One of the crucial issues in any assessment of climate change policy is how to handle discounting and risk. The Stern review (Ch 2) goes back to first principles and gets the main issues exactly right. The reason for both discounting and risk premiums, in economic analysis, is that the marginal value of a dollar of income is lower when we are rich than when we are poor. Hence, we’re prepared to pay for insurance when we are well off in order that it will pay out when we are badly off. Similarly, if we expect income to rise over time, a dollar of income now is worth more, at the margin, than a dollar in the future. The same points are relevant in considering income distribution but this isn’t covered in the parts of the report I’ve read so far.

In addition, there’s a justification for “inherent discounting”, reflecting the fact that some future event (most probably bad, but perhaps good) may mean that “all bets are off” in relation to future consumption levels. Individuals should have reasonably high inherent discount rates, since we may not be around next year, but the appopriate rate for a community is much lower, being confined to the risk of catastrophes like nuclear war.

The Stern review also has a good discussion of probabilities, including the recent literature on problems where there do not exist well-defined probabilities.

The quality of the economics here is very high, and sets a new bar for discussion of these issues.

There’s more on Stern from James Wimberley

One of the issues that’s been debated at length here is the choice of exchange rates to use in converting different currencies for projections of future economic growth and energy demand. The scenarios developed by the IPCC have used market exchange rates (MER) Ian Castles has argued, in very strong terms, that it’s crucial to use exchange rates adjusted so as to exhibit Purchasing Power Parity (PPP). In my submission, I made a couple of points. First, that there is no uniquely satisfactory method of obtaining PPP exchange rates. Second, and more importantly, the choice doesn’t make much difference to projections of energy use or CO2 emissions, as long as the same values are used consistently. A method like MER, which tends to overstate income differences between poor and rich countries relative to PPP will yield a lower income elasticity of demand for energy. And since MER data have been, until recently more readily available for more countries, there are some practical arguments in favour of using them.

That said, there are a couple of reasons to favour a move to PPP-based scenarios. First, since these are now becoming the norm, continued use of MER numbers is likely to cause confusion. Second, while the crucial numbers regarding emissions aren’t much affected (and any error may be either up or down) other variables, particularly those used in calculations of economic welfare, might be significantly affected.

In this context, it’s unfortunate that the debate has been seized upon by denialists as a basis for attacking the whole IPCC process. The energy that’s gone into pointless disputes could have better been used in a constructive attempt to improve things.

Where does the Stern report come out on all this? Pretty much right in my view. Key quote

efforts are under way to improve the provision of PPP data. The International Comparison Programme (ICP), launched by the World Bank when Nicholas Stern was Chief Economist, is the world’s largest statistical initiative, involving 107 countries and collaboration with the OECD, Eurostat and National Statistical Offices. It produces internationally comparable price levels, economic aggregates in real terms, and Purchasing Power Parity (PPP) estimates that inform users about the relative sizes of markets, the size and structure of economies, and the relative purchasing power of currencies.

In the IPCC SRES scenarios that use MER conversions, it is not clear that the use of MERs biases upwards the projected rates of emissions growth, as the SRES calibration of the past relationship between emissions per head and GDP per head also used GDPs converted at MERs as the metric for economic activity (Holtsmark and Alfsen (2003)). Hence the scenarios are based on a lower estimate of the elasticity of emissions growth per head with respect to (the incorrectly measured) GDP growth per head. As Nakicenovic et al (2003) have argued, the use of MERs in many of the IPCC SRES scenarios is unlikely to have distorted the emissions trajectories much.

I should point out that the World Bank ICP is a successor to the earlier ICP work of Heston and Summers who initiated the idea of systematic PPP comparisons and produced the well-known Penn World Tables. Still, as the quote makes clear, Stern can speak with authority on this topic.

Read More »

The Stern review report is big, and I haven’t had time to digest more than a little bit so far. One point to make is that the apocalyptic numbers that have dominated early reporting represent the worst-case outcomes for 2100 under business-as-usual policies. But even looking at the less dramatic cases, the same basic messages emerge.

• We can stabilise CO2 levels over the next fifty years at very low costs of around 1 per cent of GDP.
• The costs of doing nothing are large and unpredictable
• The costs of stabilisation will be greater the longer we delay
• Poor countries will be worst affected

More on all these points soon.

If a global emissions trading system is to be implemented, there needs to be a method of deterring free riders – countries that choose not to limit their own emissions. The obvious candidate is a border tax on embodied CO2 emissions. This possibility looks a lot closer with the EU considering trying it out for cement. The issue is unlikely to go away, and will no doubt cause huge ructions in WTO and similar bodies if it goes ahead. (via Dan Drezner).

I don’t imagine John Howard reads this blog, or even my columns in the Financial Review, but it was striking, after the discussion we had here to see him make an explicit link between climate change and the severity of the current drought. This is big progress even on his position of month ago, where he was still trying to have a bit each way.

It will be interesting to see how denialists in the commentariat and blogosphere, most of whom are also Howard partisans, respond to this.

Also, while I’m praising Howard, the training package he announced recently was a good thing, and seems to mark an abandonment of the silly idea that it’s OK to finish your education at year 10. Not everyone needs a university education, but failing to finish school (or achieve an equivalent outcome) and get some sort of post-school qualification is a recipe for low wages and regular unemployment.