According to James Hansen, the Paul Revere of global warming, the safe level for CO2 may be 350 ppm. Hansen is concerned that “ice sheet disintegration, vegetation migration, and GHG release from soils, tundra or ocean sediments, may begin to come into play on time scales as short as centuries or less.” But currently the atmospheric concentration is 385 ppm. The 350 ppm level was reached twenty years ago in 1988, the same year that James Hansen sounded the alarm over global warming at a Congressional hearing.

Is the world better off today compared to 1988?

Let’s check:

• Life expectancy in developing countries was 4–5 years lower in 1988 than it is today (62 years rather than the current 67 years). Even in the US, it increased from 74.9 years in 1988 to 77.8 years in 2004!
• Compared to today, at least 15 more infants out of every 1,000 in developing countries died in 1988 before reaching their first birthdays. In industrialized countries, the infant mortality rate dropped from 9 to 5.
• India’s per capita income (in constant dollars adjusted for purchasing power) has more than doubled since 1988. China’s has more than quadrupled. As a result, hundreds of millions are no longer living in absolute poverty today. Even the US’s per capita income has increased by 40 percent.
• Food production per capita in developing countries has increased 36 percent since 1988, despite a population increase of 40% (that is, 1.5 billion more people). [What fraction of this was due to the increase in carbon dioxide in the atmosphere, and petroleum-based and greenhouse gas-emitting fertilizers, all of which stimulates crop growth?].

Much of these improvements are due to economic growth and agricultural activity that fueled the rise of CO2 concentrations beyond 350 ppm. Because of technological change, it is likely that a portion of these improvements would have occurred absent any economic growth (as pointed out in the book, The Improving State of the World ). But had CO2 concentrations been capped at 350 ppm, we would have to forgo many of the above improvements in the quality of life, and not only in the developing world.

But would we want to go back to the world of 1988 — or even 1998 for that matter?

If we can go back to 350 ppm without giving up the real and tangible advances in human well-being that have accrued since that “benchmark” was passed, I’d have nothing against that, but based on the precautionary principle, one needs a stronger reason than the speculative catastrophes that Hansen is concerned “may begin to come into play on time scales as short as centuries or less,” whatever that means.