Video description

On the 19th of July in 2011 the National Press Club of Australia held a debate on climate change. I will be analysing the claims Monckton made during the debate and if they are correct or not.

In this particular section of the debate Monckton makes the following claim:
"Why do we think that we're going to suddenly get 3.3 Celsius for a doubling of CO2 concentration this century - that's the IPCC's central estimate - or 5.1 - which is your [Australia's] government's central estimate - when all the science done by measurement and observation rather than by models, suggests just one Celsius degree?"

I will be going into the difference between the stated warming of the IPCC report and the number used by the Australian Government. As Monckton goes into more depth about the 1 degree warming later in the debate I will talk about it then.

Transcript

And why do we think that we're going to suddenly get 3.3 Celsius for a doubling of CO2 concentration, this century, that's the IPCC's central estimate, or 5.1 which is your government's central estimate, when all the science done by measurement and observation rather than by models, suggests just one Celsius degree?

This is a part of the debate that drew my attention.

The 5.1 degrees warming is an actual number used by the Australian government. It is mentioned on their page “Global action - facts and fiction”, it is also used on other information sites about the carbon tax.

This number comes from the 2008 report “The Garnaut Climate Change Review”, for which also an update was published in 2011. They projected a 5.1 degrees increase in global temperatures above 1990 levels by the year 2100 if CO2 emissions aren't reduced.

For this they used the same climate sensitivity, in other words how much the temperature would increase for a doubling of CO2 in the atmosphere, as the IPCC has in it's 2007 report. And they used the same way of calculating this as the IPCC would. Then why the difference in numbers?

The reason is that the IPCC assumed we would act on the available science and start reducing our emissions. The number they mention, the 3.3 degrees warming, is based on at least some reduction of our emissions. Which is their A2 scenario in the 2007 report.

If you take a look at our current emissions, the best apparent fit would indeed be the A2 scenario, which eventually leeds to a CO2 level of 1,250ppm. This translates to a warming of about 3.4 degrees above the 1990 baseline temperature the IPCC uses.

However, we are currently coming very close to the IPCCs most pessimistic scenario, the A1FI, where FI stands for Fossil Intensive. In this scenario they project CO2 levels of 1,550ppm and a projected temperature increase of about 4 degrees. This is the IPCC scenario that comes close to the 1,600ppm the Garnaut report uses for their 5.1 degrees increase. This last 1 degree difference is very easily explained.

If you take a look at the possible temperature range for the Garnaut report projection you will see it is between 3 degrees and 6.6 degrees. Almost the exact same range the IPCC uses for their A1FI scenario, which is between 2.4 and 6.4 degrees. So this last degree difference comes from how they calculated their best estimate. Calculating this estimate is not an easy thing to do as we don't have a lot of research on these high CO2 level scenarios, for the simple reason that many scientists thought we would never reach these CO2 levels.

It's because of our delayed action that scientists are now doing more research on these scenarios. Similar figures as to what the Garnaut report gave are now being mentioned in the results, which is a signal that the IPCC might actually have underestimated the amount of warming. This is not that strange as their estimates for sea level rise are tracking the upper bounds of their projections. Or the loss of arctic sea ice, which exceeds their worst case scenario.

This isn't meant as a criticism towards Monckton, as the only thing he does here is mention two projected numbers. He doesn't say anything about its meaning in relation to each other. I talked about this since these two different numbers would raise questions for members in the audience as to why they are different. As such you should take this as me responding to these questions from the audience.

He also talked about what the actual warming would be, which is with its 1 degree of warming by 2100, a lot lower than the 3.3 degrees the IPCC projects. A warming of just 1 degree is extremely unlikely, and research confirms this.

We have decades worth of research which has precisely quantified how much energy CO2 can absorb. Because of that we know how much energy CO2 would absorb in our atmosphere. This is an effect we've been measuring, and confirming, by satellites and ground based stations.

Another very important point is that climate has changed before on our planet. We can use the traces this has left in the geological record to reconstruct how the climate reacted. This is one of the biggest contributors to our understanding of how our planet responds to increases in CO2 and other greenhouse gasses. The vast majority of these findings give a temperature range of about 2 degrees Celsius to 4.5 degrees Celsius warming for a doubling of CO2.

All this, and much, much more, is used for climate models and is the basis for figures mentioned in the IPCC reports.

These models themselves are then tested against observed changes in past climates. They are also tested against the direct measurements we have. The results this yields are then scrutinised by scientists worldwide in order to make the models more accurate and fit the real world better. Thanks to this the models have become quite good.

This was just a small sampling of the science involved with determining how our climate will respond, I opened the door a tiny bit so to speak. As Monckton goes into more detail several times during this debate I'll expand more on the subject to make it clear that the number he cites is a gross underestimate of what we can expect in the real world.

Sources

1. Australian Government – Department of Climate Change and Energy Efficiency - Opponents of climate change action (page is no longer available, an archived copy can be found here)
2. Australian Government - Clean Energy Future - Chapter 1 – The need for action (page is no longer available, an archived copy can be found here)
3. The Garnaut Climate Review
4. Garnaut Climate Change Review Update 2011
5. ECONOMIC MODELLING TECHNICAL PAPER 2 - CLIMATE DATA METHODOLOGY AND ASSUMPTIONS (page is no longer available, an archived copy can be found here)
6. A report of Working Group I of the Intergovernmental Panel on Climate Change - Summary for Policymakers
7. Betts 2010 - When could global warming reach 4°C?
8. Papers on laboratory measurements of CO2 absorption properties
9. Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997
10. Measurements of the Radiative Surface Forcing of Climate
11. The equilibrium sensitivity of the Earth’s temperature to radiation changes
12. On the generation and interpretation of probabilistic estimates of climate sensitivity
13. Global temperature change
14. Climate simulations for 1880–2003 with GISS modelE
15. Recent Climate Observations Compared to Projection

Media resources

1. CO2 Emissions vs IPCC Scenarios
2. Sea Ice Prediction
3. NASA – Piecing Together the Temperature Puzzle
4. Climate Sensitivity
5. NASA | Supercomputing the Climate