Economists Think They are Climatologists

The CBC has a new story on global warming, Study suggests Earth to warm more than 2 C this century. I’m going to examine both the abstract of the study, Less than 2 °C warming by 2100 unlikely (the full article is behind a paywall), the IPPC’s Climate Change 2014 Synthesis Report, which it cites, and the CBC’s article. First, here’s the relevant part of the abstract:

Using data for 1960–2010, including the UN’s probabilistic population projections for all countries, we develop a joint Bayesian hierarchical model for Gross Domestic Product (GDP) per capita and carbon intensity. We find that the 90% interval for cumulative CO2 emissions includes the IPCC’s two middle scenarios but not the extreme ones. Population growth is not a major contributing factor. Our model is not a ‘business as usual’ scenario, but rather is based on data which already show the effect of emission mitigation policies.

The study is modeling expected future CO2 emissions. This is as opposed to the IPCC report which, for four different scenarios of future emissions, gives the estimated ranges of temperature increase. What this study finds is that the IPCC’s two middle scenarios, RPC-4.5 and RPC-6.0, are the most likely. This is not surprising. Here’s a picture of the CO2 emissions projected by each of the scenarios, from page 26 of the report:

IPCC-RPC-Scenarios

You can see that in scenario RCP4.5, emissions continue to rise until 2050, then drop back to their 1950 levels by 2100. RCP6.0 has emissions rising until 2080 before dropping back to their 2050 levels. Given the advances in electrification, solar, nuclear, and other renewable energy sources and the switch from coal to LNG, RCP4.5 seems fairly doable to me. What does the IPCC report say that, based on climate models, they think will be the likely temperature increase?

The increase of global mean surface temperature by the end of the 21st century (2081–2100) relative to 1986–2005 is likely to be 0.3°C to 1.7°C under RCP2.6, 1.1°C to 2.6°C under RCP4.5, 1.4°C to 3.1°C under RCP6.0 and 2.6°C to 4.8°C under RCP8.5.

Assuming RPC4.5 is indeed the way things go and the low end of the temperature range predicted by the IPCC’s climate models is correct, there will be 1.4°C of warming over 1995 temperatures. Let’s see what the CBC’s article has to say.

A new study from the University of Washington suggests that there is a 90 per cent chance Earth will warm anywhere between 2°C and 4.9°C above pre-industrial levels by the end of the century.

The study says that they are 90% confident that CO2 emissions will follow either RPC4.5 or RPC6.0. That gives a temperature range of 1.4°C and 4.8°C. The range given here is from the abstract of the study, but the study is predicting carbon dioxide emissions, not temperature changes based on them. The IPCC’s models are questionable as it is; it seems unwise then to ignore their temperature ranges and come up with your own.

There was only a one per cent chance it would warm below 1.5°C, a target set out by almost 200 countries in the Paris climate agreement.

Presumably this means that they believe there is only a 1% chance that something like RPC2.6 can be achieved. This makes little sense to me. If RPC4.5 and RPC6.0 are 90% likely, surely RPC2.6, with it’s temperature increase of 0.3°C to 1.7°C must have a 5% chance.

The models also predicted a global population of 11 billion by 2100. But that didn’t play a significant role in CO2 production and rising temperatures. That’s because three quarters of the population increase will occur in sub-Saharan Africa, where emissions are low and will continue to be low.

Good to know. This presumes that Africa won’t somehow lift itself up the same way China and India have. Since economic models are the bailiwick of the study’s authors, I’m going to hope that they’re right about this.

“It’s more urgent to address the issue, because up until now it’s been couched in terms of a target of 1.5 degrees or 2 degrees which would already have consequences,” lead author Adrian Raftery said. “I think our work puts into sharper focus that we’re not very likely to make those targets and we could be going for much higher numbers. If they’re realized, the consequences would be much more severe.”

Based on my analysis, I’m going to go with 1.5 to 3 degrees, assuming we will reach peak emissions in 2050 and then begin to decrease back to 1950 levels, and hope that the more conservative end of the IPCC’s range is correct.

Raftery said that the world should look to countries like France which has a low-carbon infrastructure, including carbon-efficient public transportation, high gas tax and nuclear power.

Taxing gas won’t work unless people are given an alternative. Electric cars need to be more competitive, and we need to stop generating electricity by burning coal. Ideally, we should be using renewables and nuclear power. The greens need to get behind nuclear power instead of protesting against it.

As for the Paris agreement, signed by almost 200 countries in an effort to prevent Earth from warming 2°C above pre-industrial levels, Raftery said it’s disappointing to see the U.S. — a major contributor of CO2 emissions — pull out.

The Paris agreement is a political accord that has more to do with transferring wealth around than actually reducing emissions. I can understand why the US pulled out. If people would propose measures that will actually reduce CO2 emissions, maybe there would be broader support for them. I predict that brow beating the Republicans will only make them dig in their heels.

The solution to these problems is not going to come from government legislation. We need to use market forces to achieve real reductions. Hearing an economist argue for more government regulation isn’t surprising. I trust their predictions less than I trust those of the Climatologists.

About jimbelton

I'm a software developer, and a writer of both fiction and non-fiction, and I blog about movies, books, and philosophy. My interest in religious philosophy and the search for the truth inspires much of my writing.
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1 Response to Economists Think They are Climatologists

  1. Pingback: Global Warming Scare Mongering Conflicts with Article from One Day Earlier | Jim's Jumbler

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