The only way to get dangerous global warming is to assume stagnation

See More growth, less warming by Matt Ridley.

"The debate over climate change is horribly polarized. From the way it is conducted, you would think that only two positions are possible: that the whole thing is a hoax or that catastrophe is inevitable. In fact there is room for lots of intermediate positions, including the view I hold, which is that man-made climate change is real but not likely to do much harm, let alone prove to be the greatest crisis facing humankind this century.

After more than 25 years reporting and commenting on this topic for various media organizations, and having started out alarmed, that’s where I have ended up. But it is not just I that hold this view. I share it with a very large international organization, sponsored by the United Nations and supported by virtually all the world’s governments: the Intergovernmental Panel on Climate Change (IPCC) itself.

The IPCC commissioned four different models of what might happen to the world economy, society and technology in the 21st century and what each would mean for the climate, given a certain assumption about the atmosphere’s “sensitivity” to carbon dioxide. Three of the models show a moderate, slow and mild warming, the hottest of which leaves the planet just 2 degrees Centigrade warmer than today in 2081-2100. The coolest comes out just 0.8 degrees warmer.

Now two degrees [above pre-indistrial levels] is the threshold at which warming starts to turn dangerous, according to the scientific consensus. That is to say, in three of the four scenarios considered by the IPCC, by the time my children’s children are elderly, the earth will still not have experienced any harmful warming, let alone catastrophe.

But what about the fourth scenario? This is known as RCP8.5, and it produces 3.5 degrees of warming in 2081-2100 [or 4.3 degrees above pre-industrial levels]. Curious to know what assumptions lay behind this model, I decided to look up the original paper describing the creation of this scenario. Frankly, I was gobsmacked. It is a world that is very, very implausible.

For a start, this is a world of “continuously increasing global population” so that there are 12 billion on the planet. This is more than a billion more than the United Nations expects, and flies in the face of the fact that the world population growth rate has been falling for 50 years and is on course to reach zero – i.e., stable population – in around 2070. More people mean more emissions.

Second, the world is assumed in the RCP8.5 scenario to be burning an astonishing 10 times as much coal as today, producing 50% of its primary energy from coal, compared with about 30% today. Indeed, because oil is assumed to have become scarce, a lot of liquid fuel would then be derived from coal. Nuclear and renewable technologies contribute little, because of a “slow pace of innovation” and hence “fossil fuel technologies continue to dominate the primary energy portfolio over the entire time horizon of the RCP8.5 scenario.” Energy efficiency has improved very little.

These are highly unlikely assumptions. With abundant natural gas displacing coal on a huge scale in the United States today, with the price of solar power plummeting, with nuclear power experiencing a revival, with gigantic methane-hydrate gas resources being discovered on the seabed, with energy efficiency rocketing upwards, and with population growth rates continuing to fall fast in virtually every country in the world, the one thing we can say about RCP8.5 is that it is very, very implausible.

Notice, however, that even so, it is not a world of catastrophic pain. The per capita income of the average human being in 2100 is three times what it is now. Poverty would be history. So it’s hardly Armageddon.

But there’s an even more startling fact. We now have many different studies of climate sensitivity based on observational data and they all converge on the conclusion that it is much lower than assumed by the IPCC in these models. It has to be, otherwise global temperatures would have risen much faster than they have over the past 50 years.  As Ross McKitrick noted on this page earlier this week, temperatures have not risen at all now for more than 17 years. With these much more realistic estimates of sensitivity (known as “transient climate response”), even RCP8.5 cannot produce dangerous warming. It manages just 2.1C of warming by 2081-2100 [see table 3 in the report by Lewis and Crok here]

That is to say, even if you pile crazy assumption upon crazy assumption till you have an edifice of vanishingly small probability, you cannot even manage to make climate change cause minor damage in the time of our grandchildren, let alone catastrophe. That’s not me saying this – it’s the IPCC itself.

But what strikes me as truly fascinating about these scenarios is that they tell us that globalization, innovation and economic growth are unambiguously good for the environment. At the other end of the scale from RCP8.5 is a much more cheerful scenario called RCP2.6. In this happy world, climate change is not a problem at all in 2100, because carbon dioxide emissions have plummeted thanks to the rapid development of cheap nuclear and solar, plus a surge in energy efficiency.

The RCP2.6 world is much, much richer. The average person has an income about 16 times today’s in real terms, so that most people are far richer than Americans are today. And it achieves this by free trade, massive globalization, and lots of investment in new technology. All the things the green movement keeps saying it opposes because they will wreck the planet.

The answer to climate change is, and always has been, innovation. To worry now in 2014 about a very small, highly implausible set of circumstances in 2100 that just might, if climate sensitivity is much higher than the evidence suggests, produce a marginal damage to the world economy, makes no sense. Think of all the innovation that happened between 1914 and 2000. Do we really think there will be less in this century?

As for how to deal with that small risk, well there are several possible options. You could encourage innovation and trade. You could put a modest but growing tax on carbon to nudge innovators in the right direction. You could offer prizes for low-carbon technologies. All of these might make a little sense. But the one thing you should not do is pour public subsidy into supporting old-fashioned existing technologies that produce more carbon dioxide per unit of energy even than coal (bio-energy), or into ones that produce expensive energy (existing solar), or that have very low energy density and so require huge areas of land (wind).

The IPCC produced two reports last year. One said that the cost of climate change is likely to be less than 2% of GDP by the end of this century. The other said that the cost of decarbonizing the world economy with renewable energy is likely to be 4% of GDP. [See fro example, this summary.] Why do something that you know will do more harm than good?"