The Economist – which has long been concerned about the rise in Earth’s temperature and its consequences for civilization — has a significant article in the current issue. It begins this way:
Over the past 15 years air temperatures at the Earth’s surface have been flat while greenhouse-gas emissions have continued to soar. The world added roughly 100 billion tonnes of carbon to the atmosphere between 2000 and 2010. That is about a quarter of all the CO₂ put there by humanity since 1750. And yet, as James Hansen, the head of NASA’s Goddard Institute for Space Studies, observes, “the five-year mean global temperature has been flat for a decade.”
Temperatures fluctuate over short periods, but this lack of new warming is a surprise. Ed Hawkins, of the University of Reading, in Britain, points out that surface temperatures since 2005 are already at the low end of the range of projections derived from 20 climate models. If they remain flat, they will fall outside the models’ range within a few years.
“The mismatch between rising greenhouse-gas emissions and not-rising temperatures is among the biggest puzzle in climate science right now,” The Economist adds.
The article rightly does not argue that anthropological global warming is a delusion. But it does make the point that an awful lot depends on whether the climate is less sensitive to CO2 emissions than previously believed. It makes (almost literally) a world of difference if Earth’s temperature increases 0.8-1.9°C v. 4.0-6.0°C. The low end would be something we could easily absorb; the high end would justify drastic interventions. So much depends on the model one uses and the confidence one places in them.
Based on the latest science, the Economist summaries things this way:
given the hiatus in warming and all the new evidence, a small reduction in estimates of climate sensitivity would seem to be justified: a downwards nudge on various best estimates from 3°C to 2.5°C, perhaps; a lower ceiling (around 4.5°C), certainly. If climate scientists were credit-rating agencies, climate sensitivity would be on negative watch. But it would not yet be downgraded.
When I wrote on this subject a couple of years ago (see here and here), I pointed out (a) the concentration in the atmosphere of carbon dioxide has increased markedly during the past 150 years; (b) humans have been responsible for a significant increase in atmospheric CO2 concentration during the past two centuries; (c) as a result, the earth is getting warmer; but (d) there’s a good deal of uncertainty based on future climate projections and what needs to be done. In light of that, adaptation rather than a completely unworkable system of global carbon rationing may be the way to go.
Here’s how I put it at the time:
Many climate scientists fear that unless dramatic steps are taken soon, we’ll see rising sea levels, contracting ice sheets, more floods and intense tropical cyclones, the spread of tropical diseases like malaria, the submergence of parts of continents, alterations in our ecosystems, and food and water shortages. Perhaps so; those concerns are certainly worth considering. But as Jim Manzi – who combines a sophisticated understanding of the scientific and economic stakes of the climate-change debate — has pointed out, pumping out more CO2 triggers an incredibly complicated set of feedback effects, and the most important scientific debate is really about these feedback effects. In Manzi’s words, “Climate models generate useful projections for us to consider, but the reality is that nobody knows with meaningful precision how much warming we will experience under any emissions scenario. Global warming is a real risk, but its impact over the next century could plausibly range from negligible to severe.”
Conservatives should be part of that conversation. There’s an intellectually credible case to be made that it’s unwise to embrace massive, harmful changes to our economy in the face of significant uncertainties based on incomplete knowledge of how the climate system will respond in the middle part of the 22nd century.
That is, I think, very much where we are today. Even the Economist is beginning to think so.