°C per decade) assuming the IPCC Scenario A (Business-as-Usual) emissions of greenhouse gases;

So they actually said 0.3 per decade. The 0.2 figure referred to was not for the BAU scenario but a scenario of increasing levels of controls of emissions. And we have been told for the last 20 years that there has been no significant control of emissions – none of the major emitters joined Kyoto and that applied to 2008 to 2012 only. So I think this is a case of cherry picking the scenario which fits the data. The BAU prediction was clearly 0.3. Also the sea level rise was predicted to be:

Under the IPCC Scenario A (Business-as-Usual) emissions, an average rate of global mean sea-level rise of about 6 cm per decade over the next century (with an uncertainty range of 3—10 cm per decade).

Now what has been the increase? Well the NASA data says:

  • 1990 – 0.37 (above century average)
  • 2011 – 0.52

That’s an increase of 0.15, and the IPCC BAU prediction was 0.60. So again there is an increase but I wouldn’t hold the 1990 1st assessment report as an uncanny oracle that is flawless.  Again I can’t see the full report, to see which data they have selected to back their argument, but all I have done is choose the BAU prediction and the NASA global average data. I’ve not gone looking for a particular dataset to support the case that warming, while happening, has not been as fast as predicted.

There is no scientific debate about the fact that increased greenhouse gas emissions will increase the temperature. This aspect of the science is unchallenged. What is more uncertain is how does nature respond to this. What are the other factors that may either speed up warming, or mitigate it.

If China, India and the US do not control or reduce their emissions, then I have little doubt that the average temperature in say 2050 will be warmer than today. But I do have doubt over just how much warmer.

With the sea level rise prediction of 6 cm per decade, the data is that it has been 3 cm a decade. This is within their margin of error of 3 cm to 10 cm a year. So it can be consistent to say the 1st IPCC report predictions were accurate for sea level rise, but also that they are at the lower end.

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